Behavioural Divergence in Allopatric and Sympatric Gerbil Species (Rodentia: Gerbillinae)

AbstractSouthern African gerbils comprise 3 genera, each genus represented by morphologically‐ and ecologically‐similar species. All species are monomorphic, with social systems varying from asocial (Desmodillus auricularis) to colonial (Tatera species).This study compares the behaviour patterns of an allopatric species, T. afra, 2 sympatric species, T. leucogaster and T. brantsii, and a species of a different genus, D. auricularis which is sympatric with T. leucogaster and T. brantsii.Interactions between males and females of the same species were staged and quantified in terms of the frequencies of each of 23 behavioural acts. D. auricularis performed 2 acts, namely “sidle” and “fight” which have not been identified in Gerbillurus or Tatera interactions. Sequences of behaviour were similar in all species, and involved females moving away from males, which followed, sniffed the anogenital region and attempted to mount the females. Females responded by presenting, if receptive, or agonistic behaviour such as aggressive or upright postures. Exploration of the terrarium accounted for a large proportion of the behaviour during the 20 min encounter, and watching the opponent also occurred frequently.Discriminant function analysis successfully separated all 4 species on the basis of behaviour frequencies. Individuals were assigned to the correct species with an accuracy of 80%, indicating that each species exhibits species‐specific patterns of behaviour. D. auricularis displayed more agonistic and sexual behaviour and less huddling behaviour than any of the Tatera species.The sympatric species‐pair, T. leucogaster and T. brantsii, exhibited more significant difference in behaviour than either of the allopatric species‐pairs, T. afra and T. brantsii, and T. afra and T. leucogaster. Divergence in behaviour patterns has occurred in allopatric species, but divergence is more marked in species which are sympatric. It is not known whether divergence between T. leucogaster and T. brantsii occurred during a period of allopatry, or whether divergence has occurred due to selection against hybrids in sympatry.