@article {1791,
	title = {Genital morphology and fertilization success in the dung beetle Onthophagus taurus: an example of sexually selected male genitalia},
	journal = {Proceedings of the Royal society of London B},
	volume = {270},
	year = {2003},
	pages = {447-455},
	abstract = {In animals with internal fertilization and promiscuous mating, male genitalia show rapid and divergent evolution. Three hypotheses have been suggested to explain the evolutionary processes responsible for genital evolution: the lock-and-key hypothesis, the pleiotropy hypothesis and the sexual-selection hypoth- esis. Here, we determine whether variation in male genital morphology influences fertilization success in the dung beetle Onthophagus taurus, as predicted by the sexual-selection hypothesis. Variation in four out of five genital sclerites of the endophallus influenced a male{\textquoteright}s fertilization success, supporting the general hypothesis that male genitalia can evolve under sexual selection. Furthermore, different genital sclerites were found to enhance first versus second male paternity, indicating that different sclerites serve offensive and defensive roles. Genital-trait variability was comparable to that in other species but was less variable than a non-genital sexually selected trait (head horns). We suggest that directional selection for genital elaboration may be countered by natural selection, which should favour genitalia of a size and shape necessary for efficient coupling and sperm transfer. },
	keywords = {male genitalia, Onthophagus, paternity, sexual selection, Sperm competition},
	author = {House, Clarissa M. and Simmons, Leigh W.}
}
@article {1793,
	title = {Offensive and defensive sperm competition roles in the dung beetle Onthophagus taurus (Coleoptera: Scarabaeidea)},
	journal = {Behavioral Ecology and Sociobiology},
	volume = {60},
	year = {2006},
	pages = {131-136},
	abstract = {Sperm competition is predicted to generate op- posing selection pressures on males. On one hand, selec- tion should favour {\textquoteleft}defensive{\textquoteright} adaptations that protect a male{\textquoteright}s ejaculate from displacement, while, on the other hand, selection should favour {\textquoteleft}offensive{\textquoteright} adaptations that overcome paternity assurance mechanisms of rivals. Here, we use the sterile male technique to assess sperm pre- cedence when a male dung beetle Onthophagus taurus mates in both a defensive (first male) and an offensive (second male) role. Significant variation in a male{\textquoteright}s sperm precedence (both P1 and P2) was detected, and an individual{\textquoteright}s defensive (P1) and offensive (P2) abilities were positively correlated. Thus, it appears that sexual selection simultaneously selects for {\textquoteleft}defensive{\textquoteright} and {\textquoteleft}of- fensive{\textquoteright} adaptations in O. taurus. We discuss a variety of male traits in O. taurus that potentially contribute to a male{\textquoteright}s ability to be successful whenmatinginan{\textquoteleft}of-fensive{\textquoteright} and a {\textquoteleft}defensive{\textquoteright} role. },
	keywords = {Defensive role, male genitalia, Offensive role, Onthophagus taurus, Sperm competition},
	author = {House, Clarissa M. and Simmons, Leigh W.}
}
@article {1603,
	title = {Sperm competition and evidence of sperm fertilization patterns in the carrion ball-roller Canthon cyanellus cyanellus LeConte (Scarabaeidae: Scarabaeinae)},
	journal = {Behavioral Ecology and Sociobiology},
	volume = {59},
	year = {2005},
	pages = {38-43},
	abstract = {Field observation and laboratory experiments were conducted to investigate sperm competition and pat- terns of sperm fertilization under different experimental conditions in the carrion ball-roller beetle Canthon cyanel- lus cyanellus. Males in nature can mate with females whose spermathecae contains fertile sperm from other males. Sperm precedence was investigated using a visible genetic marker. The progeny of red (homozygous recessive) virgin females mated once with a red male and afterward, once with a green beetle (homozygous dominant) and vice versa, revealed that regardless of its color, the last male to mate fertilized c.a. 50\% of the eggs, suggesting strong sperm competition. Males were able to achieve higher levels of pa- ternity (more than 80\%) when mated ad libitum with previ- ously mated females, although large amount of variance in paternity does not exclude the possibility of first male sperm precedence or female cryptic choice. These results suggest that repeated mating and sperm replacement are the mech- anisms by which last males achieve sperm precedence.},
	keywords = {Canthon cyanellus, Fertilization patterns, Genetic marker, Scarabaeidae, Sperm competition},
	author = {Favila, Mario E and Nolasco, Janet and Chamorro Florescano, Ivette and Equihua, Miguel}
}
@article {2108,
	title = {Male differentiation patterns in two polyphenic sister species of the genus Onthophagus Latreille, 1802 (Coleoptera: Scarabaeidae): a geometric morphometric approach},
	journal = {JZS},
	volume = {44},
	number = {1},
	year = {2006},
	pages = {54-62},
	abstract = {This paper focuses on morphological (both shape and size) differences that quite similar polyphenic sister species evolve during divergence processes. Traits were analysed using a geometrical morphometric approach, which has the ability to evidence also very subtle differences in shape. As a case study, we considered males of the dung beetle sister species pair Onthophagus taurus and Onthophagus illyricus (Coleoptera, Scarabaeidae); these species represent a typical example of polyphenic trait expression concerning the facultative development of horns and considerable body size differences. External shape morphology failed to discriminate O. taurus from O. illyricus, whereas the reproductive system shape showed significant interspecific discrimination power. However, the head of O. taurus was significantly larger than that of O. illyricus and the reverse was true for the elytra. The two species also showed different allometric values of the head with respect to body size. This complex pattern of interspecific morphological divergence is discussed in the light of the differential trait divergence rate hypothesis. In both species, differences between major and minor forms concern the overall shape of head and pronotum: we suggest that such different forms, which likely reflect morphological readjustment to accommodate horns of considerable bulk and disproportionate length, may be nevertheless advantageously used by the two male morphs in their alternative reproductive tactics. Male genitalia sizes were virtually constant with respect to body size; however, the ratio between phallotheca and body size was significantly higher in minor males, in keeping with the hypothesis of a higher investment in genitalia borne by this morph.},
	keywords = {allometry, developmental investment, differentiation between species and morphs, external morphology, male genitalia, Sperm competition, {\textendash}},
	author = {Pizzo, A. and Mercurio, D. and Palestrini, Claudia and Roggero, A. and Rolando, Antonio}
}
