Investigating the Evolution of Vocal Communication in Xenopus

For many vertebrate species, vocalizations are essential components of social communication. Animals call in a variety of social contexts including courtship, mating, rivalry, and alarm signaling. In diverging populations, co-evolution of courtship signals and preferential responses to those signals can generate barriers to reproduction and lead to speciation. In the 29 species of the fully aquatic frog genus Xenopus, vocal signaling predominates in social interactions and is innate. Males produce an advertisement call in which the combination of spectral (pitch) and temporal (rhythm and pattern) features is a unique species identifier. To uncover genetic differences across species that support divergent advertisement calls, we performed quantitative trait locus (QTL) mapping using F2 hybrids between related species with different male advertisement calls: X. petersii and X. laevis. To phenotype each individual F2 male, we developed a pipeline for automated analysis of spectral and temporal features. To genotype the F2 males, we first identified ~3.8 million candidate species-specific markers from whole genome sequences (>10x coverage) of 4 X. laevis and 2 X.petersii including the founders of the F2 intercross. We then whole genome sequenced the F2s at 0.01-0.03x coverage, and used a HMM-based imputation and pruning of the initial candidate SNP set to obtain 533 informative genome-wide markers for QTL analysis. Our preliminary results identify QTLs on chromosomes 3, 5, 8, and 9 for vocal spectral features. Determining how variations in spectral features affect female preference will help to elucidate the genetic basis and evolution of courtship-based vocal signaling in Xenopus and more broadly, provide further insight to how vocal communication has evolved across vertebrates.