Laboratory of Evolutionary Ecology, Graduate School of Environmental Science, Okayama University, Japan.
Evol Dev. 2012 Jul;14(4):363-71. doi: 10.1111/j.1525-142X.2012.00554.x.
Sexually selected exaggerated traits are often coupled with modifications in other nontarget traits. In insects with weapons, enlargements of nontarget characters that functionally support the weapon often occur (i.e. supportive traits). The support of sexual traits requires developmental coordination among functionally related multiple traits-an explicit example of morphological integration. The genetic theory predicts that developmental integration among different body modules, for which development is regulated via different sets of genes, is likely to be coordinated by pleiotropic factors. However, the developmental backgrounds of morphological integrations are largely unknown. We tested the hypothesis that the juvenile hormone (JH), as a pleiotropic factor, mediates the integration between exaggerated and supportive traits in an armed beetle Gnatocerus cornutus. During combat, males of this beetle use exaggerated mandibles to lift up their opponents with the supportive traits, that is, the head and prothoracic body parts. Application of methoprene, a JH analog (JHA), during the larval to prepupal period, induced the formation of large mandibles relative to the body sizes in males. Morphometric examination of nontarget traits elucidated an increase in the relative sizes of supportive traits, including the head and prothoracic body parts. In addition, reductions in the hind wing area and elytra length, which correspond to flight and reproductive abilities, were detected. Our findings are consistent with the genetic theory and support the idea that JH is a key pleiotropic factor that coordinates the developmental integration of exaggerated traits and supportive characters, as well as resource allocation trade-offs.
性选择导致的夸张特征通常与其他非目标特征的改变有关。在具有武器的昆虫中，与武器功能相关的非目标特征通常会增大（即支持性特征）。性特征的支持需要功能相关的多个特征之间的发育协调——这是形态整合的一个明确例子。遗传理论预测，不同身体模块之间的发育整合，其发育受不同的基因集调控，很可能由多效因子协调。然而，形态整合的发育背景在很大程度上是未知的。我们检验了这样一个假设，即保幼激素（JH）作为一个多效因子，介导了具有武器的甲虫 Gnatocerus cornutus 中夸张特征和支持性特征之间的整合。在战斗中，这种甲虫的雄性用夸张的大颚抬起它们的对手，这是通过支持性特征，即头部和前胸体部分来实现的。在幼虫到预蛹期应用保幼激素类似物（JHA），会诱导雄性大颚相对于身体大小形成更大的比例。对非目标特征的形态学检查表明，支持性特征的相对大小增加，包括头部和前胸体部分。此外，还检测到与飞行和生殖能力相对应的后翅面积和鞘翅长度的减少。我们的研究结果与遗传理论一致，支持 JH 是一个关键的多效因子，它协调了夸张特征和支持性特征的发育整合以及资源分配的权衡。
