“제비, 정말 바람피운다” 과학적으로 증명 > 자유 게시판

과학 전문지 ‘사이언스’는 최신호(9월 30일자, 사진)에서 ‘멋진 외모’를 가진 제비가 수컷으로서 우세한 경향을 보였으며, 외모가 변화하면 수컷으로서의 ‘위상’도 변화한다는 미국 코넬대 연구팀의 논문을 커버스토리로 다루었다.


논문에 따르면 암컷 제비들은 사회적으로 짝을 이루고 난 뒤에도 더 나은 수컷 제비를 찾아 교미하는데, 여기서 더 나은 제비는 먹이를 잘 물어다 주는 제비도 아니고, 좋은 친구도 아니고, 그야말로 ‘멋진 외모’의 제비를 말한다.

수컷 제비의 ‘멋진 외모’의 기준이란 빨간색이 선명한 가슴과 깃털, 배라는 것을 연구팀은 확인했다.

사진#01

Rebecca Safran, a Cornell postdoctoral researcher in ecology and evolutionary biology, removes a captured barn swallow from a net in Groton, N.Y. (Photo Credit: Kevin Stearns/University Photography)

“수컷 제비들에게 좋지 않은 뉴스는 암컷 제비들이 더 나은 외모의 수컷을 찾아 교미하려는 습성은 결코 끝이 없다는 것”이라고 연구팀을 이끌었던 레베카 새프런이 말했다.

“이것은 안정된 관계를 확립한 이후에도 많은 시간과 돈을 들여 외모에 신경 쓰는 사람들의 모습과 관련지을 수 있을 것”이라고 그녀는 덧붙였다.

제비들은 사회적인 쌍을 이루고 생활하며, 수컷들이 둥지를 돌보는 부계 습성을 가졌는데, 암컷 제비들은 자신의 짝보다 가슴 깃털이 더욱 선명한 수컷을 발견하면 몰래 교미해 알을 낳는다고 한다.

1대 1의 사회적 관계 형성 이후에도 수컷 제비들에게는 양질의 외모를 유지하는 것이 중요하다는 결론이다.

실험을 위해 새프런과 연구팀은 30쌍의 제비를 자연스레 짝짓게 한 후 알을 낳게 했다. 그러고 나서 알을 숨겨 새로 교미하도록 시도했다.

암컷이 두 번째 교미 상대를 고르기 전에 수컷을 잡아 마커로 가슴과 배에 색칠을 하고 DNA를 채취, 알에서 태어나는 새끼를 확인했다.

모든 암컷들은 사회적으로 본래 짝과의 관계를 유지하면서도 다른 수컷과 교미를 했는데, 빨간 마커로 가슴에 선명한 색을 덧입힌 수컷이 둥지에 더 많은 알을 얻었다.

깃털에 변화를 주지 않은 수컷은 알의 숫자가 그대로이거나 줄어들었다. 불행하게도 어떤 수컷들은 둥지 가득 들어찬 다른 수컷의 알을 돌보게 된다고 연구팀은 밝혔다.

연구팀은 가슴 깃털이 인위로 선명하게 색칠 된 경우에도 암컷에게 대접을 받는다는 결과를 얻었다. 다른 색의 마커를 색칠하기도 하고, 인위적인 냄새를 갖게도 했으나, 빨간 색칠만 부계 우성에 변화를 가져왔다. 조류 전문가에 의하면 깃털은 새의 건강을 반영한다고 한다.

“우리의 최종 목표는 특정 수컷 제비가 ‘멋진 외모’를 유지하는 비결을 찾아내는 것”이라고 이번 연구에 참여했던 케븐 맥그로가 밝혔다.

“태양으로부터 받는 적외선의 양, 깃털을 얼룩지게 하는 박테리아가 가슴 깃털의 색에 영향을 미칠 것으로 예측하고 있으며 아마도 최고의 수컷은 많은 시간을 들여 부리로 깃털을 다듬고 깃털 보호에 공을 들이는 새일 것”이라고 그는 덧붙였다.



http://www.sciencedaily.com/releases/2005/10/051003233317.htm





Date: 2005-10-04

Looks Matter To Female Barn Swallows
ITHACA, N.Y. -- Even after they have paired with a male, the female North American barn swallow still comparison-shops for sexual partners. And forget personality; the females judge males by their looks -- the reddish color of the males' breast and belly feathers.
If the male's red breast is not as dark as other males in the population, the female is more likely to leave him and then secretly copulate with another male, according to a Cornell University study featured on the cover of the journal Science (Sept. 30, 2005).

"The bad news for male swallows is the mating game is never over," said lead author Rebecca Safran, who conducted the study while a Cornell postdoctoral researcher in ecology and evolutionary biology, and in the Cornell Laboratory of Ornithology. "It is dynamic and continual. This is something that most humans can relate to -- think of how much time and money we spend on our looks and status long after we have established stable relationships."

Barn swallow (Hirundo rustica erythrogaster) males have a wash of reddish-chestnut color from their throats to their bellies, and this color varies among birds from very pale red-brown to a dark rusty-red. Like many songbirds, half of all male barn swallows typically care for at least one young chick that was actually fathered by another bird. The researchers used this widespread phenomenon of cheating to test the factors that may keep a female barn swallow faithful to her mate. Sometimes males even rear an entire nest of illegitimate young.

After all pairs had laid their first set of eggs, Safran removed the eggs so that the females would mate again. Before the females chose their mates for their second nest, Safran captured the males and randomly assigned them to one of three treatments. She either painted their throats, breast and belly feathers with a red marker to enhance their feathers to match the darkest -- and most attractive -- males in the population, or left them alone or painted them with a clear marker to ensure that results were not biased by the coloring process. Then she let the pairs breed again. She conducted comparative DNA tests on the offspring from the first and second nests.

In the research, all 30 females remained socially paired with their original male mate, but they were sexually active with other males. The males with enhanced color fathered a substantially larger percentage of offspring in their second nests. Males whose color was unchanged fathered the same number or fewer chicks than they had in their first nests. "The study shows that the females are paying close attention to these signals and that they respond quickly to changes in their mate's appearance," said Safran.

The reddish breast and belly feathers indicate a male's quality, such as his health, status or ability to raise young, Safran speculates.

The actual cue that female barn swallows use to assess potential mates differ according to regional tastes. For example, classic studies have shown that in the very closely related European barn swallow (H. rustica rustica), males with long tail feathers attract more mates. Although many previous studies have investigated mating patterns in birds and other animals, this is the first study of its kind to meticulously rule out biases such as age, size and initial variation in signals of male quality, like coloration, and to demonstrate that mate-selection decisions are continual and dynamic. The results of the study have implications for the evolution and upkeep of showy ornamental traits -- such as a peacock's tail or a deer's antlers -- that are costly for males to maintain but give them an edge over rival males. "If females are assessing mates on a day-to-day basis, it explains why males continue to maintain costly ornaments even when they might appear to have served their purpose," said co-author Irby Lovette, assistant professor and director of the Cornell Lab of Ornithology's Evolutionary Biology program.

"Our goal is now to understand how certain males keep a better plumage than others," said Kevin McGraw, Cornell Ph.D. '03, one of the co-authors who is now an assistant professor at Arizona State University in Tempe. "Factors like ultraviolet radiation from the sun, soiling and even feather degrading bacteria are known to affect the color of bird feathers once they are grown, and perhaps the best males are those who spend more time preening and protecting their plumage."

The paper's other co-author is Colby Neuman, Cornell B.S. '05. In early September, Safran began a new position as a postdoctoral researcher at Princeton University. Supporters of the study included: the National Science Foundation, the American Association of University Women, the American Ornithologists' Union and the Animal Behavior Society.

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