Written by Lucia Yllan
Taking care of children is a full-time job – feeding, bathing, clothing, cleaning, and the list go on. However, humans are not the only animals that take care of their offspring. ‘Parental care’ is a behaviour that is widely spread throughout the animal kingdom, and fish are no exception.
First, let’s define what we call ‘parental care’. Parental care is any behaviour that increases the survival of the next generation [1]. This includes behaviours such as building a nest, feeding the offspring or protecting the offspring from predators [2,3]. Although these behaviours are beneficial for offspring, there is a cost for parents that take care of them. Parents suffer a higher risk of predation when guarding their eggs and might lose new opportunities to reproduce [3,4]. Svensson (1988) showed that male Broadnosed pipefish (Syngnathus typhle) were 11 times more likely to be predated on when caring for offspring than when not. In addition, parents may interrupt their feeding while caring for their offspring, which is also energetically demanding, and this causes a reduction in parent body condition such as weight and size [3,6].
If we take a look at all the vertebrates that display parental care we would see that, in most cases, either both parents (biparental care) or only the females (female uniparental care) take care of the offspring and that males taking on the caretaker role (male uniparental care) is extremely rare. In mammals and reptiles, there are no reports about male uniparental care while in birds, only 1% of species show male uniparental care [7]. Amphibian species show higher frequency of male uniparental care, which is equal to the frequency of female uniparental care. However, in fish, male uniparental care is the most common form of parental care [8,9]. Why? This is a question that researchers have been wondering for decades.
Studies [9,10] suggest that the cost associated with parental care is lower for male fish than what it was initially thought. Egg guarding usually overlaps with territorial defence of males and as a result, protecting the eggs does not suppose an additional energy cost for the male. Other behaviours such as nest preparation or egg fanning (which consists in the parent moving the water around the eggs using their fins to increase the oxygen the eggs receive) also have a small energetic cost for the males. In addition, in over 90% of cases, males were found to keep mating despite having a clutch to tend to, so caring for eggs does not reduce their reproductive opportunities. Thus, the difference in cost and benefits of parental care for males and females could explain why male uniparental care is so common for fish.
In addition to this, Goldberg et al. (2020) have found that female fish prefer to mate with males that take care of their eggs than those that don’t and prefer males that have larger clutches compared to those with small ones. Although this preference is not universal for all fish species with male parental care, these results show a clear trend for most species. The reasons for this preference for caring males is still unclear, however, scientists have several hypotheses.
One of the most interesting hypotheses is related to filial cannibalism in fish species. Although some fish fathers are great at taking care of their eggs, this task can be demanding. In some cases, when the environmental conditions are harsh, males might have to resort to desperate measures to survive such as cannibalising their own eggs [6]. This behaviour is not only negative for the reproductive success of the male but also the female. Despite females not taking part in parental care for these species, they still invest their energy in reproduction. To avoid their investment going to waste, females might choose males that are taking care of other eggs to reproduce. That way females decrease the possibilities of the male eating their eggs as there are other eggs from other females available for the male to eat [10]. This could also explain their preference for males with larger clutches to care for, as more eggs translate into a lower chance of their eggs being cannibalised by the male if the conditions require it.
Another peculiar characteristic of fish male parental care is the great diversity of strategies they use to take care of their offspring. Fish such as the sergeant major (Abudefduf saxatilis) guard their eggs to protect them from predators. Other fish such as the tompot blenny (Parablennius gattorugine) creates nests with shells or rocks to lay their eggs on and then cover the eggs with sand and algae. Some fish don’t lay their eggs in the substrate but use their own body to keep the eggs safe, for example the cardinalfish (family Apogonidae) carry their eggs inside their mouth [10,11].
In conclusion, male parental care in fish is a very interesting topic that breaks with the established gender roles that are usually associated with non-human animals. However, there are still a lot of questions about male uniparental care in fish species that need answers such as what are the factors that select for male parental care in species with no filial cannibalism but, luckily, research groups are working on finding these answers. With their work, researchers are helping us understand the evolution of parental care throughout the vertebrates.
References
1 Azad, T. et al. (2022) Life history, mating dynamics and the origin of parental care. J. Evol. Biol. 35, 379–390
2 Barbasch, T.A. et al. (2022) Parental Care Patterns, Proximate and Ultimate Causes, and Consequences. Evol. Dev. Ecol. Anemonefishes. CRC Press. DOI: 10.1201/9781003125365-18
3 Alonso-Alvarez, C. and Velando, A. (2009) Chapter 3 : Benefits and costs of parental care. Evol. Parent. Care
4 Gross, M.R. (2005) The evolution of parental care. Q. Rev. Biol. 80, 37–45
5 Svensson, I. (1988) Reproductive Costs in Two Sex-Role Reversed Pipefish Species ( Syngnathidae ). Br. Ecol. Soc. 57, 929–942
6 Bose, A.P.H. (2022) Parent–offspring cannibalism throughout the animal kingdom: a review of adaptive hypotheses. Biol. Rev. 97, 1868–1885
7 Balshine, S. (2013) Patterns of parental care in vertebrates. Evol. Parent. Care DOI: 10.1093/acprof:oso/9780199692576.003.0005
8 Maciejewski, M.F. and Bell, A.M. (2022) Insights into Parental Care from Studies on Non-mammalian Vertebrates. Affect. Sci. at <https://link.springer.com/article/10.1007/s42761-022-00127-4https://link.springer.com/10.1007/s42761-022-00127-4>
9 Gross, M.R. and Sargent, R.C. (1985) The Evolution of Male and Female Parental Care in Fishes 1 sex would seem to be better preadapted . for live bearing , yet males in some species of approximately 422 families ( primarily Fertilization is external in approxi- mately 89 % of families , and. Am. Zool. 25, 807–822
10 Goldberg, R.L. et al. (2020) The costs and benefits of paternal care in fish: A meta-analysis: Female choice for male care in fish. Proc. R. Soc. B Biol. Sci. 287,
11 Bessa, E. et al. (2022) Integrative approach on the diversity of nesting behaviour in fishes. Fish Fish. 23, 564–583
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