为什么鸟类动物雄性的羽毛颜色美丽鲜明,而雌性的则相
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为什么鸟类动物雄性的羽毛颜色美丽鲜明,而雌性的则相
在动物界,从较为低等的蜘蛛、昆虫等节肢类动物,直至高等的鸟类、哺乳类动物等,在众多的动物类群中,雌雄间都存在着不同程度的差异。这种差异不仅表现在外生殖器上,而且还表现在体型、体色、声音乃至行为上,这些差异即为生物学上的性二型。对于大多数动物来说,人们通过观察这些外形上的不同即可确认雌雄个体。对于性二型不明显的动物,科学家也研究出了一些新的方法进行辨别。
动物界也“男女有别”
在动物类群中,雌雄间除在外生殖器上存在差异外,在体态、体色、声音乃至行为上也存在差异,这些差异被称为动物的“性二型”。
许多动物具有明显的性二型。一些雄性虾、蟹具有雌性远远不能与之相媲美的大螯,彰显出“男子汉”的威猛。很多蜘蛛却是“阴盛阳衰”,雌蛛体型远大于雄蛛,有些种类的雌蛛体型是雄蛛的1000〜1500倍,交配时雌蛛甚至会吃掉雄蛛,这些可怜的“小丈夫”也算是为爱,为下一代“鞠躬尽瘁,死而后已”了。庞大的昆虫家族更是不乏性二型的物种。一些蛾类的雄虫长有翅,雌虫则无翅,或雄虫触角为羽毛状,雌虫则为丝状;许多雄虫还具有发声的器官,借助优美的鸣声打动雌虫的芳心。
进化地位较高的鸟类和哺乳类动物,更是将性二型发挥得淋漓尽致。雄性孔雀具有如屏风般华贵的尾羽,雄性鸳鸯身着五彩斑斓的羽毛。一些小型雄鸟则在喉部、眉纹、胸部等多处存在着明显区别于雌鸟的鲜艳羽色,而这些鸟类的雌鸟则全部“身披素装”,远不如它们的“夫婿”光彩夺目。还有一些鸟类的雄鸟身上出现了冠、垂肉、隆起、角、气囊、翎羽等各种各样的漂亮装饰。有些鸟类的雌雄间的鸣叫声也常常有着很大的差别。哺乳类的雄性也毫不逊色,它们往往体型威猛,长毛獠牙,齿尖爪利,更具冒险行为。雄狮身材魁梧,“长发”飘逸,而雌狮则身材纤细,“短发”飒爽
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