Ancestral plasticity and mating system evolution in the stickleback radiation

当一个祖先种群入侵许多新的栖息地时，适应性辐射就会发生，而后代种群则会根据不同栖息地之间自然选择模式的差异而进化。最初，行为的转变可以缓冲种群在变化的条件下的变化，对不同环境的反应的差异可以决定哪些行为模式在随后的几年里暴露于选择中。因此，祖先可塑性的模式可能使种群倾向于向特定方向进化，并可能导致不同栖息地表达模式的重复进化，正如最近的一些适应性辐射所示。在冰期后三刺棘鱼（Gasterosteus aculeatus）的辐射中，古代海洋种群反复产生淡水种群，这些淡水种群具有形态和行为特征，使它们专门以浮游生物（沼泽型）或底栖无脊椎动物（底栖型）为食。先前的研究表明，在繁殖过程中，雌性的交配偏好与雄性的颜色和行为表达共同变化，并且底栖和沼泽种群的差异是可以预测的。然而，数据也提供了这些特征在海洋祖先中表达的表型可塑性的证据，这与淡水辐射中两种类型的可塑性的不同模式相似。这项研究将涉及饲养三种祖先的刺鱼，海洋种群，以及三种衍生的淡水底栖动物和沼泽种群。雄性的交配行为和颜色表达将与雌性在暴露于同类相食的觅食群体之前和之后的交配偏好进行比较，因为这些群体是这些特征中可塑性反应的触发因素。只有海洋和底栖鱼类才会形成这样的群体。海洋形式中的塑性表达式将用于推断祖先的条件，以便与派生类型中的条件进行比较。这项研究将有助于深入了解适应性辐射中可塑性的作用——这是进化生物学中一个令人兴奋的重要问题。另一个将被评估的问题是，在某些情况下，祖先表型的可塑性可能会导致雌性交配偏好与这种选择最初所青睐的特征的反应规范脱钩，这与信号和接收器特征应该紧密耦合的观点不一致。更广泛的影响：该研究将涉及在科学理论和实践方面培训至少15名本科生。克拉克大学提供了特别丰富的研究经验，对于那些进入五年级硕士课程的人来说，可以持续长达五年的时间，并发表一篇或多篇论文。从项目中收集的数据也将用于关注行为、统计和进化的实验室练习。中学和大学教师将能够从一个网站上免费下载练习和数据。最后，这项研究可能有助于保护主义者了解一对非常不寻常的刺鱼物种的消失，它们生活在加拿大不列颠哥伦比亚省的一个湖泊里。这一对已经失去了杂交，其中一个可能的解释是，浑浊度的增加降低了视觉信号的有效性，而视觉信号对分类交配至关重要。这项研究将使我们能够评估这一假设的合理性。

Adaptive radiation occurs when an ancestral population invades many novel habitats, and the daughter populations evolve in response to differences in the patterns of natural selection across habitats. Initially, shifts in behavior may buffer populations from the changing conditions, and differences in the responses to different environments can determine which behavior patterns are exposed to selection in the ensuing years. Thus, the patterns of ancestral plasticity could predispose populations to evolve in particular directions, and could lead to the repeated evolution of divergent patterns of expression across habitats as is seen in a number of recent adaptive radiations. In the post-glacial radiation of the threespine stickleback fish (Gasterosteus aculeatus), ancient oceanic populations have repeatedly given rise to freshwater populations that possess morphological and behavioral features that cause them to be specialized for feeding on plankton (limnetic type) or bottom-dwelling invertebrates (benthic type). Prior research has shown that female mating preferences covary with male color and behavior expression during breeding, and that benthic and limnetic populations differ predictably. However, data also offer evidence of phenotypic plasticity in the expression of these traits in the oceanic ancestor that parallels divergent patterns of plasticity of the two types in the freshwater radiation. This research will involve rearing sticklebacks from three ancestral, oceanic populations, and from three derived freshwater benthic and limnetic populations. Male nuptial behavior and color expression will be compared with female mating preferences before and after exposure to cannibalistic foraging groups, as these groups are the trigger for plastic responses in these traits. Such groups are formed only by oceanic and benthic fish. Plastic expression in the oceanic forms will be used to infer the ancestral condition for comparison with that in the derived types. This research should offer insight into the role of plasticity in adaptive radiation - an exciting and fundamentally important issue in evolutionary biology. Another question that will be evaluated is the intriguing possibility that ancestral phenotypic plasticity could, under certain scenarios, lead to the decoupling of female mating preferences and the norms of reactions of the traits original favored by this selection, a suggestion at odds with the view that signal and receiver characteristics should be tightly coupled. Broader Impact: The research will involve training at least 15 undergraduate students in scientific theory and practice. Clark University offers an especially rich research experience that, for those entering the fifth year masters program, can last as long as five years and result in one or more publications. Data collected from the project will also be used in laboratory exercises that focus on behavior, statistics and evolution. Secondary and college teachers will be able to download exercises and data from a web site free of charge. Finally, this research may help conservationists understand the loss of a very unusual pair of stickleback species that inhabited a single lake in British Columbia, Canada. This pair has been lost to hybridization, and one of the possible explanations is that increased turbidity decreased the effectiveness of visual signals critical to assortative mating. This research will allow us to evaluate the plausibility of this hypothesis.