Development vs. behavior: a role for neural adaptation in evolution?

We examine the evolution of sensory organ patterning in the lateral line system of fish. Based on recent studies of how this system develops in zebrafish, and on comparative analyses between zebrafish and tuna, we argue that the evolution of lateral line patterns is mostly determined by variations in the underlying developmental processes, independent of any selective pressure. Yet the development of major developmental innovations is so directly linked to their exploitation that it is hard not to think of them as selected for, i.e., adaptive. We propose that adaptation resides mostly in how the nervous system adjusts to new morphologies to make them functional, i.e., that species are neurally adapted to whatever morphology is provided to them by their own developmental program. We show that recent data on behavioral differences between cave forms (blind) and surface forms (eyed) of the mexican fish Astyanax fasciatus support this view, and we propose that this species might provide a unique opportunity to assess the nature of adaptation and of selection in animal evolution.