Sexual Selection in Dung Beetles .2. Female Fecundity as an Estimate of Male Reproductive Success in Relation to Horn Size, and Alternative Behavioral Strategies in Onthophagus-Binodis Thunberg (Scarabaeidae, Onthophagini)

Abstract

One component of the reproductive success (fitness) of Onthophagus binodis Thunberg males was estimated by the number of offspring their mate produced relative to male horn and body size. O. binodis males consist of large horned and small hornless morphs. Female fecundity was significantly increased when reproducing with: (1) large horned males compared with small hornless males; (2) the horned morph compared with the hornless morph of males with similar body size. Horned males cooperating with females invest a considerable effort in providing each egg with dung. Hornless males do not appear to assist females after mating. Alternative male mating strategies are predicted under intense intrasexual competition. As hornless O. binodis males persist in large numbers alongside cooperative, mate guarding horned males, selection should favour alternative tactics by hornless males to gain reproductive opportunities.

Confidence of paternity and paternal care: covariation revealed through the experimental manipulation of the mating system in the beetle Onthophagus taurus

“…However, in dung beetles belonging to the genus Onthophagus, biparental care is common (Lee & Peng, 1982;Cook, 1988;Sowig, 1996;Hunt & Simmons, 1998a, 2000Moczek, 1999). During reproduction, members of this genus typically remove portions of dung from the pad and pack it into the blind end of tunnels constructed beneath the dung pad.…”

“…Furthermore, studies examining patterns of parental care have shown that it is typically only the horned males that provide assistance during brood mass construction (Cook, 1988;Hunt & Simmons, 1998a, 2000Moczek, 1999). In Onthophagus taurus, male provisioning commences with the production of head horns and represents an Ôall-ornoneÕ tactic with all horned males providing a fixed level of care (Hunt & Simmons, 2000).…”

INFLUENCE OF ADULT BODY SIZE AND THE MALE PRONOTAL HORN ON PHENOTYPIC VARIATION IN ONTHOPHAGUS BINODIS THUNBERG (COLEOPTERA: SCARABAEIDAE)

“…Males of the scarabaeine dung beetle Onthophagus binodis Thunberg are dimorphic with respect to a pronotal horn and consist of both horned and hornless individuais (Cook 1987). Horn size variation in the males is not allometric and only large males possess horns (Cook 1988). Both large, horned and small, hornless individuals are commonly found in high numbers within single dung pads.…”

“…Only large, horned 0. binodis males cooperate with a female in gathering brood mass provisions after copulation (Cook 1990). Although females paired with horned males produce significantly more brood masses than females paired with hornless males (Cook 1988), heritability of the horn character has not been studied. Adult size in a related species 0. gazella (F.) is directly related to the quantity of dung supplied to each larva, regardless of the size of its parents (Lee and Peng 1981); there is no evidence on whether the male horn influences the offspring's phenotype.…”

“…1982). Each brood mass represents a larval provision supporting only one offspring (Cook 1988). Only large, horned 0. binodis males cooperate with a female in gathering brood mass provisions after copulation (Cook 1990).…”