02024nas a2200133   4500008004100000245010100041210006900142300001400211490000800225520149500233100001901728700002301747856012001770       2006                        eng d00aAdjustment of parental investment in the dung beetle Onthophagus atripennis (Col., Scarabaeidae)0 aAdjustment of parental investment in the dung beetle Onthophagus  a1239-12450 v1123 aIf parents can invest resources optimally per offspring, they should adjust the amount of investment in an offspring according to environ- mental heterogeneity. Many studies have demonstrated changes in egg size or the amount of resource supplied in response to environmental heterogeneity. However, it remains unclear whether parents simply know the resource type a priori or can assess resource quality and adjust the quantity of investment accordingly. We examined the parental capa- bility to adjust the amount of investment per offspring by providing Onthophagus atripennis dung beetle parents with one of three dung types of different quality: monkey dung (high quality), cow dung (low qual- ity), or a mixture of monkey and cow dung (medium quality). The bee- tle parents cooperatively produce dung brood masses each with one egg under the ground. The size of a brood mass, on which a larva can only feed until adult, represents a large part of the amount of investment. Parents produced a greater number of smaller brood masses given high- quality resource, while they compensated for low quality of the resource by providing a larger amount of the resource, at the cost of offspring number. However, despite this compensation in the amount of food, off- spring raised on low-quality food was still smaller than offspring raised on high-quality food. Thus, O. atripennis parents assessed resource qual- ity partly and adjusted the amount of resource provided for their off- spring. 1 aKishi, Shigeki1 aNishida, Takayoshi  uhttps://scarabnet.myspecies.info/adjustment-parental-investment-dung-beetle-onthophagus-atripennis-col-scarabaeidae02277nas a2200193   4500008004100000245009700041210006900138300001200207490000700219520159100226653001601817653001601833653002301849653002201872653002701894100001901921700002301940856012001963       2008                        eng d00aOptimal investment in sons and daughters when parents do not know the sex of their offspring0 aOptimal investment in sons and daughters when parents do not kno  a607-6150 v623 aOptimal parental i nvestment usually differs depending on the sex of the offspring. However, parents in most organisms cannot discriminate the sex of their young until those young are energetically independent. In a species with physical male–male competition, males are often larger and usually develop sexual ornaments, so male offspring are often more costly to produce. However, Onthophagus dung beetles (Coleoptera; Scarabaeidae) are highly dimorphic in secondary sexual characters, but sexually monomorphic in body size, despite strong male–male competition for mates. We demonstrate that because parents provide all resources required by their offspring before adulthood, O. atripennis exhibits no sexual size dimorphism irrespective of sexual selection pressure favoring sexual dimorphism. By con- structing a graphic model with three fitness curves (for sons, daughters, and expected fitness return for parents), we demonstrate that natural selection favors parents that provide both sons and daughters with the optimal amount of investment for sons, which is far greater than that for daughters. This is because the cost of producing small sons, that are unable to compete for mates, is far greater than the cost of producing daughters that are larger than necessary. This theoretical prediction can explain sexual dimorphism without sexual size dimorphism, widely observed in species with crucial parental care such as dung beetles and leaf- rolling beetles, and may provide an insight into the enigmatic relationship between sexual size dimorphism and sexual dimorphism.10adung beetle10aOnthophagus10aOptimal investment10aSexual dimorphism10aSexual size dimorphism1 aKishi, Shigeki1 aNishida, Takayoshi  uhttps://scarabnet.myspecies.info/optimal-investment-sons-and-daughters-when-parents-do-not-know-sex-their-offspring