Abstract
Animals employ an array of signals (i.e. visual, acoustic, olfactory) for communication. Natural selection favours signals, receptors, and signalling behaviour that optimise the received signal relative to background noise. When the signal is used for more than one function, antagonisms amongst the different signalling functions may constrain the optimisation of the signal for any one function. Sexual selection through mate choice can strongly modify the effects of natural selection on signalling systems ultimately causing maladaptive signals to evolve. Echolocating bats represent a fascinating group in which to study the evolution of signalling systems as unlike bird songs or frog calls, echolocation has a dual role in foraging and communication. The function of bat echolocation is to generate echoes that the calling bat uses for orientation and food detection with call characteristics being directly related to the exploitation of particular ecological niches. Therefore, it is commonly assumed that echolocation has been shaped by ecology via natural selection. Here we demonstrate for the first time using a novel combined behavioural, ecological and genetic approach that in a bat species, Rhinolophus mehelyi: (1) echolocation peak frequency is an honest signal of body size; (2) females preferentially select males with high frequency calls during the mating season; (3) high frequency males sire more off-spring, providing evidence that echolocation calls may play a role in female mate choice. Our data refute the sole role of ecology in the evolution of echolocation and highlight the antagonistic interplay between natural and sexual selection in shaping acoustic signals.
Highlights
Acoustic components of the call of a wide range of animals including humans have been shown to contain reliable indicators of body size [1,2,3,4] or body strength [5], which are used by females in the context of mate choice [2,3]
It is commonly assumed that echolocation has been shaped by ecology via natural selection alone [12,13]
Based on wild caught animals, we demonstrated that body length and weight of individuals caught during the mating season showed a strong positive and significant correlation with peak frequency in males and females (Figure 2, Table 1; Spearman’s test, rho range: 0.48–0.73, P,0.05 for all relationships, n = 15 and n = 75 for males and females respectively) while forearm length did not (Table 1; Spearman’s test, rho = 0.04 and 0.16, P.0.05 in males and females)
Summary
Acoustic components of the call of a wide range of animals (mammals, birds, amphibians, reptiles, and insects) including humans have been shown to contain reliable indicators of body size [1,2,3,4] or body strength [5], which are used by females in the context of mate choice [2,3]. Echolocating bats represent a fascinating group in which to study the evolution of signalling systems as unlike bird songs or frog calls, echolocation has a dual role in foraging and communication [10,11]. To date, no study has yet experimentally investigated the role of echolocation calls in the context of sexual selection in bats, despite their role being repeatedly suggested and discussed [15,16,17,18]
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