【作者】 张建新；

【导师】 丁平；

【作者基本信息】 浙江大学 ， 动物学， 2010， 博士

【摘要】 雀形目扇尾莺属的部分物种具有一种奇特的身体特征变化模式,作为性特征存在的锲形尾羽,其繁殖羽时的长度短于冬羽时的长度。而性选择理论认为雌性青睐长尾羽的雄性个体,因此繁殖羽较短的尾羽可能不利于雄性个体在繁殖季进行占域和求偶。这种繁殖季性特征消退的奇特身体变化模式在自然界中比较少见并且产生及进化机制不明,可能意味着这些物种具有一种未知的生存和繁殖策略。我们提出假说认为：这些物种在冬羽时,利用长尾羽进行占域和求偶,在完成占域和求偶之后,再进行春季换羽,将冬羽的长尾羽换成繁殖羽的短尾羽。繁殖羽较短的尾羽空气动力学效果更好,有利于躲避敌害和提高繁殖率。为验证我们的假说,我们选取黄腹山鹪莺(Prinia flaviventris)和纯色山鹪莺(P. inornata)为研究对象,从2008年9月到2010年1月在广州市南沙地区,在野外通过雾网捕捉这两种鹪莺个体,使用面包虫和雀鸟饲料相混合的方法进行饲养,使用十字笼和斗笼等方法对其尾羽在配偶选择和雄雄竞争中的作用等方面进行研究,希望能够了解这种身体变化模式的产生机制和这种生存和繁殖策略的特征。雌性青睐实验的研究结果发现:黄腹山鹪莺的雌性个体青睐长尾羽的雄性个体,尾羽短的雄性个体通过增加跳动次数和求偶次数来吸引雌性,并且雌性的尾羽长度越长,所能够得到的雄性的求偶越多。我们的结果说明黄腹山鹪莺性特征的消失并不是由雌性青睐引起的,而是其它作用力超过了性选择的作用力所产生的。我们推测繁殖季躲避敌害和捕食压力所产生的自然选择压力,可能是造成繁殖季性特征消退的主要原因。雄雄实验的研究结果发现：已经开始换羽的短尾羽雄性和未开始换羽的长尾羽雄性获胜的次数相同,但是长尾羽雄性获胜却需要更多的打斗次数。我们的结果说明换羽并不会对雄雄竞争的结果产生影响,雄性即使在换羽后也不会因为尾羽短而在雄雄竞争中输于延迟换羽的雄性而失去配偶和领域,这可以有效的防止欺骗者的存在。我们的认为短尾羽较好的空气动力学效果可能能够增加短尾羽雄性的灵敏度,使其在打斗中获胜几率更高。通过对黄腹山鹪莺和纯色山鹪莺身体特征变化率的分析表明:在这两种鹪莺中,繁殖羽尾羽的变化率明显高于繁殖羽其它身体特征的变化率,并且高于冬羽所有身体特征的变化率。这个结果说明繁殖羽尾羽所承受的进化压力比冬羽的尾羽更加强烈。我们认为决定身体特征变化率的是作用于此身体特征的选择压力的强度,而不是选择压力的性质。我们推测这两种鹪莺独特的身体特征变化率模式的出现依赖两个前提条件。第一,自然选择作用于尾羽的时间和性选择作用于尾羽的时间错开。第二,自然选择的作用力强于性选择的作用力,而这恰好也是这两种鹪莺出现繁殖季性特征消退的原因。通过对黄腹山鹪莺和纯色山鹪莺身体特征对称性的分析表明：作为性特征的尾羽长度和对称性呈负相关,尾羽长度越长对称性越好；而包括跗蹠和趾长在内的骨质特征表现出了相反的特征,即对称性随着长度的增加而降低。我们的结果验证了对称理论,性特征的对称性是由性选择压力产生,只有适应性好的雄性才能够保持对称性好的性特征,这说明尾羽能够作为雄性适应性的信号。综上所述,我们认为繁殖季性特征消退的产生并不是由雌性青睐导致,是由于其它作用力超过了性选择作用力的原因。而身体特征变化率的研究也证实,这些物种繁殖季承受的进化压力更为强烈。繁殖季性特征的消退并不会对雄雄竞争的结果产生影响,这可以有效的防止欺骗者的存在。我们的研究结果虽然能够解释我们假说中的部分问题,例如配偶选择和限制欺骗者等问题,但是还无法完全理解这两种鹪莺独特身体特征变化模式,包括春季换羽的机制、雌性修饰和尾羽的空气动力学等很多重要问题需要解答。我们会开展更深入的研究,希望能够完整解释这种独特身体特征变化模式的产生机制和适应性意义。更多还原

【Abstract】 Some species of cisticolidae Passeriformes show a special pattern, that graduate tail which is served as sexual trait, of breeding plumage is shorter than that of winter plumage. This special pattern may be contradict with sexual selection theory, because females prefer males with longer tail and males with shorter tail may be disadvantage in mating choice and male-male competition. This special pattern is rare and unclear, and may indicate a new breeding and survival strategy which is unknown. We advance a hypothesis that:females of these species choose mate while males with longer tail of winter plumage, and then males moult to shorter tail after mating. Shorter graduated tail which is better aerodynamic effect, could save energy and be good for breeding. From September 2008 to January 2010, we captured yellow-bellied prinia (Prinia flaviventris) and plain prinia(Prinia inornata) with mistnet at Nansha area Guangdong city, and feed them with mixture of Alphitobius diaperinus and bird feedstuff. We used cross choice chamber to test whether female preference exist, and used fight cage to test whether moult would affect the male-male competition result.Results of female preference experiments showed that female preference of yellow-bellied prinia was still exist, and females prefered males with longer tail. Loss of male sexual traits was not caused by female preference, but other forces overcomed the force of sexual selection. This result is consistent with our hypothesis that tail of winter plumage may be used for sexual selection. We conjecture that natural selection forces include prey and breeding may be the main reason why sexual traits are lost in breeding season.Experiment of male-male competition showed that:moulting males whose tail was longer, won the game as many times as unmoulted males whose tail is shorter, but moulting males had to try more attacks when they win the game. Our result means that moult would not affect the male-male competition, and male which starts moult early, would not loss the mate and territory, and cheaters would be handicapped for this reason. We conjecture that better aerodynamic of shorter tail would be good for fighting.Coefficient of variation of body traits of yellow-bellied prinia and plain prinia showed that:tail of breeding plumage were more variable than other traits of breeding plumage, and more variable than all traits of winter plumage in both two species. Tails of breeding plumage which were naturally selected, were more variable than tails of winter plumage which were sexual trait. We conclude that morphological variation is determined by strength of selection force, but not kind of selection force. Special pattern of morphological variation of these two species appeared under two preconditions. First, natural selection and sexual selection are sperated at time. And then, natural selection is more intense than sexual selection in breeding season.Symmetry degree of tail increased with length of tail, but skeletal traits just like tarsus and claw was reverse with tail pattern. Our result consistent with symmetry theory, and symmetry of sexual triats were determined by sexual selection.We conclude that loss of sexual traits of breeding season is not caused by female preference, and other forces which are more intense than sexual selection may be the main reason. Coefficient of variation of body traits also proved that evolution force of breeding season is more intense. Loss of sexual traits would not affect the male-male competition, and cheaters would be handicapped for this reason.Our research could answer the some aspects of our hypothesis, but there are also many questions about this pattern include moult mechanism, female plumage and aerodynamic of tail are still unclear. We will conduct future research on these sides and try to explain the origin and mechanism of this special pattern.更多还原