Female fish can influence which males fertilize their eggs even after releasing their eggs into the water, reports a study published in Nature Communications this week. This ability to exert mate choice after mating was previously thought to be restricted to species with internal fertilization.
In the ocellated wrasse (Symphodus ocellatus), males that build nests and provide extensive care for their offspring are strongly preferred as mates by females. However, there are also ‘sneaker males’ that do not provide care or court females on their own. Instead, they sneak up while a female and nesting male are mating and attempt to fertilize a proportion of the eggs by releasing large numbers of sperm.
Suzanne Alonzo and colleagues demonstrate that female ocellated wrasse can control which sperm fertilize their eggs by producing an ovarian fluid that surrounds the eggs. They found that ovarian fluid increases the speed and accuracy of sperm movement towards the eggs, decreasing the importance of sperm number and increasing the importance of sperm velocity. As a result, the ovarian fluid gives an advantage to nesting males, which produce fewer but faster sperm than sneaker males.
These findings demonstrate that females can exert mate choice after mating even in species with external fertilization.