Does Development Bias the Evolution of Beetle Horns?

埃姆伦9807932 许多种类的甲虫都有只由雄性产生的“角”。这些角可以是极端的（如麋鹿的鹿角），雄性对角的生产投资被认为是巨大的。在许多种类的甲虫中，只有部分雄性长角。其他雄性则无家可归在Onthophagus属（鞘翅目：金龟子科）的大多数物种中，雄性角的表达是兼性的，并且取决于雄性是否长得比阈值身体尺寸大：雄性长得比这个尺寸大会产生角，而雄性没有达到这个尺寸不会。 雄性角的兼性表达提供了一个不寻常的机会来研究角是如何发育的，以及角是否对雄性来说是“昂贵的”。先前的研究表明，男性分配发展资源的角生产被迫补偿减少分配给其他特征，包括眼睛。这表明，可能有分配权衡操作过程中甲虫的发展，限制了范围内的甲虫形状，可以生产，这些也可能限制属内的进化方向。在这里，PI扩展了他以前的工作，（1）使用发育幼虫的操纵实验来确认资源分配权衡的存在和性质，以及（2）测试预测从这种机制产生的偏差是否表现在分类群之间的形状变化中。这项研究将增强我们对发育机制与进化变化之间关系的理解，并提高我们对与甲虫角等夸张第二性征产生相关的“成本”的理解。

Emlen 9807932 Many beetle species have "horns" which are only produced by males. These horns can be extreme (as dramatic as the antlers of elk), and investment by males into the production of horns is presumed to be substantial. In many beetle species only some of the males produce horns. other males being completely homless. In most species of the genus Onthophagus (Coleoptera: Scarabaeidae), male horn expression is facultative, and depends on whether or not a male grows larger than a threshold body size: males growing larger than this size produce horns, whereas males not attaining this size do not. Facultative expression of male horns provides an unusual opportunity to study how horns develop, and whether horns are "costly" to males to produce. Prior research revealed that males allocating developmental resources to horn production were forced to compensate by reducing allocation to other traits, including eyes. This suggests that there may be allocation tradeoffs operating during beetle development which restrict the range of beetle shapes that can be produced, and these may also restrict the directions of evolution within the genus. Here the PI extends his prior work by (1) using manipulative experiments on developing larvae to confirm the existence and nature of resource allocation tradeoffs, and (2) testing whether the biases predicted to arise from such a mechanism are manifest in the shape variation among taxa. This study will enhance our understanding of the relationship between developmental mechanisms and evolutionary change, as well as improve our understanding of the "costs" associated with the production of exaggerated secondary sexual characters like beetle horns.