| Sperm precedence, defined as non-random, differential fertilization success among mating males, is a common phenomenon. However, both its evolutionary significance and the mechanism(s) by which it occurs remain poorly understood. This dissertation describes research on sperm precedence using the red flour beetle, Tribolium castaneum herbst (Coleoptera: Tenebrionidae) as a model system.;Experiments were conducted to learn how sexual selection acts on male morphological traits and to determine sources of trait variation. Relationships were examined among reproductive success, reproductive performance, and morphological traits of males raised in three different larval densities (0.5, 5, 50 larvae g-1 flour). Relative male reproductive success was found to be positively correlated with insemination rate, but not with olfactory attractiveness or sperm precedence. Of the three morphological traits measured (elytron length, adult mass, and setiferous gland surface area), only male adult mass was positively related to insemination rate. Larval density affected male traits and reproductive success, but not measures of reproductive performance. The heritability of male morphological traits was measured by sire-son regression. Adult mass had significant additive genetic variation, while elytron length and setiferous gland surface area had low heritable variation.;Sperm transfer, sperm storage dynamics, and sperm utilization were examined to describe the mechanism of sperm precedence in T. castaneum. Sperm storage in the female spermatheca was found to be nearly complete within one hour after copulating. Using anesthetized females, a significant female influence on sperm storage was demonstrated. Detailed analysis of copulatory behaviors revealed that female behavior influences sperm transfer and sperm storage dynamics, but has no significant effect on sperm precedence. A female influence on sperm utilization was demonstrated by examining the associations between genetic similarity and within-male variability in sperm precedence.;Insemination rate is significantly related to a male's reproductive success and selects for increased male mass. Male mass is determined by both environmental and heritable genetic factors. Males with large mass will produce sons who will also have large mass and greater relative reproductive success in the population. Females influence both sperm storage and sperm precedence, and therefore are important selective agents affecting male reproductive success. |
