Multigene Molecular Systematics Confirm Species Status of Morphologically Convergent Pagurus Hermit Crabs

Joana Matzen Da Silva,Marina R Cunha,Simon Creer,Antonina Dos Santos,Filipe O Costa,Gary R Carvalho

doi:10.1371/journal.pone.0028233

Joana Matzen Da Silva, Marina R Cunha + Show 4 more

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https://doi.org/10.1371/journal.pone.0028233

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Abstract

IntroductionIn spite of contemporary morphological taxonomy appraisals, apparent high morphological similarity raises uncertainty about the species status of certain Pagurus hermit crabs. This is exemplified between two European species, Pagurus excavatus (Herbst, 1791) and Pagurus alatus (Fabricius 1775), whose species status is still difficult to resolve using morphological criteria alone.Methodology/Principal FindingsTo address such ambiguities, we used combinations of Maximum Likelihood (ML) and Bayesian Inference (BI) methods to delineate species boundaries of P. alatus and P. excavatus and formulate an intermediate Pagurus phylogenetic hypothesis, based upon single and concatenated mitochondrial (cytochrome oxidase I [COI]) and nuclear (16S and 28s ribosomal RNA) gene partitions. The molecular data supported the species status of P. excavatus and P. alatus and also clearly resolved two divergent clades within hermit crabs from the Northeast Atlantic Ocean and the Mediterranean Sea.Conclusions/SignificanceDespite the abundance and prominent ecological role of hermit crabs, Pagurus, in North East Atlantic Ocean and Mediterranean Sea ecosystems, many important aspects of their taxonomy, biology, systematics and evolution remain poorly explored. The topologies presented here should be regarded as hypotheses that can be incorporated into the robust and integrated understanding of the systematic relationships within and between species of the genus Pagurus inhabiting the Northeast Atlantic Ocean and the Mediterranean Sea.

Highlights

In spite of contemporary morphological taxonomy appraisals, apparent high morphological similarity raises uncertainty about the species status of certain Pagurus hermit crabs
The high observed percentage of parsimony-informative character suggests that cytochrome oxidase I (COI) is sufficiently diverse for intrageneric phylogeny and clearly resolved all eleven Pagurus species examined in the present study (Figure 1) [31,32]
A similar pattern has been observed in penaied shrimps [33], porcelanids crabs [34], diogenid hermit crabs [35] and has been attributed to stabilizing selection on morphological/ecological characters, or that they are on independent evolutionary trajectories

Summary

Introduction

In spite of contemporary morphological taxonomy appraisals, apparent high morphological similarity raises uncertainty about the species status of certain Pagurus hermit crabs. This is exemplified between two European species, Pagurus excavatus (Herbst, 1791) and Pagurus alatus (Fabricius 1775), whose species status is still difficult to resolve using morphological criteria alone. 172 species (of which five are fossil records) are recognised [9] , that possess specialized adaptations for housing stability, relying upon gastropod shells for protection Such commensalism has constrained morphological evolution over 150 million years [7,8] by requiring a decalcified asymmetrical abdomen capable of looping into gastropod shells. Despite the abundance of hermit crabs in the North East Atlantic and Mediterranean Sea [6] many important aspects of their taxonomy [10], biology [11,12,13,14,15,16,17,18], ecology [17,19,20,21,22], systematics and evolution [3,8,23] are poorly documented

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