September 28, 2012
Bizarre Mosquito Fish Genitalia Redefine Hooking Up
Brett Smith for redOrbit.com - Your Universe Online
While the battle of the sexes can get quite ugly among humans, in the animal kingdom it can get downright nasty.North Carolina State University researchers have described a new species of fish in which the male´s genitalia are equipped with four hooks while the female sports a colorful anal spot that it likely uses to attract a mate.
The new species, the llanos mosquito fish, or Gambusia quadruncu, lives throughout eastern central Mexico and is described in the Journal of Fish Biology.
According to lead author Brian Langerhans, these sexually-specific characteristics may have developed as a result of the mating habits and realities for the fish. Although more research is needed for confirmation, the NC State professor suspects that males may have developed their hooked genitalia to increase their chances of mating success with females that are adept at blocking or restricting mating attempts.
“Typically, reproduction is more costly in females, so females favor ways of reducing mating with ℠lower quality´ males,” Langerhans said in a statement. “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,” he added. “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.”
According to Langerhaus, that counter response could be the hooked genitalia.
“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,” Langerhans explained.
The professor added that the females probably use their colorful anal spot as a signal to specific males.
“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,” Langerhans said.
“So it may be that G. quadruncus evolved different anal spots to help reduce interspecies matings and possible formation of hybrids.”
The researchers performed a mitochondrial and nuclear gene sequencing analysis and found that the mosquito fish likely diverged from their closest relative around one million years ago.
According to the report, this differentiation was probably the result of a so-called vicariant evolutionary event that differentiated populations of fish by somehow isolating them from each other. Experts suspect that this event probably took place in a section of the Sierra Madre Oriental range.
The area of Mexico where the mosquito fish were found is a hotspot for their diversity and the diversity of their closest genetic relatives, the researchers added.