Dr. Brian Hollis

I study sexual selection and genomic conflict using experimental evolution, primarily with the fruit fly Drosophila melanogaster. Many of my experiments involve testing predictions of evolutionary theory using long-term populations that have adapted to different mating systems. I use both phenotypic and genomic approaches to address three interconnected questions:

- How does sexual selection influence the process of 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. I have tested these ideas by manipulating the strength of sexual and nonsexual selection in populations either carrying a known deleterious allele [Hollis et al. 2009] or elevated levels of genetic variation for fitness [Hollis and Houle 2011]. Although sexual selection does accelerate adaptation, it appears that populations are forced to simultaneously carry a sexual conflict load due to the divergent interests of males and females. I am currently 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.

- What is the extent and evolutionary impact of conflict 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 [Hollis et al. 2014]. We are now investigating whether sexually antagonistic fitness effects extend to the juvenile, nonsexual portion of the life cycle. I am also using new experimental populations to look at what happens when both sexual and nonsexual selection are relaxed on one sex via an artificial sex chromosome.

- What is the role of sexual selection in the evolution of cognition?
Sexual selection is responsible for the evolution of male ornaments and armaments, but its role in the evolution of cognition is less clear. We found that males evolved under monogamy became less proficient than polygamous males at relatively complex cognitive tasks [Hollis and Kawecki 2014], including locating, courting, and mating with a single receptive female amongst many unreceptive females.

This learning deficit is also apparent in a nonsexual context (e.g. an aversive olfactory learning test). We are now trying to get a better understanding of monogamous male learning differences at the mechanismal level. We're also interested in the female side of things, and to that end are looking at whether female choosiness has evolved under monogamy.


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Currently lecturer, Imperial College.