Résumé
During the Cenozoic, Australia experienced major climatic shifts that have
had dramatic ecological consequences for the modern biota. Mesic tropical
ecosystems were progressively restricted to the coasts and replaced by
arid-adapted floral and faunal communities. Whilst the role of
aridification has been investigated in a wide range of terrestrial
lineages, the response of freshwater clades remains poorly investigated.
To gain insights into the diversification processes underlying a
freshwater radiation, we studied the evolutionary history of the
Australasian predaceous diving beetles of the tribe Hydroporini (147
described species). We used an integrative approach including the latest
methods in phylogenetics, divergence time estimation, ancestral character
state reconstruction, and likelihood-based methods of diversification rate
estimation. Phylogenies and dating analyses were reconstructed with
molecular data from seven genes (mitochondrial and nuclear) for 117
species (plus 12 outgroups). Robust and well-resolved phylogenies indicate
a late Oligocene origin of Australasian Hydroporini. Biogeographic
analyses suggest an origin in the East Coast region of Australia, and a
dynamic biogeographic scenario implying dispersal events. The group
successfully colonized the tropical coastal regions carved by a rampant
desertification, and also colonized groundwater ecosystems in Central
Australia. Diversification rate analyses suggest that the ongoing
aridification of Australia initiated in the Miocene contributed to a major
wave of extinctions since the late Pliocene probably attributable to an
increasing aridity, range contractions and seasonally disruptions
resulting from Quaternary climatic changes. When comparing subterranean
and epigean genera, our results show that contrasting mechanisms drove
their diversification and therefore current diversity pattern. The
Australasian Hydroporini radiation reflects a combination of processes
that promoted both diversification, resulting from new ecological
opportunities driven by initial aridification, and a subsequent loss of
mesic adapted diversity due to increasing aridity.