2009年3月21日 星期六

南非扁石蜥男扮女裝以閃避同性攻擊

以下是"生物谷"中一篇譯自Whiting et al. (2009)的文章 (已轉為正體中文), 但是這篇譯文完全搞錯了. 這個研究團隊是由澳洲與南非學者所組成的, 但是他們所研究的蜥蜴是南非產環尾蜥科的扁石蜥. 根本不是澳洲的種類.

在自然界中,當年輕的雄蜥蜴向雌蜥蜴尋求交配時,它們經常會遭到其他成年雄蜥蜴的攻擊和驅離。為順利地完成交配,這些年輕的雄蜥蜴有時會改變身體的顏色,讓自己看起來更像是一隻“雌蜥蜴”,從而麻痹其他雄性蜥蜴並避免遭到攻擊。

在最新一期出版的英國《皇家學會學報B》(Proceedings of the Royal Society B)上,澳大利亞國立大學生物學院副教授斯科特•基奧詳細介紹了他的這一新發現。斯科特•基奧說,“在這一群體中,成年雄性蜥蜴的顏色極其豔麗,而且它們具有極強的領地意識。而雌性蜥蜴則通常是淡褐色。因此,年輕的雄性蜥蜴只有自覺地改變自己腹部的顏色,這樣它們會在性成熟之前看起來仍然像是雌性。”最初,雌性蜥蜴也會允許年輕雄性與之交配,只要不被體型較大的、佔有欲強的成年雄性發現,否則這些成年雄性蜥蜴會驅趕和撕咬年輕的對手。這些偽裝起來的年輕蜥蜴只有假裝成雌性,才能夠避免被攻擊而擁有繁殖的機會。

斯科特•基奧認為,“如果它們只是改變背部或側部的顏色,那就很容易被辨認出是雄性,也就根本沒有機會靠近雌性。”這種性別伎倆可以讓年輕雄性蜥蜴在繁殖季節獲得性優勢。它們雖然看起來像是雌性,事實上已經是性成熟的雄性。這樣他們就可能一整個繁殖季節都會與雌性呆在一起,不過不管它們怎麼偽裝,它們的氣味仍然是雄性的氣味。為了驗證這一事實,研究人員從野外捕獲了一些蜥蜴,並將能夠表明它們性別的所有資訊素都去除掉。然後把分別帶有雄性或雌性氣味的雌性和假雌性蜥蜴全部放到典型的成年雄性蜥蜴面前。這些成年蜥蜴會用它們的舌頭去品嘗這種化學氣味,標注為雌性的假雌性立即有所反應,而標注為雄性的假雌性則沒有這種反應。因此研究人員認為,雄性蜥蜴會被外表迷惑,但不會被氣味迷惑。

此外,研究還發現這些假雌性會刻意與那些愛“嚼舌根”的雄性保持距離,以防止它們的這種秘密洩露出去。其他動物,如魚類,通常也會採用性別偽裝取得性優勢。這項研究是首次發現爬行類動物也有這種伎倆,同時該研究最特別之處在於分離了視覺和嗅覺的聯繫。研究人員還發現,並非是所有年輕雄性蜥蜴都會這種偽裝技術。蜥蜴的變色能加很強,特別是避役類蜥蜴以其善於變色獲得“變色龍”的美名。變色樹蜥在陽光照射的乾燥地方通身顏色變淺而頭頸部發紅,當轉入陰濕地方後,紅色逐漸消失,通身顏色逐漸變暗。蜥蜴的變色是一種非隨意的生理行為變化。它與光照的強弱、溫度的改變、動物本身的興奮程度以及個體的健康狀況等有關

以下是Whiting et al. (2009)原文的摘要
Understanding what constrains signalling and maintains signal honesty is a central theme in animal communication. Clear cases of dishonest signalling, and the conditions under which they are used, represent an important avenue for improved understanding of animal communication systems. Female mimicry, when certain males take on the appearance of females, is most commonly a male alternative reproductive tactic that is condition-dependent. A number of adaptive explanations for female mimicry have been proposed including avoiding the costs of aggression, gaining an advantage in combat, sneaking copulations with females on the territories of other males, gaining physiological benefits and minimizing the risk of predation. Previous studies of female mimicry have focused on a single mode of communication, although most animals communicate using multiple signals. Male Augrabies flat lizards adopt alternative reproductive tactics in which some males (she-males) mimic the visual appearance of females. We experimentally tested in a wild population whether she-males are able to mimic females using both visual and chemical signals. We tested chemical recognition in the field by removing scent and relabelling females and she-males with either male or female scent. At a distance, typical males (he-males) could not distinguish she-males from females using visual signals, but during close encounters, he-males correctly determined the gender of she-males using chemical signals. She-males are therefore able to deceive he-males using visual but not chemical signals. To effectively deceive he-males, she-males avoid close contact with he-males during which chemical cues would reveal their deceit. This strategy is probably adaptive, because he-males are aggressive and territorial; by mimicking females, she-males are able to move about freely and gain access to females on the territories of resident males.