Comparative phylogeography reveals consistently shallow genetic diversity in a mitochondrial marker in Antarctic bdelloid rotifers

Abstract

Aim The long history of isolation of the Antarctic continent, coupled with the harsh ecological conditions of freezing temperatures, could affect the patterns of genetic diversity in the organisms living there. We aim (a) to test whether such pattern can be seen in a mitochondrial marker of bdelloid rotifers, a group of microscopic aquatic and limno‐terrestrial animals and (b) to speculate on the potential mechanisms driving the pattern. Location Focus on Antarctica. Taxon Rotifera Bdelloidea. Methods We analysed different metrics of genetic diversity, also spatially explicit ones, including number of haplotypes, accumulation curves, genetic distances, time to the most recent common ancestor, number of independently evolving units from DNA taxonomy, strength of the correlation between geographical and genetic distances, population genetics neutrality and differentiation indices, potential historical processes, obtained from an extensive sample of cytochrome oxidase subunit I (COI) sequences obtained from bdelloid rotifers. We included 2242 individuals from 23 species in a comparison between Antarctic and non‐Antarctic taxa, correcting for sample size directly in the analyses and then by confirming the results also using only a restricted dataset of nine well‐sampled species. Results Antarctic species had consistently lower genetic diversity and potential younger relative age than non‐Antarctic species, even if they were similar in sample size, geographical extent, neutrality and differentiation indices, and correlation between genetic and geographical distances. Main conclusions The extensive survey of genetic diversity in one mitochondrial marker in Antarctic bdelloids supports previous suggestions from other organisms that the origin and maintenance of terrestrial Antarctic fauna are different from those of other continents. Such differences could be speculated to be due, in the case of bdelloid rotifers, to the more recent origin of the species living there in comparison to non‐Antarctic species.

Exploring the plant environmental DNA diversity in soil from two sites on Deception Island (Antarctica, South Shetland Islands) using metabarcoding

“…If so, this would suggest that most plants present today should be relatively recent in origin, colonizing as ice retreated. This possibility has been widely challenged in recent years by a range of molecular biological and biogeographical studies across multiple groups of invertebrates, microbes and plants (Chong et al 2015, Iakovenko et al 2015, Biersma et al 2018b, Cakil et al 2021, Verleyen et al 2021) that support a much more ancient origin and Antarctic distinctness of much of the contemporary terrestrial biota that must therefore have survived in situ in Antarctica during repeated glaciations (Convey et al 2020). However, some studies of both mosses (Biersma et al 2018a) and the native angiosperm Colobanthus quitensis (Biersma et al 2020) have pointed to species with more recent, mid-to late Pleistocene, origins in Antarctica.…”

Meta‐analysis of Antarctic phylogeography reveals strong sampling bias and critical knowledge gaps

“…2) and obtaining data from an array of species from less-sampled regions should be a key priority for future research (Box 1). Low sample sizes for some regions and taxa, as noted in other studies (McGaughran et al 2019, Cakil et al 2021) has likely affected our analyses. In particular, the low sample sizes from regions beyond the Peninsula and Victoria Land could mean we are drastically underestimating the true genetic diversity of some parts of Antarctica.…”

The need for increased protection of Antarctica's inland waters

“…Dartnall's (2017) review also indicates that, while all other oases contain one or more of these copepods, none have yet been reported from the Schirmacher Oasis, although this apparent gap may simply reflect the absence of sampling. Iakovenko et al (2015) and Cakil et al (2021) have examined Antarctic bdelloid rotifers, a group that is abundant within a variety of inland waters. Their studies emphasize how a fauna that was historically assumed to be largely cosmopolitan is now recognized as highly endemic, and they also stressed that 'the concept of endemism is itself limited by the quality and extent of the data available'.…”

“…Iakovenko et al (2015) and Cakil et al (2021) have examined Antarctic bdelloid rotifers, a group that is abundant within a variety of inland waters. Their studies emphasize how a fauna that was historically assumed to be largely cosmopolitan is now recognized as highly endemic, and they also stressed that ‘the concept of endemism is itself limited by the quality and extent of the data available’.…”