Whether an animal develops into a male or female depends on either environmental cues or genetic differences between males and females. The environmental cues or genes that initiate this male/female-determination differ across species, and they can even be variable within a species. It is not well understood how ecological factors contribute to the maintenance of genetic variation in male/female-determination within species. To address this shortcoming, this research uses the house fly as a model system because this species has substantial variation in how the male/female decision is made. Notably, there are two common ways that male development can be initiated, and they differ in their geographical distributions. One male-determining variant predominates at northern latitudes, and the other is more common in the south. The researchers are investigating if the two different variants are both maintained because they are beneficial at different temperatures. In addition, female development can be initiated independently from the male-determining variants in house fly. The researchers are also investigating if the variants that initiate male development have deleterious effects in females. These antagonistic effects could further explain why variation in male/female-determination is maintained in house fly populations. Undergraduate students training to be high school teachers will contribute to this research. Those students will work with the researchers to provide continuing education training to current teachers. They will also lead middle and high school classrooms in exercises that use house flies to illustrate core concepts in genetics and evolution. These activities will impact students from under-served communities that are under-represented in the sciences.

To determine how natural selection can maintain variation in male/female-determination, the researchers are combining laboratory experiments, surveys of natural populations, and genomic techniques. Specifically, the research tests the hypothesis that male/female-specific genotype-by-environment interactions affect selection pressures acting on Y chromosomes to maintain variation in male/female-determination in house fly. The environment-dependent phenotypic effects of very young Y chromosomes will be assessed using laboratory experiments and high throughput gene expression profiling. Predictions about allele frequencies in laboratory populations and over seasons in the wild will be tested, and fitness effects will be modeled. The hypothesis that suppressed recombination maintains linkage between male-determining genes and other genetic variation with male/female-antagonistic or environment-specific effects will be evaluated using recombination mapping, genome sequencing, and population genetic data to test for X-Y differentiation. This research connects ecologically relevant selection pressures and male-female conflict with the evolution of an essential developmental pathway, joining population genetics and the evolution of development in a single framework.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

National Science Foundation (NSF)
Division of Environmental Biology (DEB)
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George Gilchrist
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University of Houston
United States
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