Abstract With the ongoing climate change, widespread changes could be noticed in both the extent of the geographical distribution as well the patterns of phenotypic variation of plant species in response to environmental heterogeneity. Whether these changes are a direct consequence of global climate change, and whether they result from phenotypic plasticity or evolutionary forces, are currently main areas of interest. In the present study, 130 lines belonging to ten Tunisian Brachypodium hybridum populations differing greatly in climatic conditions were exposed to water stress and the pattern of their genetic variation was analyzed using sixteen functional traits in order to unravel the main drivers of their response to drought. Our results showed that B. hybridum populations exhibited an extensive intra-population genetic variation in control and water stress, whereas principal component analysis did not show any clear populations grouping pattern. In addition, ANOVA showed that most of analyzed traits revealed a significant population and line effects, indicating that their response to drought was, in part, controlled at the genetic level. These results suggest that the natural selection on standing intra-population genetic variation plays a major role in dealing with drought in B. hybridum. On the other hand, we found that many traits exhibited phenotypic plasticity in response to water stress. The plasticity index showed that the populations responded differently to water stress, with Ain Drahem and Djerba populations showed the highest and the lowest plasticity levels, respectively. However, plasticity of most analyzed traits seems to be unrelated to climatic factors, except for the precipitation of wettest month, which showed significant correlation with five traits related to biomass production and the mean plasticity index. In summary, the present study revealed that the genetic variation in response to drought in the natural populations of B. hybridum was most likely governed by an interplay between two major evolutionary and ecological processes: natural selection and phenotypic plasticity.

中文翻译：

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突尼斯杂交短柄草（禾本科）种群响应干旱的遗传变异：自然选择与表型可塑性之间的相互作用

摘要 随着气候的不断变化，植物物种的地理分布范围以及响应环境异质性的表型变异模式都发生了广泛的变化。这些变化是否是全球气候变化的直接后果，以及它们是由表型可塑性还是进化力量引起的，是目前主要的关注领域。在本研究中，属于 10 个气候条件差异很大的突尼斯 Brachypodium hybridum 种群的 130 个品系受到水分胁迫，并使用 16 个功能性状分析了它们的遗传变异模式，以揭示它们对干旱反应的主要驱动因素。我们的结果表明，B. hybridum 种群在控制和水分胁迫方面表现出广泛的种群内遗传变异，而主成分分析没有显示任何明确的种群分组模式。此外，方差分析表明，大多数分析的性状显示出显着的种群和品系效应，表明它们对干旱的反应部分受到遗传水平的控制。这些结果表明，群体内遗传变异的自然选择在应对 B. hybridum 干旱方面起着重要作用。另一方面，我们发现许多性状在应对水分胁迫时表现出表型可塑性。可塑性指数显示种群对水分胁迫的反应不同，Ain Drahem 和 Djerba 种群分别表现出最高和最低的可塑性水平。然而，大多数分析性状的可塑性似乎与气候因素无关，除了最潮湿月份的降水与生物量生产相关的五个性状和平均可塑性指数显着相关。总之，本研究揭示了 B. hybridum 自然种群中响应干旱的遗传变异很可能受两个主要进化和生态过程之间的相互作用控制：自然选择和表型可塑性。