@article {1858,
	title = {Optimal investment in sons and daughters when parents do not know the sex of their offspring},
	journal = {Behavioral Ecology and Sociobiology},
	volume = {62},
	year = {2008},
	pages = {607-615},
	abstract = {Optimal 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{\textendash}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{\textendash}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.},
	keywords = {dung beetle, Onthophagus, Optimal investment, Sexual dimorphism, Sexual size dimorphism},
	author = {Kishi, Shigeki and Nishida, Takayoshi}
}
@article {2098,
	title = {Rapid antagonistic coevolution between primary and secondary sexual characters in horned beetles},
	journal = {Evolution},
	volume = {62},
	number = {9},
	year = {2008},
	month = {sep},
	pages = {2423-2428},
	abstract = {Different structures may compete during development for a shared and limited pool of resources to sustain growth and differ- entiation. The resulting resource allocation trade-offs have the potential to alter both ontogenetic outcomes and evolutionary trajectories. However, little is known about the evolutionary causes and consequences of resource allocation trade-offs in natural populations. Here, we explore the significance of resource allocation trade-offs between primary and secondary sexual traits in shaping early morphological divergences between four recently separated populations of the horned beetle Onthophagus taurus as well as macroevolutionary divergence patterns across 10 Onthophagus species. We show that resource allocation trade-offs leave a strong signature in morphological divergence patterns both within and between species. Furthermore, our results suggest that genital divergence may, under certain circumstances, occur as a byproduct of evolutionary changes in secondary sexual traits. Given the importance of copulatory organ morphology for reproductive isolation our findings begin to raise the possibility that secondary sexual trait evolution may promote speciation as a byproduct. We discuss the implications of our results on the causes and consequences of resource allocation trade-offs in insects. },
	keywords = {Aedeagus, Horned beetle, Onthophagus, resource allocation trade-off, speciation},
	author = {Parzer, Harald F. and Moczek, Armin P.}
}
