Is Antarctica an evolutionary incubator? Phylogenetic comparative study of the amphipod family Iphimediidae on the Antarctic shelf

Around 40 million years ago, Antarctica’s geographic isolation led to a dramatic cooling of its marine shelf, causing many lineages to go extinct whilst others adapted and flourished. Among the successful ones is the amphipod family Iphimediidae. Here, we apply advanced phylogenetic, comparative, and morphometric methods to explore the evolutionary processes which generated the exceptional diversity of this clade. To this purpose, three types of data were collected: (1) a novel phylogeny of the family was reconstructed from a multigene molecular dataset, (2) 3D shape data were obtained by applying geometric morphometric methods on micro-CT scans, and (3) stable isotope ratios (δ13C and δ15N) were measured and used as proxy for trophic ecology. First, possible evolutionary correlations between mouthpart shapes and stable isotope ratios were examined. Significant correlations suggest that mouthpart shapes are adapted to the food source. Second, species boundaries were investigated using a combination of DNA-based delimitation methods and detailed morphological/morphometric analyses, revealing that Iphimediidae species diversity is greatly underestimated. Most described species were found to be complexes of multiple, morphologically similar species. Finally, changes in lineage diversification rates were explored alongside the evolution of morphological traits. Late bursts of lineage diversification (appr. 7-3 Mya) combined with a late partitioning of mouthparts’ shape diversity might result from the invasion of novel ecological niches. Plio-Pleistocene glacial cycles, which have been hypothesized to act as a diversity pump, might also have promoted such late diversification events in Antarctic iphimediids. This integrative approach, applied here for the first time in Antarctic invertebrates, enhances our understanding of the evolutionary dynamics shaping Antarctic shelf biodiversity.

Abstract of an Oral Presentation or a Poster