TALLAHASSEE, Fla. — Even for fish, blood is thicker than water. A fun new study just released by Florida State University has found that male guppies act as little cupids for their brothers in pursuit of love. Male Trinidadian guppies impede the path of their brothers’ dating rivals so their kin can approach the female they’re interested in.
These findings are especially noteworthy because they clearly show that guppies’ ability to recognize their family plays a significant role in their mating behavior and procreation.
“The results strongly suggest that males use kin recognition to minimize sexual competition with their close relatives,” says Mitchel J. Daniel, a postdoctoral researcher at Florida State and the lead author on the study, in a university release. “There is evidence of kin recognition in a wide range of animal species, including humans. Does kin recognition affect male-male competition in similar ways in other species? I’m hoping this study will help motivate other researchers to ask this question.”
Daniel had already previously discovered that female guppies use their ability to recognize family to avoid inbreeding. It was that discovery that motivated Daniel to investigate if familial recognition played a role in the male aspect of guppy dating. Other studies had already tested the same theory among fruit flies but the results were largely inconclusive.
“Those previous studies led to a lot of debate in the literature about whether relatedness among males really does relax sexual competition,” he adds. “Part of the motivation for our study was to help resolve this ongoing controversy by testing the idea in another species – guppies.”
When a male guppy is interested in a female he usually puts on a sort of dance to make his feelings known. Sounds pretty similar to what goes on in nightclubs and bars all over the world, doesn’t it?
If the female likes what she sees, she’ll move closer to the male. However, around this time is when any other nearby interested males usually interject themselves into the situation and ruin all the work the first male had put in.
The research team used two complex mathematical models to estimate the best ways for a guppy to maximize their “Darwinian fitness.” Basically, how can a guppy pass on his genes as much as possible? Well, brothers share genes, and it appears guppie brothers instinctively know that helping their kin reproduce is nearly as good as reproducing themselves. That’s why, researchers theorize, brothers help brothers court females in the guppie world.
To put that theory to the test, 600 guppies were placed into 12 groups for monitoring. Sure enough, the subsequent observations confirmed what Daniel’s mathematical models had suggested: male guppies helped their brothers reproduce by physically blocking out nearby rivals.
“This was really exciting to see because it suggests that males are competing in a way that increases how often their genes get passed, even if those genes are getting passed on by their relatives,” he says. “It supports an evolutionary theory called kin selection, which can promote cooperation among relatives.”
Another fascinating finding was that guppies apparently have a penchant for revenge. If a guppie blocked another male from approaching a female, that blocked guppie would often return the favor.
“When one male interrupted another male, it was usually reciprocated,” Daniel said. “More often than not, males went back and forth interrupting one another half a dozen times or so in quick succession before one male finally gave up. At times, it felt a bit like watching jealous lovers, each male desperate to keep ‘his’ female to himself.”
The study is published in Nature Ecology & Evolution.