New research from the University of Oxford looks at fish species where males provide all of the parental care, and examines the factors influencing this behavior.
In most animals, females are heavily involved in rearing offspring, with males instead focusing their energy on attempting to mate with as many females as possible. Bizarrely, however, in many fish species it is the male that provides all of the parental care.
Researchers collected data from previous studies on 48 fish species with male-only care which had measured the costs and benefits to males of providing parental care. They then conducted a phylogenetic meta-analysis, which determined the average size of these costs and benefits across species, while controlling for the fact that species that are more closely related are likely to share similar traits.
Parental care has been thought to have evolved to improve the survival of offspring, but this study finds that in fish, male parental care does not provide much benefit to offspring. Instead, females preferred to mate with males already caring for eggs. Thus, in fish, good fathers are attractive and end up mating with more females. This preference in females is strongest in species where males work harder when they are caring for larger numbers of offspring, which might help to explain why females choose males already with eggs.
Lead author Rebecca Goldberg says, “It was surprising to find that male care had little effect on offspring survival as this is usually considered the main purpose of parental care. In the absence of this effect, it is unclear what benefits females gain from choosing caring males.”
The prevalence of male-only care in fish does not fit with standard theories about the evolution of parental care, and has proved difficult to explain. Synthesising results from many different species provides an explanation for this behaviour that greatly improves our understanding of how parental care has evolved in fish, and helps to explain why we observe such different parental care strategies across animals.
One thing that remains unclear is why females prefer to mate with males who are already caring for the eggs of other females, and further investigation into this area is planned. Filial cannibalism (where males eat some of their eggs) is very common in these species, and the team are currently exploring the idea that a preference for good fathers ensures that a female’s eggs are not eaten once she leaves them in the care of a male.
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