Tracing patterns of glacial refugia with Scottnema lindsayae nematode in McMurdo Dry Valleys, Antarctica.

Background/Question/Methods

: As part of a Long-Term Ecological Research (LTER) site, the McMurdo Dry Valleys (MDV) of Antarctica boast thirty plus years of multidisciplinary data from an infamously harsh environment that fosters neither high terrestrial biodiversity nor species recruitment. Freezing temperatures and saline soils limit terrestrial life to simple, patchily dispersed microbial communities and microscopic soil invertebrates, providing a unique opportunity to study nematodes in a naturally simplified environment. Taking advantage of this natural laboratory, we aimed to test phylogeographic hypotheses regarding dispersal patterns of terrestrial free-living nematodes after large-scale environmental disruptions like ice-sheet dynamics, glacial advance and recession, and climate-driven changes to the soil environment. We tested putative glacial refugia on a fine-scale utilizing the mitochondrial COI gene of the most ubiquitous terrestrial animal in Antarctica – Scottnema lindsayae – by determining phylogeographic patterns shaped by historical glacial cycles and subsequent dispersal. We sequenced 250 bp COI haplotypes from 24 sites across eight valley systems in the MDV. These sites represent high and low elevations corresponding to putative refugia and recolonized glacial forefields respectively. We analyzed phylogeographic patterns of haplotype diversity in the context of hypothesis testing consistent with persistent refugia.

Results/Conclusions

: Results reveal highly structured genetic diversity of S. lindsayae in the MDVs. High elevational, putative refugial populations predicted to have signatures of higher genetic diversity are found to have low haplotype diversity indicating the slow rate of evolutionary change in these frozen environments and dispersal limitations. Conversely, recently colonized glacial forefields have comparatively higher haplotype diversity within populations perhaps due to increased connectivity on the valley floor through ephemeral streams, channelized katabatic winds, or paleolake legacies. Utilizing phylogeographic approaches on the most ubiquitous microfauna species, S. lindsayae, refugia hypothesis testing can be applied on a fine, universally applicable scale. Foremost, this study demonstrates phylogeographic patterns of dispersal from Antarctic refugia where terrestrial biota survived in situ periods of extreme climate-driven environmental changes. Secondly, as populations are highly structured and gene flow is low, our results support that S. lindsayae respond slowly to disturbances. With future climate-driven disturbances, slow response, colonization, and dispersal will likely have a disproportionate impact on carbon cycling given S. lindsayae’s dominant role in this low-diversity ecosystem.