The Drivers of Cytonuclear Discordance

与野生动物物种关系密切的个体雌性动物，如母亲和女儿、姐妹和表亲，在自然界中往往彼此更接近，而不是广泛地混杂在更远亲的雌性动物中。随着时间的推移，雌性血统的多样性出现了，在大多数动物物种中，这种接近的模式被远亲雌性在只有几公里或更少的非常狭窄的地理区域并排出现打破了。这种所谓的基因不一致，我们从DNA中检测到，严格地从母亲传给女儿，导致了一种与第一次世界大战战壕相似的模式。与雌性模式不同，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。亲缘关系密切的雌性和双亲遗传的特征之间的差异是所谓的细胞核不协调的一种形式。在广泛分布的物种中，母鼠的远距离接触区可能只有6公里或更少。这种不协调甚至可能仅限于一个阿罗约人。奇怪的是，在墨西哥下加利福尼亚州狭窄的半岛上，大多数动物物种在半岛中央显示出一种细胞核不协调的模式。一些物种共享多达四个这样的接触区。接触带在多个物种中的出现反映了一个共同的历史。在下加利福尼亚州的例子中，一条古老的短暂海道很可能孤立了曾经连续的种群。海道消失后，人们又团聚了。这些动物现在已经在一起生活了300多万年，但没有母系的混合。在一些地区，例如半岛南端附近，人们可能已经接触了更长的时间，可能是800万年，但仍然保持着不和谐。我研究的一个关键重点是确定为什么这种常见的不和谐模式在半岛上的动物中如此普遍。换句话说，为什么女性在300多万年的时间里没有分散到6公里以上呢？毕竟，这一微小的距离意味着女性血统每年的迁徙不会超过令人难以置信的2毫米！对这种模式的一种解释，也被称为细胞核不协调，表明这些谱系没有混合，因为当不同的谱系混合时，它们产生能量的分子机制不能有效地工作。以此类推，这种现象就像是试图将一种血统的正方形钉子放入另一种血统的圆孔中。另一种可能性是，女性会积极地保护自己的家人免受远亲女性的侵扰，而这种类似于战线的新奇解释，我称之为姐妹关系假说。让情况变得复杂的是，这两种机制可能会协同工作。我将使用一套尖端的实验和技术，首先以树蜥蜴为对象，评估细胞核不协调和姐妹关系假说。我还将探讨这些机制中的每一种在维持母系并行的模式方面所起的相对作用。我的实验范围从确定树上附近雌性的亲缘关系--母女、姐妹、表亲或更远的亲戚--到产生能量的机械(酶)的复杂模型。这些分析不仅对了解物种是如何进化的，以及攻击性雌性行为在其进化中可能发挥的自然作用有意义，而且对保护和管理倡议也有意义。例如，个体动物从一个位置到另一个位置的移位往往失败，也许细胞核不协调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.