|Abstract or Summary
- The benefits of reproduction are clear, but there are also costs. Much is known about the costs of reproduction in females, but only recently have male costs been investigated in any depth. These costs of reproduction may be minimized by appropriately modifying behavior, but there has been little research on such behavioral minimization, especially in males. Male red-sided garter snakes, Thamnophis sirtalis parietalis, are an excellent model for the study of reproductive behavior because they form large breeding aggregations and tolerate human observation and manipulation. They are particularly useful for the study of reproductive costs because their investment in reproduction ends at copulation, and thus all reproductive effort is spatially and temporally constrained to the breeding sites during the breeding season. We investigated two ways in which male garter snakes use behavior to minimize reproductive costs. First, we investigated whether male garter snakes can discriminate between the pheromone trails of mated and unmated females. After
mating, females are unable to remate for two to four days due to a mating plug that occludes their cloaca. As males search for females by following their pheromone trails, they are exposed to high costs in terms of energetics, risk of predation, and lost opportunities with other females. Males discriminated between the pheromone trails of mated and unmated females, and they preferentially followed the trails of unmated females. They followed mated females once the mating plug had disintegrated and the female was able to remate. These results suggest that by discriminating between the trails of mated and unmated females, males can minimize the costs associated with searching for females by preferentially following females that provide a mating opportunity over those with which mating is not possible. Second, we investigated seasonal anorexia in male garter snakes. Despite high daily energy expenditure in the breeding season and eight months of aphagia preceding the breeding season, males are never found with prey items in their stomachs at the dens. This aphagia has been attributed to extrinsic causes (a lack of prey at the dens) and to intrinsic causes (seasonal anorexia). We determined that males at the breeding grounds exhibit a seasonal anorexia, whereby they show no interest in feeding during the breeding season. This anorexia appears to be adaptive in light of the high cost of searching for prey during the breeding season. We conclude that male garter snakes adjust their behavior to minimize the costs of reproduction. However, at this point our understanding of the nature of these costs is primarily qualitative. Future work should expand our knowledge of the costs associated with reproduction, especially in quantifying costs experienced by the male. Historically these costs have been neglected.