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

Abstract

Background Marine 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. Results A 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. Discussion The 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.

Patterns of variation of mutation rates of mitochondrial and nuclear genes of gastropods

“…1, Table 2). The species contained in the ten datasets that have relatively large values of µ m /µ n exclusively represent members of single genera that have radiated recently [15][16][17][18][19][20][21][22][23]. For example, the Conus dataset that represents an outlier ( µ m /µ n = 56.7) includes 44 members of the Cape Verde species flock, a group of species that may have radiated explosively during the past few million years [15,24,25].…”

An approach using ddRADseq and machine learning for understanding speciation in Antarctic Antarctophilinidae gastropods

“…Contrary, the deep-sea fauna is less diverse, with only two species known to date. Independent colonization of the continental shelf from the slope during interglacial cycles, < 23 Mya 14 , 41 , and the presence of habitat refugia in the Antarctic Peninsula tip and adjacent islands 42 , 43 may explain the high species endemism and richness found in this study—but this remains to be tested. This phenomenon has been referred to as the Antarctic Biodiversity Pump 21 , 44 and sustains habitat fragmentation during glacial maxima as the driving force towards allopatric speciation.…”

“…The onset of the ACC led to the isolation of the Antarctic continent and subsequent cool down with the likely extinction of shallow-water faunas 17 . During interglacial periods of shelf ice retreat, the unpopulated shelf could have been re-colonized by fauna from the slope 54 or shelters on the continental shelf 14 , 42 , 43 . Species dispersal and gene flow at subtidal and shelf depths have been increasingly studied in SO areas with enough evidence of contrasting patterns related to the disparity in species life histories 55 , 56 , usually challenging the concept of well-connected, circumpolar distributions 57 – 59 but see Moore et al 60 .…”

New records of associations between ectoparasitic snails of the genus <i>Mucronalia</i> (Caenogastropoda: Eulimidae) and their ophiuroid hosts from Japan and New Caledonia, with description of a new species

“…A similar pattern of host specificity has been observed in the asteroid-endoparasitic eulimid genus Asterophila. Layton et al (2019) reconstructed relationships of Antarctic species of the genus based on multi-gene sequences, resulting in six infrageneric lineages where species of each lineage parasitize asteroids of a single order. Furthermore, the host of several eulimid genera has been so far restricted to a single echinoderm family (Ponder & Gooding 1978, Warén 1980b, Warén & Crossland 1991, Takano & Goto 2021): e.g., Asterolamia to Astropectinidae (Asteroidea); Goodingia to Comatulidae (Crinoidea); Pulicicochlea to Diadematidae (Echinoidea); Trochostilifer to Cidaridae (Echinoidea); and Turveria to Mellitidae (Echinoidea).…”