Host specificity versus plasticity: testing the morphology-based taxonomy of the endoparasitic copepod family Splanchnotrophidae with COI barcoding

Abstract

The Splanchnotrophidae is a family of highly modified endoparasitic copepods known to infest nudibranch or sacoglossan sea slug hosts. Most splanchnotrophid species appear to be specific to a single host, but some were reported from up to nine different host species. However, splanchnotrophid taxonomy thus far is based on external morphology, and taxonomic descriptions are, mostly, old and lack detail. They are usually based on few specimens, with intraspecific variability rarely reported. The present study used molecular data for the first time to test (1) the current taxonomic hypotheses, (2) the apparently strict host specificity of the genus Ismaila and (3) the low host specificity of the genus Splanchnotrophus with regard to the potential presence of cryptic species. Phylogenetic analyses herein used sequences of the barcoding region of the cytochrome oxidase I (COI) gene from 40 specimens representing 13 species of five genera. Species delimitation approaches include distance and barcoding gap analyses, haplotype networks and diagnostic nucleotides. Molecular results are largely compatible with the commonly accepted, morphology-based taxonomy of the Splanchnotrophidae. Strict host specificity could be confirmed for two Ismaila species. COI analyses also supported the idea that Splanchnotrophus angulatus is host-promiscuous. In Ismaila, morphology seems more suitable than barcoding to display speciation events via host switches in a recent Chilean radiation. In Splanchnotrophus, some genetic structure suggests ongoing diversification, which should be investigated further given the inadequate morphology-based taxonomy. The present study thus supports the presence of two different life history strategies in splanchnotrophids, which should be explored integratively.

Polyphyly of the traditional family Flabellinidae affects a major group of Nudibranchia: aeolidacean taxonomic reassessment with descriptions of several new families, genera, and species (Mollusca, Gastropoda)

“…In aeolidaceans clear preference is currently given to the molecular data and a classification is often constructed following the molecular phylogenetic trees (e.g., Carmona et al 2013 ; Cella et al 2016 ). Because there is no epistemological evidence that molecular data should have preference over morphological features (e.g., Mishler 1994 ; Giribet 2010 ; Bazsalovicsová et al 2014 ; Jenner 2015 ; Anton et al 2016 ), we have developed several operational rules: 1) Both morphological and molecular data should be utilised in the resulting classification; 2) Morphologically highly aberrant taxa (e.g., family- or genus-level) nested inside numerous taxa with disparate morphology should not be united with the rest of the related taxa but kept separate to highlight significant morphological differences; 3) Taxa for which molecular data persistently indicate the heterogeneous nature of a traditional taxon (e.g., family level) with apparently similar morphology (“para-” or “polyphyly”) should be separated into several taxa of the same rank; 4) Large-volume genera incorporating numerous species should be avoided because they considerably obscure both morphological and molecular diversity and do not properly allow the recognition of hidden diversity.…”

External diversity is restrained by internal conservatism: New nudibranch mollusc contributes to the cryptic species problem

“…Furthermore, there are cases of the opposite situation, that is, “morphologically cryptic species,” when a valid and universally accepted species pair display morphological differences, but are very similar genetically, for example, in cichlid fishes, blue butterflies and bats (Bickford et al., ; Mayer & von Helversen, ; Wiemers & Fiedler, ). Most recently morphologically distinct endoparasitic copepods have been recovered as genetically identical (Anton et al., ). There are also numerous theoretical and practical problems in molecular species delimitation (Carstens, Pelletier, Reid, & Satler, ; Dejaco, Gassner, Arthofer, Schlick‐Steiner, & Steiner, ; Murphy, King, & Delean, ; Pante et al., ; Puillandre, Lambert, Brouillet, & Achaz, ).…”

A newly discovered radiation of endoparasitic gastropods and their coevolution with asteroid hosts in Antarctica

“…Recent studies have also highlighted difficulties in using morphological characters for species delimitation in highly modified endoparasites (e.g. splanchnotrophid copepods [24, 31]), and this work further demonstrates that molecular data is critical for resolving species boundaries in endoparasites that often lack informative external characters.…”

“…Alternatively, the high level of host specificity and host switching observed in this system, and the sympatric distribution of most parasites and hosts, could indicate that parasites are able to diversify and adapt to new hosts in sympatry, rather than through allopatric speciation (e.g. [24]).…”

“…myzostomid worms and crinoids [22], nematodes and stick insects [23]), and some endoparasites show host promiscuity (e.g. copepods and nudibranchs [24]). Although echinoderm-parasitizing eulimid gastropods are diverse and exhibit a variety of parasitic lifestyles [25, 26], most prior work has focused only on the morphology and ecology of this clade and little is known about the evolution of parasitism in the group.…”