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David Froman
Professor, Animal Sciences
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RESEARCH:
Any trait that increases male reproductive success is under strong sexual selection, especially when females obtain sperm from more than one male, such as the domestic fowl. Nonetheless, the manner in which male traits interact to determine paternity and the heritability of such traits remain unresolved. To date, paternity in the domestic fowl was deemed a function of male social dominance and the number of sperm inseminated. However, the discovery of a new quantitative trait, i.e. sperm mobility (the net movement of a sperm population), has shown the traditional view to be incomplete; for extreme variation in sperm mobility has been found within populations of normal, fertile males. My collaborators and I have found, to our surprise, that subdominant males tend to be characterized by a high sperm mobility phenotype and that maternal inheritance appears to have a strong effect on sperm mobility phenotype. We believe these factors contribute to the maintenance of variation in male reproductive fitness from one generation to the next.
One means by which dams may affect the fitness of their sons is through the mitochondrial genome. Sperm mobility has been shown to be positively correlated with spermatozoal oxygen consumption and spermatozoal ATP content. These variables, in part, are affected by the mitochondrial genome. Even though this genome encodes very few proteins -- none of which constitute a functional enzyme -- the mitochondrial genome is proving to be important to a wide-range of phenomena, including reproduction. The possibility that male fitness may be maternally determined has received surprisingly little attention in sexual selection studies. Perhaps this is why male fitness has remained variable after directional selection. In any event, the long-range goal of my research program is the identification of genes that affect male fitness.
The systematic study of sperm mobility has had several unexpected spin-offs. For example a 40-year-old mystery was resolved in field of gamete biology. A model for sperm storage within the avian oviduct resulted from insights gained from computer-assisted sperm motion analysis. Likewise, an integrated understanding is emerging of the variables that affect the initiation and maintenance of fowl sperm motility at body temperature, in particular, proteins that regulate ion fluxes. Effective September 1, 2003, a proteomics approach will be initiated in order to identify key proteins and thereby genes that regulate male fitness.