H Gifford1, S Lin1, Y Ding1

From the vibrant dances of Birds of Paradise to the smelly nuptial gifts of dung beetles, mating signals have incredible diversity across the animal kingdom. The evolution of mating signals is a question with major implications for speciation and sexual isolation. Drosophila courtship song is an innate behavior where males vibrate their wings to produce context-dependent and species-specific acoustic signals for potential female mates. We found that the hybrid offspring of D. teissieri and D. santomea, two closely related species that sing distinct song types, produce “chimeric” courtship songs. These chimeric song types consist of simultaneous production of different parental song elements used for similar social contexts, suggesting that the species divergence of song types lie in the motor patterning circuits downstream of courtship song decision-making nodes. The genetic differences underlying this change are unknown. To explore the genetic differences, we generated a backcross F2 population of 570 individuals, scored song phenotypes, and used multiplexed shotgun genotyping to genotype the population. Quantitative trait locus mapping reveals a highly polygenic basis underlying the divergence in courtship song traits. Intriguingly, we also uncover pervasive inter-chromosomal epistasis, with any song phenotype effect being highly contingent on the extent of D. teissieri chromosomal introgression into the D. santomea genetic background. Our results indicate that species divergence in courtship song types involves changes at many gene loci that work together in a highly non-additive manner to shape the evolution of motor patterning circuits, highlighting the complexity of the genetic basis for neuronal and behavioral evolution.

1Department of Biology, University of Pennsylvania, Philadelphia, PA, USA

Funding Support: NIGMS Grant GM142678