Research Projects

Phytophagous insects and angiosperms are highly speciose - they together comprise about half of all eukaryotes. Coevolutionary interactions with host plants has been correlated with high diversification rates in phytophagous insects. However, the mechanisms by which interactions of insects with their host-plants influence diversification through reproductive isolation and speciation are poorly known. Phytophagous insects feeding on multiple host plants, i.e., generalists, are thought to form host races that are better adapted to particular host plants, and eventually undergo speciation, resulting in specialized species that can later evolve into generalists by adding host plants to their repertoire. Understanding the ecology of host race formation and maintenance can offer important insight into speciation and diversification of phytophagous insects. Butterflies are excellent models to understand coevolutionary diversification. Among the plants in the host plant repertoire of a species, females tend to prefer some plants for oviposition - the oviposition preference hierarchy. Female oviposition preference hierarchy is often positively correlated with larval performance hierarchy (hierarchy of host-plants in terms of larval fitness), but there are interesting exceptions. Host race formation involves evolution of preference and performance. Preliminary work in our lab has indicated that populations of the butterfly Catopsilia pomona have diverged strongly in their host use. The Trivandrum population appears to have specialized on Cassia fistula. Larvae starve to death when offered other known host plants of the species. Preliminary data from our lab suggests that the Kolkata population can utilizes other plants - Senna tora, S. occidentalis, S. alata, S. siamea and Sesbania grandiflora. The divergences in host use across populations offer an exciting opportunity to test hypotheses related to host race formation and maintenance. Additionally, these populations allow us to test hypotheses about the trade-offs between specialization and generalization in host use. I propose to use common garden experiments and reciprocal crosses between populations to investigate differences in preference and performance hierarchy in the two populations, with the aim of addressing the following questions Is there a correlation between preference and performance in the two populations? If not, what explains the discordance? How heritable are preference and performance? What are the genetic bases of preference and hierarchy? Are they paternally or maternally inherited? How variable are the between and within populations? What are the trade-offs of host generalization, i.e. what are the benefits of specialization? Is there incipient reproductive isolation between the divergent specialist and generalist population?