CANCELLED - Rapid evolution during habitat invasions

Background/Question/Methods

An intriguing question remains as to why some groups show the evolutionary capacity to invade novel habitats, whereas most do not. In recent years, many species invading freshwater habitats have originated from more saline environments, disproportionate to their rate of transport. Identifying the specific genetic mechanisms that underlie physiological evolution during freshwater invasions might bring us closer to determining why particular populations have the capacity to cross this formidable boundary, and also provide general insights into why certain species have the ability to invade. The copepod Eurytemora affinis has invaded freshwater habitats multiple times independently from saline sources within the past century. Interestingly, some populations of E. affinis have the capacity to invade, whereas others do not. What properties characterize the invasive populations? To dissect evolutionary responses during these independent habitat invasions, we integrated analyses of physiological function with comparative functional genomics. We analyzed evolutionary shifts during invasions for pairs of ancestral saline source and derived freshwater populations across four independent invasions from two genetically distinct clades.

Results/Conclusions

We found evolutionary shifts in function (ion efflux, ion uptake), as well as in expression of genes spanning many functional categories, including osmoregulation, energy production, and stress response. In many cases, there were striking parallel evolutionary shifts across independent invasions, particularly with respect to ion uptake activity and expression. Physiological evolution during invasions appeared to occur through selection on standing genetic variation in the native range. The evolutionary parallelism observed here might have relevance for taxonomically different but ecologically similar species that invade across similar habitat clines. Moreover, a striking pattern that emerges is that the invasive populations appear to originate from habitats characterized by fluctuating conditions.