Venom research has focused on front-fanged venomous snakes with fewer than three percent of rear-fanged snake venom proteomes characterised. These venoms have been neglected due to difficulties obtaining venom for characterisation and a lack of toxin sequences in databases for proteomic identifications. We characterized venom gland transcriptomes, venom proteomes, and toxin biological activities, using both enzymatic and toxicity assays, for two Old World and two New World rear-fanged snake species. Venoms were dominated by either three-finger toxins (3FTxs) or metalloproteinases, paralleling the venom dichotomy of front-fanged venomous snakes. Rear-fanged snakes Boiga irregularis and Spilotes sulphureus had venoms dominated by 3FTxs, and shared similar heterodimeric 3FTxs with lizard specific toxicity. In addition, S. sulphureus venom contained a monomeric 3FTx with mammal specific toxicity, allowing this non-constricting snake to capture mammalian prey, whereas B. irregularis uses constriction. Metalloproteinase dominated venoms from Ahaetulla prasina and Borikenophis portoricensis rapidly degraded the alpha subunit of fibrinogen, and within five minutes A. prasina venom also degraded beta subunits. Beta subunit degradation rate for A. prasina was even faster than observed for the front-fanged rattlesnake Crotalus viridis viridis. The majority of bites from rear-fanged venomous snakes do not produce systemic effects in humans, however, these venoms provide insight into toxin binding selectivity and mechanisms of action, as well as predator-prey toxin evolution.

Heritable variation in traits that enhance dispersal rates can accumulate at population margins by spatial sorting. This mechanism of selection differs from natural selection as evolutionary change can ensue even in the absence of differential lifetime reproductive success. Although evidence suggests that populations are rapidly evolving at the margins due to global change pressures, such as invasions and range shifts, we lack a mathematical theory of spatial sorting to understand these evolutionary patterns. To this end, I present an algebraic theorem of evolution, which we call the sorting theorem, to elucidate the general mechanism of selection at margins. The sorting theorem suggests that at population margins, evolution can ensue by any biological mechanism that yields a statistical association between the number of offspring that individual leaves at the margin and the mean phenotype of those offspring. Thus, the sorting theorem can facilitate axiomatic development and criticism of spatial sorting theory. Its role in guiding research in this context is analogous to that of Price’s theorem in natural selection theory.

Given India’s ancient association with Gondwana and subsequent separation from Africa and Madagascar, vicariance has often been invoked to explain the current distribution of some of its so-called Gondwanan biota. In this talk, I review phylogenetic studies and fossil data of Indian tetrapods to ascertain the relative contribution of dispersal and vicariance in shaping their distributions. Results indicate that Paleogene dispersal into India better explains the current distribution of most of the tetrapods in India. Vicariance is invoked for three fossorial groups, namely caecilians, frog family Nasikabatrachidae and blindsnake family Gerrhopilidae. It is plausible that much of India’s Late Cretaceous tetrapod fauna of Gondwanan origin went extinct due to Cretaceous-Paleogene mass extinction and Deccan volcanism. Subsequently, it was replaced by intrusive elements as India proceeded to dock with Asia in the Paleogene. In this regard, soil invertebrates might be a promising study system to understand the Gondwanan component of Indian biota.  

CES IHS 2020
Talks, Posters, Short documentaries, Panel discussion, Science and Creativity stalls