ON THE EVOLUTIONARY PATHWAY OF PARENTAL CARE IN MOUTH-BROODING CICHLID FISH

Evolutionary theory predicts that differences in par ental care patter ns among species arose from interspecific differences in the costs and benefits of care for each sex. In Galilee St Peter's fish, Sarotherod on galilaeus (Cichlidae), male care, female care and biparental care a ll occur in the same population. We exploit this unusual variability t o isolate conditions favouring biparental versus uniparental mouth-bro oding by males or females. We first review a game-theoretic model of p arental care evolution, predictions of which we test experimentally in this paper. :Manipulations of the operational sex ratio show that mal es and females desert their offspring more frequently when the costs o f care are high (in terms of lost mating opportunities). Breeding tria ls with males of different sizes show that small fathers desert more f requently than large fathers. We attribute this to the associated diff erence in the fitness benefit of biparental care relative to female-on ly care. Our experimental results confirm that in St Peter's fish the probability of caring is determined facultatively according to current conditions at each spawn. The experiments and model together suggest that interspecific variation in remating opportunities and clutch size may be responsible for differences in care patterns within the subfam ily Tilapiini. Our results support the hypothesis that biparental mout h-brooding was the ancestral state of both male and female uniparental mouth-brooding in cichlid fishes.