This week EEB welcomes Dr. Bob Cox from the Department of Biology, University of Virginia:
Two phenotypes, one genome: Integrating endocrine, transcriptomic, and quantitative genetic perspectives on sexual dimorphism
The evolution of sexual dimorphism presents a puzzle – how do males and females express dramatically different phenotypes despite sharing essentially the same underlying genome? The answer to this question often depends on whom you ask. An endocrinologist might reply that the development of sexual dimorphism requires sex steroids such as testosterone and estradiol. A quantitative geneticist might say that it involves the reduction of genetic correlations between the sexes. A molecular geneticist might view the problem as one of regulating the expression of shared genes differently in each sex. These apparently disparate perspectives may often describe the same underlying phenomenon of genetic dis-integration between the sexes. For example, in the lizard Anolis sagrei, the gradual development of extreme sexual size dimorphism is accompanied by the ontogenetic breakdown of between-sex genetic correlations for body size and growth rate. This breakdown of genetic constraint is mirrored by a sharp increase in the sex-biased expression of hundreds of autosomal genes in the liver, particularly those genes that regulate growth, metabolism, and cell proliferation. Mechanistically, treatment of females with testosterone stimulates the expression of male-biased genes while inhibiting the expression of female-biased genes, thereby masculinizing phenotypes at both organismal and transcriptomic levels. Collectively, these findings suggest that hormones such as testosterone can orchestrate sex-biased gene expression to facilitate the phenotypic development of sexual dimorphism while simultaneously reducing genetic correlations that would otherwise constrain the independent evolution of the sexes. Moreover, changes in the coupling of testosterone to gene expression can facilitate rapid evolutionary shifts in sexual dimorphism at the organismal level.
The EEB Seminars run weekly, on Thursdays, in the EEB Lounge of the BioSciences Complex, Room 4338, from 12:30-1:30pm. Light refreshments are served starting at 12:15.