Identification of Follower Status Based on Male Proximity Score in Crested Macaque

Crested macaque live in multimale-multifemale social groups where temporary association (consortship) typically occurs. Current theory and these limited qualitative observations suggest the hypothesis that behavior functions as a means for males to gain access to fertile females. The aim of this study was to investigate follower status based on quantitative method. Males were classified as either “consort males,” “followers,” and “non-followers” based on proximity maintanance every 15 minute uses scan sampling. Tactics used by followers were classified into 1) individual challenge, 2) coalitionary challenge, 3) abandoned takeover, and 4) opportunistic takeover. The proportion of successful takeovers by followers was calculated by dividing the number of takeovers by followers by the total number of observed takeovers. The proportion of followers is higher than average on D-5 and earlier, D-4, and D-3. Only two of the four consort takeover tactics were used by followers. For abandoned which made up 40% and for individual tactic was made up to 11.5% of consort takeovers tactic used. This study contribute to our understanding of alternative mating strategy in primate and provide the first quantitative data demonstrating that following is an alternative mating strategy in crested macaque (Macaca nigra).

The discovery of the ‘transient’ male Tibetan wild ass: alternative ‘sneaky’ mating tactics in a wild equid?

Male asses usually consist of two classes, social bachelors and solitary, territorial males. However, our observations of the Tibetan wild ass (Equus kiang) suggested a third class may exist. Unexpectedly, unidentified males were often found courting females within another male’s territory. To test our hypothesis that a new social class existed, we compared 12 social behaviours among three putative groups. The third male-type spent less time herding and demonstrating flehmen, while spending more time retreating, trotting and in proximity of females, where they were more likely to engage in courtship and urine-marking. Based on increased time spent among females within other territories, the most courtship events, and minimal time invested in each courtship, they appear to employ ‘sneaky’ mating tactics. We discuss whether these ‘transient’ males are demonstrating an adaptive alternative mating strategy, or whether these behaviours result from a discrete developmental stage of bachelors unready to challenge a rival.

Stay or stray? Evidence for alternative mating strategy phenotypes in both men and women

In all comparative analyses, humans always fall on the borderline between obligate monogamy and polygamy. Here, we use behavioural indices (sociosexuality) and anatomical indices (prenatal testosterone exposure indexed by 2D : 4D digit ratio) from three human populations to show that this may be because there are two distinct phenotypes in both sexes. While males are more promiscuous and display higher prenatal testosterone exposure than females overall, our analyses also suggest that the within-sex variation of these variables is best described by two underlying mixture models, suggesting the presence of two phenotypes with a monogamous/promiscuous ratio that slightly favours monogamy in females and promiscuity in males. The presence of two phenotypes implies that mating strategy might be under complex frequency-dependent selection.

Evolution of deceit by worthless donations in a nuptial gift-giving spider

Males of the nursery web spider Pisaura mirabilis usually offer an insect prey wrapped in white silk as a nuptial gift to facilitate copulation. Males exploit female foraging preferences in a sexual context as females feed on the gift during copulation. It is possible for males to copulate without a gift, however strong female preference for the gift leads to dramatically higher mating success for gift-giving males. Females are polyandrous, and gift-giving males achieve higher mating success, longer copulations, and increased sperm transfer that confer advantages in sperm competition. Intriguingly, field studies show that approximately one third of males carry a worthless gift consisting of dry and empty insect exoskeletons or plant fragments wrapped in white silk. Silk wrapping disguises gift content and females are able to disclose gift content only after accepting and feeding on the gift, meanwhile males succeed in transferring sperm. The evolution of deceit by worthless gift donation may be favoured by strong intra-sexual competition and costs of gift-construction including prey capture, lost foraging opportunities and investment in silk wrapping. Females that receive empty worthless gifts terminate copulation sooner, which reduces sperm transfer and likely disadvantages males in sperm competition. The gift-giving trait may thus become a target of sexually antagonistic co-evolution, where deceit by worthless gifts leads to female resistance to the trait. We discuss factors such as female mating rate and intensity of sperm competition that may shape the evolution of male deception, and how ecological factors may influence the evolution and maintenance of worthless gifts as an evolutionarily stable alternative mating strategy by frequency dependent selection.

Adaptive value of same-sex pairing in Laysan albatross

Same-sex pairing is widespread among animals but is difficult to explain in an evolutionary context because it does not result in reproduction, and thus same-sex behaviour often is viewed as maladaptive. Here, we compare survival, fecundity and transition probabilities of female Laysan albatross in different pair types, and we show how female–female pairing could be an adaptive alternative mating strategy, albeit one that resulted in lower fitness than male–female pairing. Females in same-sex pairs produced 80% fewer chicks, had lower survival and skipped breeding more often than those in male–female pairs. Females in same-sex pairs that raised a chick sometimes acquired a male mate in the following year, but females in failed same-sex pairs never did, suggesting that males exert sexual selection by assessing female quality and relegating low-quality females into same-sex pairs. Sexual selection by males in a monomorphic, non-ornamented species is rare and suggests that reconsideration is needed of the circumstances in which alternative reproductive behaviour evolves. Given the lack of males and obligate biparental care in this species, this research demonstrates how same-sex pairing was better than not breeding and highlights how it could be an adaptive strategy under certain demographic conditions.

Influence of density and major histocompatibility genotype on sexual selection in a salmonid alternative mating strategy

Various mechanisms of sexual selection can occur at both the whole organism and gamete levels. Fertilization success in salmonid fishes is largely determined by behavioural competition within and between “fighter” and “sneaker” male strategies, but is also influenced by interactions among gametes. We investigated the influence of density, fighter male presence, and major histocompatibility (MH) genotype on patterns of fertilization success in sneaker Atlantic salmon ( Salmo salar ). At low density and in the absence of fighter males, monopolization by single sneaker males occurred, suggesting that male–male competition was the main determinant of fertilization success. By contrast, at high density and (or) in the presence of fighter males, several sneakers succeeded in fertilizing eggs. Our study, the first to investigate the role of MH-mediated fertilization for a genetically based alternative male mating strategy, suggests that a larger proportion of eggs were fertilized by sneakers whose MH genotypes were more similar to those of the female than expected by chance. These findings highlight the importance of examining sexual selection under different competitive conditions.