Abstract
AbstractAimWe investigated evolutionary relationships and biogeographical patterns within the genus Boeckella to evaluate (1) whether its current widespread distribution in the Southern Hemisphere is due to recent long‐distance dispersal or long‐term diversification; and (2) the age and origin of sub‐Antarctic and Antarctic Boeckella species, with particular focus on the most widely distributed species: Boeckella poppei.LocationSouth America, sub‐Antarctic islands, maritime Antarctica, continental Antarctica and Australasia.MethodsTo reconstruct phylogenetic patterns of Boeckella, we used molecular sequence data collected from 12 regions and applied Bayesian and Maximum Likelihood analyses using multiple loci. We also estimated divergence times and reconstructed ancestral ranges using two different models of species evolution.ResultsPhylogenetic analyses and divergence time estimates suggested that Boeckella originated on the Gondwanan supercontinent and initially split into two main clades during the late Cretaceous (ca. 80 Ma). The first clade diversified in Australasia, and the second clade is currently distributed in South America, various sub‐Antarctic islands and Antarctica. Dispersal from South America to the Kerguelen and Crozet archipelagos occurred during the Eocene/Oligocene (B. vallentini) and in the late Pliocene (B. brevicaudata), while South Georgia and the maritime Antarctic were likely colonized during the late Pleistocene (B. poppei).Main conclusionsBoeckella has a Gondwanan origin, with further diversifications after the physical separation of the continental landmasses. Extant populations of Boeckella from the Scotia Arc islands and Antarctic Peninsula originated from South America during the Pleistocene, suggesting that original Antarctic Gondwanan lineages did not survive repeated glacial cycles during the Quaternary ice ages. A continuous decline in the species accumulation rate is apparent within the genus as the early Eocene, suggesting that Boeckella diversification may have decreased due to progressive cooling throughout the Cenozoic era.
Highlights
In the Southern Hemisphere, clades with widely distributed taxa have long represented fascinating models to study historical biogeography and diversification patterns
Among the newly collected samples, we identified B. vallentini from Kerguelen (KRG) and Crozet Islands (CRZ), B. brasiliensis from southern South America (SA), B. brevicaudata from Kerguelen and southern South America, B. meteoris from southern South America and B. poppei from southern South America, South Georgia (SG), Antarctic Peninsula (AP), South Orkney Islands (SOI) and South Shetland Islands (SSI), the latter three locations being within maritime Antarctica (MA) (Figure 1)
We suggest that the nominal species, B. poppei, corresponds to clade i, which includes specimens collected at the type locality, South Georgia (Poppe & Mrázek, 1895)
Summary
In the Southern Hemisphere, clades with widely distributed taxa have long represented fascinating models to study historical biogeography and diversification patterns. The species B. poppei (Mrázek, 1901) has the broadest distribution and is the only representative of the genus in Antarctica today (Bayly et al, 2003; Díaz et al, 2019; Maturana et al, 2019; Menu- Marque et al, 2000), where it is restricted to freshwater bodies in seasonally or permanently snow- or ice-free areas, on glacier surfaces and epishelf lakes (Laybourn-Parry & Pearce, 2007) It has been reported in lakes in continental Antarctica (King Charles Mountains, Bayly et al, 2003; Gibson & Bayly, 2007), Alexander Island, the Antarctic Peninsula, the South Shetland and South Orkney Islands in maritime Antarctica and sub-Antarctic South Georgia, as well as in southern South America and the Falkland/Malvinas Islands (Bayly et al, 2003; Maturana et al, 2019; Menu-Marque et al, 2000). This study provides new information on the biogeography and evolution of higher latitude freshwater biota, whose ecosystems are sensitive to environmental change (Convey & Peck, 2019)
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