RESEARCH

While biologists aim to link genetic variation to phenotypes that mediate species interactions, studies on insect-plant interactions often overlook interactions between the insect and its microbial endosymbionts. Endosymbionts range from recently acquired, free-living microbes to ancient associations nearing organelle status, such as mitochondria in eukaryotic cells, which are essential to eukaryotic life. Maternally transmitted Wolbachia are among the most common endosymbionts in nature, associating with more than half of all insect species. Wolbachia influences host reproduction by killing or feminizing males, causing cytoplasmic incompatibility (CI, where Wolbachia devoid eggs fertilized by Wolbachia positive sperm leads to loss of embryos), or inducing parthenogenesis. Additionally, Wolbachia prevalence varies widely across insect hosts influenced by maternal transmission, host effects, and environmental effects. Although much work has been carried out in model systems, we are yet to understand the influences of rapid environmental change on the mode and tempo of evolution and maintenance of endosymbiont prevalence in divergent hosts in natural environments.

As a post-doc with Brandon Cooper at the University of Montana, I have developed a research program focused on the evolution of Wolbachia interactions with diverse Lepidoptera—a hyper-diverse insect order with over 180,000 species. Using field sampling, molecular biology and bioinformatics, I have identified hundreds of new Wolbachia-Lepidoptera associations. In the Cooper lab I am sequencing whole genomes of over 150 species, complemented with over 5000 publicly available genomes to determine how diverse insects acquire Wolbachia. I have also identified several divergent Lepidoptera species with varying Wolbachia prevalence across time and space. Finally, in field mesocosm experiments, I discovered that Wolbachia prevalence can change rapidly within weeks in Drosophila melanogaster populations. I am currently investigating how environmental factors, such as nutrition and temperature, influence maternal transmission to understand the rapid, fine-scale spatio-temporal changes in Wolbachia prevalence in D. melanogaster. These data will help identify target systems and key environmental variables that drive variations in Wolbachia prevalence within and among host populations.

Insects carrying Wolbachia navigate complex landscapes and encounter novel resources either due to anthropogenic introduction of non-native plants and/or climate change induced range shifts. Native herbivores may rapidly adapt to novel resources, enhancing their fitness, or they may be maladapted, leading to reduced fitness and population declines. Endosymbionts can facilitate or hinder adaptation to novel resources in insects, yet the genetic mechanisms underlying these interactions are not fully understood. I use large-scale genome sequencing to assess natural genetic variation and pinpoint genomic regions in both endosymbionts and insect herbivores that respond to novel resources, shedding light on the genetic basis of rapid adaptation.

As a graduate student with Carol Boggs at the University of South Carolina, I explored the factors influencing local adaptation in a specialist native herbivore, Pieris macdunnoughii, to an invasive, novel, toxic hostplant, Thlaspi arvense. Using population genomics, I identified signatures of local adaptation despite high gene flow and low genetic variation in herbivore populations interacting with the novel hostplant (Ravikanthachari et al., Mol. Ecol., 2024; a). By combining oviposition preference and larval performance experiments with transcriptome sequencing, I showed that adaptation to the novel hostplant depended on the larvae’s ability to feed on the novel plant rather than the females’ ability to distinguish between the native and novel hosts (Ravikanthachari & Boggs, in revision, Heredity; bioRxiv; b). Finally, I used comparative genomics to analyze whole genomes of generalist and specialist herbivores, investigating the constraints on adaptation to novel hostplants in specialist herbivores (Ravikanthachari & Boggs, bioRxiv; c).

I am investigating how environmental changes influences adaptation in specialized herbivore-plant interactions to novel resources, using Pieris butterflies as a model system. Pieris butterflies are specialist feeders on native Brassicaceae (mustard) plants. A third of the Pieris species in North America are associated with Wolbachia. Several Pieris species interact with novel mustard hostplants due to anthropogenic introduction and laying eggs on the plants. While some Pieris species have adapted to specific novel resources, other Pieris species have reduced fitness on novel plants. I am using population genomics and whole genome sequencing to examine the role of Wolbachia in mediating fitness on novel resources and identify the genetic basis underlying these interactions. Additionally, I use functional and comparative phylogenomic to understand the consequences of spatio-temporal environmental change on adaptation to novel resources in specialist herbivores.

Ever since Ehrlich and Raven published their seminal work on butterflies and their hostplants in 1964, biologists have tried to understand what determines the hostplant range, the structure of these interactions and the evolution of these relationships through time and space. I am interested in understanding how hostplant-butterfly interactions at a local geographic scale influence global hostplant range and diet breadth. Do local interactions mirror what is observed throughout the entire range of a species? Can the evolution of local hostplant-butterfly interactions provide light on the evolution of global hostplant range and diet breadth? Using the Western Ghats butterfly assembly as a system, I try to address if hostplant use evolution in the Western Ghats mirror global hostplant use along with understanding the hostplant evolution in endemic species.

India is home to over 1800 species of butterflies and many species are still being discovered or rediscovered.  A significant portion of the butterflies are rare and/or endemic with narrow geographic ranges. The rich diversity and varied geography of India provides an excellent opportunity to document the natural history, undertake long-term monitoring and help form policies to conserve butterflies. I am one of the editors of the Butterflies of India, a citizen science initiative started by Dr. Krushnamegh Kunte that aims to document and conserve butterflies in India.

            I am also one of the co-founders of the Bangalore Butterfly Club (BBC), a citizen science initiative that aims to conserve and scientifically document butterfly populations in Bengaluru. The BBC is involved in spreading awareness through conducting butterfly walks, working with the Karnataka Forest Department, and recording butterfly populations across various location in Bengaluru. I have co-authored a book and a brochure as a product of these initiatives. I am interested in getting involved in various citizen science initiatives/programs that specifically involve butterflies either in India or the USA. If you are interested in collaborating, please feel free to get in touch with me.