Determining how biodiversity is produced and maintained remains one of the fundamental questions in ecology. This diversity is not distributed uniformly across the Earth; a large proportion of global biological diversity is concentrated in tropical areas, many of which are biodiversity hotspots. The phenomenon of diversification, which occurs via the interplay of speciation and extinction, holds the key to understanding these processes. However, our understanding of species diversity in the tropics and the factors influencing diversity has been constrained by inadequate knowledge about the large number of undescribed species. This dearth of information about undescribed species is closely related to the problem of species delimitation. It is crucial to delimit species boundaries in a systematic manner, as species are units at which evolutionary processes operate.

In my thesis, I studied diversification in Nyctibatrachus, a genus of endemic frogs from the Western Ghats, a biodiversity hotspot in peninsular India. I first attempted to uncover the species diversity in this genus by employing a systematic spatial sampling strategy and subsequently carrying out lineage delimitation through a stepwise protocol. I then explored the key characteristics of lineage, morphological and ecological diversification in Nyctibatrachus. Finally, I examined the relationship between morphological diversity, phylogeny and distribution patterns among lineages belonging to this genus. My findings reveal the existence of 21 new putative species, most of which are morphologically cryptic in nature but distributed allopatrically. Furthermore, I establish that Nyctibatrachus manifests features of an adaptive radiation, with accompanying ecomorphological diversification. I also found that there were distinct patterns of body size evolution in Nyctibatrachus, and significant differences in body size between lineages distributed in sympatry versus parapatry.