This research is in a preliminary state. Peter plans to determine the cellular differences responsible for variation in brain shape among populations. This will allow him to determine whether similiarities in spatial cognition have the same or a different cellular basis in different populations with similar spatial cognition and gross brain morphology. Once the cellular basis for differences in spatial cognition in stickleback is understood, it will be possible to use hybrids between planktivore and benthic-feeding stickleback to use linkage mapping to infer the genes responsible for differences in spatial learning ability and brain development between benthic-feeding and planktivore threespine stickleback populations.