Patterns of geographic variation in communication systems can provide insight into the processes that drive phenotypic evolution.Although work in birds, anurans, and insects demonstrates that acoustic signals are sensitive to diverse selective and stochastic forces, processes that shape variation in mammalian vocalizations are poorly understood. We quantified geographic variation in the advertisement songs of sister species of singing mice, montane rodents with a unique mode of vocal communication. We tested three hypotheses to explain spatial variation in the song of the lower altitude species, Scotinomys teguina: selection for species recognition in sympatry with congener, S. xerampelinus, acoustic adaptation to different environments, and stochastic divergence. Mice were sampled at seven sites in Costa Rica and Panamá; genetic distances were estimated from mitochondrial control region sequences, between-site differences in acoustic environment were estimated from climatic data. Acoustic, genetic and geographic distances were all highly correlated in S. teguina, suggesting that population differentiation in song is largely shaped by genetic drift. Contrasts between interspecific genetic-acoustic distances were significantly greater than expectations derived from intraspecific contrasts, indicating accelerated evolution of species-specific song. We propose that, although much intraspecific acoustic variation is effectively neutral, selection has been important in shaping species differences in song. K E Y W O R D S :Acoustic adaptation, bird song, character displacement, ecological selection, mammal, speciation.Understanding the origins of phenotypic diversity is a fundamental goal of evolutionary biology; few phenotypes are as diverse as signals used in intraspecific communication (Endler 1992;Bradbury and Vehrencamp 1998). Acoustic signals make particularly good models for signal evolution because variation is readily quantifiable, and population and species differences can accrue over short evolutionary timescales with significant impact

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The Laotian rock rat (Laonastes aenigmamus) is the single surviving member of the family Diatomyidae, which has a distribution restricted to the karstic region of Lao-PDR. Here we describe the development of 12 polymorphic microsatellites markers for the endangered Laotian rock rat using 454-sequencing. We successfully tested 12 markers in 30 individuals from 2 populations. Eleven of the 12 loci were polymorphic and the number of alleles detected per locus ranged from 2 to 11. Three of these loci deviated significantly from Hardy-Weinberg equilibrium, which coincides with the detection of possible null alleles. These microsatellite markers are expected to contribute in future research and conservation of L. aenigmamus.

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