| dc.description.abstracteng | Cognition, the process by which animals acquire, process, store and use information from their environment, plays a major role in various behaviours across all aspects of an individuals’ life. However, despite this overall importance of cognitive abilities, we still know little about how cognitive traits evolved. In the past, research on cognitive evolution focussed on comparing different species in their cognitive abilities and linked variation in cognition to inter-specific differences in ecological and social conditions. This comparative approach helps to understand when in evolutionary history and under which conditions particular cognitive abilities evolved. Individual variation in cognitive abilities has been widely ignored in these studies on the species level, however. This changed only recently when the interest in how and why individuals differ in cognitive traits emerged. Only by investigating inter-individual variation in cognitive abilities and their link with fitness outcomes, we can begin to understand the causes and consequences of this variation and finally unravel how cognition evolved. Because fitness can only be studied in wild, free-ranging individuals, the study of individual differences in cognitive abilities and their fitness consequences is challenging and has been conducted mainly in different species of birds until today. The few studies so far focused largely on single measures of cognition and fitness and revealed not only positive but also negative and not significant correlations between cognitive performance and fitness outcomes.
With my thesis, I contribute to this young field of research aiming to better understand the adaptive value of cognitive traits. I investigated cognitive abilities in five cognitive tasks in wild grey mouse lemurs (Microcebus murinus), a primate species endemic to Madagascar, and linked cognitive performance with different fitness proxies. The cognitive tasks addressed different ecologically relevant cognitive abilities. They included associative and motor learning during repeated problem solving, causal reasoning and spontaneous problem solving in a string-pulling task, spatial learning, inhibitory control and behavioural flexibility during reversal learning. Subjects were tested during short-term captivity of up to three nights and subsequently released back into the wild. Furthermore, individuals were tested in two personality tests and their neophilia and activity during a novel object and an open field test was assessed.
In the first part of my thesis, I focused on inter- and intra-individual differences of cognitive performance: the potential confounding effects of non-cognitive factors on cognitive performance and the structure of cognitive performance across different cognitive abilities. My results demonstrated that, first of all, subjects differed greatly in cognitive performance and performance was not systematically affected by non-cognitive factors such as personality, body condition, motivation, age or sex. Furthermore, performance in one cognitive task was generally a weak predictor of performance in any other tasks of the test battery and could not be summarized into a general factor. Thus, I could not find evidence for a general factor of cognitive performance similar to the general intelligence factor (g) in humans, where performance is positively correlated across cognitive tasks and domains.
In the second part of the thesis, I studied different fitness-related traits in grey mouse lemurs and linked cognitive performance with two fitness proxies. I found that efficient repeated solving of a food extraction task correlated positively with the ability to maintain body condition during the long dry season with low food availability. This suggests that the ability to quickly apply a newly discovered motor technique during problem solving also facilitates the exploitation of new, natural food resources when food is scarce. By contrast, cognitive performance, irrespective of cognitive task, did not correlate with survival or longevity, suggesting that the assessed cognitive abilities did not provide (net) benefits in survival. Moreover, difficulties in validating a physiological condition factor, that summarized measures of body condition, hematocrit and long-term cortisol levels, demonstrated that identifying and operationalizing meaningful fitness proxies can be challenging for many taxa.
In summary, my thesis contributes the first study on a wild primate to the growing body of research investigating individual differences in cognitive abilities and their link with fitness outcomes. Together with the other recent findings revealing heterogenous links between cognitive performance and fitness measures, my thesis demonstrates that cognitive abilities are involved in complex interactions between various traits. At the same time, they are likely to have costs and benefits, and thus do not necessarily correlate positively with fitness outcomes. Further studies in different species in the wild, that investigate multiple cognitive traits and fitness outcomes as well as potentially confounding covariates simultaneously, will help to unravel this complex system, the evolution of cognition. | de |