Large horns cause small organs to mate

According to Indiana Bloomington University biologists, the sometimes bizarre gimmicky traits that increase the chance of finding animals' partners also affect the reproductive process of populations and processes. Evolution of forming new species.

In the September 2008 issue of Evolution, Armin Moczek and Harald Parzer investigated males belonging to the four populations of Onthophagus taurus horned beetles that were geographically separated. They differ significantly in the size of the male sex organs. Natural selection also affects the symmetry of the other side - the horns on the animal's head.

Moczek said: ' Biologists have learned that in beetles there is a balanced investment between secondary sexual characteristics and key sexual characteristics. The bigger the horns, the smaller the structure and vice versa. What we still don't know is how often and how quickly things happen in nature, can this affect new species formation? '

The structure directly related to the mating behavior is considered to be the main sexual characteristics, while the bodies used to fight like horns as well as the characteristics used to attract heterosexuals such as fluffy feathers the beauty of the patriarchal bird, or the frog's deep bass call is considered secondary sexual characteristics.

Evolutionary biologists believe that changes in mating bodies' sizes and shapes can promote species formation by creating reproductive individuals in different populations. .

The difference in the horn size of horned beetles is probably the result of evolutionary changes in favor of new species formation. The image shows the males of the two beetle species O. watanabei and O. sagittarius of the Onthophagus family. (Photo: Armin Moczek)

The beetle O. taurus is a native species in Italy, which exists separately because of human activities. According to Moczek and Parzer, this means the significant deflection they observed in the horns as well as the mating organ size of the O. taurus beetle certainly occurs only in a very short process - about 50 years or less.

Although many of us are forced to believe, changes in reproductive organ size in species tend to be low, including beetles as well as humans. But four populations of O. taurus beetles that Moczek and Parzer studied in the United States (North Carolina), Italy, Western Australia and Eastern Australia show significant changes in both horns as well as organ length. External sex with a difference of 3.5 times when it comes to the 'investment' category that scientists have set up including body size.

They studied 10 other species of Onthophagus, as expected, they discovered a lot of differences between species from horns to mating bodies. According to Moczek, this shows that the balance between primary and secondary sex characteristics continues to mold the species' separation pathway after the species formation process has occurred.

The speed and intensity of separation in O. taurus contains something unusual. Why can mating organ size be strictly maintained in a population of a species that keeps changing?

Moczek explains: 'When talking about the status of a species, it is important not to change too much. There is plenty of evidence to suggest that in a species or in a population, natural selection has maintained sexual characteristics. But if the key gender characteristics are related to other traits that are capable of rapid transformation, then what we consider to be an interesting mechanism is likely to separate reproductive populations. '.

Double-horn length as well as its shape vary for many reasons. In densely packed species, fighting (big horns) may not be an effective strategy to win a mate. When males are aggressively fighting, another tiny male with small horns can easily adopt a mischievous strategy to capture females without a mate. In this situation, reducing investment in horns will bring about a larger mating body. Similarly, in populations with a lower density, most male beetles spend a lot of time fighting. Those with longer and larger horns have an advantage, which also leads to small-sized external genitalia.

Moczek said: 'If that is just to change the external genitalia, then creating new species is simpler than we think.'

The idea that the external genitalia is related to the origin of the species is not new. But their connection makes evolutionary biologists headaches. Individuals of most species do not choose partners based on size and shape of the genitalia. In fact, external genitalia may not play a role only when the male approaches the final flirtatious stage.

The original ' lock and key ' model of reproductive separation proposed for the first time by L. Dufour in 1844 explains why some species are very similar in appearance but cannot mate. The research discussed in Evolution received support from the National Science Foundation.

Refer:
Harald F. Parzer and Armin P. Moczek.Rapid Antagonistic Coevolution Between Primary And Secondary Sexual Characters In Horned Beetles.Evolution, 2008;DOI: 10.1111 / j.1558-5646.2008.00448.x