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Brain size can vary between populations in different environments because of different selection pressures on behaviours, such as learning and memory, related to spatial, social and environmental differences. We investigated the variation in total and broad‐scale regional brain size in the murid rodent genus Rhabdomys from different environments. We assessed taxon‐, population‐ and sex‐level differences in total and regional brain volume in three populations each of three taxa (arid‐occurring Rhabdomys pumilio and mesic‐occurring Rhabdomys dilectus chakae and R. d. dilectus) originating across southern Africa. We μCT‐scanned crania obtained from museums in South Africa and used digital software to create endocasts and extract total endocranium and regional volumes: olfactory bulb, anterior cerebrum, posterior cerebrum, cerebellum volume and petrosal volume. Total endocranial volume scaled with basal skull length and all‐region volumes scaled with total endocranial volume. We found taxon‐, and population‐level differences in total endocranial volume. Relative anterior and posterior cerebrum volume did not differ significantly between taxa or populations, but relative cerebellum volume was larger in arid populations than mesic populations. Relative olfactory bulb volume was larger in mesic R. dilectus than in the R. pumilio, but petrosal lobule volume was larger in R. pumilio populations than in R. dilectus. Males had larger total endocranial volumes than females. Drivers of larger total endocranial volumes in R. pumilio are not immediately clear from our results. Environmental seasonality of food availability, cognitive buffering and locomotion may all correlate with total endocranial volume size, whereas the influence of sociality cannot be excluded. The environment and degree of semi‐arboreality are likely driving variation in cerebellum, olfactory bulb and petrosal lobule volumes.

The ability to distinguish between familiar and strange conspecifics is important in group-living animals and influences the types of interactions between conspecifics.Social systems differ in sister taxa of the striped mouse genus Rhabdomys originating from different environments. Xeric-adapted R. pumilio displays facultative group-living whereas the mesic-adapted R. d. chakae is solitary. We assessed social recognition and attraction to strangers in females of two populations each of R. pumilio and R. d. chakae by means of a social discrimination task. We used a three-chamber apparatus developed in an established protocol and measured the latency of test females to approach and the duration of their investigation of stimulus females. Differences in social recognition of and preference for unfamiliar conspecifics in group-living and solitary-living taxa occurred at the taxon-level, even though constituent populations occurring kilometers apart showed similar responses. Females differed in the latency (testing phase) and duration of investigation (familiarization and testing phases) inter-specifically but not intra-specifically. Female R. pumilio approached stimulus females faster than female R. d. chakae. Female R. pumilio also investigated stimulus females for longer, regardless of stimulus type compared to R. d. chakae, but both taxa spent more time investigating familiar females than novel females and approached the familiar females faster than novel females. Social recognition, short-term memory, and social preference do not appear to differ between closely related taxa and differences in behavior between the two taxa might be related to inherent personality and social proclivity.

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