Short CommunicationNew insights about species delimitation in red snappers (Lutjanus purpureus and L. campechanus) using multilocus data
Graphical abstract
Introduction
In the Western Atlantic, the “red snapper-complex” represents a group of eupercarian fishes of the family Lutjanidae with high commercial value that have conserved morphology and coloration, being formed by L. vivanus, L. peru, L. campechanus and L. purpureus (Gold et al., 2015, Rivas, 1966). The northern red snapper (L. campechanus) and the southern red snapper (L. purpureus) have non overlapping distributions since the former is found from the Gulf of Mexico to the Florida Keys (Allen, 1985, Anderson, 2003), while L. purpureus is distributed in some localities in Florida, Yucatan Peninsula, the Caribbean Sea, extending southwards up to the northeastern coast of Brazil (Anderson, 2003, Moura and Lindeman, 2007). The taxonomic status of L. campechanus and L. purpureus has been a matter of controversy in the past. Rivas (1966) diagnosed both species based on differences in the number of scales on, above, and below the lateral line and in the length of pectoral fins. Later, Cervigón (1993) pointed out a remarkable similarity in the putative diagnostic features for both species, such as the overlapped number of spines in anal fins, suggesting that L. campechanus and L. purpureus should be regarded as a single species with some degree of morphological variation throughout their range.
Molecular studies based on mitochondrial DNA (mtDNA) failed to differentiate haplogroups corresponding to each species, revealing high genetic similaritiy between L. campechanus and L. purpureus, with several shared mtDNA haplotypes (Gomes et al., 2008, Gomes et al., 2012). In agrement with these results, Da Silva et al. (2018) tested the performance of molecular delimitation methods in snappers based on a single locus (cytochrome oxidase subunit I), and found that L. campechanus and L. purpureus formed a single unit under all methods tested. Thus, the mtDNA data corroborate the hypothesis proposed by Cervigón (1993) placing L. purpureus and L. campechanus as variant forms of a widespread species with recent genetic divergence among populations.
In contrast to these studies, a genome-wide analysis based on RAD sequence data (Pedraza-Marrón et al., 2019) with more than 15,000 loci strongly supported the isolation and differentiation of the northern and southern red snappers as distinct taxonomic entities. They also provided evidence of hybridization in some intermediate populations, with an inferred direction of gene flow across species boundaries (introgression) from north to south (L. campechanus to L. purpureus). This putative introgression would explain the lack of differentiation at mtDNA loci between the two species. However, available methods to study the delimitation of species in the presence of gene flow (Jackson et al., 2017, Morales et al., 2017) require gene trees as input, which could not be implemented with SNP data.
Under this context, the development of multilocus coalescent methods represents an advantageous approach in molecular taxonomy, allowing the accurate delimitation of evolutionary units (Yang and Rannala, 2012), including those that have recently diverged (Leaché et al., 2018), as well as a precise estimate of demographic parameters such as gene flow and historical effective size (Hey and Pinho, 2012, Morales et al., 2017). This information is particularly relevant to infer speciation processes over short periods of genetic divergence (Leaché et al., 2014). The goal of this study is to estimate the demographic history and species-specific boundaries in L. campechanus and L. purpureus based on multiple mitochondrial and nuclear loci (Control region, ribosomal protein S7-intron 1, Myostatin-Intron 2, and Insulin Growth Factor) using multilocus coalescent methods.
Section snippets
Sample collection
The samples (muscle or fin tissue) of L. campechanus were collected in four sites of Western Atlantic coast (Fig. 1 and Table 1). All specimens were identified according the identification keys available in literature (Cervigón, 1993). The samples were stored in microtubes with 96% ethanol. In the case of L. purpureus, we used the DNA sequences available in da Silva et al. (2016) for Brazilian coast and we also collected in two sites of Western Atlantic (Fig. 1 and Table 1).
Laboratorial procedures
The DNA extraction
Characterization of the dataset
In the present study, a total of 1478 base pairs were obtained, corresponding to four genomic regions, including a mitochondrial fragment and three nuclear loci (Table 1). Recombination events were observed in both S7 and Myostatin introns (Phi w < 0.05). In these cases, the largest recombination-free regions (Myostatin 2 = 316 bp and S7 1 = 245 bp) were used in analyses that demand non-recombinant regions (e.g., IMa2). The number of sequenced specimens (N), size of fragments (bp), number of
Discussion
The visual analysis of the genealogies based on each independent nuclear genomic region revealed some degree of admixture between both species herein studied. In turn, the interpretation of the genealogy inferred from mtDNA data suggested an asymmetric flow of individuals from each putative taxon (L. campechanus → L. purpureus).
The species delimitation methods support the hypothesis that Lutjanus campechanus and Lutjanus purpureus should represent two independent evolutionary units, since high
CRediT authorship contribution statement
Raimundo da Silva: Conceptualization, Methodology, Formal analysis, Writing - original draft. Carmen del R. Pedraza-Marrón: Conceptualization, Resources, Writing - original draft. Iracilda Sampaio: Funding acquisition, Supervision, Resources, Writing - review & editing. R. Ricardo Betancur: Conceptualization, Resources, Writing - original draft. Grazielle Gomes: Funding acquisition, Supervision, Resources, Writing - review & editing. Horacio Schneider: Funding acquisition, Supervision,
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001 and by Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq (Grants 484601/2013-0 to GG). The authors would like to thank to the fishermen that helped during the field sampling, David L. Nieland, Kristin Foss, Debra Murie and Jonathan Deeds for collecting and providing tissue samples.
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