Though we are far from celebrating February 14th, Valentine’s Day, a recently published research paper comes as a late-year reminder of the importance of love, or the avian equivalent. The study published in PLOS Biology shows that zebra finches with free choice in mates fare much better, in terms of reproductive success, than finches that are forced to mate.
The present study divided a group of 160 finches into either the free choice group and the no choice group and gave the pairs a few months to bond. Three pairs of birds from each group were then released back into a communal aviary and were given time to breed for five months, thus producing three successful broods after that time period ended.
In a second breeding season, zebra finches from the first breeding season were placed into a communal aviary and allowed to choose a mate again, and were separated into the chosen partner or not-chosen partner group, as before.
The authors determined the reproductive success based on the number of dead and alive offspring. From their observations, the pairs that were more likely to have surviving chicks were those that were allowed to choose their mates. On the other hand, pairs that were not allowed to choose their partners were more likely to have infertile eggs and “disappeared eggs”, or buried eggs, and their chicks were more likely to die – even if they were the foster parents. Interestingly, there was no difference in the embryo mortality between the groups indicating that the choice of partner is not dependent on the genetic quality of the partner.
Mate choice is important in nature, if your species is terrible at choosing mates that will produce strong and adaptable individuals (though, of course, it’s not as simple as that—more on that later) your species is sure to die-off the evolutionary tree. Mate selection is subject species dependent, but all tactics boil down to the costs of finding a mate in terms of time, energy, and resources when the goal is to ensure that your genetic material will get passed on to subsequent generations. Genetically compatible individuals can, but not always, have the best chance for passing on their genes because of the viability of their offspring.
The current research conducted by Malika Ihle and colleagues is evidence that zebra finches have evolved on the basis of behavioral compatibility, not genetic compatibility, but the results are not unique to zebra finches. The common mouse, Mus musculus, also has higher offspring survival if the females choose their partners. The same is observed with insects, such as the seed beetle, Callosobruchus chinensis, and other animals.
This research is the poetic counterargument to eugenics: genes are not entirely what makes your species thrive, it is how well you get along with your partner. Love is just as important for the species—or at least the animal equivalent.