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

Abstract

Abstract This study describes variation patterns in the constant frequency (CF) segment of echolocation calls of the bat Hipposideros ruber within and among populations across the region of the Gulf of Guinea. Correlations of variation 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 adapt the frequency to humidity, and that CF may evolve under interspecific interactions, either of ecological or of social nature. The results support an adaptive value for the high values of CF, and challenge the ‘Allotonic Frequency Hypothesis’. We found correlation between frequency and a body condition index, which may trigger social selection processes in this species sexually dimorphic in CF. Combined social and environmental selection on CF could trigger diversification of bats along ecotones separating habitats with contrasting air humidity.