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，这一挑战早在查尔斯·达尔文之前就存在。尽管物种形成在概念上很简单，涉及防止不同种群杂交的特征的进化，但仍存在关键的知识差距。例如，为什么新的姐妹物种通常是从地理上孤立的种群开始的，是什么选择性力量导致了分歧？当孤立的种群重新聚集在一起时会发生什么，这对完成物种形成起到了作用吗？哪些基因变化有助于物种的进化？一种新的想法提出，执行关键功能(细胞中的能量产生)的核和线粒体基因编码的蛋白质在地理上孤立的种群之间存在分歧，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，理解物种起源的一个新问题是，这种线粒体-核共同进化是否可能导致物种之间的杂交功能障碍。我们提出的由NSERC资助的研究解决了这些问题，重点是春季窥视者，一种小型北美树蛙。先前的工作揭示了一个动态的进化史，有3个起源于避难所的核谱系，以及明显的次级接触区域。我们发现雄性广告叫声和行为在不同血统之间存在差异(从地面或栖息地叫喊)。我们将使用回放实验来测试雌性青蛙是否感知到叫声的差异，并使用石膏模型青蛙来评估从栖息叫声的生理成本(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孤立的谱系之间接触的结果。我们将使用功能基因组学、生理学和分子进化的方法来测试由于核和线粒体编码蛋白之间的不匹配而导致的杂交成本。对于两种春蛙的同类，西部和北方的合唱青蛙，我们将使用生态位模型和基因组学来测试二次接触的结果，以及物种间的相互作用或非生物因素对物种分布的影响是否更重要。这项研究将为至少4名博士、3名硕士和10名理科学生提供基因组学、定量方法和专业发展方面的主要培训。这项工作将基因组学、生理学、生物地理学和空间生态学的观点结合在一起，帮助加拿大走在物种形成研究的前沿。它帮助我们了解哪些因素决定了物种范围，以及它们如何随着过去的气候变化而变化，并可以为濒危物种的保护战略提供投入；例如，如何最好地保持进化潜力，以及物种的分布可能如何受到气候变化的影响。我还将利用NSERC的研究来确保加拿大濒危物种保护研究的其他机会。

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.