Dissertation Research: Consequences of Hybridization in the Harvester Ant Pogonomyrmex

像骡子一样，物种或血统之间的杂交通常被认为是进化的死胡同。然而，最近的研究表明，杂交种可能在塑造进化过程中发挥重要作用。虽然大多数杂交基因混合是不成功的，但也有一些是有益的，并产生了应对不断变化的生态和社会环境的新策略。在Pogonomyrmex种子收获器蚂蚁中，杂交产生了一种独特的社会和生殖结构，在这种结构中，蚁后必须与两种不同遗传谱系的雄蚁交配，才能同时产生工蚁蚁和女儿蚁。女王的女儿和同种血统的男性发育成女王。女王和交替血统的男性之间的杂交女儿成为不育的工蚁。这一遗传种姓确定系统违反了普遍存在的假设，即女性是否成为工蚁或女王必须基于营养或其他环境因素的差异，而不是遗传因素，因为产生不育的基因组合应该被选择出来。这一系统发生在两个密切相关的收割机蚂蚁物种--P.rugous和P.barbatus中，导致了一种假说，即它最初是由于这两个物种之间的不完全杂交而进化的，导致了两个相互依赖的遗传谱系的发展。然而，初步证据表明，情况并非如此，它可能最初在一个物种(半枝莲)中进化，然后传播到另一个物种。为了验证这些假设，将使用线粒体和核遗传分析来检查这些种子收获蚂蚁物种内和之间杂交的程度和后果。这项工作将有助于我们理解杂交在进化中所起的作用，特别是社会制度的进化。这项研究还将为一名研究生和几名本科生提供学习在进化生物学中具有广泛应用的分子技术和分析的机会。

Like the mule, hybrids between species or lineages are often considered an evolutionary dead end. However, recent studies suggest that hybrids can be important in shaping evolution. While most hybrid gene mixtures are unsuccessful, some are beneficial and result in new strategies to cope with changing ecological and social environments. In Pogonomyrmex seed-harvester ants, hybridization has produced a unique social and reproductive structure, in which queens must mate with males of two different genetic lineages to produce both workers and daughter queens. Daughters of the queen and males of the same lineage develop into queens. Hybrid daughters between the queen and males of the alternate lineage become sterile workers. This system of genetic caste determination violates the widely held assumption that whether a female becomes a worker or queen has to be based on differences in nutrition or other environmental factors, and not genetics, because gene combinations producing sterility should be selected against. This system occurs within two closely related harvester ant species, P. rugosus and P. barbatus, leading to the hypothesis that it originally evolved as a result of incomplete hybridization between the two species that lead to the development of two interdependent genetic lineages. However, preliminary evidence suggests that this is not the case and that it may have evolved initially in one species (P. barbatus) then spread to the other. To test these hypotheses, the extent and consequences of hybridization within and between these species of seed-harvester ants will be examined using mitochondrial and nuclear genetic analyses. This work will contribute to our understanding of the role that hybridization plays in evolution, especially the evolution of social systems. This research will also provide opportunities for a graduate student and several undergraduates to learn molecular techniques and analyses with broad applications in evolutionary biology.