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

Citation

Fontaneto, Diego et al. (2021), Comparative phylogeography reveals consistently shallow genetic diversity in a mitochondrial marker in Antarctic bdelloid rotifers, Dryad, Dataset, https://doi.org/10.5061/dryad.sj3tx964b

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 (1) 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 (2) 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 geographic 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 by 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 geographic 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.

Methods

In total, 228 new sequences of 661 base pairs of the mitochondrial marker cytochrome c oxidase subunit I (COI) from Antarctic bdelloid rotifers were generated from single animals collected in the field. Animals were collected across the continent, mostly from Scott and Enderby areas and the Antarctic Peninsula. DNA was extracted using Chelex or HotShot protocol and the COI Folmer fragment was amplified using the HCO2198 and LCO1490 primers. 263 other previously published sequences from the same species were gathered from the literature.

1587 sequences from species of bdelloid rotifers living outside Antarctica were gathered from published literature. We kept all the species with at least 15 sequences longer than 500 base pairs and that passed quality filtering controls, such as not having stop codons within the reading frame. In addition, 164 sequences were obtained from Philodina megalotrocha in North America.

For each Antarctic COI sequence, we obtained the WGS84 geographic coordinates of the population of origin. For the previously published sequences, such data were obtained from the archives of the authors of the sequences. For the non-Antarctic species, we gathered detailed geographic coordinates only for a subset of well-sampled species with at least 60 sequences.

Funding

Italian National Antarctic Research Program (PNRA, www.pnra.it), Award: 2013/AZ1.13

Italian National Antarctic Research Program (PNRA, www.pnra.it), Award: PNRA16_00120-A1 (TNB-CODE)

National Science Foundation, Award: DEB 0516032

Czech OP RDE, Award: EVA4.0 No. CZ.02.1.01/0.0/0.0/16_019/0000803

Italian National Antarctic Research Program (PNRA, www.pnra.it), Award: 2013/AZ1.13

Czech OP RDE, Award: EVA4.0 No. CZ.02.1.01/0.0/0.0/16_019/0000803