The Evolutionary Genetics of an Adaptive Maternal Effect: Egg Size Plasticity in a Seed Beetle

福克斯9807315 在许多生物体中，雌性的环境提供了其后代将遇到的环境条件的可靠指标。 在这种情况下，母体效应可能演变为跨代表型可塑性的机制，从而响应于预测性环境线索（例如高或低的宿主密度，短或长的光周期），母亲可以改变她所产蛋的类型，或者可以在她的后代中编程发育开关，产生为线索预测的环境条件做好准备的后代。 这些母性效应通常有遗传基础，在许多生物体中似乎是适应性的。 然而，人们对母性效应的进化遗传学或选择对母性效应的性质和后果知之甚少，因此它们对自然选择做出反应的潜力在很大程度上仍然是推测性的。 该提案描述了一系列旨在测试解释种子甲虫（Stator limbatus）卵大小、卵数量和卵大小可塑性（明显的适应性母体效应）进化的假设的实验。 具体而言，本研究将（1）量化的来源，这种表型变异（遗传，母亲，父亲和环境）的鸡蛋大小和鸡蛋大小可塑性的群体内的S。具缘的;（2）验证了多花尾孢子虫幼虫在种子上发育时，选择提高存活率的假设。（3）验证了增加繁殖力的选择导致较小卵大小的进化的假设;（4）检验卵大小可塑性的进化受到响应于相思树的卵的大小之间的遗传相关性的约束的假设。（catclaw acacia）和卵的大小。（5）验证了寄主间的遗传相关性是通过对卵大小和卵大小可塑性的选择而进化的假说。 母性效应在自然界中普遍存在;它们在产生我们观察到的许多表型模式和种群动态中很重要，并且通常是种群对自然选择反应的重要组成部分。 事实上，对选择的进化反应可能通过母体效应表现出来，因此母体效应可能提供适应可变环境的机制。然而，母性效应的进化动力学，以及母性效应对性状的影响，却很少有人研究。 在实验室和田间实验中，可以证明选择有利于或反对母性效应的进化。 然而，证明选择有利于母体效应的进化并不足以证明母体效应已经进化为一种适应。同样严格的技术应用于行为，形态学和生活史的研究，现在需要应用于母性效应的研究，以确定适应性母性效应在自然界中有多普遍，以及母性效应仅仅作为父母和后代特征进化的结果而进化的频率。 这些实验的目的是（a）使用严格的定量遗传实验设计研究适应性母性效应（种子甲虫Stator limbatus的卵大小可塑性）的进化遗传学，以及（B）模拟自然选择对母性效应的影响，因为它被认为发生在自然界中，以研究母性效应和相关生活史特征的进化。

Fox 9807315 In many organisms, a female's environment provides a reliable indicator of the environmental conditions that her progeny will encounter. In such cases, maternal effects may evolve as mechanisms for trans-generational phenotypic plasticity, whereby, in response to a predictive environmental cue (such high or low host density, short or long photoperiod), a mother can change the type of eggs that she makes, or can program a developmental switch in her offspring, producing offspring prepared for the environmental conditions predicted by the cue. These maternal effects often have a genetic basis, and appear to be adaptive in many organisms. Yet little is understood about the evolutionary genetics of maternal effects or the nature and consequences of selection on maternal effects, such that the potential for them to respond to natural selection remains largely speculative. This proposal describes a series of experiments designed to test hypotheses that explain the evolution of egg size, egg number, and egg size plasticity (an apparently adaptive maternal effect) in a seed beetle, Stator limbatus. Specifically, this research will (1) quantify the sources of this phenotypic variation (genetic, maternal, paternal, and environmental) in egg size and egg size plasticity within populations of S. limbatus; (2) test the hypothesis that selection for improved survivorship when larvae develop on seeds of Cercidium floridum (blue paloverde) results in the evolution of larger egg size; (3) test the hypothesis that selection for increased fecundity results in the evolution of smaller egg size; (4) test the hypothesis that the evolution of egg size plasticity is constrained by the genetic correlation between the size of eggs laid in response to Acacia greggii (catclaw acacia) and the size of eggs laid on C. floridum; (5) test the hypothesis that the genetic correlation across hosts evolves in response to selection on egg size and egg size plasticity. Maternal effe cts are ubiquitous in nature; they are important in generating many of the phenotypic patterns and population dynamics that we observe, and are often important components of population responses to natural selection. In fact, evolutionary responses to selection may be manifest through maternal effects, such that maternal effects may provide mechanisms for adapting to variable environments. However, the evolutionary dynamics of maternal effects, and characters influenced by maternal effects, have been little explored. In lab and field experiments, selection can be demonstrated to favor or oppose the evolution of maternal effects. However, demonstrating selection favoring the evolution of a maternal effect is not sufficient evidence to demonstrate that a maternal effect has evolved as an adaptation. The same rigorous techniques applied to studies of behavior, morphology, and life history need now be applied to the study of maternal effects to determine how pervasive adaptive maternal effects are in nature and how often maternal effects evolve simply as consequences of the evolution of parental and offspring characters. The objectives of these experiments are (a) to study the evolutionary genetics of an adaptive maternal effect (egg size plasticity in the seed beetle, Stator limbatus), using rigorous quantitative genetic experimental designs, and (b) to simulate natural selection on the maternal effect as it is thought to occur in nature to study the evolution of both the maternal effect and correlated life history characters.