Abstract
AbstractEnvironmental conditions were particularly severe during the Last Glacial Maximum, altering the distribution of the Southern Hemisphere biota, particularly at higher latitudes. The copepod Boeckella poppei is the only macroscopic continental invertebrate species known to be distributed today across the three main biogeographic regions in Antarctica as well as in southern South America. Signy Island (South Orkney Islands) is a unique location for the study of Antarctic freshwater ecosystems due to its location and geographic isolation; it contains 17 lakes in several low altitude catchments. We conducted phylogeographic and demographic analyses using the cox1 gene on 84 individuals of B. poppei from seven lakes across Signy Island. We recorded low levels of genetic diversity and a strong genetic differentiation signal between the eastern and western valleys within the island. Phylogeographic structure and demographic inference analyses suggested at least one asymmetrical dispersal event from west to east. Demographic inference detected a strong signal of population growth during the deglaciation process, which may have followed either (1) a strong genetic bottleneck due to a reduction in population size during the last glacial period, or (2) a founder effect associated with postglacial recolonization of Signy Island from elsewhere. The genetic architecture of this island's populations of B. poppei shows that historical events, rather than continuous dispersal events, likely played a major role in the species' current distribution. Finally, our study considers possible mechanisms for dispersal and colonization success of the most dominant species in the Antarctic freshwater community.
Highlights
Environmental conditions were severe during the Last Glacial Maximum (LGM), between 23,000 and 18,000 years before present (YBP), with thicker and more extensive ice sheets covering low-altitude terrain in continental and maritime Antarctica, including the Scotia Arc archipelagos as well as sub-Antarctic South Georgia, Patagonia and parts of New Zealand (Hodgson et al 2014; Brown et al 2017)
In Three Lakes Valley, Heywood Lake exhibited the lowest diversity in terms of haplotype diversity (Hd) and allelic richness (R) (Hd = 0.389, R = 1.972, n = 8), while Pumphouse Lake showed the greatest diversity (Hd = 0.464, R = 3.748, n = 14), with five haplotypes (Table 1)
Concluding remarks Our results clearly emphasize the complexity of historical and recent processes, which have molded the genetic architecture of B. poppei within Signy Island
Summary
An alternative scenario for the E–C model, “cryptic or in situ refugia”, proposes that some populations may have persisted throughout the period of glaciation in suitable high-latitude refugia within the affected area, from which they recolonized the impacted area during deglaciation (Stewart and Lister 2001; Provan and Bennett 2008; Fraser et al 2014). This model gives rise to predictions routinely tested using genetic data. It predicts that, once habitats became available again during the Holocene, recently colonized higher-latitude populations should retain the genetic signature of a short demographic history, denoting recent population expansion following the loss of genetic variation due to a prior reduction in population size (i.e., genetic bottleneck) and low levels of current genetic diversity (Hewitt 2000, 2004)
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