by Piter Kehoma Boll
Parental care, here defined as any behavior in which an animal takes care of its young, is a widespread practice in the animal kingdom, having evolved repeatedly in many taxa. It is not difficult to see, considering natural selection, why parental care is an adaptative trait. It enhances the chance of one’s offspring to survive and thus carry one’s genes to the next generation.
On the other hand, the related behavior known as alloparental care is not that easy to explain in every instance of its occurrence.
While parental care means caring for your own offspring, alloparental care means caring for the offspring of another individual. If you spend time and resources in taking care of an animal that is not your direct descendant, you must have a good reason to do it, a reason that somehow benefits you. Or you may just be too dumb.
Most animals reject or even kill the offspring of other individuals of the same species. A classic example is a male lion that kills the cubs that he knows are not his. He does that because he sees no advantage in allowing the offspring of another male to survive.
An extreme example of caring for juveniles that are not your direct offspring is found in social insects such as bees and ants. Worker ants usually do not reproduce but they raise their siblings as if they were their own children. In this case, it is more advantageous to make siblings than to make children because of the peculiar reproductive system of hymenopterans. I will not enter in details but, basically, ants share 100% of their father’s DNA and 50% of their mother’s DNA, so that two sibling ants have 75% of their genes in common, while the relationship between a female ant and her female offspring is of only 50%.
However, alloparental care is found in many other animals, especially in mammals. Although not having 75% of similarity between siblings as in ants, many mammals and other animals help their mothers and/or fathers to raise their siblings. This has less direct advantages but they are still there. After all, your siblings (if they are of the same mother AND father) share 50% of your DNA, the same amount that you share with your children. But alloparental care may also happen with more distantly related relatives, such as grandchildren and half-siblings, which share only 25% of their DNA with you. This is not a problem, though, because if you are unable to have your own kids at that time, it is better to help raise those juveniles that share some DNA with you than to do nothing because 25% of your genes is still better than nothing.
A recently published paper reports the first observation of alloparental care in the field in the cichlid fish Neolamprologus savoryi. The team observed a male fish helping take care of the eggs of another male that was found to be his father, although the mother of the eggs was not his mother. The male helper was small and probably sexually immature, so that, as said above, helping his half-siblings, which have 25% of his genes, survive is better than doing nothing.
A really hard thing to explain is why some animals accept to take care of the offspring of unrelated individuals, in which there is no clear adaptative advantage. Such a situation was recently discovered to occur with the common earwig Forficula auricularia. Females that had their egg clutches replaced with the eggs of an unrelated female took care of them as if they were their own. No advantage of any kind can be extracted from this behavior, so the most likely explanation is simply the lack of adaptative pressure to reject unrelated eggs. It is likely that, under natural conditions, a female earwig never encounters the eggs of another female. Thus, there was never a scenario in which the capacity to recognize one’s own eggs (and differentiate them from others) could evolve. Natural selection needs opportunities to act.
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Josi D, Taborsky M, Frommen JG (2019) First field evidence of alloparental egg care in cooperatively breeding fish. Ethology 125(3): 164–169. doi: 10.1111/eth.12838
Royle NJ, Moore AJ (2019) Nature and Nurture in Parental Care. In: Genes and Behaviour, pp. 131–156. John Wiley & Sons, Ltd. doi: 10.1002/9781119313663.ch7
Van Meyel S, Devers S, Meunier J (2019) Love them all: mothers provide care to foreign eggs in the European earwig Forficula auricularia. Behavioral Ecology. doi:10.1093/beheco/arz012
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