My students and I use laboratory populations of fruitflies as a system to address various questions falling under two main areas and also the interface between them: life-history evolution and population ecology. We also occasionally do supporting theoretical work that is rooted in our primary work which involves long-term experiments using laboratory selection or time-series of population sizes under different environments. In recent years, our work has focused on correlated responses to selection for rapid egg-to-adult development, multiple routes to the evolution of greater competitive ability under crowding, the evolution of population stability as a by-product of life-history evolution and the effects on constancy and persistence stability of the interaction between local dynamics and migration rates in spatially-structured populations.
The evolution of rapid development has been shown to lead to the evolution of a complex phenotype including reduced body size, fecundity and competitive ability, as well as to a postponement of some aspects of sexual maturation from the pupal to early adult phase. Our faster developing populations have shortened their development time by about 60 h over several hundred generations of selection, a reduction of over 30%, and every life-stage (egg, all three larval instars and pupa) is reduced in duration. The faster developing populations have also evolved specific patterns of non-genetic maternal effects on offspring phenotypes in response to maternal age and rearing density. There is also evidence for reduced levels of inter-locus sexual conflict in these populations, most likely mediated in large part by the size reduction. The faster developing populations also exhibit incipient reproductive isolation from their ancestral control populations.
Past work on density-dependent selection has typically used density of larvae per unit food as a convenient descriptor of the level of crowding. We find that density interacts in a complex way with the total amount and depth of food present in a culture. Thus, cultures with similar larval density can actually evolve very different sets of traits as they adapt to crowding, depending on the ecological details of the culture regime. In general, we have been arguing that the evolution of competitive ability needs to be looked at in a more ecologically nuanced way than has often been the case in the canonical theory of density-dependent selection.
Our work on the evolution of population stability has provided the first empirical evidence for the evolution of greater constancy and persistence stability as a by-product of either selection for rapid development or for adaptations to larval crowding. In particular, we have shown that crowding can lead to the evolution of greater stability even in the absence of r-K tradeoffs, indicating that density-dependent selection may in fact play a larger role in mediating the evolution of enhanced population stability than commonly believed.
Our work on migration and stability in spatially-structured populations has been aimed at bridging the gap between theory and experiment in metapopulation dynamics. We have documented the first experimental evidence of metapopulation stability via asynchrony and of increased metapopulation extinctions due to synchrony among locally unstable subpopulations. Our work has also revealed complex interactions between migration rate and local dynamics on the patterns of population growth and stability in metapopulations.
In the past, I have worked on the coevolution of competing species, the evolutionary maintenance of sexual reproduction in the face of the so-called cost of sex, the evolution of extreme host or habitat specialization and the evolution of circadian organization. I also have an enduring interest in philosophical issues in evolutionary biology.
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