No abstract

Males of many insects directly defend their mates from rival males (i.e. mate guard) as a way to avoid sperm competition and thus increase their reproductive success. However, mate guarding may have associated costs for these males. We examined costs of mate guarding in Japanese beetles (Popillia japonica), a pest species which exhibits post-copulatory mate guarding during which the guarding male cannot feed. In this species, food provides both energy and water for thermoregulation. Consequently, we focused on possible thermoregulatory and energetic costs of their mate guarding. In a field study, we found that guarding males had significantly higher thoracic temperatures than non-guarding males, indicating a difference in their ability and/or need to thermoregulate. Paired males had significantly lower water levels than single males in the morning and evening, but not in the afternoon. In the laboratory, we found that mate-guarding duration was significantly shorter at higher ambient temperature than at lower temperature, and males that had been starved guarded for less time than males that had not been starved. Our results suggest that because guarding males are unable to feed, they suffer energetic and thermoregulatory costs that appear to limit the amount of time that they can guard a female.

Larvae of the striped chorus frog (Pseudacris triseriata), plains leopard frog (Rana blairi), northern leopard frog (Rana pipiens), and spadefoot toad (Scaphiopus bombifrons), were readily accepted as food by three fish predators (largemouth bass, Micropterus salmoides; green sunfish, Lepomis cyanellus; and the black bullhead, lctalurus melas). In contrast, tadpoles of the bullfrog (Rana catesbeiana), were accepted only rarely by bass and sunfish and not at all by bullheads. Preference experiments demonstrate that bass prefer Rana blairi larvae to Rana catesbeiana larvae, and if provided with sufficient numbers ofRana blairi larvae, almost totally refuse bullfrog tadpoles. The data suggest existence of an inverse relationship between the permanency of larval frog habitat and larval frog palatability. North temperate anurans vary greatly in larval duration and breed in a wide variety of catchment (pond) types, from ephemeral ponds (those that do not last one season) to permanent bodies of water (those that never completely dry or freeze to the bottom). The bullfrog, Rana catesbeiana, which has a long larval duration (2-3 years) in the north central plains states, breeds in quasipermanent to permanent ponds; in contrast, the spadefoot toad Scaphiopus bombifrons, having a very short larval period (2-3 weeks) is able to exploit transient waters (Billings 1973).Since tadpoles are generally inept swimmers, it seems logical that alternative predator-escape adaptations might have evolved, especially in those larval species that are locked into permanent catchments by long larval durations, and are consequently forced to coexist with fish predators as well as the entire suite of aerial and

Following bouts of courtship and copulation, female giant waterbugs (Belostoma flumineum Say) deposit eggs on the backs of their mates. Throughout a 6-to 12-day brooding period, males display several behaviors that are vital to egg-nymph survival. Consequently, females depend on male post-copulatory behaviors for successful reproduction and the possibility exists for male backspace availability to limit female reproduction in this species. I studied seasonal trends and factors that affect male backspace availability in populations of B. flumineum in east-central Illinois (USA). Early in the spring/summer, giant waterbug populations are relatively small and a large majority (188/205=91.7%) of the males are egg-laden; males experimentally added to the population during this period quickly became encumbered. In contrast, later in the summer after youngof-the-year emerge as adults, the waterbug population density increases dramatically and fewer (670/1274= 52.6%) of the males are encumbered (egg-laden). Of the males that are egg-laden both early and late in the season, significantly more are completely encumbered (i.e., 100% of the dorsum egg covered) early in the spring. The adult sex ratio is generally not biased and the number of eggs/pad that completely covers a male approximates a full ovarian complement. Therefore, these factors probably do not cause male backspace to become limited. The primary factor that appears to limit male backspace availability is the ability of females to synthesize a second partial clutch in a short time, often within 1 to 4 days. Females are capable of ovipositing partial clutches on 12 males within 30 days, whereas male brooding period is temperature dependent and ranges from 6 to 13 days. Newly emerged males are capable of breeding significantly sooner than can newly emerged females, thereby creating ample oviposition substrate for the females in the population after young-of-the-year adults appear. The evolution of sex-role reversal is not well understood; however it should not evolve in waterbugs unless male backspace limits female reproduction.Such a situation appears to exist in B. Jlumineum early in the season but not later in the summer.

Homosexual pairing between males occurs under natural conditions in a wide variety of taxa, including many insect species, but few studies have investigated