ETH Zürich, Institute of Integrative Biology, Experimental Ecology, CH-8092 Zürich, Switzerland.
BMC Evol Biol. 2012 Feb 13;12:18. doi: 10.1186/1471-2148-12-18.
One of the big remaining challenges in evolutionary biology is to understand the evolution and maintenance of meiotic recombination. As recombination breaks down successful genotypes, it should be selected for only under very limited conditions. Yet, recombination is very common and phylogenetically widespread. The Red Queen Hypothesis is one of the most prominent hypotheses for the adaptive value of recombination and sexual reproduction. The Red Queen Hypothesis predicts an advantage of recombination for hosts that are coevolving with their parasites. We tested predictions of the hypothesis with experimental coevolution using the red flour beetle, Tribolium castaneum, and its microsporidian parasite, Nosema whitei.
By measuring recombination directly in the individuals under selection, we found that recombination in the host population was increased after 11 generations of coevolution. Detailed insights into genotypic and phenotypic changes occurring during the coevolution experiment furthermore helped us to reconstruct the coevolutionary dynamics that were associated with this increase in recombination frequency. As coevolved lines maintained higher genetic diversity than control lines, and because there was no evidence for heterozygote advantage or for a plastic response of recombination to infection, the observed increase in recombination most likely represented an adaptive host response under Red Queen dynamics.
This study provides direct, experimental evidence for an increase in recombination frequency under host-parasite coevolution in an obligatory outcrossing species. Combined with earlier results, the Red Queen process is the most likely explanation for this observation.
进化生物学中仍存在的一个重大挑战是理解减数分裂重组的进化和维持。由于重组会破坏成功的基因型，因此它应该只在非常有限的条件下被选择。然而，重组非常普遍且在系统发育上广泛存在。红皇后假说（Red Queen Hypothesis）是关于重组和有性生殖的适应性价值的最突出假说之一。该假说预测，对于与寄生虫共同进化的宿主而言，重组具有优势。我们使用红粉甲虫（Tribolium castaneum）及其微孢子虫寄生虫（Nosema whitei）进行了实验性共同进化，以此来检验该假说的预测。
通过直接在受选择的个体中测量重组，我们发现，在 11 代的共同进化后，宿主种群中的重组增加了。对共同进化实验中发生的基因型和表型变化的详细了解，进一步帮助我们重建了与重组频率增加相关的共同进化动态。由于共同进化的系保持了比对照系更高的遗传多样性，而且没有证据表明杂合子有利或重组对感染有可塑性反应，因此观察到的重组增加很可能代表了在红皇后动态下宿主的适应性反应。
这项研究提供了直接的、实验性的证据，证明在强制性异交物种的宿主-寄生虫共同进化中，重组频率增加了。结合早期的结果，红皇后过程是对这一观察结果最可能的解释。
