Male llanos Mosquitofish Have Four Hooks on Their Genitalia
Posted on September 27, 2012
The males of a new species of freshwater fish - the llanos mosquitofish, or Gambusia quadruncus - have four hooks on their genitalia. Females of the species do not have hooks, but they do have distinguishing characteristics, including a colorful anal spot. A male fish is pictured above and the hooked genitalia is pictured below. The fish is described in a new paper published in the Journal of Fish Biology.
Dr. Brian Langerhans, assistant professor of biology at NC State and the lead author of the paper, says in a release that hooked genitalia on males can serve a purpose when females attempt to block or restrict mating attempts.
Langerhans says, "Typically, reproduction is more costly in females, so females favor ways of reducing mating with 'lower quality' males, but reproduction is cheap in males and so selection favors ways of mating with as many females as possible. In Gambusia, some females, including G. quadruncus, have evolved modifications that appear to function as a blocking device - essentially a big ball of tissue blocking most of the genital pore - restricting entry of the male's gonopodial tip. Thus, the female would have to behaviorally allow the male to mate or the male would have to evolve a counter response to avoid this problem."
Langerhans also says, "Having four hooks on the gonopodium may provide a means of overcoming female resistance, latching on to the gonopore and transferring sperm in a manner that facilitates effective sperm transfer. Or it may serve to stimulate the female in a manner that causes responses in the female that facilitate effective sperm transfer."
Some insects also use hooks for mating. For example, male water striders grab the females by the eyes using barbed hooks.
Langerhans says the colorful anal spot on the females could serve as a signal that only certain males are desirable mates. He says, "The differing, species-specific female anal spots appear to influence male mating behavior by signaling the location of the gonopore to the male, sometimes indicating the reproductive status of the female, and distinguishing fish of their own species from fish of other species to reduce costly cross-breeding, which can result in fish with reduced fitness. So it may be that G. quadruncus evolved different anal spots to help reduce interspecies matings and possible formation of hybrids."