The Influence of Operational Sex Ratio on the Intensity of Competition for Mates

Abstract

The evolution and maintenance of secondary sexual characteristics and behavior are heavily influenced by the variance in mating success among individuals in a population. The operational sex ratio (OSR) is often used as a predictor of the intensity of competition for mates, as it describes the relative number of males and females who are ready to mate. We investigate changes in aggression, courtship, mate guarding, and sperm release as a function of changes in the OSR using meta-analytic techniques. As the OSR becomes increasingly biased, aggression increases as competitors attempt to defend mates, but this aggression begins to decrease at an OSR of 1.99, presumably due to the increased costs of competition as rivals become more numerous. Sperm release follows a similar but not significant trend. By contrast, courtship rate decreases as the OSR becomes increasingly biased, whereas mate guarding and copulation duration increase. Overall, predictable behavioral changes occur in response to OSR, although the nature of the change is dependent on the type of mating behavior. These results suggest considerable flexibility of mating system structure within species, which can be predicted by OSR and likely results in variation in the strength of sexual selection.

Grandmothering life histories and human pair bonding

“…39-44). The hypothesized relationship between biased sex ratios and mate guarding has also been supported by observational and experimental studies conducted across a range of species (45)(46)(47)(48)(49)(50). Although mate guarding is not synonymous with pair bonding, similar tradeoffs are involved.…”

Outline of Biological Effects, Fecundity, Eclosion and Lifespan on Adult Tropical Warehouse Moth, Cadra cautella (Lepidoptera: Pyralidae) by using Sex Ratio

“…Sex ratio for a population is an indicator of mating intensity [6]. Almost equal sex ratio for males and females exists in many animal species including insects [5,[7][8][9].…”

“…Almost equal sex ratio for males and females exists in many animal species including insects [5,[7][8][9]. The mating system have strong effects on mechanism and sex ratio in population and also may be have effects in properties of sex ratio in older ages [6]. A favor in sex ratio might occur because of many factors such as local mate competition (LMC) [10,11], birth, death and migration rates [5], edaphic factors [12], micro-organism infection [13] and inbreeding [14].…”

Keeping up appearances: male fiddler crabs wave faster in a crowd

“…Surprisingly, few studies have, however, examined how competing sexual signals influence male behaviour in a visual signalling context [11][12][13]. Nevertheless, plasticity in visual signalling behaviour during mate attraction is likely to be widespread.…”

“…Courtship signals are often costly because of the increased expenditure of energy and time, and a greater risk of predation. Selection should therefore favour males that minimize these costs by adjusting their signalling behaviour according to the level of competition and/or likelihood of attracting a mate [13,14].…”