Natural environments are constantly changing. To survive, organisms will either need to rapidly adapt to new conditions or colonize new habitats. Colonization has been hypothesized to select for increased plasticity as well as increased brain size, though empirical tests of these effects have proven difficult to evaluate. In particular, the degree to which plasticity of brain morphology can evolve, and its subsequent ecological consequences have rarely been explored. Trinidadian guppies (Poecilia reticulata) are known for their repeated adaptation to ancestral high-predation (HP) and derived low-predation (LP) environments. We used this system to examine the evolution and plasticity of brain morphology. We exposed second-generation offspring of individuals collected from HP and LP sites to two different kinds of environmental treatments: predation cues and conspecific social environment. We found that guppies descended from a colonized LP habitat showed greater plasticity in brain morphology than descendants of their ancestral HP population, supporting the hypothesis that plasticity of brain morphology may increase fitness after colonization of a novel habitat. Additionally, we show sexual dimorphism in brain morphology plasticity. Overall, these results suggest the evolution of brain morphology plasticity as an important mechanism that allows for ecological diversification and colonization of novel habitats.

Data aquired via analysis of brain region volumes and brain mass of Trinidadian guppies raised in a plasticity experiment.