Life history, patchy distribution, and patchy taxonomy in a shallow-water invertebrate (Mollusca: Polyplacophora: Lepidopleurida)

Julia D Sigwart,Chong Chen

doi:10.1007/s12526-017-0688-1

Abstract

Things without names are difficult to rationalise, and so species that go without names are difficult to conserve or protect. This is a case study in resolving conflicts in historical taxonomy and ‘real’ species (identifiable and evolutionarily relevant groupings) using an approach including population genetics, natural history, and pragmatism. We report the observation that populations of a shallow-water chiton species from Washington and British Columbia demonstrate extremely high site fidelity and patchy distribution. Their limited dispersal potential and isolation could be explained by a brooding life history. This stands in direct contrast with the supposedly wide distribution of this “species”, Leptochiton rugatus (Carpenter in Pilsbry, 1892) sensu lato, from the Sea of Japan to Baja California. But this lineage has previously been suggested to comprise several cryptic species. Indeed, a haplotype network analysis using 61 individual sequences of the cytochrome oxidase c subunit I gene for L. rugatus s.l. revealed four discrete clusters which correspond to different parts of the geographic range. We infer these to represent four distinct species, at least two of which are likely novel. Leptochiton rugatus sensu stricto is herein reinterpreted as restricted to California and Baja California, and the new name L. cascadiensis sp. nov. is established for the lineage with a distribution in the Cascadia coastal bioregion from the panhandle of Alaska to Oregon. There are minor morphological differences among these species in the L. rugatus species complex, but genetic data or morphological observations alone would not have been sufficient to definitively recognise these groups as species-level lineages. The observation that different species within the complex may have different life history strategies provides important support for interpreting different populations as genuinely separate species.

Highlights

Genetic information has repeatedly revealed higher levels of first-order diversity than traditional morphological assessment
Many species of the genus Leptochiton are known from deepsea habitats, but several species are known from shallow water, including the North Pacific Leptochiton rugatus (Carpenter in Pilsbry, 1892)
To examine the potential genetic differences among the Leptochiton aff. “rugatus” species complex, we assembled all available published COI sequences attributed to Leptochiton rugatus sensu lato and species that resolved within the L. rugatus clade in previous analyses (Sigwart et al 2011; Sigwart 2016), and added sequences from two intermediate populations in Washington and Oregon, USA

Summary

Introduction

Genetic information has repeatedly revealed higher levels of first-order diversity than traditional morphological assessment. Many species of the genus Leptochiton are known from deepsea habitats, but several species are known from shallow water, including the North Pacific Leptochiton rugatus (Carpenter in Pilsbry, 1892) This species (complex) ranges from the Sea of Japan across to Alaska, down the coast of North American to Baja California (Kaas and Van Belle 1985). We report an example of a cryptic species complex, describing one new species and noting the presence of two additional lineages that remain unresolved In this case, morphological or molecular differences alone would not have been sufficient to recognise species-level lineages, but new observations of brooding behaviour in one population and the inferred limitation on dispersal in the group shed new light on these animals

Materials and methods

Discussion

Compliance with ethical standards