Ramos Margarita, Irschick Duncan J, Christenson Terry E
Department of Ecology and Evolutionary Biology, 310 Dinwiddie Hall, Tulane University, New Orleans, LA 70118, USA.
Proc Natl Acad Sci U S A. 2004 Apr 6;101(14):4883-7. doi: 10.1073/pnas.0400324101. Epub 2004 Mar 19.
One potential consequence of sexual size dimorphism is conflict among characters. For example, a structure evolved for reproduction can impair performance during other activities (e.g., locomotion). Here we provide quantitative evidence for an animal overcoming an evolutionary conflict generated by differential scaling and sexual size dimorphism by obligatorily removing an undamaged reproductive organ, and thus dramatically enhancing its locomotor performance. The spider genus Tidarren (Araneae, Theridiidae) is interesting because, within several species presenting extreme sexual size dimorphism (males representing approximately 1% of the total mass of the female), males voluntarily remove one of their two disproportionately large pedipalps (modified copulatory organs; a single one represents approximately 10% of the body mass in an adult) before achieving sexual maturity. Whether the left or right pedipalp is removed appears to be random. Previous researchers have hypothesized that pedipalp removal might enhance locomotor performance, a prediction that has remained untested. We found that, for male Tidarren sisyphoides, maximum speed increased (44%) significantly and endurance increased (63%) significantly after pedipalp removal. Furthermore, spiders with one pedipalp moved approximately 300% greater distances before exhaustion and had a higher survival after exertion than those with two pedipalps. Removal of the pedipalp may have evolved in male Tidarren because of enhanced abilities to search for females (higher endurance and survival after exertion) and to out-compete rival males on the female's web (higher maximum speed). Our data also highlight how the evolution of conflicts can result in the evolution of a novel behavior.
两性体型差异的一个潜在后果是性状之间的冲突。例如，为繁殖而进化出的结构可能会损害其他活动（如运动）时的表现。在此，我们提供了定量证据，证明一种动物通过强制性地移除一个未受损的生殖器官，克服了由异速生长和两性体型差异产生的进化冲突，从而显著提高了其运动表现。蜘蛛属Tidarren（蜘蛛目，球蛛科）很有趣，因为在几个呈现极端两性体型差异的物种中（雄性约占雌性总质量的1%），雄性在性成熟前会主动移除其两个比例失调的大螯肢之一（经过改造的交配器官；单个螯肢在成年个体中约占体重的10%）。移除左螯肢还是右螯肢似乎是随机的。先前的研究人员推测，螯肢移除可能会提高运动表现，但这一预测尚未得到验证。我们发现，对于雄性Tidarren sisyphoides来说，移除螯肢后，最大速度显著提高（44%），耐力显著增加（63%）。此外，与拥有两个螯肢的蜘蛛相比，只有一个螯肢的蜘蛛在精疲力竭前移动的距离大约多300%，并且在运动后的存活率更高。雄性Tidarren进化出移除螯肢的行为，可能是因为寻找雌性的能力增强了（更高的耐力和运动后的存活率），以及在雌蛛的蛛网上战胜竞争对手雄性的能力增强了（更高的最大速度）。我们的数据还突出了冲突的进化如何导致新行为的进化。
