Covers: a conspiracy of silence

Evolution is happening before our eyes. Crickets, for which chattering has become deadly, have lost the ability to make sounds in just 20 generations. In a short time, especially when you consider that with their “songs” crickets are lulling and fascinating the female. Now they look after silently.

This story began at the end of the last century, when two brooded species met in the Hawaiian Islands: the field crickets Teleogryllus oceanicus from Australia and the Pacific Islands and the small flies of Ochracea from North America. The males of the crickets are shaken at night, attracting females. Unfortunately, O. Ochracea fly on the same sounds, they lay eggs on the covers of the crickets, and the larvae that are removed from them, bite into the body of the host and eat it. The insect dies in a week.

Since 1991, T. Oceanicus has been studied by Marlene ZUK from the University of California in Riverside (University of California Riverside). Crickets live in three islands: Kauai, Oha and Hawaii. The most of all the flies overcame the crusts of Kauai, in the late 90s they parasitized already by a third of males. It seemed that the island population came to an end, but it turned out differently. At first, the structure of the song changed, and then they fell silent. In 2001, Marlene Zak still heard their chirping, in 2003 there was silence on the island. At the same time, T. Oceanicus were numerous and felt great.

The crickets shake, rubbing against each other with embossed wings, which have special swollen veins with teeth and scrapers. During friction, the scraper on the cloves sounds: as if it is carried out with a fingernail along a comb. It turned out that all the silent crusts of the Kauai dentists on the wings almost disappeared, and the few remaining decreased in size and are located at an angle that excludes the production of sounds. The mutation is called Flatwing , since the wings of insects have lost the relief. However, they are suitable for flight. In 2003, 96% of T. Oceanicus males had flat wings.

The crosses conducted by the researchers showed that the Flatwing is caused by a change in the only genuine located on the sex chromosome (female german are two X-chromosome, the male has one, and the Y chromosomes). Like any mutation, Flatwing can occur in any population, but on Kaui it was fixed as a result of a strong pressure of the selection. The tool turned out to be effective: out of 122 males caught in 2003, only one was infected with O. Ochracea larvae.

Two years later, in 2005, the flat-winged males of the crickets appeared on the island of Ohaha, 101 km from Kauai. To date, almost half of them is silent. Specialists from the Scottish Institute of St. Andrews became interested in the appearance of mute crickets in different populations under the leadership of Nathan Bailey, who joined the research of Marlene Zach.

At first, scientists suggested that flat -winged crickets simply migrated to Oha from the neighboring island. However, their wings are so different from the wings of Flatwing on Kauai that the difference is noticeable to the naked eye. The crickets of the oah have retained much more chattering devices. Brightening and analysis of DNA sequences confirmed that Flatwing on OHA has a different nature than Kauai. In this case, the mutation also occurred in the only genus located on the X chromosome, but it is either another gene or another section of the same gene. Now researchers are clarifying exactly what sequences have changed in crickets and whether these changes affect other signs.

Silence reliably defended T. Oceanicus from parasites, but they must multiply. The male lures the female with a chatter, and when she approaches, he performs a “courtship song” for her. This is a mandatory ritual without which the female will not allow the partner to start mating. Silent insects take care of ladies for other people's songs. Even on Kauai, 4% of males still shake. Silents are hidden nearby (the average distance is about 75 cm), wait for the appearance of the female and crawl out of the shelter. The same behavior is characteristic of Gryllus texensis crops, on which O. Ochracea is parasitized in homeland, in America. There, one male sings, and somewhat await the female silently, sitting about a meter from the singer.

It remains a mystery to how the mute T. Oceanicus hold the attention of females. In other places, the male without a song of courtship is doomed to celibacy, and the females accept silent partners on Kauai and Oahu. Perhaps on the islands, where there were few crickets at first, the females became less picky, otherwise they risked not to find a suitable male. In addition, their offspring from flat -winged fathers will also be silent and, therefore, protected from terrible flies.

Scientists believe that males, deprived of the opportunity to conjure, will soon develop another way to declare themselves, for example, pheromones. T. Oceanicus select carbohydrate compounds. Researchers have found that females distinguish between the smell of the selection of males and females, react to the smell of males, and the chemical signals of normal males and males Flatwing attract them equally. It is possible that they will continue to develop a chemical alarm. Be that as it may, they so far solve the problem of communication communication very successfully.

As for O. Ochracea , there are no alternative owners on the Hawaiian islands for them. Perhaps they will die out if the crickets are finally silent. Or remain in a small amount, since the plane -blanket does not serve as absolute protection. On the island of Hawaii, also inhabited by T. Oceanicus , but almost not suffering from flies, in 2010 2% of males no longer chattered. Scientists have yet to figure out what mutation caused a plane -blanket in them. But if the flies attack the island, the genetic tank has already had a crickets.

The case of Hawaiian crickets is interested in scientists as an amazing example of convergent evolution, and incredibly fast - in just a few years, different mutations arose in different populations, which led to similar changes. Well, the islands have always been a treasury for evolutionists. The earthen at the Galapagos Islands are mentioned in all textbooks as a visual example of the divergence of the species in different habitats. It is possible that soon a worthy place next to them will be occupied by Hawaiian crickets - a sample of convergence.

ZUK M., Rotenberry Jt, Tinghitella Rm. Silent Night: Adaptive Disapperate of axual Signal in a Parasitized Population of Field Cricket. Biol. Lett. 2006; 2: 521-524. DOI: 10.1098/RSBL.2006.0539. Pascoal S., CEZARD T., Eik-Nes a, Gharbi K., Majewska J., Payne E., Ritchie G., Zuk M., Bailey NW Rapid Convergent Evolution in Wild Cricket. Current Biology. 2014. DOI: 10.1016/J.Cub 2014.04.053 Gray B., Bailey NW, Poon M., ZUK M. Multimodal Signal Compensation: Do Field Crickkets Flexibly SigNALINALITY MODALITY After the Evolutionary Loss of Acoustic Communication? Animal Behavior. 2014. DOI: 10.1016/j. Anbehav 2014.04.033