The evolutionary biology of seminal fluid

Professor Simmons is an evolutionary biologist whose research programs seek to determine the direction and strength of selection acting on male and female reproductive strategies, and on the morphological and life history traits that contribute to fitness, from the whole organism to its gametes. His current research, funded in part through an ARC Professorial Fellowship, combines strengths in evolutionary biology with cutting edge technology from molecular biochemistry to identify novel proteins and their biological functions from the seminal fluid of invertebrate and vertebrate taxa, including humans.

A major challenge facing humanity is the often reported declines in semen quality and increasing rates of male infertility, a problem that plagues human and non-human animals alike. Our understanding of the evolutionary pressures that shape normal male fertility are at best basic. We have little or no understanding of the functional significance of seminal fluid chemistry for male reproductive fitness, or the genetic and environmental factors that might interact in determining the fertile phenotype. A holistic understanding of male reproductive fitness will require fundamental research on the environmental factors that both influence and impose selection on the ejaculate, and on the ability for ejaculates to respond in evolutionary time to that selection.

Seminal fluid proteins are among the most rapidly diverging molecules known to man. Sexual selection, a selective force known to generate rapid and divergent evolution, has been implicated as a major player in the evolution of seminal fluid proteins.

The research has a three strands. Using an invertebrate model the team uses proteomic and genomic approaches to identify seminal fluid proteins in the ejaculate and their biological functions. This work aims to explore the degree to which genetic and environmental variation can impact male fertility.

Using the mouse model, the team uses laboratory evolution to show that male fertility can respond to selection. Genomic screens are revealing which genes are subject to selection, and thus responsible for male fertility.

The research makes both direct and indirect contributions to the teams understanding of male fertility. First, they are exploring how dietary antioxidants impact health, including male reproductive health in humans and other animals. Second, the mouse model is widely used in human fertility because genes involved in fertility are often highly conserved. Identifying the reproductive proteins and their genes that are under selection for male fertility in mice may thus provide a more targeted approach for understanding human infertility which plagues 10% of human couples.