Determining how variation in brain morphology affects cognitive abilities is important to understand inter-individual variation in cognition and, ultimately, cognitive evolution. Yet, despite many decades of research in this area, there is surprisingly little experimental data available from assays that quantify cognitive abilities and brain morphology in the same individuals. Here, we tested female guppies ( Poecilia reticulata ) in two tasks, colour discrimination and reversal learning, to evaluate their learning abilities and cognitive flexibility. We then estimated the size of five brain regions (telencephalon, optic tectum, hypothalamus, cerebellum and dorsal medulla), in addition to relative brain size. We found that optic tectum relative size, in relation to the rest of the brain, correlated positively with discrimination learning performance, while relative telencephalon size correlated positively with reversal learning performance. The other brain measures were not associated with performance in either task. By evaluating how fast learning occurs and how fast an animal adjusts its learning rules to changing conditions, we find support for that different brain regions have distinct functional correlations at the individual level. Importantly, telencephalon size emerges as an important neural correlate of higher executive functions such as cognitive flexibility. This is rare evidence supporting the theory that more neural tissue in key brain regions confers cognitive benefits.

Determining how variation in brain morphology affects cognitive abilities is important to understand inter-individual variation in cognition and, ultimately, cognitive evolution. Yet, despite many decades of research in this area, there is surprisingly little experimental data available from assays that quantify cognitive abilities and brain morphology in the same individuals. Here, we tested female guppies (Poecilia reticulata) in two tasks, colour discrimination and reversal learning, to evaluate their learning abilities and cognitive flexibility. We then estimated the size of five brain regions: telencephalon, optic tectum, hypothalamus, cerebellum, and dorsal medulla, in addition to relative brain size. We found that optic tectum relative size, in relation to the whole brain, correlated positively with discrimination learning performance, while relative telencephalon size correlated positively with reversal learning performance. The other brain measures were not associated with performance in either task. By evaluating how fast learning occurs and how fast an animal adjusts its learning-rules to changing conditions, we find support for that different brain regions have distinct functional correlations at the individual level. Importantly, telencephalon size emerges as an important neural correlate of higher executive functions such as cognitive flexibility. This is rare evidence supporting that more neural tissue in key brain regions confers cognitive benefits.

Genetic structures are generally the outcome of interactions among species' social traits, geographic features limiting dispersal, and historical distribution patterns (Wright 1943;Slarkin 1985;Hartl and Clark 1997;Epperson 2003), although ecological processes have also been shown to play an important role (Pilot et al. 2006). Information on the genetic structures of populations are therefore relevant for a broad range of topics ranging from evolutionary biology to directly applied environmental resource management (Epperson 2003;Manel et al. 2003). Genetic structure is particularly relevant considering the current rate of broad scale environmental change, largely driven by climate change and landscape transformation (Nelson 2005). Such environmental change can alter distribution patterns of species at a range of scales (Parmesan 2006;Sexton et al. 2009), and subsequently also the genetic structures of populations (Alsos et al. 2012; Franks and Hoffman 2012;Theodoridis et al. 2020). Furthermore, genetic variation is the raw material for evolution and therefore crucial for adapting to changing environmental conditions (Barrett and Schluter 2008).Southern Africa may suffer significantly from projected global warming, primarily related to increased frequency and severity of droughts (Makholela et al. 2017). The direct ecological consequences of a potential increase in the magnitude and frequency of drought, induced by global warming, are difficult to predict in southern African arid grasslands and savannas (Le Houérou 1996; Sankaran 2019). However, increased woody plant cover, coupled with accelerated spatial expansion and intensification of agricultural activities are likely to have substantial ecological effects (Dobrovolski et al. 2011;Midgley and Bond 2015; however, see Hoffman et al. 2019 for an alternate view), including range shifts, range contractions and species loss of terrestrial mammals (Thuiller et al. 2006;Visconti et al. 2011). This expected range contraction and fragmentation is likely to influence interpopulational genetic exchange as well as genetic diversity within populations of southern African mammals.The bat-eared fox (Otocyon megalotis) is a small, primarily insectivorous canid that has a disjunct distribution in southern and eastern Africa (Clark Jr 2005). The species is mainly confined to open grasslands and largely relies on termites (Isoptera) and other arthropods for its diet (Klare et al. 2011;Jumbam et al. 2019). Although classed as 'Least Concerned' in a recent South African IUCN Redlist assessment (Dalerum et al. 2016), quantification of spatial population structures and genetic diversity were identified