Abstract
BackgroundIn most species, males compete to gain both matings (via pre-copulatory competition) and fertilizations (via post-copulatory competition) to maximize their reproductive success. However, the quantity of resources devoted to sexual traits is finite, and so males are predicted to balance their investment between pre- and post-copulatory expenditure depending on the expected pay-offs that should vary according to mating tactics. In Artiodactyla species, males can invest in weapons such as horns or antlers to increase their mating gains or in testes mass/sperm dimensions to increase their fertilization efficiency. Moreover, it has been suggested that in these species, males with territory defence mating tactic might preferentially increase their investment in post-copulatory traits to increase their fertilization efficiency whereas males with female defence mating tactic might increase their investment in pre-copulatory sexually selected traits to prevent other males from copulating with females. In this study, we thus test the prediction that male’s weapon length (pre-copulatory trait) covaries negatively with relative testes size and/or sperm dimensions (post-copulatory traits) across Artiodactyla using a phylogenetically controlled framework.ResultsSurprisingly no association between weapon length and testes mass is found but a negative association between weapon length and sperm length is evidenced. In addition, neither pre- nor post-copulatory traits were found to be affected by male mating tactics.ConclusionsWe propose several hypotheses that could explain why male ungulates may not balance their reproductive investment between pre- and post-copulatory traits.
Highlights
In most species, males compete to gain both matings and fertilizations to maximize their reproductive success
Males compete for mating opportunities and individuals who invest in secondary sexual traits such as ornaments or weapons are often better competitors and gain more mating events (e.g. [4,5])
Lengths of all sperm components are significantly longer as total sperm length increases, only tail length was found to be strongly negatively associated with weapon length (r = − 0.30) this relation was found to be significant only with the phylogenetic tree derived from Bininda-Emonds et al [31] (p = 0.03 with BinindaEmonds et al [31]; r = − 0.26, p = 0.07 with Agnarsson and May-Collado [32] tree) (Figure 1b, Table 1, Additional file 2: Table S2a)
Summary
Males compete to gain both matings (via pre-copulatory competition) and fertilizations (via post-copulatory competition) to maximize their reproductive success. Since males can allocate only a limited amount of resources to sexual competition [6], theoretical models of sperm competition predict that, when the relative intensity of pre- or post-copulatory pressures change, males should modulate their reproductive investment between traits involved in competition for mating and traits involved in the production of high quality ejaculates depending on the expected pay-offs [6,18]. [22]), inter-specific studies involving male armaments or ornamental traits remain scarce In this context, investment in sperm quality has never been considered, maybe because models of allocation to sperm competition according to the level of pre-copulatory competition are principally focused on sperm quantity [6,18]
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