Résumé
Pleistocene Climatic Fluctuations (PCF) are frequently highlighted as
important evolutionary engines that triggered cycles of biome expansion
and contraction. While there is ample evidence of the impact of PCF on
biodiversity for continental biomes, the consequences in insular systems
depend on the geology of the islands and the ecology of the taxa
inhabiting them. The idiosyncratic aspects of insular systems are
exemplified by the islands of the Sunda Shelf in Southeast Asia
(Sundaland), where PCF-induced eustatic fluctuations had complex
interactions with the geology of the region, resulting in high species
diversity and endemism. Emergent land in Southeast Asia varied drastically
with sea level fluctuations during the Pleistocene. Climate-induced
fluctuations in sea level caused temporary connections between insular and
continental biodiversity hotspots in Southeast Asia. These exposed lands
likely had freshwater drainage systems that extended between modern
islands: the Paleoriver Hypothesis. Built upon the assumption that aquatic
organisms are among the most suitable models to trace ancient river
boundaries and fluctuations of landmass coverage, the present study aims
to examine the evolutionary consequences of PCF on the dispersal of
freshwater biodiversity in Southeast Asia. Time-calibrated phylogenies of
DNA-delimited species were inferred for six species-rich freshwater fish
genera in Southeast Asia (Clarias, Channa, Glyptothorax, Hemirhamphodon,
Dermogenys, Nomorhamphus). The results highlight rampant cryptic diversity
and the temporal localization of most speciation events during the
Pleistocene, with 88% of speciation events occurring during this period.
Diversification analyses indicate that sea level-dependent diversification
models poorly account for species proliferation patterns for all clades
excepting Channa. Ancestral area estimations point to Borneo as the most
likely origin for most lineages, with two waves of dispersal to Sumatra
and Java during the last 5 Myrs. Speciation events are more frequently
associated with boundaries of the paleoriver watersheds, with 60%, than
islands boundaries, with 40%. In total, one-third of speciation events are
inferred to have occured within paleorivers on a single island, suggesting
that habitat heterogeneity and factors other than allopatry between
islands substantially affected diversification of Sundaland fishes. Our
results suggest that species proliferation in Sundaland is not wholly
reliant on Pleistocene sea-level fluctuations isolating populations on
different islands.