terpkristin
03-21-2006, 06:40 PM
From http://dsc.discovery.com/news/briefs/20060320/beetles_ani.html?source=rss
Diving beetles engage in such exhausting, uncomfortable sex that these insects have actually evolved two different types of females, as well as unusual variations among males, according to a new study. The find adds to the growing body of evidence that sexual conflict between males and females influences evolution. In many cases, individuals over time develop characteristics that are appealing to the opposite sex.
For diving beetles, however, researchers believe females have tried to avoid the painful sex for so long that some have actually evolved a feature that enables them to spurn most suitors.
The result is that the insect family Dytiscidae includes species, such as the diving beetles Dytiscus lapponicus and Graphoderus zonatus verrucifer, which each have two distinct types of females.
D. lapponicus has females with smooth and furrowed backs, while G.z. verrucifer has females with smooth and granulated backs. The furrows and granulation allow these types to avoid frequent sex with males, which grab onto the females with suction-cupped feet.
Findings are published in the current issue of The American Naturalist.
Lead authors Roger Härdling and Johannes Bergsten told Discovery News, "Here is one vivid description of mating in diving beetles from Wichard et al (2002, Biological Atlas of Aquatic Insects) 'At the beginning of sexual union, during precopulation, the male constantly shakes the female back and forth with the middle legs while swimming. This mating game increases the need for oxygen.'
While the male's abdominal tip often comes to the surface to draw in air, the female is prevented from doing so. This apparently goes on until the female is exhausted. During this phase of weakness, copulation lasting 15 minutes takes place.'"
At the end of the ordeal, the male brings the weak female to the water's surface so she can breathe again.
Härdling, a scientist at Sweden's Lund University, and Bergsten, a scientist at Umeå University, also in Sweden, said the number of suction cups on the male beetle's front foot varies among individuals and species. One species, Dytiscus latissimus, actually has males with an average of 1,500 suction cups on one front foot.
The researchers explained that these cups, just like any suction device, work better on a smooth, rather then on an uneven or textured, surface.
They said, "Our hypothesis is therefore that the female sculptured form has evolved because it benefits females to easier get rid of males attempting to mate when the harassment rate is high."
For their study, the researchers used mathematical modeling to determine how the beetles' sexual arms race would play out over time.
They determined that the furrows and grooves would give males with more suction cups a better chance of mating. Smooth-backed females would then enjoy better fitness, since they would not have to frequently endure the horrific mating ritual.
Males then would develop better ways of mating with smooth-backed females, with the result being a currently stable equilibrium that favors both smooth and textured-backed females, along with males possessing varying numbers of suction cups.
Göran Arnqvist, an assistant professor of animal ecology at Uppsala University in Sweden, told Discovery News: "What is particularly interesting is that their model shows that one can get stable polymorphism in both sexes, such that each male shows one of several possible persistence traits and each female shows one of several possible resistance traits, if there is assortative (non-random) mating such that certain males tend to mate with certain females."
Härdling and Bergsten predict that female diving beetles will evolve new adaptations to thwart males, while males could evolve better means of catching females, which all could lead to the evolution of an entirely new species.
The researchers suspect sexual conflict acts as a "speciation engine" that could drive the formation of new species, but they suggest further research is needed to prove the theory.
/tk
Diving beetles engage in such exhausting, uncomfortable sex that these insects have actually evolved two different types of females, as well as unusual variations among males, according to a new study. The find adds to the growing body of evidence that sexual conflict between males and females influences evolution. In many cases, individuals over time develop characteristics that are appealing to the opposite sex.
For diving beetles, however, researchers believe females have tried to avoid the painful sex for so long that some have actually evolved a feature that enables them to spurn most suitors.
The result is that the insect family Dytiscidae includes species, such as the diving beetles Dytiscus lapponicus and Graphoderus zonatus verrucifer, which each have two distinct types of females.
D. lapponicus has females with smooth and furrowed backs, while G.z. verrucifer has females with smooth and granulated backs. The furrows and granulation allow these types to avoid frequent sex with males, which grab onto the females with suction-cupped feet.
Findings are published in the current issue of The American Naturalist.
Lead authors Roger Härdling and Johannes Bergsten told Discovery News, "Here is one vivid description of mating in diving beetles from Wichard et al (2002, Biological Atlas of Aquatic Insects) 'At the beginning of sexual union, during precopulation, the male constantly shakes the female back and forth with the middle legs while swimming. This mating game increases the need for oxygen.'
While the male's abdominal tip often comes to the surface to draw in air, the female is prevented from doing so. This apparently goes on until the female is exhausted. During this phase of weakness, copulation lasting 15 minutes takes place.'"
At the end of the ordeal, the male brings the weak female to the water's surface so she can breathe again.
Härdling, a scientist at Sweden's Lund University, and Bergsten, a scientist at Umeå University, also in Sweden, said the number of suction cups on the male beetle's front foot varies among individuals and species. One species, Dytiscus latissimus, actually has males with an average of 1,500 suction cups on one front foot.
The researchers explained that these cups, just like any suction device, work better on a smooth, rather then on an uneven or textured, surface.
They said, "Our hypothesis is therefore that the female sculptured form has evolved because it benefits females to easier get rid of males attempting to mate when the harassment rate is high."
For their study, the researchers used mathematical modeling to determine how the beetles' sexual arms race would play out over time.
They determined that the furrows and grooves would give males with more suction cups a better chance of mating. Smooth-backed females would then enjoy better fitness, since they would not have to frequently endure the horrific mating ritual.
Males then would develop better ways of mating with smooth-backed females, with the result being a currently stable equilibrium that favors both smooth and textured-backed females, along with males possessing varying numbers of suction cups.
Göran Arnqvist, an assistant professor of animal ecology at Uppsala University in Sweden, told Discovery News: "What is particularly interesting is that their model shows that one can get stable polymorphism in both sexes, such that each male shows one of several possible persistence traits and each female shows one of several possible resistance traits, if there is assortative (non-random) mating such that certain males tend to mate with certain females."
Härdling and Bergsten predict that female diving beetles will evolve new adaptations to thwart males, while males could evolve better means of catching females, which all could lead to the evolution of an entirely new species.
The researchers suspect sexual conflict acts as a "speciation engine" that could drive the formation of new species, but they suggest further research is needed to prove the theory.
/tk