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Abstract

The historical processes underlying high diversity in tropical biodiversity hotspots
like the Western Ghats of Peninsular India remain poorly understood.
We sampled bush frogs on 13 massifs across the Western Ghats Escarpment
and examined the relative influence of Quaternary glaciations, ecological
gradients and geological processes on the spatial patterns of lineage and
clade diversification. The results reveal a large in situ radiation (more than
60 lineages), exhibiting geographical structure and clade-level endemism,
with two deeply divergent sister clades, North and South, highlighting the biogeographic
significance of an ancient valley, the Palghat Gap.Amajority of the
bush frog sister lineages were isolated on adjacent massifs, and signatures of
range stasis provide support for the dominance of geological processes in allopatric
speciation. In situ diversification events within the montane zones (more
than 1800 m) of the two highest massifs suggest a role for climate-mediated
forest-grassland persistence. Independent transitions along elevational gradients
among sub-clades during the Miocene point to diversification along the
elevational gradient. The study highlights the evolutionary significance of
massifs in theWestern Ghats with the high elevations acting as centres of lineage
diversification and the low- and mid-elevations of the southern regions,
with deeply divergent lineages, serving as museums.