Spiders of the family Theraphosidae, commonly known as tarantulas, represents the largest group within the infraorder Mygalomorphae. Tarantulas have a Gondwanan affiliation, more than 1000 species distributed worldwide and carry a repertoire of adaptive traits like urticating hairs, stridulatory setae, colour, and venom. All these features make them an exciting model system for evolutionary studies. Through my thesis, I will try to understand the macroevolutionary dynamics and historical biogeography of tarantulas at both broad and specific levels.

Widespread taxa of ancient origin represent ideal systems for studying continental scale biogeography. In the first chapter, using tarantulas as a model system, I aim to explore how the breaking up of Gondwana and subsequent tectonic activity of former Gondwanan landmasses have caused cladogenesis and shaped the modern-day distribution of these spiders.

The tree of life is highly asymmetrical in terms of species richness, and the theraphosid tree of life is no different. In the second chapter, I aim to investigate the causation of such disparity in clade sizes, i.e., why some clades are extremely specious while others are depauperate. Using an extensive time-calibrated phylogeny of tarantulas, I will test different macroevolutionary hypotheses. First, I will test the clade age hypothesis, which states that the bigger clades are older, so they have more time to diversify than younger clades. I will measure the net diversification, speciation, and extinction rates across the phylogeny. Using phylogenetic comparative methods, I will test the role of two potential candidate factors- microhabitat and defensive traits, which I suspect to have influenced the diversification dynamics and as potential explanations for this unevenness of diversity across clades.

The first two chapters will give us a broader picture, i.e., a zoomed-out view of the biogeography and diversification of the whole family. In the third chapter, I will zoom in on a particular subfamily Thrigmopoeinae, which represents an ancient endemic lineage restricted to the wet evergreen forests of Western Ghats. There is considerable taxonomic ambiguity in this subfamily. First, I will identify the species limits within this subfamily by employing a multicriteria approach using genetics, morphological and ecological data. Taking this result forward, I will explore the diversification and biogeography of this group. Being an ancient, niche conserved, and species-poor group, I hypothesize that the cretaceous volcanism which eventually wiped out all the wet evergreen forests of Northern and Central Western Ghats, as well as the topological discontinuity in the Western Ghats, might have played a significant role shaping the distribution and diversification of this lineage.