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Recent & Current Collaborators
Aneil Agrawal (University of Toronto) Russell Bonduriansky (University of New South Wales) Vincent Careau (uOttawa) Kelly Dyer (University of Georgia) Amanda Moehring (Western University) Locke Rowe (University of Toronto) |
Current Research
A selection of ongoing research projects in the lab, some involving our collaborators.
The ecology of interlocus sexual conflict
Sexual conflict arises when the reproductive interests of males and females are not aligned, generating sexually antagonistic selection on a shared trait. If different genes control the trait in either sex, then selection can favour loci that enhance a male’s reproductive success relative to intrasexual competitors, even if males carrying such alleles reduce female fitness. Reciprocally, selection will also favour loci that increase a female’s resistance to such harm, even if these reduce male fitness. As a model system, Drosophila laboratory studies have contributed enormously to our understanding of such interlocus sexual conflict. However, laboratory populations of Drosophila are normally maintained under conditions that are very different from those in nature, often involving individuals that are kept at extremely high densities in spatially-restricted environments that lack any structural complexity (e.g., standard vials/bottles). Populations are also usually maintained using highly abbreviated reproductive lifespans in which adults are allowed to mate and lay eggs for only a short period (e.g., 8-72 h) before being discarded. Under such conditions, males have unfettered access to females that have little opportunity to escape unwanted male attention, potentially altering the nature and costs/benefits of both male persistence and female resistance. The greatly shortened adult lifespan also renders neutral any costs to females that would normally be experienced later in life. The economics and evolutionary dynamics of sexual conflict under such conditions may therefore be a poor indicator of that in populations under more natural conditions. We are testing whether and how sexual conflict varies when assayed in different environments and when using lab populations that have evolved under different life history schedules. |
Sexual selection and the purging of deleterious mutations
If reproductive success depends on an individual's health and/or vigour, then alleles that are deleterious to non-sexual fitness will also tend to reduce sexual fitness, causing both natural and sexual selection against them. However, sexual selection may also hamper the purging of deleterious alleles if males are harmful to females (i.e. interlocus sexual conflict occurs) and they direct this harm preferentially towards otherwise intrinsically high fitness (i.e. non-mutant) females, thereby reducing or evening eliminating the fitness advantage of such females over non-mutant females. Previous work from our lab has suggested a net cost of sexual selection in hampering the purging of deleterious mutations in an ecologically simple environment [pdf]. We are currently using experimental evolution to test the effects of ecological complexity on the rate at which several different visible deleterious mutations are eliminated, and together with Aneil Agrawal (University of Toronto) on the rate at which a larger set of presumably deleterious gene disruptions are purged. In both cases, we are interested in whether larger and/or structurally complex mating environments may alter the net effect of sexual selection, potentially making it more beneficial by decreasing the harm of sexual conflict (see 'The ecology of sexual conflict' above). |
Genomics of adaptation to novel environments under natural and sexual selection
From an evolution experimental we conducted that involved a factorial manipulation of natural and sexual selection in 12 replicate populations, we previously showed that sexual selection did not promote adaptation to a novel abiotic environment in terms of phenotypic measures of fitness [see figure at right and this pdf]. However, sexual selection's impact on net fitness may obscure opposing effects among loci that could effectively cancel each other out. Therefore, to more finely dissect the response to selection in these populations, in collaboration with Steve Chenoweth (University of Queensland) we are using genotyping-by-sequencing (RAD sequencing) to identify selection-induced allele frequency changes across the genome, providing direct insight into the population genetics of adaptation including the effects of natural selection, sexual selection, and their interaction. In addition, in collaboration with Aneil Agrawal (University of Toronto), we are studying how ecological complexity of the mating environment affects the genomics of adaptation to three different abiotic environments. We are again interested whether sexual selection tends to better align with natural selection in more complex mating environments. |
Diet influences on senescence in the wild
Much attention has been given to the apparent longevity-enhancing effect of diet restriction on a variety of organisms under laboratory conditions. Whether and how patterns of senescence vary between laboratory and wild populations has received limited attention, however, and the effects of diet variation on this are poorly understood. Male antler flies spend essentially their entire adult life courting and mating females on a single discarded moose/deer antler. Their extreme site fidelity means that they can be individually marked, released on an antler, and then their lifetime mating success and lifespan can be tracked. Working with Russell Bonduriansky (University of New South Wales) and Brian Mautz (Uppsala University), a former postdoctoral fellow from our lab, we are measuring actuarial and reproductive senescence contemporaneously in both the laboratory and in nature using males raised on different diet treatments. For more information about antler flies, visit Russell's antler fly page. |
Speciation in nature: mate choice and population divergence of sexual displays and mate preferences
Behavioral isolation is often the predominant reproductive barrier between recently diverged taxa, suggesting its evolution plays a key role in initiating speciation. The strengthening of behavioural isolation following secondary contact (i.e. reinforcement) also appears to often be the final step in completing the speciation process. A comprehensive understanding of the origin of species therefore requires knowing the phenotypes generating behavioural isolation and why they have diverged . Behavioural isolation is assumed to arise from differences in mate preferences and the sexual displays they target, but direct links between these are lacking and little is known about the selective mechanisms driving the divergence of mate recognition in nature. In collaboration with Kelly Dyer (University of Georgia), we are studying the evolution of behavioural isolation in the N. America mushroom-feeding D. recens and D. subquinaria. D.. subquinaria females display a pattern of reproductive character displacement in nature such that those sympatric with the closely related D. recens reject mating with heterospecific males more strongly than do allopatric females. Sympatric females also discriminate against their own conspecific males from allopatry. Females use chemosensory cues in mate choice [pdf] and male pheromones differ among populations in a pattern that precisely matches the behavioural isolation [pdf] . Selection for increased behavioural isolation is hypothesized to result from the reduced fitness of hybrids, which itself is due in part to a Wolbachia infection in D. recens that kills hybrid offspring produced by D. subquinaria females. To test hypotheses about the evolution of behavioural isolation we are using experimental evolution, manipulating the presence/absence of the other species and when present, the strength of selection against hybrids. |
Condition dependence
Theory suggests that costly traits enhancing reproductive success (or fecundity) should evolve heightened condition dependence, a form of plasticity that links trait expression to the availability and processing efficiency of metabolic resources. Working with a multivariate suite of sexual display pheromones in D. serrata, we have previously shown that the strength of condition dependence is positively associated with the strength of sexual selection among various chemical blends, providing one of the first quantitative tests of this prediction [pdf]. More recently we have explore the effects of environmental and genetic quality on the expression of condition-dependent morphological and chemical traits in D. melanogaster, demonstrating that different traits appear to exhibit different forms of condition dependence, with some responding consistently to both genetic and environmental quality and others responding almost exclusively to the latter [pdf]. Theory also suggests that the extent of sexual dimorphism should itself be condition dependent, and that a genetic correlation should exist between the strength of condition dependence and the extent of sexual dimorphism. We are currently testing both of these predictions in antler flies and Drosophila. |