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The Darwin-Bateman paradigm recognizes competition among males for access to multiple mates as the main driver of sexual selection. Increasingly, however, females are also being found to benefit from multiple mating so that polyandry can generate competition among females for access to multiple males, and impose sexual selection on female traits that(More)
Polyandry generates selection on males through sperm competition, which has broad implications for the evolution of ejaculates and male reproductive anatomy. Comparative analyses across species and competitive mating trials within species have suggested that sperm competition can influence the evolution of testes size, sperm production and sperm form and(More)
The avoidance of genetic incompatibilities between parental genotypes has been proposed to account for the evolution of polyandry. An extension of this hypothesis suggests polyandry may provide an opportunity for females to avoid the cost of inbreeding by exploiting postcopulatory mechanisms that bias paternity toward unrelated male genotypes. Here we test(More)
Evolutionary theory is firmly grounded on the existence of trade-offs between life-history traits, and recent interest has centred on the physiological mechanisms underlying such trade-offs. Several branches of evolutionary biology, particularly those focusing on ageing, immunological and sexual selection theory, have implicated reactive oxygen species(More)
Beetle horns are enlarged outgrowths of the head or thorax that are used as weapons in contests over access to mates. Horn development is typically confined to males (sexual dimorphism) and often only to the largest males (male dimorphism). Both types of dimorphism result from endocrine threshold mechanisms that coordinate cell proliferation near the end of(More)
Reproductive males face a trade-off between expenditure on precopulatory male-male competition--increasing the number of females that they secure as mates--and sperm competition--increasing their fertilization success with those females. Previous sperm allocation models have focused on scramble competition in which males compete by searching for mates and(More)
Female sexual promiscuity can have significant effects on male mating decisions because it increases the intensity of competition between ejaculates for fertilization. Because sperm production is costly, males that can detect multiple matings by females and allocate sperm strategically will have an obvious fitness advantage. The presence of rival males is(More)
The psychological mechanisms underlying attractiveness judgements in humans are thought to be evolved adaptations for finding a high quality mate. The phenotype-linked fertility hypothesis proposes that females obtain reliable information on male fertility from male expression of sexual traits. A previous study of Spanish men reported that facial(More)
Alternative mating tactics can generate asymmetry in the sperm competition risk between males within species. Theory predicts that adaptations to sperm competition should arise in males facing the greater risk. This prediction is met in the dung beetle Onthophagus binodis where minor males which sneak copulations have a greater expenditure on the ejaculate.(More)
Parents often have important influences on the development of traits in their offspring. One mechanism by which parents are able to influence offspring phenotype is through the level of care they provide. In onthophagine dung beetles, parents typically provision their offspring by packing dung fragments into a brood mass. Onthophagus taurus males can be(More)