A pair of talks from Duke University took different approaches to examining anole smarts. Recently minted Ph.D. Brian Powell reported on his examination of the brain size and composition of different anole species. Brian reasoned that anoles living in different habitats would evolve differences in brain structure corresponding to the different challenges they faced, and thus that species that use the same habitat should have converged on brain morphology. However, results failed to support this hypothesis and instead indicated that the size of different brain components evolves in concert. More details below.
Later in the meeting, Manuel Leal reported on the cognitive flexibility of several anole species. Previous work has shown that A. evermanni is not only adept at solving novel problems, but can reverse previously learned patterns so as to ignore the stimulus that previously was rewarded and instead respond to a stimulus that previously hadn’t been rewarded. Leal has now extended that work to show that two other anoles can do the same. He then went on to test how adept anoles are at telling apart two similar patterns. He found, surprisingly, that they could tell very different patterns apart, but did not seem to be able to distinguish more similar patterns. Leal concluded by wondering whether minor differences in signals are detectable by receivers, which is an underlying assumption of many studies of sexual selection and communication. Manuel’s abstract is below the fold as well, although he went off-script in much of the talk he presented.
Powell, Brian (Duke University); Leal, Manuel (Duke University, Canada)
Brain Evolution Across the Puerto Rican Anole Radiation
Patterns of brain evolution have been widely studied across vertebrates, with the bulk of studies using mammals and/or birds. Within these groups, species occupying different habitats have been shown to have divergent neuroanatomy, particularly differences in the relative size of different brain structures, correlated with differences in habitat size or structure. We examine the pattern of allometric scaling across the telencephalon, dorsal cortex, dorsomedial cortex, medial cortex, dorsal ventricular ridge, medulla, and cerebellum in six species of Puerto Rican Anolis lizards, which are grouped in three distinct ecomorphs according to interspecific differences in structural habitat preferences. The differences in habitat preferences are accompanied by morphological and behavioral adaptations for effective used of each habitat type. However, our results challenge this trend and demonstrate a lack of convergence in the relative size of different brain structures between species using similar structural habitats. We found differences in the relative volume of the medulla across species, suggesting mosaic evolution in this structure. Overall brain volume explained between 92.5% and 99.7% of the variance in volume of each of the brain regions measured, and 93.7% and 98.5% of the variance in volume of each component measured within the telencephalon. This pattern of brain allometry is generally consistent with concerted brain evolution, with the exception of the medulla. Concerted brain evolution has also been observed in mammals and cartilaginous fishes, and its presence in Anolis lizards provides additional evidence supporting the hypothesis that concerted brain evolution might result from a conserved pattern of brain development common to all vertebrates.
Leal, Manuel (Duke University); Leal, Manuel (Duke University, Durham, NC, United States)
Behavioral flexibility and problem-solving in lizards
The role of behavioral flexibility in responding to new or changing environmental challenges is a central theme in cognitive ecology. Studies of behavioral flexibility have focused mostly on mammals and birds because theory predicts that behavioral flexibility is favored in species or clades that exploit a diversity of habitats or food sources and/or have complex social structure, attributes not associated with ectothermic vertebrates. Here, we present the results of a series of experiments designed to test cognitive abilities across multiple cognitive modules in three species of Anolis lizards. Anoles exhibited behavioral flexibility across multiple cognitive tasks, including solving a novel motor task using multiple strategies and reversal learning, as well as rapid associative learning. However, the species differ in the degree of behavioral flexibility. The observed levels of flexibility were unexpected because lizards are commonly believed to have limited cognitive abilities and highly stereotyped behavior. Also, interspecific differences in flexibility might be related to differences in the ecology of each species, although it is also possible that other factors such as differences in species “personality” can contribute to our results. More generally, our findings strongly suggest a re-thinking of our understanding of the cognitive abilities of lizards and of the factors favoring the evolution of behavioral flexibility.