Gone with Gondwana: Amphipod diversification in freshwaters followed the breakup of the supercontinent.

The evolutionary origins of modern taxa are best understood as arising from the interplay of vicariance and dispersal. Vicariant events have long been considered responsible for Gondwanan distributions; such species are relics of the eponymic supercontinent on which they were thought to have originated. One such set of taxa are the freshwater members of the amphipod superfamily Hyaloidea, which due to their marine relatives and current distributions serve as an excellent model for testing vicariance and dispersal hypotheses. We investigated the evolutionary and biogeographic histories of the Hyaloidea using a molecular phylogenetic approach. Maximum likelihood analyses and Bayesian inference, using two nuclear genes and one mitochondrial gene, reveal the freshwater amphipods within the superfamily (Hyalellidae/Chiltoniidae) as a monophyletic group diverging from their extant marine ancestors during the Mesozoic. This is suggestive of the group entering freshwater relatively early, instead of geologically recent marine invasions as have been previously hypothesized. Despite the group's apparent monophyly, it is likely that marine hyaloids exploited shallow water marine/brackish habitats created following the breakup of Gondwana to invade continental freshwaters. Given the divergence times recorded and shallow cladogenetic events observed, it is possible that this occurred through multiple invasions by closely related taxa. Mesozoic invasions by the Hyaloidea suggest that freshwater members represent a much older lineage than previously considered, occupying continental freshwaters prior to the gammarids in the Cenozoic and contemporaneouslywith the crangonyctids in the Mesozoic. Our results highlight the Gondwanan origin of taxa with enigmatic distributions and the utility of amphipods for testing biogeographic hypotheses that infer the origin of freshwater taxa.

Past climate cooling promoted global dispersal of amphipods from Tian Shan montane lakes to circumboreal lakes.

Climate changes have substantial impacts on the geographic distribution of montane lakes and evolutionary dynamics of cold-adapted species. Past climate cooling is hypothesized to have promoted the dispersal of cold-adapted species via montane lakes, while future climate warming is thought to constrain their distributions. We test this hypothesis by using phylogeographic analysis and niche modeling of the Holarctic crustacean Gammarus lacustris with global sampling comprised of 567 sequenced individuals and 3180 occurrence records. We found that the species arose in Tian Shan in Central Asia and dispersed into montane lakes along the Alps, Himalayas, Tibet, East Asia, and the North American Rocky Mountain ranges, with accelerated diversification rates outside Tian Shan. Climatically suitable regions for geographic lineages of G. lacustris were larger during cooling periods (LGM), but smaller during warming periods (Mid-Holocene). In the future (2070) scenario, potential distributions in the Himalayas, North Tibet, South Tibet and North America are predicted to expand, whereas ranges in East Asia, Europe and Tian Shan will decline. Our results suggest that Mid-Miocene-to-Pleistocene continuous cooling promoted multiple independent dispersal events out of Tian Shan due to increased availability of montane lakes via "budding" of lineages. Montane lakes are conduits through which cold-adapted amphipods globally dispersed, dominating circumboreal lakes. However, future climate warming is likely to force organisms to shift upward in altitude and northward in latitude, leading to a future change in local populations. These findings highlight the importance of conservation of montane lakes, especially in the context of climate change.

Two new species of the genus Crangonyx Bate, 1859 (Amphipoda: Crangonyctidae) from the St. Marks River Basin with notes on the "Crangonyx floridanus complex".

Crangonyx ephemerus n. sp. and Crangonyx pseudoephemerus n. sp. are described from the headwaters of the St. Marks River in Leon County, Florida, based on detailed morphological and molecular comparisons with the closely related species Crangonyx floridanus Bousfield, 1963. The morphological and molecular data, including three species delimitation models, lend support to the hypothesis that the taxon C. floridanus sensu lato represents a species complex. Diagnostic morphological characteristics are highlighted and discussed within this group to assist in future morphological analyses.