Operational sex ratio affects female Japanese medaka (Oryzias latipes) behaviours

Abstract

Operational sex ratio (OSR) is the ratio of sexually active males to fertilizable females in a population. The OSR can be used to predict variation in mating behaviours across different social contexts and is used to predict how selection and conflict will vary within species. There exist two characteristics that influence the way species behave in regard to reproduction: sexual conflict and sexual selection. Within the literature about sexual behaviour, most focus on males rather than females. The goal of this research is to determine how OSR influences the behaviour of female Japanese medaka (Oryzias latipes). During the experiment, behavioural observations of individual female medaka were recorded across four OSRs (male: female): of 0.5, 1, 2, and 5. Rates of behaviour associated with conflict and competition were recorded for two minutes per female over three discrete observation periods. Conflict behaviours, female refusal and male-female aggression increased with increasing OSR, while female-male aggression decreased. Competition behaviours, females receiving aggression and females initiating aggression, decreased with increasing OSR. Body size was another factor analyzed to see the influence on both conflict and competition. Two of the conflict behaviours, female refusal and male-female aggression were influenced by the body size of the female, but none of the competition behaviours were affected by body size. Determining which behaviours are influenced by OSR and body size can be used to predict the outcomes of sexual conflict and sexual selection in different mating systems.