SANTA CRUZ, Calif., Aug. 16 (UPI) -- Female animals have found myriad ways to select the most preferable mates. The method used by the ocellated wrasse, a small, colorful fish from the Mediterranean, is especially unusual.
The species' females manipulate their ovarian fluids to ensure their eggs are fertilized by preferred males. The strategy, dubbed "cryptic female choice," is a rare example of females influencing external fertilization.
Like other females, female ocellated wrasse prefer a male who is a committed father. For the ocellated wrasse, that means a male who builds a nest and protects fertilized eggs.
Spotting the males who build nests is easy. But lurking nearby are "sneaker males" -- males who let others do all the work and then fertilize a clutch of eggs when the would-be committed father isn't looking.
"The sneaker males release more sperm than the nesting males, and you'd think that would give them a better chance to fertilize the eggs, but there is something in the ovarian fluid that removes that advantage," Suzanne Alonzo, professor of ecology and evolutionary biology at the University of California, Santa Cruz, explained in a news release.
In petri dish tests, researchers found the female's ovarian fluid allows the sperm of nesting males to be more successful than sneaker males. The fluid works by bolstering the speed and directional abilities of the sperm. The steroidal effect favors quality over quantity, lending nesting fathers an advantage.
Eggs fertilized by sneaker males will be dutifully raised by nesting males, but females want the genes of nesting males.
"We know that the nesting males grow faster and have survived into their second year, so if either of those has a genetic basis it makes sense that females would prefer their offspring to carry those genes," Alonzo said.
The new research is published in the journal Nature Communications.