Variation in the frequency of the echolocation calls of Hipposideros ruberin the Gulf of Guinea: an exploration of the adaptive meaning of the constant frequency value in rhinolophoid CF bats

This study describes variation patterns in the constant frequency (CF) segm ent of echolocation calls of the bat Hipposideros ruber within and among po pulations across the region of the Gulf of Guinea. Correlations of variatio n in CF with variation in body size, body condition, environmental humidity and presence of ecologically similar species are studied in an attempt to identify the forces driving the evolution of CF. We found that bats may ada pt the frequency to humidity, and that CF may evolve under interspecific in teractions, either of ecological or of social nature. The results support a n adaptive value for the high values of CF, and challenge the 'Allotonic Fr equency Hypothesis'. We found correlation between frequency and a body cond ition index, which may trigger social selection processes in this species s exually dimorphic in CF. Combined social and environmental selection on CF could trigger diversification of bats along ecotones separating habitats wi th contrasting air humidity.