The benefits of uniparental versus biparental mouth brooding in Galilee St. Peter's fish

In Galilee St. Peter's fish Sarotherodon galilaeus the care system is naturally labile; biparental, male-only and female-only care all exist in one population. This unusual flexibility facilitates comparisons between the forms of care. The costs of parental care were considered in a previous study. Here, the benefits of parental care were quantified by observing wild fish, both held in pond enclosures and free-swimming in Lake Kinneret, Israel. Parental care was shown to be essential for offspring survival in St. Peter's fish. The reproductive success of parents who shared incubation duties was nearly twice as high as that of parents caring alone. However, per brood (or mouth cavity) reproductive success was 20% higher for uniparental parents. Both sexes were equally capable and efficient in care; when both sexes cared, they each incubated a similar number of eggs and released a similar number of fry. The results are discussed in terms of the relationship between caring Strategies and clutch size.     

On the evolutionary pathway of parental care in mouth-brooding cichlid fishes

Evolutionary theory predicts that differences in parental care patterns among species arose from interspecific differences in the costs and benefits of care for each sex. In Galilee St Peter''s fish, Sarotherodon galilaeus (Cichlidae), male care, female care and biparental care all occur in the same population. We exploit this unusual variability to isolate conditions favouring biparental versus uniparental mouth-brooding by males or females. We first review a game-theoretic model of parental care evolution, predictions of which we test experimentally in this paper. Manipulations of the operational sex ratio show that males and females desert their offspring more frequently when the costs of care are high (in terms of lost mating opportunities). Breeding trials with males of different sizes show that small fathers desert more frequently than large fathers. We attribute this to the associated difference in the fitness benefit of biparental care relative to female-only 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 sub-family Tilapiini. Our results support the hypothesis that biparental mouth-brooding was the ancestral state of both male and female uniparental mouth-brooding in cichlid fishes.     

A field survey of the bredding habits of Eretmodus cyanostictus, a biparental mouthbrooding cichlid in Lake Tanganyika

Oral incubation of young or mouthbrooding reduces the selective advantages of care by two parents and thus biparental care is rare among mouthbrooding fish. We surveyed the breeding biology of Eretmodus cyanostictus, a biparental mouthbrooder from Lake Tanganyika, to understand what factors maintain biparental care. We found larger males than females, a male-biased sex ration and indications that spawning is synchronized around the full moon. These preliminary findings suggest that the benefits of desertion for males are low; males may maximize their reproductive success by helping raise young while females regain reproductive condition.     

Paying to stay or paying to breed? Field evidence for direct benefits of helping behavior in a cooperatively breeding fish

Several hypotheses aim to explain the evolution of helping behavior,but conclusive experimental support for evaluating the relativeimportance of individual hypotheses is still lacking. We reporton two field experiments conducted to test the "territory inheritance"and "pay-to-stay" hypotheses in the cooperatively breeding cichlidfish Neolamprologus pulcher The territory inheritance hypothesiswas tested by removing one parent, which created breeding vacancies.In 39% of cases, same-sex helpers took over the breeding spot;in 44% of cases helpers continued helping new breeders, and17% were evicted by new breeders. Helpers that were closelysize matched to the removed breeder had a better chance of gainingthe breeding spot Male helpers tended to continue helping aftera takeover more often than females.The pay-to-stay hypothesiswas tested-by temporarily removing helpers. Whereas breedersdid not respond aggressively to removals, other group membersattacked the removed helpers on their return, and 29% were eventuallyevicted. The returning helpers assisted more by increasing theirrate of territory maintenance and defense and visiting the broodchamber more frequently Size and sex of removed helpers didnot explain the observed aggressive reactions of other groupmembers. Thus, our results support both hypotheses: N. pulcherneeds to pay with help to be allowed to remain protected inthe family group, and there they may inherit the natal territory.N. pulcher helpers gain direct benefits from helping behavior.     

Evolutionary transitions in parental care in cichlid fish

Cichlid fishes (Cichlidae) are well suited for testing theories of the evolution of vertebrate parental care. These freshwater teleost fish provide parental care for their offspring, display many different forms of care and have interspecific variation in which sex stays with the young. Here, we assemble the first family-wide composite phylogeny based on morphological and molecular studies, and trace two sets of character evolution: form of care (substrate guarding and mouthbrooding), and sex of care-giver (biparental, female-only, and male-only). Mouthbrooding has evolved from ancestral substrate guarding with 10 to 14 transitions and 0 to 3 reversals. The data support hypothesized transitions in the sex of care-giver, with uniparental female care having arisen from biparental care 21 to 30 times with 0 to 10 reversals. There is also evidence that male-only care evolved once from biparental care. These transitions in parental care characters are the most numerous reported for any family of vertebrates and, to our knowledge, provide the first quantitative support for models of parental care evolution in fish.