Does Development Bias the Evolution of Beetle Horns?

埃姆伦9807932许多种类的甲虫都有只由雄虫产生的“角”。这些角可以是极端的(就像麋鹿的鹿角一样戏剧性)，雄性在角的生产上的投资被认为是巨大的。在许多甲虫物种中，只有一些雄性甲虫产生角。其他雄性则完全无家可归。在金龟属(鞘翅目：金龟科)的大多数物种中，雄性角的表达是兼性的，取决于雄性是否长得超过阈值体型：雄性长得超过这个大小就会产生角，而没有达到这个大小的雄性就不会。雄性角的兼性表达提供了一个不同寻常的机会来研究角是如何发育的，以及角对雄性来说是否“昂贵”。先前的研究表明，将发育资源分配给角生产的男性被迫通过减少对其他特征的分配来进行补偿，包括眼睛。这表明在甲虫发育过程中可能存在分配权衡，这限制了可以产生的甲虫形状的范围，这些也可能限制了甲虫属内的进化方向。在这里，PI通过(1)使用对发育幼虫的操纵实验来证实资源分配权衡的存在和性质，以及(2)测试预测从这种机制中产生的偏差是否在分类群之间的形状变化中明显地表现出来，从而扩展了他之前的工作。这项研究将加深我们对发育机制和进化变化之间关系的理解，以及对甲壳虫角等夸张的第二性特征产生的“代价”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.