Affiliations: 1) University of Pennsylvania; 2) Janelia Research Campus of the Howard Hughes Medical Institute
Keywords: g. courtship and mating; d. evolution of gene expression
Understanding the evolution of complex traits, including behavior, is a main goal of evolutionary biology. Behavioral diversity across species is expected to be the result of evolutionary changes in neural morphology and function. In turn, a neuron’s morphology and function is the product of its molecular makeup. Therefore, comparing gene expression differences in homologous neurons between species is a powerful approach to identify genes that contribute to the evolution of neural differences underlying behavioral diversity. Drosophila courtship song, wing vibrations generated by a male while courting a female, displays a wide range of diversity across species. For example, D. melanogaster males sing two types of song, pulse and sine, by extending and vibrating one wing. In contrast, D. yakuba males do not sing sine song but instead sing a song called clack by vibrating both wings without obvious extension. A male-specific single bilateral pair of neurons named pIP10 is necessary for pulse song in D. melanogaster but clack song in D. yakuba. In both species, we genetically labeled pIP10 neurons with a GFP marker and manually isolated them for transcriptomic profiling. We found that many genes are expressed in a species-specific or -biased manner including some with known neural or behavioral functions. Next, in D. melanogaster we used pIP10-specific RNAi to knock down genes upregulated in D. melanogaster pIP10 neurons relative to D. yakuba pIP10 neurons and found that some of our knockdowns resulted in mutant D. melanogaster song phenotypes.Overall, our study is one of the first to compare gene expression in homologous neurons across species and offers a novel perspective on how evolution has shaped gene expression patterns to result in functional adaptation across species.