Meeting Abstract
Evolutionary novelty is particularly difficult to define and demonstrate- a problem that is exacerbated by the possibility that ancestral phenotypes unexpressed over evolutionary time frames can re-emerge as environments change. The re-emergence of ancestral traits can be difficult to discriminate from the evolution of true novelties unless the ancestral condition can be identified, and ideally, experimental manipulation can be used to elicit the ancestral phenotype or one sufficiently similar that homology is likely. The adaptive radiation of the threespine stickleback fish, Gasterosteus aculeatus, offers an unusual opportunity to explore the possibility that behavioral traits, apparently lost from certain derived populations, can re-emerge under conditions approximating those to which oceanic ancestors were exposed. Specifically, as oceanic stickleback invaded freshwater habitats following the last glacial retreat, populations that invaded lakes most suited to planktivory appear repeatedly and independently, to have lost ancestral expression of cannibalism and a diversionary display that males use to defend young in nests from cannibalistic conspecifics. These plastic behaviors have been re-elicited in one population as a consequence of recent productivity transitions in one lake, and can be elicited in other populations, though the threshold for eliciting the behavior is higher than in populations in which the behaviors persist. I discuss the importance of this phenomenon further using additional, more ancient examples.
