Incorrect identification of invasive Indo-Pacific member of the bivalve genus Mytilopsis can affect construction of molecular phylogenies
Introduction
The bivalve family Dreissenidae includes two genera that have a long history of becoming invasive species, Dreissena (Beneden, 1835) has invaded fresh waters of Eurasia and North America (Locard 1893; Hebert et al. 1989; Mills et al. 1996; Bij de Vaate et al., 2002, Carlton, 2008; Benson 2009; Higgins and Vander Zanden 2010). Mytilopsis (Conrad, 1831) has invaded brackish waters of Western Europe, Western equatorial Africa, South America, the Indo-Pacific region and, recently, Eastern Europe (Laine et al., 2006, Nuttall, 1990; Verween et al. 2010; Mumladze et al., 2019, Tan and Tay, 2018; Fernandes et al. 2020). In 1967, a species of Mytilopsis was discovered in Visakhapatnam, India and identified as Mytilopsis sallei (Récluz, 1849) based on unreported morphological criteria (Ganapati et al. 1971; Morton 1970). Papp (1950) had previously reported that a species of Congeria occurred in “middle India,” but did not assign a specific name to this species. Morton (1981) described the biology and functional morphology of the bivalve from Viskhapatnam and later reported the life history of presumably the same species in the newly invaded Hong Kong (Morton 1989). Morton, 1981, Morton, 1989 suggested that the Indo-Pacific Mytilopsis was M. sallei, a western Atlantic tropical species, and that it had likely been introduced to the Pacific by shipping through the Panama Canal. Four species of Mytilopsis have been described from the Pacific: M. trautwineana (Tryon, 1866), M. adamsi Morrison 1946, M. allyneana Hertlein and Hanna 1949 and M. zeteki Hertlein and Hanna 1949, although Morton (1981) believed that M. allyneana was a junior synonym of M. sallei and that the species exhibited extremely variable morphology. Marelli and Gray (1985) considered M. allyneana and M. zeteki to be junior synonyms of M. adamsi and that M. trautwineana was a separate and distinct species. Similarly, Marelli and Gray (1985) affirmed that the western Atlantic M. leucophaeata (Conrad, 1831) and M. sallei should be treated as unique species and distinct from the eastern Pacific and Indo-Pacific representatives of Mytilopsis. Tan and Tay (2018) consider M. adamsi to be a junior synonym of M. sallei, suggesting that M. allyneana and M. zeteki should also be considered junior synonyms of M. sallei.
Recently Queiroz et al. (2020), working with an invasive population of M. sallei in Brazil, supported the invasive history described by Morton, 1981, Morton, 1989. Phylogenies of Dreissenidae have been created from molecular data of the Mytilopsis cf. sallei collected from the Indo-Pacific (2010; Wong et al. 2011; Bilandžija et al. 2013; Geda et al. 2018). I review the history of Mytilopsis in the Indo-Pacific region and explain why the invasive Mytilopsis is unlikely to be M. sallei.
Section snippets
Methods
Specimens of Mytilopsis were examined from the collections of the United States Museum of Natural History (USNM), the Academy of Natural Sciences, Philadelphia (ANSP), and the California Academy of Sciences (CAS). Included in the USNM collection was the holotype of M. adamsi (USNM 542184). Included in the CAS collection were the holotypes of M. allyneana (CAS-IZ Cat. No. 65461) and M. zeteki (CAS-IZ Cat. No. 65463). Specimens of Mytilopsis from recent samplings in Serangoon (Singapore),
Morphological characters
The valves of members of Mytilopsis share characters that may be used as basis for morphological comparison. The mussel-like valve is narrowly rounded or pointed in the anterior end, and the dorsal margin can be smoothly arched in its entirety or resemble a flattened curve in the anterior end, becoming more rounded in the posterior portion of the valve. The posterior margin may be smoothly rounded or more quadrate in form. The ventral margin may be nearly straight, gently convex, a combination
Results and discussion
Mytilopsis sallei can be distinguished from M. adamsi on the basis of morphology. Valves of M. sallei are higher and narrower than those of M. adamsi, and the M. sallei shell is typically sharply convex on its dorsal margin and sharply concave on its ventral margin with a well-developed byssal notch. The dorsal margin of M. adamsi is smoothly arched and the ventral valve margin is nearly straight with a weakly-developed byssal notch. The posterior byssal retractor muscle scars of M. adamsi are
Conclusion
The brackish water bivalve Mytilopsis probably invaded Fiji in the late 1800s and has subsequently been spread by invasive vectors to many places in the Indo-Pacific. Morphological evidence, historical documentation, scientific literature, museum records and genetic evidence suggest that this species is M. adamsi and not M. sallei.
Additional research on the genome of the various Mytilopsis populations along with further work on the morphology of the animals can help to determine the
Ethical approval
This article does not contain any studies with animals performed by any of the authors.
Sampling and field studies
No permits were required to conduct the work described in this article.
Data availability
Information on material examined during the course of this work is available from the author on request.
Declaration of Competing Interest
The author declares no conflict of interest.
Acknowledgments
This work was greatly improved by access to collection in the U.S. National Museum (USNM), the Academy of Natural Sciences of Philadelphia (ANSP), and the California Academy of Sciences (CAS). Dr. Barry Roth, formerly of The CAS Geology Department, was particularly helpful in providing space to work with shell collections. Christina Piotrowski, CAS Invertebrate Zoology collections manager helped to locate information on the type specimens of Mytilopsis adamsi and arranged for images of the
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