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I am an SNF Ambizione fellow studying the evolutionary genetics of sexual selection and sexual conflict. Much of my work involves generating and testing predictions of evolutionary theory using experimental evolution with the fruit fly Drosophila melanogaster and a combination of phenotypic and genomic approaches. A major aim is to better understand the ways sexual selection constrains and facilitates adaptation, in particular with respect to the evolution of differences between the sexes.
Sexual conflict comes in two varieties. First, there may be direct antagonism (e.g. male harassment of females), resulting in an 'arms race' between the sexes that ultimately depresses population productivity. Another, different kind of sexual conflict occurs when the two sexes have different optima for a trait but are constrained from reaching these optima because they must share the genome. We recently showed that many genes exhibiting sex-biased expression are not at sex-specific optima, and relaxing sexual selection on males causes rapid evolution towards the optima of females. We are now investigating whether sexually antagonistic fitness effects extend to the juvenile, nonsexual portion of the life cycle.
Hollis, B. and Kawecki, T.J. 2017. Sexual selection shapes development and maturation rates in Drosophila. Evolution doi: 10.1111/evo.13115.
Hollis, B., Houle, D., and Kawecki, T.J. 2016. Evolution of reduced post-copulatory molecular interactions in populations lacking sperm competition. Journal of Evolutionary Biology 29: 77-85.
Hollis, B., Houle, D., Yan, Z., Kawecki, T.J., and Keller, L. 2014. Evolution under monogamy feminizes gene expression. Nature Communications 5 (3482): 1-5.
SEXUAL SELECTION IN ADAPTATION
The "good genes" hypothesis for the evolution of preference suggests that male sexual traits will honestly signal genetic quality, allowing choosy females to gain indirect benefits through higher-quality offspring. Theoretical work built on this idea predicts that populations with relatively strong sexual selection should show increased rates of adaptation to novel environments, faster fixation of beneficial alleles, and reduced mutation load. We have tested these ideas with manipulations of the strength of sexual and nonsexual selection in populations carrying a known deleterious allele or elevated levels of genetic variation for fitness. Currently, we are studying the adaptive value of sexual selection further by measuring its effects on different components of fitness, including those specific to a certain stage of life, a certain sex, or a certain selective pressure like disease.
Hollis, B. and Houle, D. 2011. Populations with elevated mutation load do not benefit from the operation of sexual selection. Journal of Evolutionary Biology 24: 1918-1926.
Hollis, B., Fierst, J.L., and Houle, D. 2009. Sexual selection accelerates the elimination of a deleterious mutant in Drosophila melanogaster. Evolution 63: 324-333.
Sexual selection is responsible for the evolution of male ornaments and armaments, but its role in the evolution of cognition is less clear. We have recently found that males evolved under monogamy became less proficient than polygamous males at relatively complex cognitive tasks, including locating, courting, and mating with a single receptive female amongst many unreceptive females. This learning deficit is also apparent in a nonsexual context, an aversive olfactory learning test. We have also used this same averse learning paradigm to investigate the genetic basis of cognitive aging in flies.
Zwoinska, M.K., Maklakov, A.A., Kawecki, T.J., and Hollis, B. in press. Experimental evolution of slowed cognitive aging. Evolution.
Hollis, B. and Kawecki, T.J. 2014. Male cognitive performance declines in the absence of sexual selection. Proceedings of the Royal Society B 281: 20132873.
THE ROLE OF KINSHIP IN COOPERATION
Cooperation can evolve when interacting individuals are highly related. We have studied this possibility with experimental evolution of altruistic self-sacrifice in the social amoeba Dictyostelium discoideum, and more recently in the context of male-male competition for and harm to females in Drosophila.
Hollis, B., Kawecki, T.J., and Keller, L. 2015. No evidence that within-group male relatedness reduces harm to females in Drosophila melanogaster. Ecology and Evolution 5(4): 979-983.
Hollis, B. 2012. Rapid antagonistic coevolution between strains of the social amoeba Dictyostelium discoideum. Proceedings of the Royal Society B 279: 3565-3571.