Cognitive adaptations in two sympatric mouse lemur species occupying different ecological niches

Abstract

Cognition describes an individual's abilities to perceive, process, and act on information of the abiotic and biotic environment. The investigation of cognitive variation between individuals and species has been of interest for many decades and several hypotheses have been proposed to explain the evolution of cognition. Sizes of certain brain areas covary with the cognitive abilities they process, and socio-ecological factors have been related to various brain size measures. However, covariations of phenotypic cognitive performances with socio-ecological factors are essential to understand the adaptive value of cognitive abilities. While links with social factors have been the focus of comparative studies, which and how cognitive abilities and ecological factors link with each other, has been less systematically investigated. Precisely, it is assumed, that ecological generalists consistently outperform ecological specialists in cognitive challenges, but a respective link lacks systematic empirical evidence.In my first theoretic approach, I reviewed the literature for comparative studies that experimentally assessed cognitive performances among at least two species of the same phylogenetic order. I found that cognitive variation can be related to species-specific dietary preferences, related foraging behaviors, migratory behavior, or habitat complexity. However, other ecological factors, such as the synecology with predators or parasites, or the degree of ecological specialization, have largely been disregarded to be linked with cognitive performances. Only a subset of the reviewed studies specifically mentioned the degree of ecological specialization of the species in comparison. After complementing the respective information using additional literature, I applied a sign-test to estimate whether the degree of dietary or habitat specialization consistently covaries with cognitive performances. Across a total of 34 comparisons, N = 26 cognitive performances differed between the species in comparison. In 62% of these comparisons, the dietary generalist achieved higher performance scores than the relative dietary specialist. Habitat generalists achieved higher scores than relative habitat specialists in 72% of the comparisons. However, ecological generalism was not significantly associated with higher performances that go beyond innovative and flexible learning abilities. It Summary IV remains therefore questionable, whether generalist species consistently outperform more specialist species across a broader range of cognitive abilities.In my second empirical approach, I applied a conclusive cognitive test battery to two wild primate sister species. The gray and the Madame Berthe's mouse lemur possess a comparable social system, occur in sympatry at the chosen study site, but are differentially adapted to ecological factors. Essentially, the gray mouse lemur is a dietary and habitat generalist, while the Madame Berthe's mouse lemur is more specialized along these ecological niche axes. Occupying different ecological n...