Geographic Variation in the Songs of Neotropical Singing Mice: Testing the Relative Importance of Drift and Local Adaptation

Abstract

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

Parallel body shape divergence in the Neotropical fish genus Rhoadsia (Teleostei: Characidae) along elevational gradients of the western slopes of the Ecuadorian Andes

“…Adaptive evolution is not the only mechanism responsible for the phenotypic divergence of geographically isolated populations. Genetic drift, a process that is especially important in small populations, can also lead to genetically based non-adaptive phenotypic divergence [10–12], as can phenotypic plasticity, phenotypic divergence resulting from environmental variation and not DNA sequence changes [13, 14]. …”

How populations differentiate despite gene flow: sexual and natural selection drive phenotypic divergence within a land fish, the Pacific leaping blenny

“…The extent to which neutral evolution in itself might ultimately instigate reproductive isolation among populations is debatable [12,13]. However, theoretical models and a growing number of empirical studies have begun to link population variation in mating and territorial signals to neutral genetic differentiation among populations [14-20]. At the very least, then, neutral evolution among populations represents an important null model that should be considered in studies of population divergence.…”

Geographic Variation in the Status Signals of Polistes dominulus Paper Wasps

“…For example, social factors such as the degree and nature of interspecific and intraspecific competition shape signal evolution such that signals can diverge genetically in sympatry in order to reduce the costs of inter-specific mating or agonistic competition with heterospecifics [9], [10], [11]. Genetic divergence that arises via non-selective processes such as genetic drift may also produce geographic variation in signals [12]. Second, geographic variation in signals may also be a consequence of developmental plasticity that reflects variation in the environment.…”