Study looks at mitochondrial variation in sperm traits and sperm competitive ability

University of Nevada, Reno researchers Jeanne and David Zeh of the Department of Biology have received a five-year, $650,000 grant from the National Science Foundation to investigate the effects of natural mitochondrial variation on sperm traits and sperm competitive ability.

Researchers have found mitochondrial mutations to be one of the primary causes of low sperm count and poor sperm mobility in humans. However, in the field of sexual selection, where maternal inheritance of mitochondria may well have its greatest impact, female-limited response to selection has been largely overlooked. The Zehs' study promises to fill in some of this knowledge gap in evaluating the importance of maternal inheritance of mitochondria for sexual selection and male adaptation. Mitochondria are the principal energy source of a cell, and convert nutrients into energy as well as performing many other specialized tasks.

The Zehs' study, which will use a neotropical pseudooscorpion Cordylochernes scorpioides as a model system, will encompass whole-genome mitochondrial sequencing, a comprehensive analysis of the physiological and morphological characteristics of sperm that are likely to be important in competitive ability, a large-scale sperm competition experiment designed to identify the target of selection acting on sperm traits, and a replicated, multi-generation experiment in which the evolutionary response to selection on the trait most important in sperm competition will be assessed using both maternally- and paternally-based selection regimes.

Jeanne Zeh, an assistant professor of biology, and David Zeh, an associate professor of biology, both believe that their study will help refine the efforts to understand mitochondrial effects on male fertility.

“The fundamental insight that strict maternal inheritance of mitochondria constrains the ability of males to respond adaptively to selection has led to major advances in the study of human male infertility,” said Jeanne Zeh, the principal investigator for the study, noting that other studies have also investigated this phenomenon in laboratory mice and domestic fowl. “However, these studies have not assessed the effects of natural mitochondrial DNA variation on male fertility and sperm competitive ability.

“Clearly, more research is needed, particularly on natural populations not subject to the potentially strong effects of genetic drift associated with domestication.”

In addition to their research, the Zehs' study also includes an interesting outreach component. They plan on working with a local AP biology teacher who will serve as a graduate research assistant on the project, and they will hold a series of workshops and seminars for other local high school science teachers and students that will promote the importance for society of basic research in ecology and evolution.