Mating calls are a sensitive indicator of phylogenetic relationships in tropical tree squirrels (Callosciurus spp.)

Vocal communication plays an important role in the mating behaviour of arboreal squirrels. Callosciurus is a genus of tree squirrels that includes 15 species distributed in Southeast Asia, and congeneric species often inhabit the same forest. As closely related species of Callosciurus have the potential to interbreed, species recognition from mating calls may be a fundamental reproductive barrier. We compared seven acoustic characteristics of male mating calls in six Callosciurus species and estimated whether the species differences were clear enough to function as a cue. Discriminant function analyses (DFA) classified 87.4% of mating calls to the correct species. All of the calls by C notatus, C. nigrovittatus and C. caniceps, and 88% of the calls by C. prevostii, were assigned to the correct species, while the percentage of correct classifications was lower in C. finlaysonii (71%) and C. erythraeus (63%). We compared these results with the genetic relationships to determine whether interspecific acoustic differences are caused by adaptive selection (habitat selection and body size) or by a stochastic process (drift). The genetic relationships among the six species were coincident with the differences in mating calls, which supports the stochastic divergence. Species-specific mating calls may be a useful cue for species recognition in Callosciurus, and thus these calls could be an effective trait for phylogenetic analysis in Callosciurus.