Dissertation Research: Experimentally skewed ratio of males to females as a behavioral driver of genome evolution

Cornell University, Ithaca NY

Investigators

Abstract

Why have males and females evolved to be so different? Over evolutionary time, males and females can become very different from each other in behavior and structure, but the process behind this divergence is poorly understood. This research focuses on how social interactions shape the elaborate differences we see in nature. An excess of males or females can have a strong effect on many traits by changing how frequently an individual interacts with potential mates or rivals, and therefore how likely that individual's traits are to persist in later generations if they confer a mating or competitive advantage. Using the short-lived roundworm, this project measures the genetic differences between populations kept for 50 generations with mostly females, mostly males, or equal numbers of males and females. Analyzing genetic changes in these populations will reveal the processes by which evolution can alter traits in a population entirely due to male-female interactions. Moreover, comparing the genomes of multiple populations with an excess of males or females will address a core question in evolutionary biology: how similar are evolutionary trajectories when populations face identical conditions? This project will train undergraduate students from backgrounds underrepresented in science using modern genomic techniques, and produce online resources to educate high school students and the public about genomic methods and evolution. The goal of this proposal is to measure the genomic effect of selection on the differences between males and females and to quantify genetic changes resulting from the behavioral interactions that drive selection. Experimental evolution in the nematode Caenorhabditis remanei has yielded evidence that populations faced with a consistently male- or female-biased ratio of reproductively available males to females show differences in morphology and behavior as a consequence of selection. This proposal expands the question of behavioral interactions driving evolutionary change by quantifying the degree of genomic divergence across populations, and identifying signatures of selection at outlier loci across the entire genome. The proposed study will be among the first to directly measure evolution across the genome after a known selective regime of biased ratios of males to females, and one of the few to do so using a behavioral regime. Because experimental treatments were replicated across independent populations, the project will also address the long-standing question of how repeatable evolution is at the nucleotide level. Revealing the genomic consequences of selection generated by behavior is essential to synthesizing proximate and ultimate approaches to understanding dimorphism at the phenotypic and genomic level.