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  • The responses of epilithic algal community structure and function to light and nutrients and their linkages in subtropical rivers
    Hydrobiologia (IF 2.325) Pub Date : 2019-12-19
    Jian Zhang, Xiao Shu, Yongyong Zhang, Xiang Tan, Quanfa Zhang

    Abstract Epilithic algal community structure and function are important indicators of stream ecosystem health and are sensitive to ambient environmental changes. In this study, we examined the impact of light and nutrients on epilithic algal community structure and function by an in situ nutrient addition and shaded canopy experiment in subtropical streams in China. Epilithic algae structure, dominated by diatoms, was significantly different with nutrient addition and light reduction. Nutrient addition increased the epilithic algae and diatom density, colonial life-forms, planktonic diatoms, and high-profile diatoms but decreased the low-profile diatoms. The shaded canopy increased the low-profile diatoms but decreased the adnate life-forms, planktonic diatoms, and high-profile diatoms. Epilithic metabolism, including gross primary production (GPP), net daily metabolism (NDM), and production/respiration (P/R) increased with nutrient addition, while respiration (R) only increased when the canopy was open with nutrient addition. Epilithic GPP had a significant positive correlation with diatom density (P < 0.01, R2 = 0.9425). Our results indicated that changes in epilithic algae structure due to changes in riparian canopy coverage and nutrients could affect epilithic algal community function. Quantifying the impacts of such drivers on community structure and function is vital to effective river management.

  • Complex phylogeographic relationships among the Eurasian perch ( Perca fluviatilis ) populations in the eastern part of the Baltic Sea Region
    Hydrobiologia (IF 2.325) Pub Date : 2019-12-19
    Adomas Ragauskas, Dalius Butkauskas, Petras Prakas, Karolina Gadliauskienė, Helen Gajduchenko, Dace Grauda

    Abstract The Eurasian perch (Perca fluviatilis) is an economically and environmentally important fish. Its distribution is changing because of many anthropogenic factors, including aquaculture and restocking. Careless dislocations enhance risk disrupt the established geographical genetic structure of this species. Set as a benchmark for future studies, this paper investigates the current perch status in the Baltic Sea Region. It presents the genetic diversity and phylogeographic relationships among 19 perch populations in Lithuania, Latvia and Belarus, on the basis of 489 perch sequences of the mtDNA D-loop region. Analysis of molecular data revealed that in the eastern part of the Baltic Sea Region, the genetic diversity of mtDNA D-loop of the perch was greater and different in comparison to that from other European locations. Based on SAMOVA results, perch samples were divided into four genetically distinct groups (I–IV). These groups indicate non-casual geographical distributions of genetically differentiated perch populations in Lithuania, Latvia and Belarus. The colonisation of the eastern part of the Baltic during the last deglaciation period resulted in perch populations that are genetically more complex than anticipated. The just-assessed current perch genetic diversity may be useful for monitoring its changes induced by growing anthropogenic activities in the Baltic Sea Region.

  • Late-Holocene variability in chironomid functional assemblages and carbon utilization in a tundra lake food web
    Hydrobiologia (IF 2.325) Pub Date : 2019-12-17
    E. Henriikka Kivilä, Tomi P. Luoto, Marttiina V. Rantala, Liisa Nevalainen

    Abstract High latitude freshwater systems are facing changes in catchment-mediated allochthonous input, as well as physical and chemical controls triggered by on-going climate change, which may alter their carbon processing and ecological characteristics. To explore changes in chironomid functional responses and carbon utilization in relation to long-term environmental change, we studied a sediment core covering ca. 2000 years from a tundra lake in northern Finland, which was analysed for sediment geochemistry, isotopic composition of chironomid remains and their functional assemblages. We aimed to relate changes in chironomid functional feeding assemblages and resource utilization, based on Bayesian stable isotope modelling, and determined that the long-term resource utilization was more controlled by sediment geochemistry (resource availability) and climatic variables, reflecting changes in habitat and lake ontogeny, rather than the functional feeding assemblage composition. Change horizons were observed for both sediment geochemistry and functional assemblage composition. However, different timing of these changes suggests different drivers affecting the dynamics of primary production and chironomid community functionality. We also compared the recent warming period to Medieval Climate Anomaly (MCA), observing divergent patterns, which suggests that MCA may not be a good analogue for changes induced by on-going climate warming.

  • Underestimated species diversity and hidden habitat preference in Moina (Crustacea, Cladocera) revealed by integrative taxonomy
    Hydrobiologia (IF 2.325) Pub Date : 2019-12-12
    Wataru Makino, Ryuji J. Machida, Jiro Okitsu, Nisikawa Usio

    Abstract In Japan, farm ponds retain water throughout the year while rice fields are continuously inundated for no more than 2 months, usually from spring to early summer. Although the zooplankton fauna in artificial water bodies would be expected to vary according to differences in inundation periods, scientific confirmation of this relation is largely lacking. Due to its ubiquity, the cladoceran Moina is a suitable target for studying habitat-related differences in the planktonic fauna, but its taxonomy remains unresolved, making morphological identifications potentially uncertain. We thus applied integrative taxonomy with both morphological and genetic evaluations for reliable species delimitation to Moina samples collected primarily in Japan (with smaller collections from Taiwan). This approach increased the alpha diversity of Moina species in Japan from three (in previous studies) to seven. It also revealed different habitat preferences among Moina species, with the smaller species being distributed mostly in farm ponds (followed by natural lakes), and the larger species mostly in rice fields. We argue that the phenological match/mismatch with inundation period of rice fields was a major factor for this strong trend of spatial species turnover, with differing degrees of fish predation pressure among the habitat types being another factor.

  • Growth and physiological responses of Carex schmidtii to water-level fluctuation
    Hydrobiologia (IF 2.325) Pub Date : 2019-12-18
    Dongjie Zhang, Mingye Zhang, Shouzheng Tong, Qing Qi, Xuehong Wang, Xianguo Lu

    Abstract Water-level fluctuations are common abiotic stresses influencing growth and physiological processes of wetland plants. Nonetheless, little is known about plant eco-physiological responses and growth strategy under multi-hydrological processes. Carex schmidtii was grown under the conditions with interaction of initial water-level depth (DW) and water-level amplitude (AW). Dynamics of plant eco-physiological traits and growth strategy were investigated continuously during the entire growth stages. Results indicated that leaf morphology was significantly affected by DW and lasted time, and leaf width was sensitive to AW. The SLA and LDMC of C. schmidtii varied significantly at different lased time, and their relationships indicated the trade-off in leaves between matter production and nutrient conservation. Increasing DW inhibited matter production of C. schmidtii in early growth stage, but increased nutrient conservation in late growth stage. However, increasing AW contributed to both increase of matter production and nutrient conservation of C. schmidtii. The photosynthetic pigments of C. schmidtii are relatively sensitive to DW, AW and their interaction. Slowing down water-level fluctuations and appropriate water management in the key growth stage will assist with the adaption of Carex schmidtii. The findings provide invaluable supporting information for the management and conservation of C. schmidtii tussock wetlands.

  • Carbon and nitrogen recycling during cyanoHABs in dreissenid-invaded and non-invaded US midwestern lakes and reservoirs
    Hydrobiologia (IF 2.325) Pub Date : 2019-12-27
    Trinity L. Hamilton, Jessica R. Corman, Jeff R. Havig

    Abstract Lakes and reservoirs play key roles in global carbon cycling, especially as a carbon sink. Enrichment of nutrients in lakes and reservoirs (eutrophication) and rising global temperatures favors the proliferation of bloom-forming cyanobacteria. Harmful blooms of cyanobacteria (cyanoHABs) alter carbon and nutrient cycling in freshwater ecosystems. Some evidence suggests the introduction or establishment of invasive mussel species (i.e., Dreissena spp.) also favor cyanoHAB formation through selective filter feeding, a process through which they may also impact biogeochemical processes including carbon cycling and sequestration. However, few studies have considered the combined effects of invasive mussels and cyanoHABs on carbon and nitrogen cycling in freshwater ecosystems. Here, we examined microbial community composition and biogeochemical attributes (including carbon and nitrogen stable isotopes) in eutrophic lakes, reservoirs, and rivers in western Ohio, eastern Indiana, and northern Kentucky during the cyanobacterial bloom period of the summer of 2015. Our samples include both sites impacted by invasive mussels and those where invasive mussels have not yet been observed. Based on 16S and 18S rRNA gene sequence analysis, we found that cyanobacterial and algal communities varied across sites and were most closely related to habitat (sediment or water column sample) and site, regardless of the presence of invasive mussels or other environmental factors. However, we did find evidence that invasive mussels may influence both carbon and nitrogen cycling. While the results are based on a single time point sampling, they highlight the interactions of multiple environmental stressors in aquatic ecosystems and the critical need for more temporally intensive studies of carbon and nutrient cycling in bloom- and mussel-impacted waters.

  • Impact of human activities and climate on Lake Morenito, Northern Patagonia, Argentina
    Hydrobiologia (IF 2.325) Pub Date : 2019-11-28
    Melina Mauad, Christoph Mayr, Teresa Graßl, Nathalie Dubois, Maria Noel Serra, Julieta Massaferro

    Abstract Lake Morenito located in the Argentinean Patagonia has been exposed to climatic, volcanic, and anthropogenic impacts for the last decades. In particular, the damming of the lake and the eruption of the Calbuco/Puyehue Volcanoes in AD 1960 played an important role in the lake’s history. A 80-cm-long sediment core from Lake Morenito spanning more than 100 years was studied for chironomids, stable isotopes, and organic geochemistry to investigate how natural and anthropogenic stressors impacted the lake. Chironomid assemblages display large changes around AD 1950, with the appearance of the warm-adapted Chironomus and the replacement of Apsectrotanypus by Ablabesmyia, indicating a shift to warmer conditions. By that time and up to the present, an increasing trend of δ15N coupled with a decrease of δ13C points to shifts in the carbon and nitrogen cycles associated with human activities. It is evident that the onset of human activities during the 1950s following by the lake damming in AD 1960 had significant effects on the chironomid assemblages and the geochemical composition of sediments which is reflected in the progressive deterioration of the lake ecosystem.

  • Embryonic development and microsatellite-based parentage assignment of seaweed pipefish Syngnathus schlegeli
    Hydrobiologia (IF 2.325) Pub Date : 2019-12-19
    Jian-Yu Dong, Yu-Xi Huang, Zhi Chen, Xiu-Wen Xu, Xiu-Mei Zhang

    Abstract In this study, the embryonic development of Syngnathus schlegeli is first described based on external morphological characteristics and then the genetic relationship between embryos is investigated using a microsatellite-based approach. Embryonic development proceeds from fertilized egg to prerelease of larva and can be categorized into four periods: early embryogenesis, eye development, snout formation and larva, which can be further divided into 15 stages. Embryos in the brood pouch are all in the same developmental stage. However, multi-maternity is observed in all sampled broods. Microsatellite-based parentage analysis suggests that pregnant males had, per male, mated with and received eggs from 3 to 7 females, with average being 4.3. The embryos of full sibs within a brood pouch were clustered, and seven patterns of parentage were observed. Combining previous studies with the evidence obtained from genotyped eggs inside the brood pouch in this study, we can confirm that the mating pattern of S. schlegeli is polygamous.

  • Towards a robust baseline for long-term monitoring of Antarctic coastal benthos
    Hydrobiologia (IF 2.325) Pub Date : 2020-01-20
    Paola Piazza, Stefano Antonio Gattone, Alice Guzzi, Stefano Schiaparelli

    Abstract The Southern Ocean represents one of the world regions most sensitive to warming and there is an urgent need for quantitative data to understand changes in coastal communities. This goal can be achieved through the establishment of permanent monitoring sites and robust sampling designs. In this study, we used an emerging, photogrammetry-based technique to simulate a pilot study and test the efficiency of different sampling schemes (Simple Random—SRS-, Systematic—SyS- and Strip—SS-) for estimating the abundances of megabenthic taxa. For taxa showing an aggregated distribution, we also applied an adaptive cluster sampling (ACS) design. In almost the totality of cases, the best accuracy of estimates was achieved with SyS combined with plots of 0.0625 m2. ACS design gave better performances but required a calibration of both the initial sample size and the threshold value to increase efficiency. The ‘one-size-fits-all’ 1 m2 plot size never emerged as the best in any sampling schemes, hence the previously published literature data can be biased. This study represents a fine-scale reference baseline for the study area and the simulations performed will be pivotal in establishing sound-monitoring programmes with sufficient statistical power to detect significative changes in the Antarctic benthos.

  • Assessing the potential health risk of cyanobacteria and cyanotoxins in Lake Naivasha, Kenya
    Hydrobiologia (IF 2.325) Pub Date : 2020-01-17
    M. H. Raffoul, E. M. Enanga, O. E Senar, I. F. Creed, C. G. Trick

    Abstract This study discerned the causes of cyanobacteria blooms in Lake Naivasha (Kenya). We hypothesized that phytoplankton and cyanobacteria biomass respond to hydrologic cycles, peaking during the wet season, and that microcystin (MC) concentrations are highest following the bloom collapse. Hydrologic loading (inferred from rainfall and lake level changes) and phytoplankton responses in two basins of the lake were monitored over a wet season followed by a dry season between September 2010 and March 2011. Results show that both phytoplankton and cyanobacteria biomass peaked in both basins during the wet season, with associated peaks in particulate MC concentrations. Even though phytoplankton and cyanobacteria biomass were higher in the smaller deep basin, MC concentrations were lower than in the large shallow basin. The high-MC levels during the wet season were followed by a greater MC production per cyanobacteria biomass unit in the dry season in both basins. The timing of the cyanobacteria bloom suggests that its formation was likely controlled by large nutrient influxes from the contributing catchment to the lake associated with intense rainfall following an intense drought, posing a risk to the health of the community due to increased MC levels.

  • Land use and land cover control on the spatial variation of dissolved organic matter across 41 lakes in Mississippi, USA
    Hydrobiologia (IF 2.325) Pub Date : 2020-01-16
    M. S. Sankar, Padmanava Dash, YueHan Lu, Andrew E. Mercer, Gray Turnage, Cory M. Shoemaker, Shuo Chen, Robert J. Moorhead

    Abstract While dissolved organic matter (DOM) is an important indicator of water quality, land use and land cover (LULC) of watersheds define the source, quality, and quantity of DOM delivered to a waterbody. This study examined the influence of various LULC classes in the spatial distribution of DOM in 41 lakes across the state of Mississippi. To scale the influence of LULC classes on DOM distribution, we have classified 41 lakes into five clusters based on DOM compositions determined by parallel factor analysis. Four major DOM compositions including terrestrial humic-like (C1), microbial humic-like (C2), soil-derived humic-like (C3), and tryptophan-like or tyrosine like (C4) components were identified. Higher amounts of terrestrial humic-like and soil-derived humic-like DOM compositions were observed in lakes within watersheds dominated by forested, barren, wetlands, or agricultural areas with exposed unconsolidated soil. Higher amounts of microbial humic-like composition were observed in lakes surrounded by hay/pasture, rangeland, and urbanized areas. Additionally, protein-like DOM and ammonia were more enriched in larger lakes, indicating the influences of photochemical reactions. High amounts of forested areas and higher concentrations of terrestrial humic-like DOM composition were identified in all lakes suggesting forested areas in the watershed as the principal source of DOM in Mississippi lakes.

  • Bacterial endosymbionts of Placobdella (Annelida: Hirudinea: Glossiphoniidae): phylogeny, genetic distance, and vertical transmission
    Hydrobiologia (IF 2.325) Pub Date : 2020-01-14
    Claire Manglicmot, Alejandro Oceguera-Figueroa, Sebastian Kvist

    Abstract Blood-feeding leeches of the genus Placobdella have acquired intracellular alphaproteobacterial endosymbionts of the genus Reichenowia that potentially aid in the production of B vitamins, thereby ameliorating the lack of these essential nutrients in the diet of the hosts. For Placobdella associates, little is still known about the diversity, genetic makeup, and the mode of transmission of bacteria between leeches. We aimed to (i) place the bacterial symbionts in a phylogenetic context, (ii) compare patterns of cladogenesis between the bacteria and hosts to search for evidence of co-speciation, and (iii) explore the mode of bacterial transmission between leech parent and offspring. DNA sequencing of the bacterial 16S rDNA and 23S rDNA loci suggests that, whereas Reichenowia forms a monophyletic group within the alphaproteobacterial family Rhizobiaceae, no evidence for co-speciation between hosts and bacteria can be traced. Attempts at DNA amplification for ovarial tissues were negative for a range of species, but two 16S rDNA sequences retrieved from the testisacs of P. rugosa showed very high similarity with Reichenowia. Although we cannot rule out that this may be a contamination, or a different, potentially free-living species of bacteria, our results may indicate that Reichenowia is transferred from leech parent to offspring via the testisacs.

  • Water velocity and groundwater upwelling influence benthic algal biomass in a sandy tropical river: implications for water-resource development
    Hydrobiologia (IF 2.325) Pub Date : 2020-01-14
    Ryan M. Burrows, Leah Beesley, Michael M. Douglas, Bradley J. Pusey, Mark J. Kennard

    Abstract Benthic algae are a major source of carbon supporting aquatic food webs in northern Australia, but little is known about the factors that regulate algal production. We surveyed benthic algal biomass in mainstem habitats of an unregulated sandy tropical river (the Fitzroy River) during a base-flow period. We used predictive models to reveal the physical and chemical parameters controlling algal biomass in mainstem habitats. We found that water velocity was an important driver—algal biomass was lower at higher water velocities. Subsurface flow was also influential—algal biomass increased in locations where groundwater upwelling occurred, as evident by a positive relationship between algal biomass and elevated radon and ammonium concentrations. In this sand-bed river, it is likely that high water velocity destabilises the sandy substrate reducing the establishment of algal biofilms. However, where water velocity is low enough for algal establishment, groundwater upwelling likely promotes algal growth by delivering limiting resources and/or creating stable conditions that promote algal production. The importance of surface and subsurface-flow conditions to benthic algal biomass means that any modification to the Fitzroy River catchment that alters dry-season longitudinal flows (via river regulation) or groundwater levels (via groundwater extraction) may directly influence river algal production.

  • Soil surface elevation dynamics in a mangrove-to-marsh ecotone characterized by vegetation shifts
    Hydrobiologia (IF 2.325) Pub Date : 2020-01-13
    Rebecca J. Howard, Andrew S. From, Ken W. Krauss, Kimberly D. Andres, Nicole Cormier, Larry Allain, Michael Savarese

    Abstract Mangrove forest encroachment into coastal marsh habitats has been described in subtropical regions worldwide in recent decades. To better understand how soil processes may influence vegetation change, we studied soil surface elevation change, accretion rates, and soil subsurface change across a coastal salinity gradient in Florida, USA, an area with documented mangrove encroachment into saline marshes. Our aim was to identify if variations in the soil variables studied exist and to document any associated vegetation shifts. We used surface elevation tables and marker horizons to document the soil variables over 5 years in a mangrove-to-marsh transition zone or ecotone. Study sites were located in three marsh types (brackish, salt, and transition) and in riverine mangrove forests. Mangrove forest sites had significantly higher accretion rates than marsh sites and were the only locations where elevation gain occurred. Significant loss in surface elevation occurred at transition and salt marsh sites. Transition marshes, which had a significantly higher rate of shallow subsidence compared to other wetland types, appear to be most vulnerable to submergence or to a shift to mangrove forest. Submergence can result in herbaceous vegetation mortality and conversion to open water, with severe implications to the quantity and quality of wetland services provided.

  • Metabolic analyses by metatranscriptomics highlight plasticity in phosphorus acquisition during monospecific and multispecies algal blooms
    Hydrobiologia (IF 2.325) Pub Date : 2020-01-08
    Xin Xu, Zhiming Yu, Liyan He, Xihua Cao, Nansheng Chen, Xiuxian Song

    Algal blooms have emerged as a global phenomenon affecting coastal areas, while the regulatory mechanisms are poorly understood. To explore the effects of environmental factors, especially phosphate concentrations, on the outbreak and maintenance of algal blooms, this study used a metatranscriptomic approach to analyze the molecular responses of phytoplankton during two blooms in 2013 near Qinhuangdao, China. Pico/nanophytoplanktons (< 10 μm) were dominant numerically in the two algal blooms. Significant shifts in KEGG pathway expression were observed with the succession of phytoplankton, suggesting high temporal plasticity in the expressed metabolic capacity. The KEGG pathway expression pattern in the multispecies bloom on August 22 showed higher gene expression of primary metabolic pathways and lower gene expression of secondary metabolic pathways than that in the monospecific bloom on July 20. Pico/nanophytoplankton showed species-specific transcriptional responses to the shifts in N/P ratios and phosphate concentrations. Our results demonstrate how the species specificity and temporal plasticity of resource utilization capacities enable pico/nanophytoplankton to induce monospecific and multispecies blooms under different phosphate conditions. This study provides a basis for further work on the gene responses of multispecies assemblages of algae to different environmental parameters during algal bloom succession.

  • Relationship between epipelon, epiphyton and phytoplankton in two limnological phases in a shallow tropical reservoir with high Nymphaea coverage
    Hydrobiologia (IF 2.325) Pub Date : 2020-01-08
    Thiago Rodrigues dos Santos, Maria Carolina Castilho, Raoul Henry, Carla Ferragut

    Abstract Macrophytes and phytoplankton are recognized as having roles in determining alternative stable states in shallow lakes and reservoirs, while the role of periphyton has been poorly investigated. Temporal and spatial variation of phytoplankton, epipelon and epiphyton was examined in a shallow reservoir with high abundance of aquatic macrophytes. The relationships between algae communities and abiotic factors, macrophyte coverage and zooplankton density were also analyzed. Monthly sampling was performed in three zones of the depth gradient of the reservoir. Two phases of algal dominance were found: a phytoplankton phase and epipelon phase. The phase of phytoplankton dominance was characterized by high macrophyte coverage. Rotifera was the dominant zooplankton group in all the zones. Flagellate algae were dominant in phytoplankton, epipelon and epiphyton. Macrophyte coverage was found to be a predictor for algal biomass. Changes in biomass and species composition were associated with macrophyte cover variation, mainly the Nymphaea. In addition to the abiotic factors, the macrophyte coverage was a determining factor for changes to the algal community, contributing to the alternation between dominance phases of phytoplankton and epipelon. The macrophyte–phytoplankton–periphyton relationship needs to be further known in shallow reservoirs, especially the role of epipelon as an alternate stable state.

  • Changes in the functional features of macrophyte communities and driving factors across a 70-year period
    Hydrobiologia (IF 2.325) Pub Date : 2020-01-04
    Marja Lindholm, Janne Alahuhta, Jani Heino, Jan Hjort, Heikki Toivonen

    Abstract Functional homogenisation occurs across many areas and organism groups, thereby seriously affecting biodiversity loss and ecosystem functioning. In this study, we examined how functional features of aquatic macrophytes have changed during a 70-year period at community and species levels in a boreal lake district. At the community level, we examined if aquatic macrophyte communities showed different spatial patterns in functional composition and functional richness in relation to main environmental drivers between the time periods. We also observed each species in functional space to assess if species with certain sets of traits have become more common or rare in the 70-year study period. We found changes in the relationship between functional community composition and the environment. The aquatic macrophyte communities showed different patterns in functional composition between the two time periods, and the main environmental drivers for these changes were partly different. Temporal changes in functional richness were only partially linked to concomitant changes in the environment, while stable factors were more important. Species’ functional traits were not associated with commonness or rarity patterns. Our findings revealed that functional homogenisation has not occurred across these boreal lakes, ranging from small oligotrophic forest lakes to larger lakes affected by human impacts.

  • Influence of macroalgal morphology on the functional structure of molluscan community from hypersaline estuary
    Hydrobiologia (IF 2.325) Pub Date : 2020-01-04
    Rafaela Cristina de Souza Duarte, Graciele de Barros, Silvia Vendruscolo Milesi, Thelma Lucia Pereira Dias

    Abstract Studies based on functional approach seek to understand the ecological roles developed by species as well as their interactions with the environment in which they are inserted. The hypothesis tested was that functional richness and diversity of molluscan community will be higher at the most complex macroalgal habitat. The study was carried out at Casqueira river estuary (Rio Grande do Norte, Brazil). Three species of macroalgae were collected—Gracilaria domingensis (Kützing) Sonder ex Dickie 1874, Gracilaria cuneata Areschoug 1854, and Solieria filiformis (Kützing) P.W.Gabrielson 1985—and the composition of seven functional traits of the mollusk fauna associated to the algae was characterized in 22 categories. The highest values of functional richness and diversity were for macroalgae with greater habitat complexity (G. domingensis). Some functional traits were influenced more by macroalgal morphology, like ‘life way,’ feeding strategy, body size, and larval development. Thus, we show that the greatest richness and functional diversity of the communities is related to sites with more complex habitat, sites with more shelter and refuge, and food. This highlights the importance of the quality of habitat for shellfish communities and shows that it can be assessed from the use of a functional approach.

  • Landscape-scale drivers of fish faunal homogenization and differentiation in the eastern United States
    Hydrobiologia (IF 2.325) Pub Date : 2020-01-02
    Brandon K. Peoples, Amy J. S. Davis, Stephen R. Midway, Julian D. Olden, Lauren Stoczynski

    Abstract Establishment of nonnative fishes and extirpations of native fishes have homogenized freshwater fish faunas, yet our understanding of the drivers of this process remain limited. We addressed this knowledge gap by testing three hypotheses about introductions and homogenization of fish communities is the eastern United States: First, whether nonnative fish introductions have caused fish faunas to become homogenized or differentiated; second, whether patterns of faunal change are related to native species richness, propagule pressure, and anthropogenic disturbance; third, whether invasion patterns are attributable to either biotic resistance or preadaptation. We compared taxonomic similarity among watersheds in historical and contemporary time steps, and modeled contributions of different drivers to faunal change within watersheds. Average similarity among watersheds nearly doubled in contemporary times, pointing to substantial fish faunal homogenization. No watersheds lost species; patterns of homogenization are attributable entirely to nonnative species invasion. Community change and nonnative richness were positively associated with agriculture-urban land use, recreational fishing demand, and elevation. Native richness negatively affected community change and nonnative richness. Nonnative species originated from watersheds with higher richness than the ones they invaded, suggesting a role for biotic resistance. Understanding how mechanisms operate across spatial scales will help guide future conservation efforts.

  • Interannual variation in filling season affects zooplankton diversity in Mediterranean temporary ponds
    Hydrobiologia (IF 2.325) Pub Date : 2020-01-02
    M. Florencio, R. Fernández-Zamudio, Mayca Lozano, C. Díaz-Paniagua

    Abstract In Mediterranean temporary ponds, the timing of annual flooding is highly variable and depends on heavy seasonal rains. Ponds can flood in the autumn, winter, or spring, and thus the environmental conditions faced by emerging zooplankton can be very different. We performed an experiment in a climatic chamber where we simulated annual variation in natural temperature and light conditions to study how differences in pond-filling season affected zooplankton assemblage composition. We sampled sediments from a temporary pond and placed them in aquariums that were filled with water during three different seasons: autumn (October), winter (January), and spring (March). Zooplankton abundance, species richness, diversity, and assemblage composition differed significantly among treatments, and post-inundation temperature and pH appeared to be the main drivers of these differences. Diversity was highest in the winter treatment. It was lower in the autumn treatment and the spring treatment, and no indicator species were present in the latter. Our results suggest that interannual variability in initial inundation conditions favours the emergence of different species and thus contributes to high species richness in the egg bank. However, climate change and/or groundwater drawdown could delay pond flooding, impoverishing the zooplankton assemblage in the long term.

  • Didymosphenia geminata blooms are not exclusively driven by low phosphorus under experimental conditions
    Hydrobiologia (IF 2.325) Pub Date : 2020-01-02
    Derek C. West, Jared A. Balik, Mitchell Owens, Brad W. Taylor

    Despite two decades of research, the cause of blooms of the diatom Didymosphenia geminata remains uncertain. Blooms have been associated with low nutrient, oligotrophic streams. In this study, we used available data from across the globe and conducted experiments to determine how D. geminata responds to soluble reactive phosphorus (SRP) concentrations. Globally, D. geminata blooms have been found in streams with SRP below 11 μg P l−1. In North America, blooms only occurred at high equivalent latitudes when SRP was very low, whereas at lower latitudes blooms were observed under higher SRP concentrations. Using an in situ experiment, we found that following physical removal of D. geminata from stones, regrowth did not occur despite low SRP concentrations. In a second experiment, we found that there were no differences in D. geminata growth between a treatment which depleted SRP and a treatment which maintained elevated springtime SRP levels. These findings indicate that D. geminata blooms do not always form when SRP is low, even when cells are present. Bloom formation that is not exclusively related to low SRP suggests additional chemical or biotic factors, specific physical conditions, a seasonal timing requirement, or some combination of these with low P that are necessary to produce blooms.

  • Temporal changes in the bacterioplankton of a Northeast Ohio (USA) River.
    Hydrobiologia (IF 2.325) Pub Date : 2003-10-14
    J Liu,L G Leff

    To examine temporal changes in a bacterial community, water samples were collected monthly for one year from five sites along a major use-reuse river, the Cuyahoga River, in northeastern Ohio (USA). Fluorescent in situ hybridization (FISH) was used to enumerate population sizes of two species of common bacteria, Pseudomonas putida and Acinetobacter calcoaceticus; FISH was also performed with a Domain Bacteria specific probe. In addition, the total bacteria (based on DAPI staining), colony forming units (on modified Nutrient agar) and coliforms were enumerated and supporting physical/chemical data were collected. Each variable examined exhibited a different seasonal pattern. Temporal changes in total number of bacteria and population size of P. putida were correlated with turbidity and precipitation suggesting that allochthonous sources and scouring of the benthos may be major contributors to these portions of the community. In contrast, the number of cells hybridizing the Domain Bacteria and A. calcoaceticus probes were correlated with temperature. Thus, different aspects of the bacterial community are potentially controlled by different factors and the role of allochthonous and autochthonous sources may vary among species.

  • Lipophilic pigments from the benthos of a perennially ice-covered Antarctic lake.
    Hydrobiologia (IF 2.325) Pub Date : 1989-01-01
    A C Palmisano,R A Wharton,S E Cronin,D J Des Marais

    The benthos of a perennially ice-covered Antarctic lake, Lake Hoare, contained three distinct 'signatures' of lipophilic pigments. Cyanobacterial mats found in the moat at the periphery of the lake were dominated by the carotenoid myxoxanthophyll; carotenoids: chlorophyll a ratios in this high light environment ranged from 3 to 6.8. Chlorophyll c and fucoxanthin, pigments typical of golden-brown algae, were found at 10 to 20 m depths where the benthos is aerobic. Anaerobic benthic sediments at 20 to 30 m depths were characterized by a third pigment signature dominated by a carotenoid, tentatively identified as alloxanthin from planktonic cryptomonads, and by phaeophytin b from senescent green algae. Pigments were not found associated with alternating organic and sediment layers. As microzooplankton grazers are absent from this closed system and transformation rates are reduced at low temperatures, the benthos beneath the lake ice appears to contain a record of past phytoplankton blooms undergoing decay.

  • Perennially ice-covered Lake Hoare, Antarctica: physical environment, biology and sedimentation.
    Hydrobiologia (IF 2.325) Pub Date : 1989-01-01
    R A Wharton,G M Simmons,C P McKay

    Lake Hoare (77 degrees 38' S, 162 degrees 53' E) is a perennially ice-covered lake at the eastern end of Taylor Valley in southern Victoria Land, Antarctica. The environment of this lake is controlled by the relatively thick ice cover (3-5 m) which eliminates wind generated currents, restricts gas exchange and sediment deposition, and reduces light penetration. The ice cover is in turn largely controlled by the extreme seasonality of Antarctica and local climate. Lake Hoare and other dry valley lakes may be sensitive indicators of short term (< 100 yr) climatic and/or anthropogenic changes in the dry valleys since the onset of intensive exploration over 30 years ago. The time constants for turnover of the water column and lake ice are 50 and 10 years, respectively. The turnover time for atmospheric gases in the lake is 30-60 years. Therefore, the lake environment responds to changes on a 10-100 year timescale. Because the ice cover has a controlling influence on the lake (e.g. light penetration, gas content of water, and sediment deposition), it is probable that small changes in ice ablation, sediment loading on the ice cover, or glacial meltwater (or groundwater) inflow will affect ice cover dynamics and will have a major impact on the lake environment and biota.

  • Rhopalium development in Aurelia aurita ephyrae.
    Hydrobiologia (IF 2.325) Pub Date : 1991-06-28
    D B Spangenberg

    Rhopalia of developing ephyrae were examined using the SEM and TEM at 24 h intervals following strobilation induction. Kinocilia are shorter in the ephyra stage than in polyps. A few ephyra-type kinocilia are found in rhopalia as early as 24 h after induction, before a distinct rhopalium is seen. By 72 h, the shorter kinocilia predominate and are almost as numerous as in ephyrae (120 h). Many of the kinocilia are associated with mechanoreceptor cells (MR) found in the rhopalia. These MR cells are compared to those reported for medusae. Although newly released ephyrae lack a touch plate, the MR cells in their rhopalia along with the statocyst and neuromuscular system apparently enable these organisms to detect and respond to gravity.

  • Spatial and temporal dynamics of a freshwater eukaryotic plankton community revealed via 18S rRNA gene metabarcoding.
    Hydrobiologia (IF 2.325) Pub Date : 2018-01-01
    A Banerji,M Bagley,M Elk,E Pilgrim,J Marinson,J Santo Domingo

    DNA metabarcoding is a sophisticated molecular tool that can enhance biological surveys of freshwater plankton communities by providing broader taxonomic coverage and, for certain groups, higher taxonomic resolution compared to morphological methods. We conducted 18S rRNA gene metabarcoding analyses on 214 water samples collected over a four-month period from multiple sites within a freshwater reservoir. We detected 1,314 unique operational taxonomic units that included various metazoans, protists, chlorophytes, and fungi. Alpha diversity differed among sites, suggesting local habitat variation linked to differing species responses. Strong temporal variation was detected at both daily and monthly scales. Diversity and relative abundance patterns for several protist groups (including dinoflagellates, ciliates, and cryptophytes) differed from arthropods (e.g., cladocerans and copepods), a traditional focus of plankton surveys. This suggests that the protists respond to different environmental dimensions and may therefore provide additional information regarding ecosystem status. Comparison of the sequence-based population survey data to conventional-based data revealed similar trends for taxa that were ranked among the most abundant in both approaches, although some groups were missing in each data set. These results highlight the potential benefit of supplementing conventional biological survey approaches with metabarcoding to obtain a more comprehensive understanding of freshwater plankton community structure and dynamics.

  • Pathways and places associated with nonindigenous aquatic species introductions in the Laurentian Great Lakes.
    Hydrobiologia (IF 2.325) Pub Date : 2019-07-06
    Elon M O'Malia,Lucinda B Johnson,Joel C Hoffman

    Propagule pressure (i.e., the frequency and abundance of introductions) is a common indicator of the likelihood of nonindigenous aquatic species (NAS) establishment success. Evaluating propagule pressure associated with multiple introduction pathways relative to present NAS distribution patterns may identify which pathway presents the greatest risk. Our objective was to develop and evaluate three geospatial metrics for the Laurentian Great Lakes as proxies of propagule pressure associated with three major introduction pathways: maritime commerce, organisms in trade, and water recreation. Logistic and linear regression analyses were conducted between NAS presence and introduction pathway intensity (e.g., number of vessel trips received by a port) for 23 NAS over a five-decade period (1970 - 2013). Notably, city population size was the best predictor of NAS presence, even for NAS introduced through ballast water discharge. Moreover, through time, city population size was an increasingly significant predictor of the presence of organisms in trade, signaling a change in both the types of organisms introduced and places where introductions are occurring. Nonetheless, all three metrics are reasonable proxies for propagule pressure and as such are applicable for risk assessment, monitoring, and control strategies.

  • Single colony genetic analysis of epilithic stream algae of the genus Chamaesiphon spp.
    Hydrobiologia (IF 2.325) Pub Date : 2018-03-21
    Rainer Kurmayer,Guntram Christiansen,Andreas Holzinger,Eugen Rott

    In order to understand Chamaesiphon spp. evolution and ecological diversification, we investigated the phylogenetic differentiation of three morphospecies from field samples by means of single colony genetics. Individual colonies of three different morphospecies (C. starmachii, C. polonicus, C. geitleri,) were isolated from lotic gravel streams and their 16S rDNA nucleotide variability was analyzed. For a number of individual colonies, microscopical and ultrastructural analysis was also performed. A phylogenetic tree of all major lineages of the phylum of Cyanobacteria assigned all Chamaesiphon genotypes (1149-1176 bp) most closely with the family of Gomontiellaceae of the order Oscillatoriales. The sequences obtained from colonies assigned to C. starmachii (n = 21), C. polonicus (n = 9), and C. geitleri (n = 17) were found to reveal high average (3.5%) nucleotide diversity. No phylogenetic sub-branching in correspondence with morphology was observed suggesting that the three Chamaesiphon morphospecies did not represent monophyletic taxa. We could not attribute specific thylakoid ultrastructure to phylogenetic sub-branches; however, the observed parietally and loosely arranged thylakoids indicate that for the genus Chamaesiphon, the variability in thylakoid ultrastructure might have been underestimated. In summary, the high nucleotide diversity of the 16S rDNA gene implies phylogenetic diversity that corresponds little to morphological classification.

  • Additive genetic variance of quantitative traits in natural and pond-bred populations of the Lake Tanganyika cichlid Tropheus moorii.
    Hydrobiologia (IF 2.325) Pub Date : 2012-01-01
    Martin Koch,Alastair J Wilson,Michaela Kerschbaumer,Thomas Wiedl,Christian Sturmbauer

    Quantitative genetic studies in natural populations are of growing interest to speciation research since divergence is often believed to arise through micro-evolutionary change, caused by natural selection on functional morphological traits. The species flock of cichlid fishes in Africa's oldest lake, Lake Tanganyika, offers a rare opportunity to study this process. Using the cichlid species Tropheus moorii, we assessed the potential for microevolution in a set of morphological traits by estimating their quantitative genetic basis of variation. Two approaches were employed: (1) estimation of trait heritabilities (h2) in situ from a sample of wild caught fish, and (2) estimation of h2 from first generation offspring produced in a semi-natural breeding experiment. In both cases, microsatellite data were used to infer pedigree structure among the sampled individuals and estimates of h2 were made using an animal model approach. Although power was limited by the pedigree structures estimated (particularly in the wild caught sample), we nonetheless demonstrate the presence of significant additive genetic variance for aspects of morphology that, in the cichlid species Tropheus moorii, are expected to be functionally and ecologically important, and therefore likely targets of natural selection. We hypothesize that traits showing significant additive genetic variance, such as the mouth position have most likely played a key role in the adaptive evolution of the cichlid fish Tropheus moorii.

  • Big fish, little divergence: phylogeography of Lake Tanganyika's giant cichlid, Boulengerochromis microlepis.
    Hydrobiologia (IF 2.325) Pub Date : 2015-05-20
    Stephan Koblmüller,Elizabeth A Odhiambo,Danny Sinyinza,Christian Sturmbauer,Kristina M Sefc

    The largely endemic cichlid species flocks of the East African Great Lakes are among the prime examples for explosive speciation and adaptive radiation. Speciation rates differ among cichlid lineages, and the propensity to radiate has been linked to intrinsic and extrinsic factors such as sexual selection and ecological opportunity. Remarkably, only one cichlid tribe-the Boulengerochromini-comprises just a single species, Boulengerochromis microlepis, a predominantly piscivorous endemic of Lake Tanganyika and the world's largest cichlid. While the lineage diverged from its closest relatives at the onset of the Lake Tanganyika radiation >8 MYA, mitochondrial control region sequences collected in this study dated the most recent common ancestor of B. microlepis to ~60-110 KYA. There was no evidence of phylogeographic structure in the lake-wide sample. Patterns of genetic diversity and demographic analyses were consistent with slow and steady population growth throughout the reconstructed timescale. Additionally, the shallow divergence within the species may be related to a possibly large variance in reproductive success in this highly fecund species. Trophic niche space restriction by sympatric piscivores, lack of geographic structure, low potential for sexual selection arising from the monogamous mating system and extinction may have contributed to keeping the lineage monotypic.

  • Spatial variation of phytoplankton composition, biovolume, and resulting microcystin concentrations in the Nyanza Gulf (Lake Victoria, Kenya).
    Hydrobiologia (IF 2.325) Pub Date : 2012-07-01
    L Sitoki,R Kurmayer,E Rott

    The Nyanza Gulf is a large shallow bay of Lake Victoria suffering from eutrophication by human activities. In order to characterize the harmful algal bloom formation as a consequence of eutrophication, both spatially and seasonally, environmental conditions, phytoplankton community composition, and microcystin (MC) concentrations were investigated monthly from Kisumu Bay, and bimonthly from the center of the gulf, as well as quarterly from the Rusinga Channel and the main basin of Lake Victoria between July 2008 to September 2009. The sites located in Kisumu Bay and the central gulf were most strongly affected by eutrophication, including increased nutrient concentrations and phytoplankton growth. More than 90% of the samples obtained from the gulf were dominated by cyanobacteria, whereas diatoms only dominated in the samples obtained from Rusinga Channel and the main lake. In general Microcystis accounted for the largest part (> 50-90%) of cyanobacterial biovolume. MCs were found in 35 (54%) out of 65 samples and were detected throughout the study period in the gulf, but only in two out of eight samples from the Rusinga Channel and the main lake. A significant linear relationship between Microcystis biovolume and MC concentration was observed (n = 65, R2 = 0.88, p <0.001). Highest MC concentrations were recorded in Kisumu Bay between November and March (max. 81 μg l-1) when Microcystis showed max. biovolume (18 mm3 l-1 in November 2008). The results suggest that seasonal variability did not outweigh the spatial differences in phytoplankton composition and MC production that is seasonally persistent in Kisumu Bay.

  • The ecological potentials of Phytomyxea ("plasmodiophorids") in aquatic food webs.
    Hydrobiologia (IF 2.325) Pub Date : 2011-02-23
    Sigrid Neuhauser,Martin Kirchmair,Frank H Gleason

    The Phytomyxea ("plasmodiophorids") including both Plasmodiophorida and Phagomyxida is a monophyletic group of Eukaryotes composed of obligate biotrophic parasites of green plants, brown algae, diatoms and stramenopiles commonly found in many freshwater, soil and marine environments. However, most research on Phytomyxea has been restricted to plant pathogenic species with agricultural importance, thereby missing the huge ecological potential of this enigmatic group of parasites. Members of the Phytomyxea can induce changes in biomass in their hosts (e.g. hypertrophies of the host tissue) under suitable environmental conditions. Upon infection they alter the metabolism of their hosts, consequently changing the metabolic status of their host. This results in an altered chemical composition of the host tissue, which impacts the diversity of species which feed on the tissues of the infected host and on the zoospores produced by the parasites. Furthermore, significant amounts of nutrients derived from the hosts, both primary producers (plants and algae) and primary consumers (litter decomposers and plant parasites [Oomycetes]), can enter the food web at different trophic levels in form of zoospores and resting spores. Large numbers of zoospores and resting spores are produced which can be eaten by secondary and tertiary consumers, such as grazing zooplankton and metazoan filter-feeders. Therefore, these microbes can act as energy-rich nutrient resources which may significantly alter the trophic relationships in fresh water, soil and marine habitats. Based on the presented data, Phytomyxea can significantly contribute to the complexity and energy transfer within food webs.

  • Past lake shore dynamics explain present pattern of unidirectional introgression across a habitat barrier.
    Hydrobiologia (IF 2.325) Pub Date : 2019-06-13
    Kristina M Sefc,Karin Mattersdorfer,Caroline M Hermann,Stephan Koblmüller

    Introgression patterns between divergent lineages are often characterized by asymmetry in the direction and among-marker variation in the extent of gene flow, and therefore inform on the mechanisms involved in differentiation and speciation. In the present study, we test the hypothesis that unidirectional introgression between two phenotypically and genetically distinct lineages of the littoral, rock-dwelling cichlid fish Tropheus moorii across a wide sandy bay is linked to observed differences in mate preferences between the two lineages. This hypothesis predicts bi-directional nuclear gene flow and was rejected by congruent patterns of introgression in mtDNA, AFLP and microsatellite markers, with admixture confined to the populations west of the bay. This pattern can be explained on the basis of habitat changes in the course of lake level fluctuations, which first facilitated the development of a symmetric admixture zone including the area corresponding to the present sand bay and then shaped asymmetry by causing local extinctions and cessation of gene flow when this area became once more inhabitable. This conforms with previous assumptions that habitat dynamics are a primary determinant of population-level evolution in Tropheus. In this respect, Tropheus may be representative of species whose preferred habitat is subject to frequent re-structuring.

  • Bacterial community structure in freshwater springs infested with the invasive plant species Hydrilla verticillata.
    Hydrobiologia (IF 2.325) Pub Date : 2015-07-25
    N Gordon-Bradley,N Li,H N Williams

    The phylogenetic composition and physiological profiles of bacterial communities in freshwater springs were evaluated during the blooming and non-blooming stages of the invasive plant species, Hydrilla verticillata. Community-level physiological profiles (CLPPs) and pyrosequencing of 16S rRNA gene amplicons were used to study potential Hydrilla mediated shifts in the physiological potential and phylogenetic composition of the bacterial community in infested systems. The results of CLPP revealed that the microbes in the Hydrilla invaded sites utilized less substrates during blooming periods than during nonblooming periods of the plant. Spearman's rank correlation analysis showed some relationships between the relative abundances of bacterial taxa and the Biolog substrate utilization pattern. The relative abundance of the identified taxa showed some striking differences based on the blooming status of Hydrilla and to a lesser extent on site variation. The relative abundance of Actinobacteria, Bacteriodetes, and Verrucomicrobia was generally higher during Hydrilla blooms, while Deltaproteobacteria was generally higher during non-blooming stages of Hydrilla. The detected genera also varied based on the blooming stages of the plant. Based on the findings, it appears that Hydrilla alters the phylogenetic composition and structure of the bacterial community during the blooming stage.

  • Limited hybridization between introduced and Critically Endangered indigenous tilapia fishes in northern Tanzania.
    Hydrobiologia (IF 2.325) Pub Date : 2019-03-19
    Stephanie J Bradbeer,Jack Harrington,Henry Watson,Abrahim Warraich,Asilatu Shechonge,Alan Smith,Rashid Tamatamah,Benjamin P Ngatunga,George F Turner,Martin J Genner

    Hybridization between introduced and indigenous species can lead to loss of unique genetic resources and precipitate extinction. In Tanzania, the Nile tilapia (Oreochromis niloticus) and blue-spotted tilapia (Oreochromis leucostictus) have been widely introduced to non-native habitats for aquaculture and development of capture fisheries. Here, we aimed to quantify interspecific hybridization between these introduced species and the indigenous species Oreochromis esculentus, Oreochromis jipe and Oreochromis korogwe. In the Pangani basin, several hybrids were observed (O. niloticus × O. jipe, O. leucostictus × O. jipe, O. niloticus × O. korogwe), although hybrids were relatively uncommon within samples relative to purebreds. Hybrids between the native O. jipe × O. korogwe were also observed. In the Lake Victoria basin, no evidence of hybrids was found. Analysis of body shape using geometric morphometrics suggested that although purebreds could be discriminated from one another, hybrids could not be readily identified on body and head shape alone. These results provide the first evidence of hybridization between the introduced species and the Critically Endangered O. jipe in Tanzania. Given uncertainty regarding benefits of introduced species over large-bodied indigenous species in aquaculture and capture fisheries, we suggest that future introductions of hybridization-prone species should be carefully evaluated.

  • Widespread colonisation of Tanzanian catchments by introduced Oreochromis tilapia fishes: the legacy from decades of deliberate introduction.
    Hydrobiologia (IF 2.325) Pub Date : 2019-03-19
    Asilatu Shechonge,Benjamin P Ngatunga,Stephanie J Bradbeer,Julia J Day,Jennifer J Freer,Antonia G P Ford,Jonathan Kihedu,Tabitha Richmond,Semvua Mzighani,Alan M Smith,Emmanuel A Sweke,Rashid Tamatamah,Alexandra M Tyers,George F Turner,Martin J Genner

    From the 1950s onwards, programmes to promote aquaculture and improve capture fisheries in East Africa have relied heavily on the promise held by introduced species. In Tanzania these introductions have been poorly documented. Here we report the findings of surveys of inland water bodies across Tanzania between 2011 and 2017 that clarify distributions of tilapiine cichlids of the genus Oreochromis. We identified Oreochromis from 123 sampling locations, including 14 taxa restricted to their native range and three species that have established populations beyond their native range. Of these three species, the only exotic species found was blue-spotted tilapia (Oreochromis leucostictus), while Nile tilapia (Oreochromis niloticus) and Singida tilapia (Oreochromis esculentus), which are both naturally found within the country of Tanzania, have been translocated beyond their native range. Using our records, we developed models of suitable habitat for the introduced species based on recent (1960-1990) and projected (2050, 2070) East African climate. These models indicated that presence of suitable habitat for these introduced species will persist and potentially expand across the region. The clarification of distributions provided here can help inform the monitoring and management of biodiversity, and inform policy related to the future role of introduced species in fisheries and aquaculture.

  • An exploration of the links between parasites, trophic ecology, morphology, and immunogenetics in the Lake Tanganyika cichlid radiation.
    Hydrobiologia (IF 2.325) Pub Date : 2019-03-19
    Britta S Meyer,Pascal I Hablützel,Anna K Roose,Melinda J Hofmann,Walter Salzburger,Joost A M Raeymaekers

    Differences in habitat and diet between species are often associated with morphological differences. Habitat and trophic adaptation have therefore been proposed as important drivers of speciation and adaptive radiation. Importantly, habitat and diet shifts likely impose changes in exposure to different parasites and infection risk. As strong selective agents influencing survival and mate choice, parasites might play an important role in host diversification. We explore this possibility for the adaptive radiation of Lake Tanganyika (LT) cichlids. We first compare metazoan macroparasites infection levels between cichlid tribes. We then describe the cichlids' genetic diversity at the major histocompatibility complex (MHC), which plays a key role in vertebrate immunity. Finally, we evaluate to what extent trophic ecology and morphology explain variation in infection levels and MHC, accounting for phylogenetic relationships. We show that different cichlid tribes in LT feature partially non-overlapping parasite communities and partially non-overlapping MHC diversity. While morphology explained 15% of the variation in mean parasite abundance, trophic ecology accounted for 16% and 22% of the MHC variation at the nucleotide and at the amino acid level, respectively. Parasitism and immunogenetic adaptation may thus add additional dimensions to the LT cichlid radiation.

  • Only true pelagics mix: comparative phylogeography of deepwater bathybatine cichlids from Lake Tanganyika.
    Hydrobiologia (IF 2.325) Pub Date : 2019-03-19
    Stephan Koblmüller,Lukas Zangl,Christine Börger,Daniel Daill,Maarten P M Vanhove,Christian Sturmbauer,Kristina M Sefc

    In the absence of dispersal barriers, species with great dispersal ability are expected to show little, if at all, phylogeographic structure. The East African Great Lakes and their diverse fish faunas provide opportunities to test this hypothesis in pelagic fishes, which are presumed to be highly mobile and unrestricted in their movement by physical barriers. Here, we address the link between panmixis and pelagic habitat use by comparing the phylogeographic structure among four deepwater cichlid species of the tribe Bathybatini from Lake Tanganyika. We show that the mitochondrial genealogies (based on the most variable part or the control region) of the four species are very shallow (0.8-4% intraspecific divergence across entire distribution ranges) and that all species experienced recent population growth. A lack of phylogeographic structure in the two eupelagic species, Bathybates fasciatus and B. leo, was consistent with expectations and with findings in other pelagic cichlid species. Contrary to expectations, a clear phylogeographic structure was detected in the two benthopelagic species, B. graueri and Hemibates stenosoma. Differences in genetic diversity between eupelagic and benthopelagic species may be due to differences in their dispersal propensity, mediated by their respective predatory niches, rather than precipitated by external barriers to dispersal.

  • Genetic and morphological population differentiation in the rock-dwelling and specialized shrimp-feeding cichlid fish species Altolamprologus compressiceps from Lake Tanganyika, East Africa.
    Hydrobiologia (IF 2.325) Pub Date : 2012-01-01
    Maria Luise Spreitzer,Selma Mautner,Lawrence Makasa,Christian Sturmbauer

    With about 250 endemic species, Lake Tanganyika contains an extraordinarily diverse cichlid fish fauna, and thus represents an ideal model system for the study of pathways and processes of speciation. The Lamprologini form the most species-rich tribe in Lake Tanganyika comprising about 100 species in seven genera, most of which are endemic to the lake. They are territorial substrate-breeders and represent a monophyletic tribe. By combined analysis of population genetics and geometric morphometric markers, we assessed gene flow among three populations of the highly specialized shrimp-feeding rock-dweller Altolamprologus compressiceps, separated by geographic distance and ecological barriers. Five highly polymorphic microsatellite markers were analyzed in conjunction with 17 landmarks in order to compare genetic differences to body shape differences among populations. Both genetic and morphological analyses revealed significant differentiation among the three studied populations. A significant, but overall relatively low degree of genetic differentiation supports a very recent divergence. Phenotypic differentiation was primarily found in the head region of A. compressiceps. In agreement with findings in other cichlid species, similar adaptations to specialized feeding mechanisms can consequently lead to marginal shape changes in the trophic apparatus.

  • Female preferences for male traits and territory characteristics in the cichlid fish Tropheus moorii.
    Hydrobiologia (IF 2.325) Pub Date : 2015-05-20
    Caroline M Hermann,Verena Brudermann,Holger Zimmermann,Johann Vollmann,Kristina M Sefc

    Female mate preferences for male traits and resource characteristics affect trait evolution and diversification. Here, we test the effects of male body traits and territory characteristics on within-population female preferences and on population-assortative mating in the cichlid Tropheus moorii. Within-population preferences of females were independent of male body size, coloration and territory size but were strongly dependent on territory quality and co-varied with male courtship activity. Courtship activity of individual males was contingent on the quality of their assigned territory, and therefore, courtship may not only indicate intrinsic male quality. On the basis of these results we suggest that female preferences for high-quality territories reinforce the outcome of malemale competition and ensure male mating success. Mating preferences of females for males of their own color variant (ascertained in a previous experiment) were not overturned when males of another color variant were presented in a superior territory, indicating that within- and between-population mate preferences of females depend on different cues.

  • Concordant female mate preferences in the cichlid fish Tropheus moorii.
    Hydrobiologia (IF 2.325) Pub Date : 2012-02-01
    Bernd Steinwender,Stephan Koblmüller,Kristina M Sefc

    Discriminating female mate preferences enhance the variance in reproductive success among males of a population and create a potential for sexual selection, which can account for trait evolution and diversification. Fish color patterns are among the prime targets of mate choice-driven sexual selection. Populations of the cichlid Tropheus from Lake Tanganyika display remarkable geographic color pattern variation, but the role of female choice in their rapid and rich phenotypic diversification is unclear. Males and females establish a pair bond prior to spawning monogamously, but as brood care is strictly maternal, female investment in reproduction is high and the operational sex ratio is male-biased. Therefore, variance in male reproductive success can accrue if individual males succeed repeatedly in securing a mate. To test this prediction in the red colored Tropheus moorii "Chimba", four pairs of males were presented to a series of females and female mate preferences were inferred from pairwise interactions. There was a significant difference in mating success between the males of each pair (P < 0.001 over all trials), as-with one exception-females shared preferences for the same males. Male courtship activity was strongly correlated with female choice. Our experiment suggests that female choice contributes to the variance in male reproductive success in the tested population.

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