Linking cognition to ecology in wild sympatric mouse lemur species

Abstract

Cognitive abilities covary with both social and ecological factors across animal taxa. Ecological generalists have been attributed with enhanced cognitive abilities, but which specific ecological factors may have shaped the evolution of which specific cognitive abilities remains poorly known. To explore these links, we applied a cognitive test battery (two personality, ten cognitive tests; n = 1104 tests) to wild individuals of two sympatric mouse lemur species (n = 120 Microcebus murinus, n = 34 M. berthae) varying in ecological adaptations but sharing key features of their social systems. The habitat and dietary generalist grey mouse lemurs were more innovative and exhibited better spatial learning abilities; a cognitive advantage in responding adaptively to dynamic environmental conditions. The more specialized Madame Berthe's mouse lemurs were faster in learning associative reward contingencies, providing relative advantages in stable environmental conditions. Hence, our study revealed key cognitive correlates of ecological adaptations and indicates potential cognitive constraints of specialists that may help explain why they face a greater extinction risk in the context of current environmental changes.

Keywords: cognition; ecology; evolution; habitat; learning; primates.

Figure 1.

Experimental test battery and mouse lemurs. (a) Arenas used in the open field test. (b) Plus maze. (c) Objects used in the novel object test. (d) Food extraction task and persistence test. (e) Cylinder test. (f) Left: grey mouse lemur; right: Madame Berthe's mouse lemur; scaled to size differences. (g) String-pulling task, single-string set-up. (h) Apparatus used for the visual and spatial discrimination and reversal learning paradigm; numbers indicate the position of the forms. Green (filled) arrows indicate correct routes. Red (striped) arrows indicate incorrect routes. Yellow stars represent a food reward. (Online version in colour.)

Figure 2.

(a) Open field test: time spent exploring for females and males. (b) Food extraction task: innovative propensity (N opened wells) per species. (c) Persistence test: duration spent manipulating the box as a rate to the duration spent in contact with the box per species. (d) Visual discrimination learning across sessions per species (p < 0.05). (e) Visual discrimination and reversal learning paradigm: overall performances within tasks. (f) Visual discrimination and reversal learning paradigm: flexible learning between tasks. (g) Plus maze: spatial memory performance per species. Sample sizes (n) are given below each boxplot. Dark grey: GML; light grey or orange: MBML. Significance levels: *p < 0.05, **p < 0.01, ***p < 0.001. (Online version in colour.)