Sand gobies, small fish native to the European coast, are among about 20 percent of fish families worldwide that display some form of care for eggs or hatchlings. But in experiments reported in the current issue of the journal Behavioral Ecology, a team that includes a University of Florida scientist reports that male sand gobies work harder at building nests and taking care of eggs when females are present - the first time such "courtship parental care" has been documented in any species.
Some males' behavior was even more dastardly. While the experiments showed all male gobies nibbled on the eggs in their charge, unaccompanied males not only shirked their parental duties - they also were more likely to gobble down entire clutches of eggs.
"We were interested in whether males would change their behavior in response to the perception that their future mating opportunities were different," said Colette St. Mary, an associate professor of zoology at UF and one of three authors of the paper. "We found this was the case."
Sigal Balshine, an assistant professor of psychology and specialist in animal behavior at McMaster University in Ontario, called the results "very neat and very novel."
Asked about analogies to human behavior, she said, "Being a good father is very sexy. This is almost a cliché, as it has become a standard joke that the best way to get women to be interested in you as a single guy is to borrow a baby or a puppy. Women obviously find 'caring guys' very sexy."
As part of a research effort aimed at investigating the role of sexual selection in how parental care has evolved in male fish, St. Mary, Kai Lindström and Christophe Pampoulie, both of the University of Helsinki in Finland, decided to use sand gobies to test a theory that males would provide more care for their young if females were present.
Both humans and animals often engage in two-faced behavior. But the general rule in biology is that parenting duties conflict with reproductive activity, because males would devote their energy to taking care of offspring instead of courting and mating.
"Traditionally evolutionary biologists have thought that parental care is something that is costly to other components of fitness, such as survival, growth or looking for other opportunities to reproduce," Balshine said.
Sand gobies nest under mussel and other shells, and the males not only find and defend these shells, they also hollow out a space under them and pile sand on top to disguise them from predators, St. Mary said. The fish also use their pectoral fins to fan water over the eggs, creating a current of fresh, oxygenated water needed for them to mature.
In the experiment, the researchers allowed male and female gobies to mate, then exposed half the males to additional females, which were placed in a small compartment that allowed the males to see the females and "be in chemical contact with them" but prevented physical contact, the authors write. Some males were in small nests while others were in larger ones, a variable used to determine whether nest size also played a role in the males' courting behavior. The researchers then compared the parenting efforts by the accompanied and unaccompanied males.
The researchers used a total of 48 male gobies and at least 72 females to test different combinations of nest size, female presence and absence. They filmed the males for 30-minute intervals on the second day after spawning. The results were unambiguous.
"We found that males fanned (the eggs) longer and more frequently, and did more nest construction in the presence of females and in big nests," the authors write.
Also, unaccompanied males in small nests were most likely to eat all of their eggs, the authors noted. Bigger nests provide space for additional mating, encouraging the males to improve their parenting appearances, she said.
St. Mary added that although the parental courtship behavior is the first-ever documented experimentally, a few other species have been observed doing something similar in the wild. For example, three-spined stickleback male fish fan their nests before receiving eggs, a behavior termed "courtship fanning." Also, some species of male birds and insects feed their female counterparts prior to mating, which could be interpreted as combining the twin goals of attracting mates and parenting, she said.
Although the experiments show that males improve their parental duties in response to the presence of females, the studies don't indicate whether it actually pays off in terms of wooing females to mate. St. Mary and her colleagues plan to take up that issue in experiments this summer.