The Drivers of Cytonuclear Discordance

野生动物中亲缘关系密切的雌性个体，如母亲和女儿、姐妹和表兄弟姐妹，在自然界中往往彼此更接近，而不是广泛地与远亲雌性混合在一起。随着时间的推移，雌性谱系出现了多样性，在大多数动物物种中，这种接近的模式被在只有几公里或更短的狭窄地理区域内并排出现的远亲雌性所打破。这种所谓的基因不一致，是我们从严格由母亲传给女儿的DNA中检测到的，它导致的模式与第一次世界大战的战壕没有什么不同。与雌性模式相反，雌性和雄性之间的繁殖导致在考虑从父母双方传递给后代的特征时缺乏明确的模式。亲缘关系较近的雌性和双亲遗传的性状之间的模式差异是一种被称为细胞核不一致的形式。在分布广泛的物种中，母系的远距离接触带可能只有6公里或更短。这种不一致甚至可能被限制在一个单一的阿罗约。**奇怪的是，在墨西哥下加利福尼亚州的狭窄半岛上，大多数动物在半岛中部表现出一种细胞核不一致的模式。一些物种共享多达四个这样的接触区。在多个物种中出现接触带反映了一个共同的历史。在下加利福尼亚，一个古老的短暂的海道可能隔离了曾经连续的种群。海道消失后，它们的种群重新聚集。这些动物现在已经并肩生活了300多万年，但没有母系血统的混合。在一些地区，比如靠近半岛南端的地方，人们可能已经接触了更长的时间，也许是800万年，但仍然保持着不一致。**我研究的一个重点是确定为什么这种常见的不协调模式在半岛动物中如此普遍。换句话说，为什么在300多万年的时间里，雌性恐龙没有分散超过6公里？毕竟，这一小段距离意味着女性血统的移动不超过令人难以置信的2毫米/年！对这种模式的一种解释，也被称为细胞核不协调，认为谱系不混合是因为当不同谱系混合时，它们产生能量的分子机制不能有效地工作。通过类比，这种现象就像试图将一个血统的方形钉子插入另一个血统的圆孔中。另一种可能性是，雌性会积极地保护自己的家庭免受远亲雌性的侵扰，这种类似于战线的新颖解释，我称之为“姐妹情谊假说”。使情况变得复杂的是，这两种机制可能协同工作。我将使用一套尖端的实验和技术，首先用树蜥蜴，来评估细胞核不一致和姐妹假说。我还将探讨这些机制在维持并排母系谱系模式中所起的相对作用。我的实验范围很广，从确定附近树上雌性的亲缘关系——母女关系、姐妹关系、表兄弟关系或更遥远的关系——到制造能量的机器（酶）的复杂模型。这些分析不仅有助于理解物种是如何进化的，以及雌性攻击性行为在物种进化过程中可能扮演的自然角色，还有助于保护和管理物种。例如，单个动物从一个位置到另一个位置的易位往往失败，也许细胞核不一致最好地解释了这个问题。

Closely related individual females of wild species of animals, such as mothers and daughters, sisters and cousins, often occur nearer to one another in nature rather than being broadly mixed among more distantly related females. Given time, a diversity of female lineages emerges and in most species of animals this nearness pattern is broken by the side-by-side occurrence of distantly related females in a very narrow geographic zone of only a few kilometers or less. This so-called genetic discordance, which we detect from DNA passed strictly from mother to daughter, results in a pattern that is not unlike World War I battle trenches. In contrast to female patterns, breeding among females and males results in an absence of a clear pattern when considering characters passed from both parents to their offspring. The difference between the patterns of closely related females and those of characters passed from both parents is one form of what is termed cytonuclear discordance. In broadly distributed species, the distant contact zones of matrilines may be only 6km or less across. The discordance may even be restricted to a single arroyo. **Curiously, on the narrow peninsula of Baja California, Mexico, most species of animals show a pattern of cytonuclear discordance in the middle of the peninsula. Some species share up to four such contact zones. The occurrence of contact zones in multiple species reflects a common history. In the case of Baja California, an ancient ephemeral seaway likely isolated once continuous populations. After the seaway disappeared, the populations reunited. These animals have now lived side-by-side for more than 3 million years but without the mixing of maternal lineages. In some regions, such as near the southern tip of the peninsula, populations may have been in contact for much longer periods of time, perhaps 8 million years but still keep the discordance. **A key focus of my research is to determine why this common pattern of discordance is so universal among animals on the peninsula. In other words, why have females not dispersed more than 6km in the 3+ million years they have had to do so? After all, this small distance translates to female lineages not moving more than an unbelievable 2mm/year! One explanation for the pattern, also termed cytonuclear discordance, suggests that the lineages do not mix because their energy-producing molecular machinery does not work efficiently when divergent lineages mix. By analogy, this phenomenon is like trying to put a square peg of one lineage into a round hole of another. Another possibility is that females aggressively protect their families against intrusions from more distantly related females, and this novel explanation, which is analogous to battle-lines, I call the sisterhood hypothesis. To make the situation complex, both of these mechanisms may work together in concert. I will use a suite of cutting edge experiments and technology, initially with tree lizards, to evaluate cytonuclear discordance and the sisterhood hypothesis. I will also explore the relative roles played by each of these mechanisms in maintaining the pattern of side-by-side maternal lineages. My experiments range from determining the relatedness of nearby females on trees-mother-daughter, sisters, cousins, or more distantly related-to sophisticated models of the energy-producing machinery (enzymes). The analyses have implications for not only understanding how species evolve, and the natural role aggressive female behaviour might play in their evolution, but also for conservation and management initiatives. For example, the translocations of individual animals from one site to another more often than not fails and perhaps cytonuclear discordance best explains the problem.