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

Kara K S Layton,Nerida G Wilson,Greg W Rouse

doi:10.1186/s12862-019-1499-8

Abstract

BackgroundMarine invertebrates are abundant and diverse on the continental shelf in Antarctica, but little is known about their parasitic counterparts. Endoparasites are especially understudied because they often possess highly modified body plans that pose problems for their identification. Asterophila, a genus of endoparasitic gastropod in the family Eulimidae, forms cysts in the arms and central discs of asteroid sea stars. There are currently four known species in this genus, one of which has been described from the Antarctic Peninsula (A. perknasteri). This study employs molecular and morphological data to investigate the diversity of Asterophila in Antarctica and explore cophylogenetic patterns between host and parasite.ResultsA maximum-likelihood phylogeny of Asterophila and subsequent species-delimitation analysis uncovered nine well-supported putative species, eight of which are new to science. Most Asterophila species were found on a single host species, but four species were found on multiple hosts from one or two closely related genera, showing phylogenetic conservatism of host use. Both distance-based and event-based cophylogenetic analyses uncovered a strong signal of coevolution in this system, but most associations were explained by non-cospeciation events.DiscussionThe prevalence of duplication and host-switching events in Asterophila and its asteroid hosts suggests that synchronous evolution may be rare even in obligate endoparasitic systems. The apparent restricted distribution of Asterophila from around the Scotia Arc may be an artefact of concentrated sampling in the area and a low obvious prevalence of infection. Given the richness of parasites on a global scale, their role in promoting host diversification, and the threat of their loss through coextinction, future work should continue to investigate parasite diversity and coevolution in vulnerable ecosystems.

Highlights

Marine invertebrates are abundant and diverse on the continental shelf in Antarctica, but little is known about their parasitic counterparts
A. japonica has been found in eight host species from four families and three orders [16] while A. perknasteri has been found from three different Perknaster species [15] and A. rathbunasteri has been found only from a single host (Rathbunaster californicus) [15]
Asterophila was found between the epidermis and coelomic lining, with no affiliation to specific organs or body systems

Summary

Introduction

Marine invertebrates are abundant and diverse on the continental shelf in Antarctica, but little is known about their parasitic counterparts. This study employs molecular and morphological data to investigate the diversity of Asterophila in Antarctica and explore cophylogenetic patterns between host and parasite. A. japonica has been found in eight host species from four families and three orders [16] while A. perknasteri has been found from three different Perknaster species [15] and A. rathbunasteri has been found only from a single host (Rathbunaster californicus) [15]. Because these parasites display a highly simplified body plan for their endoparasitic lifestyle, only a few morphological characters have been shown to be informative between species [16]. Little is known about Antarctic eulimids in general, despite a potentially high diversity of species in the region [12]

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