The behavioural ecology of bachelor male groups in the African striped mouse, Rhabdomys pumilio
Date
2018
Authors
Kanyile, Sthandiwe Nomthandazo
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Abstract
Males in several animal species vary in traits which confer competitive ability. Younger and old, small and large males thus regularly make use of different behavioural tactics (i.e. alternative reproductive tactics, ARTs) in order to secure mates and increase their fitness. In the Succulent Karoo, males of the African striped mouse Rhabdomys pumilio adopt one of three main ARTs, i.e. philopatric, roaming, or territorial tactics; the tactic chosen is influenced by body mass. Additionally, the occurrence of bachelor groups (two or more males sharing a nest without any female) in striped mice has recently been observed. The present study was concerned with investigating the composition and function of these bachelor groups in striped mice, especially to assess whether they represent a fourth ART. For this, I used data collected from 2009 to 2016 to determine the season (breeding versus non-breeding) during which bachelor groups occurred and how they originated. At the start of the breeding season, I compared bachelor males with the known ARTs with regard to their scrotality, body mass, and age. I also determined the tactics of bachelor males before and after they were bachelors, and whether these tactic changes were associated to changes in body mass. My results indicate that bachelor groups are mainly formed by unrelated philopatric males which have dispersed from their natal groups. These groups most frequently occur in the breeding season, when population density is low to intermediate. Bachelor males occupy the intermediate position in the body mass spectrum in striped mice, being heavier than philopatrics but lighter than breeders, and do not differ in body mass from roamers. After the bachelor tactic, more males employed the roamer than the territorial breeding tactic. I hypothesise that the bachelor tactic is a “transitional tactic” which facilitates the change from a low fitness tactic (philopatric) to a higher fitness tactic (roaming or breeding) by allowing relatively small males to cooperate in social thermoregulation. These findings provide valuable insight on a phenomenon which has not been studied before in striped mice.
Keywords: African striped mouse, alternative reproductive tactics, bachelor, behavioural plasticity, group-living, social flexibility
Description
A dissertation submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science
Johannesburg, 2018.
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Citation
Kanyile, Sthandiwe Nomthandazo (2018) The behavioural ecology of bachelor male groups in the African striped mouse, Rhabdomys pumilio, University of the Witwatersrand, Johannesburg, https://hdl.handle.net/10539/25837