Behavioral Dysfunction and the Evolution of Reproductive Isolation between Species

不同物种之间的杂交是一种常见现象，它提出了一个基本问题：如果物种可以杂交，是什么保持了它们的独特特征，并使物种分开？这个问题的答案通常集中在杂交后代上：如果杂交后代不能生存或繁殖，那么物种之间的基因交换将受到限制，物种将保持分离和独特。迄今为止，大多数探索杂交种表现不佳的可能性的工作都集中在杂交种的生理和形态上。很少有研究调查杂交是否表现出阻止它们繁殖的改变行为，从而限制了进一步的基因交换。本研究旨在评估行为对赤足蟾蜍杂交的影响。通过这样做，这项研究将为行为如何帮助维持物种边界提供重要的见解。这项研究对了解生物多样性和保护可能与其他物种杂交的濒危物种具有重要意义。在开展这项工作时，PI将培训本科生和研究生的研究技术和公共宣传。事实上，PI和她的实验室成员将通过在北卡罗来纳自然科学博物馆的工作，参与北卡罗来纳及其他地区的公众宣传。具体来说，他们将在博物馆的每日星球剧院发表演讲，该剧院为博物馆游客提供现场节目，并向北卡罗莱纳州的K-12学校、老年中心和图书馆提供现场演讲。这些演讲的视频以播客的形式被上传到iTunes大学（每月有2万次下载）和博物馆的网站（每年有大约100万次点击）。通过博物馆网站发布的节目可供任何地方的用户使用。在广泛使用的生物物种概念下，物种被定义为不交换基因的生物群体；它们拥有进化的特征，可以防止基因在它们之间流动。这类“隔离机制”的一个主要类别包括在杂交后代中产生低适应性的特征，从而阻止它们与亲本群体回交。由于杂交不适应对物种形成过程至关重要，阐明杂交不适应的原因是理解物种形成的核心。大多数物种形成研究都集中在杂交不适应的三个原因上：存活率降低、生育力降低和在亲本生态位中成功的可能性降低。相比之下，行为在杂交种适应不良中的作用，特别是杂交种可能表现出功能失调的生殖行为，研究相对不足。然而，有活力的、可生育的杂交物种可能无法对求爱信号做出适当的反应，或者，它们可能会表达配偶偏好，从而降低与健康增强的配偶交配的可能性。这种不正常的繁殖行为可能会使有活力的、可育的杂交种“行为不育”，从而成为物种之间潜在的关键隔离机制。这项工作将确定杂交的掌足蟾蜍是否表现出功能失调的生殖行为，以及这种行为是否解释了自然种群中基因交换的模式。利用两种自然杂交蟾蜍，研究将：1)评估杂交对繁殖机会的反应；2)建立杂交配偶偏好；3)衡量配偶偏好的适合度结果；4)确定杂交后代在繁殖方面的投入是否较少；5)确定田间杂交交配模式。这些项目将共同确定行为在物种边界起源和维持中的作用。

The breeding of different species, called hybridization, is a common phenomenon that raises a fundamental problem: if species can interbreed, what maintains their distinct characteristics and keeps species separated? Answers to this question have usually focused on hybrid offspring: if hybrids cannot survive or reproduce, then gene exchange between species will be restricted and species are kept separate and distinct. To date, most work exploring the possibility that hybrids perform poorly focuses on hybrid physiology and morphology. Few studies have investigated whether hybrids show altered behaviors that prevent them from reproducing and thereby limiting further gene exchange. The proposed work evaluates the impact of behavior on hybridization in spadefoot toad species. By doing so, the research will provide important insights into how behavior acts to help maintain species boundaries. The research has critical implications for understanding biodiversity and conservation of endangered species that could hybridize with others. In carrying out this work, the PI will train undergraduates and graduate students in both research techniques and public outreach. Indeed, the PI and her lab members will engage in public outreach in North Carolina and beyond through work at the North Carolina Museum of Natural Sciences. Specifically, they will give talks in the museum's Daily Planet Theater, which provides live programming to museum visitors and live streaming of presentations to K-12 schools, senior centers, and libraries throughout North Carolina. Videos of these presentations are uploaded as podcasts onto iTunes University, on which the museum receives 20,000 downloads a month, and to the museum's website, which receives approximately one million hits per year; programs distributed via the museums website are available to users anywhere.Under the widely used biological species concept, species are defined as groups of organisms that do not exchange genes; they possess evolved features that prevent gene flow between them. A major class of such 'isolating mechanisms' includes traits that engender low fitness in hybrid offspring, thereby preventing them from backcrossing to the parent populations. Because hybrid maladaptation is crucial to the speciation process, clarifying the causes of hybrid maladaptation is central to understanding speciation. Most speciation research has focused on three causes of hybrid maladaptation: decreased survival, reduced fertility, and decreased likelihood of succeeding in either parental niche. In contrast, the role of behavior in hybrid maladaptation, specifically that hybrids might exhibit dysfunctional reproductive behavior, has been relatively understudied. Yet, viable, fertile hybrids might fail to respond appropriately to courtship signals, or, alternatively, they might express mate preferences that reduce their likelihood of mating with fitness-enhancing mates. Such dysfunctional reproductive behavior could render viable, fertile hybrids 'behaviorally sterile', thereby acting as a potentially key isolating mechanism between species. The proposed work will ascertain if hybrid spadefoot toads display dysfunctional reproductive behaviors, and whether such behavior explains patterns of gene exchange in natural populations. Using two species of naturally hybridizing toads, the research will: 1) evaluate hybrid responses to breeding opportunities; 2) establish hybrid mate preferences; 3) measure the fitness consequences of mate preferences; 4) ascertain whether hybrids invest less in reproduction; and 5) determine patterns of hybrid mating in the field. Together, the projects will identify behavior's role in the origins and maintenance of species boundaries.