Antlers honestly advertise sperm production and quality

University of Castilla-La Mancha, Ciudad Real, Castille-La Mancha, Spain
Proceedings of the Royal Society B: Biological Sciences (Impact Factor: 5.05). 02/2005; 272(1559):149-57. DOI: 10.1098/rspb.2004.2933
Source: PubMed


Evolutionary theory proposes that exaggerated male traits have evolved via sexual selection, either through female mate choice or male-male competition. While female preferences for ornamented males have been amply demonstrated in other taxa, among mammals sexual characters are commonly regarded as weapons whose main function is to enhance male competitiveness in agonistic encounters. One particularly controversial hypothesis to explain the function of male sexual characters proposes that they advertise male fertility. We test this hypothesis in red deer (Cervus elaphus), a species where sexual characters (antlers) reach an extreme degree of elaboration. We find that a global measure of relative antler size and complexity is associated with relative testes size and sperm velocity. Our results exclude the possibility that condition dependence, age or time of culling, drive these associations. Red deer antlers could signal male fertility to females, the ability to avoid sperm depletion throughout the reproductive season and/or the competitive ability of ejaculates. By contrast, male antlers could also signal to other males not only their competitive ability at the behavioural level (fighting ability) but also at the physiological level (sperm competition).

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    • "Earlier studies testing for the phenotype-linked fertility hypothesis have yielded contradictory results. Some studies in nonhuman animals have found support for the hypothesis (Kortet et al., 2004; Malo et al., 2005; Locatello et al., 2006; Rogers et al., 2008), whereas others have found either no associations between secondary sexual traits and fertility or negative correlations (Liljedal et al., 1999, 2008; Skinner & Watt, 2007; Rowe et al., 2010; Klaus et al., 2011). "
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    ABSTRACT: Phenotype-linked fertility hypothesis (PLFH) predicts that male secondary sexual traits reveal honest information about male fertilization ability. However, PLFH has rarely been studied in humans. The aim of the present study was to test PLFH in humans and to investigate whether potential ability to select fertile partners is independent of sex or cultural background. We found that on the contrary to the hypothesis, facial masculinity was negatively associated with semen quality. As increased levels of testosterone have been demonstrated to impair sperm production, this finding may indicate a trade-off between investments in secondary sexual signalling (i.e. facial masculinity) and fertility or status-dependent differences in investments in semen quality. In both sexes and nationalities (Spanish and Colombian), ranked male facial attractiveness predicted male semen quality. However, Spanish males and females estimated facial images generally more attractive (gave higher ranks) than Colombian raters, and in both nationalities, males gave higher ranks than females. This suggests that male facial cues may provide culture- and sex-independent information about male fertility. However, our results also indicate that humans may be more sensitive to facial attractiveness cues within their own populations and also that males may generally overestimate the attractiveness of other men to females.
    Full-text · Article · Jul 2014 · Journal of Evolutionary Biology
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    • "By choosing males with sexual ornaments, females would also benefit if such selection maximized the chances of females to mate with high quality fertile males (Sheldon 1994). Another function of male sexual character could be that of signalling to other males the competitiveness of the ejaculate (Malo et al. 2005). Thus, sexual selection can operate through different processes in the same structure. "
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    ABSTRACT: Sexual dimorphism patterns provide an opportunity to increase our understanding of trait evolution. Because selective forces may vary throughout the reproductive period, measuring dimorphism seasonally may be an interesting approach. An increased male head size may be important in intersexual and intrasexual interactions. In Tupinambis lizards, a big head is attributed in part to a large adductor muscle mass. Competition for mating can differ in species with different sex ratio and different degrees of sexual size dimorphism. We examined sexual differences in mass of the pterygoideus muscle, its temporal variation throughout the reproductive period and the relationship between muscle and reproductive condition in Tupinambis merianae and T. rufescens. We characterized sexual size dimorphism and sex ratio in both species. Mature males had larger jaw muscles than mature females in both species, mainly during the reproductive season. The dimorphism in jaw muscle was due to an increase in muscle mass in sexually active males. Seasonal increases in muscle mass and variation between immature and mature individuals suggest that the jaw muscle might be a secondary sexual character. We propose that the pterygoideus muscle may act as a signal of reproductive condition of males because it is associated with testis size and sperm presence. The patterns of sexual dimorphism in jaw muscle in both species were similar; however, the comparison shows how sexual characters remain dimorphic in different competition contexts and in species with different degrees of body size dimorphism. Our results suggest that jaw muscle as sexual character could be influenced by interand intrasexual selective pressures.
    Full-text · Article · May 2014 · Evolutionary Biology
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    • "In the Great Tit (Parus major), Helfenstein et al. (2010) found that sperm motility and swimming ability was condition dependent, depending on male redox status, and Losdat et al. (2011) showed that sperm swimming stamina is impaired by activation of the immune system. Other studies have revealed relationships between sexually selected phenotypic traits and sperm motility; for example antlers advertise sperm quality in the Red Deer (Malo et al. 2005b) and the colorful male Guppy (Poecilia reticulata) has been reported to produce faster and more viable sperm than his less colourful counterpart (Locatello et al. 2006). However, the latter result was not supported by a subsequent study of male coloration and sperm traits in the Guppy (Pitcher et al. 2007). "
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    ABSTRACT: Sperm morphometry and motility are important male traits affecting fertility and post-copulatory competitive ability. However, studies examining consistency in sperm traits over time for individual males are rather scarce, particularly in free-living animals. Here, we report our analysis of various measures of sperm morphometry and sperm motility in the Barn Swallow (Hirundo rustica), both within and between breeding seasons. We found high within-season repeatabilities for all measures of sperm morphometry (all r > 0.70) and moderate repeatability of sperm motility (all r > 0.42). Between seasons, repeatabilities were somewhat lower, but total sperm length and flagellum length also showed very high repeatabilities between seasons (r > 0.85). Furthermore, sperm motility showed higher repeatabilities between seasons than within a season (all r > 0.63). Although measures of sperm motility are likely to be more plastic due to, for example, changes in body condition, they still showed moderate repeatabilities within and between seasons. Our study results also imply that a single ejaculate would be sufficient to obtain representative measures of an individual’s sperm quality traits within the same breeding season.
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