Sperm have tremendous diversity, but the evolutionary significance of variation in sperm form is poorly understood. One of the more unusual kinds of variation is conjugation, where two or more sperm join at the head to form a single functional unit. Conjugation is commonly interpreted as an adaptation to sperm competition and has independently arisen in groups as diverse as opossums, snails, and diving beetles. This study examines the evolutionary pathways and fitness consequences of sperm conjugation. The researchers will use behavioral observations, biochemistry, and cytology to (i) compare the intensity of sperm competition in species with and without sperm conjugation, (ii) test the hypothesis that conjugation provides protection from spermicidal environments, and (iii) quantify the effects of sperm length and conjugate size on motility, an important correlate of fertilization success.
The intellectual merit of this research program includes its potential to reveal the relationship between sperm form and function and to improve understanding of the selective environment of sperm, a greatly neglected aspect of sexual selection. This project will provide training for a PhD student and valuable laboratory and field-based research opportunities for undergraduates. Resultant data will be submitted to public databases to facilitate research, and specimens collected during the course of the project will be deposited in museum collections (e.g. NMNH).
