If you’re a male sand goby, the key to attracting the ladies lies in your fathering skills. That’s right — to female sand gobies, there’s nothing more appealing than a good dad.
In a scientific study, females showed no preference for males who were bigger or who were brighter in color. And though males fight against other males, researchers found that those who triumph in competition are not preferred by females. Instead, females consistently chose good dads as mates.
Female choice is a very powerful evolutionary force that Charles Darwin wrote about in the 1870s, but it was largely ignored by researchers for many decades. The general consensus for a long time was that males fought for the right to mate with females, and females were passive members of the system — rewards for males who were winners.
Once female choice was accepted as an important aspect of mating systems, most everyone agreed that females were making choices in order to mate with high quality males. There has been much debate about what constituted “high quality.”
The benefits from high quality males can be either direct or indirect. Direct benefits involve better resources and material advantages such as better territories, better parental care and superior protection from predators. Indirect benefits are genetic advantages that either help their offspring survive or make them more attractive so that they have enhanced mating success.
Male sand gobies mate with any female who will have them, but the females are more selective — a pattern seen in many animal species.
In the sand goby, males create nests by excavating holes underneath empty mussel shells that they cover with sand. Females lays eggs in the nests. In this species, only the males care for the eggs, so hatching success is highly dependent on males’ behavior. The males protect them from egg predators, clean the eggs, and move water over them to increase the flow of oxygen and nutrients. Males also sometimes cannibalize the eggs. Their fathering duties end when the eggs hatch, at which point the fry are on their own.
Superior paternal care explains females’ choices. The males that females preferred had higher hatching success, indicating that females make their choice based on parenting. They did not base their decision on who won in male-male competition, as that is not a good way to select the best male, since “best” really means “best dad.” The winners in competition between males did not have better hatching success than those who lost such battles.
It’s sensible to choose males who will be good fathers because that directly affects the reproductive success of the females. It’s a good question, though, what information the females are using to assess a males’ parenting skills. One possibility is that they choose males who court vigorously, which may indicate the high energy and large fat stores necessary for the demanding task of caring for eggs.
On Father’s Day and every day, we should all follow the example of the sand goby and keep in mind that great Dads are sexy.