School of Sciences, Indiana University Kokomo, 2300 S. Washington St, Kokomo, IN, 46902, USA.
Department of Biology, Hope College, 35 E. 12th St., Holland, MI, 49423, USA.
Microb Ecol. 2023 Oct;86(3):1686-1695. doi: 10.1007/s00248-022-02166-7. Epub 2023 Feb 2.
Symbiotic mutualisms are thought to be stabilized by correlations between the interacting genotypes which may be strengthened via vertical transmission and/or reduced genetic variability within each species. Vertical transmission, however, may weaken interactions over time as the endosymbionts would acquire mutations that could not be purged. Additionally, temporal variation in a conditional mutualism could create genetic variation and increased variation in the interaction outcome. In this study, we assessed genetic variation in both members of a symbiosis, the endosymbiotic fungal endophyte Epichloë canadensis and its grass host Canada wildrye (Elymus canadensis). Both species exhibited comparable levels of diversity, mostly within populations rather than between. There were significant differences between populations, although not in the same pattern for the two species, and the differences were not correlated with geographic distance for either species. Interindividual genetic distance matrices for the two species were significantly correlated, although all combinations of discriminant analysis of principle components (DAPC) defined multilocus genotype groups were found suggesting that strict genotype matching is not necessary. Variation in interaction outcome is common in grass/endophyte interactions, and our results suggest that the accumulation of mutations overtime combined with temporal variation in selection pressures increasing genetic variation in the symbiosis may be the cause.
共生互惠关系被认为是由相互作用的基因型之间的相关性所稳定的，这种相关性可能通过垂直传播和/或每个物种内遗传变异性的降低而得到加强。然而，垂直传播可能会随着时间的推移削弱相互作用，因为内共生体将获得无法清除的突变。此外，条件互惠关系的时间变化可能会产生遗传变异，并增加相互作用的结果的变异性。在这项研究中，我们评估了共生关系中两个成员的遗传变异，即内生真菌 Epichloë canadensis 和其宿主加拿大野黑麦（Elymus canadensis）。这两个物种都表现出相当程度的多样性，主要存在于种群内，而不是种群间。种群间存在显著差异，尽管两种物种的模式不同，而且差异与两种物种的地理距离无关。两个物种的个体间遗传距离矩阵显著相关，尽管所有的主成分判别分析（DAPC）组合都定义了多基因座基因型组，这表明严格的基因型匹配并不是必需的。在草/内生菌相互作用中，相互作用结果的变异性很常见，我们的结果表明，随着时间的推移，突变的积累以及选择压力的时间变化增加了共生体中的遗传变异，这可能是原因所在。
