Timing of oviposition and reproductive skew in cobreeding female burying beetles (Nicrophorus vespilloides)

Abstract

Burying beetles (genus Nicrophorus) are known for their elaborate parental care. Two or more conspecific females may reproduce on the same carcass, especially when the carcass is large. Here we present the results of experiments in which we observed patterns of larval hatching and parental care in unmanipulated cobreeders, manipulated hatching synchrony between cobreeders, and compared patterns of oviposition in cobreeding and single females. Our results show that in these cobreeding associations, one of the females may or may not monopolize the carcass during the period of larval hatching. We present evidence that in either case, infanticide based on temporal cues constitutes an important proximate mechanism underlying the observed reduction in average reproductive success in cobreeding females. Females with higher synchrony (i.e., greater overlap between their oviposition patterns) produce larger broods with lower reproductive skew. Cobreeding females oviposit later and less synchronously than single breeders. Such delayed oviposition may reduce the risk that a female’s larvae fall victim to cannibalistic acts committed by her cobreeder or maximize her own opportunity to selectively kill her cobreeder’s larvae. Key words: burying beetles, cannibalism, communal breeding, infanticide, kin recognition, Nicrophorus, parental care, reproductive competition, reproductive skew. [Behav Ecol 11:357–366 (2000)] R eproductive competition is ubiquitous among communally breeding animals. When several conspecific females share a breeding site, as is the case in some vertebrates (‘‘joint nesting’’ or ‘‘communal breeding’’) as well as in some primitively social or eusocial insects (polygyny), young in the communal nest may compete for food. In this situation, females may increase their individual reproductive success by destroying their cobreeders’ eggs or young while sparing their own. Such selective infanticide requires the perpetrator to discriminate between her own offspring and those of cobreeders. One simple mechanism that can enable such discrimination is a temporal switch (Elwood, 1994), sometimes referred to as a ‘‘change in parental state’’ (Rosenblatt and Siegel, 1983), which is possibly mediated by hormonal changes triggered by important reproductive events (‘‘state-dependent cues’’; Elwood, 1991). Selective infanticide may result if the individual shows infanticidal behavior toward young at a time at which it is likely to encounter unrelated offspring, and parental, non-infanticidal behavior at a time when it is likely to encounter its own (Elwood, 1994). Examples include many bird species with intraspecific brood parasitism or communal breeding, in which females remove eggs from the nest throughout the prelaying period (i.e., until they have laid their first egg) (e.g., Emlen and Wrege, 1986; Macedo and Bianchi, 1997; Moller, 1987; Mumme et al., 1983; Stouffer et al., 1987; Vehrencamp, 1977), and males of many mammalian species that exhibit infanticidal behavior toward the young of females with whom they have not mated or cohabited long enough for the young to be the males’ own offspring (see Hrdy and Hausfater, 1984,