Monster Seminar JAM - Rapid Evolution Following Invasions into Novel Environments
Dr. Carol Lee, Center of Rapid Evolution (CORE), University of Wisconsin, Madison
A fundamental unresolved problem in evolutionary biology regards constraints on adaptation to novel environments. Invasive species provide valuable models for exploring this problem, as many are relatively unconstrained in penetrating habitat boundaries. Within the past century, the copepod Eurytemora affinis has invaded freshwater habitats multiple times independently from saline sources. To dissect evolutionary responses during these independent 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. Using custom cDNA microarrays, we found evolutionary shifts in expression of genes spanning many functional categories, including ionoregulation, energy production, and stress response. Several genes underlying ion regulatory function (Na,K-ATPase ±, V-type ATPase B, cuticle proteins) showed parallel shifts in expression across independent invasions. Physiological assays revealed parallel evolutionary shifts in ion-motive ATPase activity associated with independent freshwater invasions, consistent with expression differences observed in the underlying genes. Activity of the ion uptake enzyme V-type ATPase exhibited an evolutionary increase in freshwater populations relative to saline populations at fresh water and a decline at higher salinity. In contrast, Na,K-ATPase activity was lower in freshwater populations across all salinities relative to saline populations. Moreover, saline lines selected for freshwater tolerance in the laboratory showed evolutionary shifts in ATPase activity concordant with natural freshwater populations. V-type ATPase localization and activity has been hypothesized to be critical for the invasion of fresh water, and perhaps of land, but no previous study had demonstrated evolution of function of this enzyme. We are currently sequencing a set of differentially-expressed candidate genes along with a set of putatively neutral loci to test for signatures of selection in wild populations. We are developing theoretical population genetic models of invasions in order to test for signatures of selection at our candidate loci while properly accounting for demography.
Date and Time:
December 3, 2009,
11:00 am - 12:00 pm