Social flexibility and environmental unpredictability in African striped mice
The resilience of an individual to environmental change depends on its ability to respond adaptively. Phenotypic flexibility, i.e., reversible phenotypic plasticity, is such an adaptive response, which has been predicted to evolve in unpredictable environments. We present data on the environmental predictability for 17 generations of socially flexible African striped mice Rhabdomys pumilio, which can switch from group living to solitary living and back to group living. Population density during the breeding season is the main predictor of social organization in striped mice, which become solitary breeding when population density is low and plural breeding when population density is high. Using time series analysis, we could not reject randomness for the variation in population density and found a 6-year cycle for food availability. However, food availability when individual females grew up did not predict the environmental conditions during which they bred in the next year, their only breeding season. Group size was predictable and most females bred plurally in communal groups. However, single breeding is the preferred tactic to avoid infanticide but for single breeding females, it was not predictable from the environment in which they grew up whether they would become single breeders in the next breeding season. Our study indicates unpredictability in the factors most important for determining the optimal breeding tactics for 322 female striped mice. In sum, striped mice exhibit social flexibility in an unpredictable environment, making it an adaptive trait.
It has long been assumed that the evolution of different forms of sociality depends on the environment. Social flexibility, i.e., the ability of individuals to switch from group living to solitary living and back to group living, has been predicted to be an adaptation to unpredictable environments. However, the extent to which unpredictability influences sociality has never been studied previously. For female African striped mice, population density is the main factor determining whether they live alone or in groups. Here, we show that females cannot predict from the population density under which they grew up the population density under which they will reproduce, making social flexibility adaptive.
KeywordsPhenotypic flexibility Phenotypic plasticity Intra-specific variation in social organization Alternative reproductive tactic
We thank Ivana Schoepf, Ed Yuen, Jörg Jäger, Milena Zduniak, Jessica Mulvey, Davina Hill, Audrey Maille, Rebecca Rimbach, several master students, and more than 80 field assistants for the help in collecting the data. We are grateful for the very helpful comments from two referees. We are grateful to Goegap Nature Reserve. This study was made possible by the administrative and technical support of the Succulent Karoo Research Station (registered South African NPO 122-134). Comments by L. Hayes significantly improved the manuscript.
CS and NP designeded the study. CS collected the data. CS and CB analysed the data. All authors contributed to writing the manuscript.
Financial support was provided by the Swiss National Science Foundation, the Claude-Leon Foundation, the German Science Foundation, the National Research Foundation, the University of the Witwatersrand, the University of Zurich, the CNRS, the University of Lausanne, the University of Strasbourg Institute of Advanced Study, the Vontobel Stiftung, the Holcim Stiftung, the Promotor Stiftung, and the Helene Biber Fonds.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
Animal ethics clearance was provided by the University of the Witwatersrand (AESC 2007/40/01), following the guidelines for the use and care of animals in teaching and research of the University of the Witwatersrand which complies with the University’s ethical and legal practices and with the National Code.
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