Effect of male aggressivity profile on female chemical choice in Nile tilapia

The attraction trick: males in early stages of disease become more chemically attractive to Nile tilapia (Oreochromis niloticus) females

In aquatic systems, olfaction plays an important role in acquiring information about the social environment and influences important behaviours in various contexts, including predator avoidance, foraging, aggressive and reproductive behaviour and mate selection. As the presence of diseases might modify individual odour, fish may use the variability in conspecifics' odours as an indicator of the health status and infectious load of potential mates. Here, female Nile tilapia were tested for their ability to detect infected males and discriminate between bacterial infected and uninfected individuals by means of chemical cues. Females were allowed to choose between the odours of males infected by Aeromonas hydrophila bacteria and uninfected males. The findings show that female Nile tilapia initially showed a preference for infected males in terms of their first choice in a dichotomous choice test, but the total duration of time spent with the stimulus from infected males was not longer than that for the uninfected males. This may indicate that males at early stages of infection, i.e., without advanced clinical signs of infection, emit odours that allow them to enjoy the benefits of socialization when the infection is not yet detected by conspecifics. Thus, in the context of reproduction, males might attract female partners and have some chance of reproducing, before being avoided.

Female preference for dominant males in the Mexican mojarra cichlid fish, Cichlasoma istlanum

It is widely assumed that female preference and male competition operate simultaneously during sexual selection. Dominance is likely an honest indicator of male quality, and females can identify and choose the dominant male to reproduce with individuals with greater competitive abilities, thus improving the quality and competitiveness of their offspring. In this context, few studies have investigated female preference in relation to male fighting ability. The Mexican mojarra, Cichlasoma istlanum, is a cichlid species native to the Balsas River basin. It is territorial during reproduction and provides parental care. Males commonly engage in territorial defence, whereas females care directly for offspring. This study examined whether females prefer dominant males that exhibit more aggressive behaviour. The authors conducted experiments using groups of two males and one female to test competitive ability in males and female preference. They also quantified the time during which the female associated with the dominant male and the subordinate male after observing the outcome of a fight between the two males. They found that Mexican mojarra females preferred dominant males and that the time females spent associating with males was positively related with their aggressive behaviours during competition. These results indicate that dominant males were more attractive than subordinate males to female Mexican mojarra. The relationship between female preference and male dominance in the Mexican mojarra demonstrates the importance of male competitive ability for future parental care in reproduction.