The roles of geographical isolation, secondary contact, and mitonuclear disequilibrium in speciation

生物学中一个持久的挑战是理解新物种是如何产生的，这个挑战早在查尔斯·达尔文之前就存在了。虽然物种形成在概念上很简单，涉及到防止不同种群杂交的特征的进化，但存在关键的知识空白。例如，为什么新的姊妹物种通常是从地理上孤立的种群开始的，是什么选择的力量导致了分化？当孤立的种群重新聚集在一起时会发生什么，这在完成物种形成中起作用吗？哪些基因变化促成了物种的进化？一种新的观点认为，由核和线粒体基因编码的蛋白质执行关键功能（细胞中的能量产生），在地理上孤立的种群中产生分歧，种群之间的杂交适应性较低，因为核和线粒体编码的蛋白质不能很好地协同工作。因此，了解物种起源的一个新问题是，线粒体-核共同进化是否会导致物种之间的杂交功能失调。我们提议的nserc资助的研究解决了这些问题，重点是春天窥视者，一种小型的北美树蛙。以前的工作揭示了一个动态的进化史，有3个核谱系起源于避难所，并有明确的二次接触区。我们发现不同血统的雄性鸣叫和行为（从地面或栖息处鸣叫）存在差异。我们将使用回放实验来测试雌性是否感知到呼叫差异，并使用石膏模型来评估从栖息处呼叫的生理成本（例如蒸发水分损失）。在5个已知的接触区，我们将结合基因组学、呼叫分析和回放来评估以前分离的谱系之间接触的结果。我们将使用功能基因组学、生理学和分子进化方法来测试由核和线粒体编码蛋白质不匹配引起的杂交成本。我们将利用生态位模型和基因组学方法，对春蝉的两个同系物——西部和北方合唱蛙——进行二次接触的结果测试，以及种间相互作用或非生物因素在形成物种分布中是否更重要。这项研究将为至少4名博士、3名硕士和10名学士提供基因组学、定量方法和专业发展方面的一流培训。这项工作有助于将加拿大置于物种形成研究的前沿，将基因组学、生理学、生物地理学和空间生态学的观点结合在一起。它帮助我们了解是什么因素塑造了物种的范围，以及它们是如何随着过去的气候变化而变化的，并可以为濒危物种的保护策略提供输入；例如，如何最好地保持进化潜力，物种分布如何受到气候变化的影响。我还将利用NSERC的研究，为加拿大濒危物种的保护研究争取其他机会。

One of the enduring challenges in biology is understanding how new species arise, a challenge that predates Charles Darwin. Although speciation is conceptually simple, involving the evolution of traits that prevent interbreeding of diverged populations, there are key knowledge gaps. For example, why do new sister species often begin as geographically isolated populations and what selective forces cause divergence? What happens when isolated populations come back together, and does this play a role in completing speciation? What genetic changes contribute to the evolution of species? One new idea proposes that proteins encoded by nuclear and mitochondrial genes that perform critical functions (energy production in cells) diverge in among geographically isolated populations, with hybrids between populations having lower fitness because nuclear and mitochondrial encoded proteins do not work well together. Thus a new question for understanding species origins asks if such mitochondrial-nuclear coevolution might cause hybrid disfunction between species. Our proposed NSERC-funded research addresses these questions, focusing on the spring peeper, a small North American treefrog. Previous work reveals a dynamic evolutionary history with 3 nuclear lineages that originated in refugia, and clear zones of secondary contact. We found differences in male advertisement calls and behavior among lineages (calling from the ground or perches). We will use playback experiments to test whether females perceive call differences, and plaster model frogs to assess physiological costs of calling from perches (e.g. evaporative water loss). At 5 known contact zones we will combine genomics, and call analysis and playbacks to evaluate outcomes of contact between previously isolated lineages. We will use functional genomics, physiological, and molecular evolution approaches to test costs of hybridization caused by mismatch between nuclear and mitochondrial encoded proteins. For two congeners of the spring peeper, western and boreal chorus frogs, we will use niche modeling and genomics to test the outcomes of secondary contact, and if interspecific interactions or abiotic factors are more important in shaping species distributions. This research will provide premier training for a minimum of 4 PhD, 3 MSc and >10 BSc students in genomics, quantitative methods, and professional development. This work helps put Canada at the forefront of speciation research, bringing together perspectives from genomics, physiology, biogeography, and spatial ecology. It helps us to understand what factors shape species ranges and how they have shifted in response to past climate change, and can provide inputs into conservation strategies for species at risk; e.g. how best to retain evolutionary potential, and how species' distributions might be affected by climate change. I will also leverage NSERC research to secure other opportunities for conservation studies of Canadian species at risk.