Abstract
With their extraordinary species richness and diversity in ecological traits and social systems, bats are a promising taxon for testing socio-ecological hypotheses in order to get new insights into the evolution of animal social systems. Regarding its roosting habits, proboscis bats form an extreme by occupying sites which are usually completely exposed to daylight (e.g. tree trunks, vines or rocks). This is accompanied by morphological and behavioural adaptations to remain cryptic in exposed day roosts. With long-term behavioural observations and genetic parentage analyses of individually marked proboscis bats, we assessed its social dispersion and male mating strategy during day and night. Our results reveal nocturnal male territoriality—a strategy which most closely resembles a resource-defence polygyny that is frequent also in other tropical bats. Its contrasting clumped social dispersion during the day is likely to be the result of strong selection for crypsis in exposed roosts and is accompanied by direct female defence in addition to male territoriality. To the best of our knowledge, such contrasting male mating strategies within a single day–night cycle have not been described in a vertebrate species so far and illustrate a possible evolutionary trajectory from resource-defence to female-defence strategy by small ecologically driven evolutionary steps.
Highlights
Animal social systems can be characterized by social dispersion, mating system and natal dispersal patterns (e.g. [1,2,3])
All other colony males were either absent at night or roosted at two to four different sites in the roost, resulting in low site fidelities per site; we refer to these males as non-territorial males
This is supported by the fact that only males with high site fidelity, i.e. territorial males, were observed copulating at night and they exclusively copulated at their territory
Summary
Animal social systems can be characterized by social dispersion (group size and spacing), mating system and natal dispersal patterns (e.g. [1,2,3]). The potential for intraspecific transitions between all four main classes of mating systems (monogamy, polygyny, polyandry and promiscuity) has been shown in several species (reviewed in [9,10]), studies on intraspecific transitions between male mating strategies (i.e. from resource defence to female defence or vice versa) are rare (e.g. guinea pig, Cavia porcellus [11]; golden-winged sunbird, Drepanorhynchus reichenowi [12]). They offer a valuable opportunity to gain new insights into ecological causes of male mating strategy evolution
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