Linking molecular and reproductive patterns - thermal adaptation in the yellow dung fly at a global scale
Zusammenfassung der Projektergebnisse
Latitudinal clines in life history, reproductive and molecular traits have often been described; however, their adaptive significances are often not well understood. Using the common yellow dung fly (Scathophaga stercoraria, Diptera: Scathophagidae), I assessed latitudinal variation in life history and reproductive traits in a crosscontinental comparison (Europe & North America). This includes a comparison of the variation in neutral molecular markers and quantitative traits (a part of the project that is still in progress, so that no final account can be made at this point). Results on European populations show linear clinal variation in development time, body size and egg size (consistent with Bergman’s rule). Furthermore, populations differ in egg glycogen and lipid content (though not showing a simple linear latitudinal cline), but not in egg protein content. These results show that there is local genetic variation in egg quality, and that egg size variation is not sufficiently indicative of qualitative changes in egg composition. Furthermore, plastic responses to rearing temperatures were found for body, clutch and egg size, but not in any of the measured egg components, suggesting that latitudinal variation in egg components may not be mediated via adaptations to ambient temperatures. Thermal stress resistance traits vary across yellow dung fly populations only for heat resistance but not for cold resistance, though again not in a simple linear latitudinal fashion, suggesting that local adaptation may mask any underlying expected large-scale geographic patterns. Exposition to even short bouts of thermal extremes elicits a physiological response (as assessed in the expression of heat shock protein 70 levels) and is costly in terms of some individual fitness components. This is especially apparent in female flies that suffer from a reduction in fecundity and egg survival, while the reproductive performance of male flies does not seem to be as severely affected. The magnitude of these costs strongly depends on the respective population origin.
