The relative roles of genes and rearing environment on the spatial cognitive ability of two sympatric species of threespine stickleback

Background: Recently diverged populations provide a powerful model for studying trait evolution. Benthic sticklebacks primarily occupy vegetated areas of lakes, a spatially complex environment. Limnetic sticklebacks primarily occupy open water in lakes, a spatially simple environment. In a T-maze spatial learning assay, wild-caught benthic sticklebacks perform better than wild-caught limnetic sticklebacks. It is not known whether this difference has a genetic basis and is thus the result of evolution or is instead a plastic response to the contrasting environments. Question: To what extent are differences in the spatial cognitive ability of benthic and limnetic sticklebacks influenced by genetic differences, rearing environment, or the interaction between the two? Methods: Using wild-caught limnetic and benthic fish from Paxton and Priest Lakes, we made pure-species crosses in the lab. We reared the fertilized eggs in spatially simple or spatially complex lab environments. We used a previously validated T-maze spatial learning assay to quantify the ability of adult fish from each rearing environment to learn an association between a visual landmark and a reward location. Results: Lab-reared benthic fish learned the spatial task faster and made fewer errors than lab-reared limnetic fish, which supports a genetic basis underlying species differences in spatial learning ability. However, we found no significant differences between fish raised in different artificial environments.