Session 3A: Symposium on Evolutionary Ecology in the Wild

Chairperson: Renee Borges, IISc, Bengaluru

Indian small mammals: Biogeography, communities and zoonoses

Many species of small mammals (including rodents) surround us. Yet our understanding of their biogeography and community ecology remains poor, especially in India. We attempted to understand speciation and geographic origins of small mammals using phylogeny of Murinae lineages in the Indian subcontinent and their affinities. Murinae is a 704-species-rich subfamily of rodents that began diversifying 20 million years ago and has several endemic lineages in Peninsular India. We built a robust phylogeny for more than 400 species of the subfamily with available sequences, and generated sequence data for 12 endemic species. Three nuclear markers (GHR, Rbp3, and RAG1) and one mitochondrial marker (Cytb) were used to construct maximum likelihood and Bayesian estimated phylogenies. A time-calibrated phylogeny was built using nine fossil calibration points, which was then used to reconstruct ancestral areas. Our biogeographic analyses considered the Indian subcontinent, Africa, and Southeast Asia as separate realms. We found multiple dispersals from Africa and Southeast Asia into the Indian subcontinent, and relatively few back dispersals. Biogeographic origins are important in the context of community assembly, vectors and associated zoonoses. We characterized Bartonella spp. (a Gram-negative bacterium) in a small mammal community and their ectoparasites in the biodiverse Western Ghats. We investigated ecological correlates of Bartonella prevalence in small mammal hosts and evolutionary relationships between Bartonella spp. and various hosts and ectoparasites to gain insight into pathogen movement pathways within ecological communities. We detected Bartonella in five out of eight small mammal species and in 86 (40.56%) out of 212 individuals, but prevalence varied widely among species (0%–75.8%). We found that Bartonella prevalence in hosts was positively correlated with their aggregated ectoparasite loads, further emphasizing the crucial role that ectoparasites may play in these transmission pathways. Our cophylogenetic analysis and ancestral trait (host) reconstruction revealed incongruence between small mammal and Bartonella phylogenies, indicating historic host shifts and validating the potential for contemporary spillover events. We found that small mammal hosts in this fragmented landscape often move across habitat boundaries, creating a transmission pathway (via shared ectoparasites) to novel hosts, which may include synanthropic species like Rattus rattus. Our results highlight the necessity to disentangle the complex relationship among hosts, ectoparasites, and bacterial pathogens to understand the implications of undetected spillover events.