Ecological history and adaptive future: A study of adaptation to stress in Tribolium castaneum

Background/Question/Methods

How is the ability of a population’s adaptation to stress influenced by past selection? Can a diversely selective history on a population enable it to more quickly and effectively produce individuals adapted to novel stresses than decedents of populations from more benign environments? Our study seeks to answer these questions using experimental populations of the red flour beetle Tribolium castaneum. We tested the hypothesis that diverse selective history would produce populations able to adaptively evolve more quickly and effectively to novel selection pressures (“stresses”) than populations from a benign environment. We measured differences in adaptation rate in populations each exposed to one of eight selective regimes (including control) varying in intensity and diversity over ten generations in one phase, and then to a uniform novel selection pressure (“stress”) in a second phase. Selective treatments employed in the first phase are related to consumption of resource. Type (wheat/corn) and physical state of food (milled/whole grains), as well as presence or absence of pesticide in the food are the three single treatment categories, and every possible combination of these formed the more diverse selective regimes. By the end of phase one population extinctions reduced the number of treatments to five (including control). In phase two, populations were all transferred to a high temperature environment. This functioned as a uniform novel stress ,unrelated to their previous selection regimes. We used population growth and size, developmental rate, and average weight of adults as proxies for rate and success of adaptation to test the following predictions: (1) adaptation will occur in populations reared for a number of generations in the stressful environments we have chosen, (2) production of adapted individuals will vary between populations , and (3) populations exposed to stronger and/or more diverse selective history will have enhanced rate and success of adaptation to the novel stress.

 Results/Conclusions

Our preliminary results reveal diverse correlations between treatments and population dynamics. The results suggest that (1) experimental populations have adapted to the different selective regimes in phase one, and (2) the type and diversity of selection are important contributors to the observed variation in adaptation between treatments. It should be noted that: physical state of food, presence/absence of pesticide, and heat stress appear to be important predictors of population size; and the relationships between some treatments and population dynamics change strongly across generations, while others come closer to exhibiting stasis.