Data from: Population divergence along lines of genetic variance and covariance in the invasive plant Lythrum salicaria in eastern North America

Evolution during biological invasion may occur over contemporary timescales, but the rate of evolutionary change may be inhibited by a lack of standing genetic variation for ecologically relevant traits and by fitness trade-offs among them. The extent to which these genetic constraints limit the evolution of local adaptation during biological invasion has rarely been examined. To investigate genetic constraints on life-history traits, we measured standing genetic variance and covariance in 20 populations of the invasive plant purple loosestrife (Lythrum salicaria) sampled along a latitudinal climatic gradient in eastern North America and grown under uniform conditions in a glasshouse. Genetic variances within and among populations were significant for all traits; however, strong intercorrelations among measurements of seedling growth rate, time to reproductive maturity and adult size suggested that fitness trade-offs have constrained population divergence. Evidence to support this hypothesis was obtained from the genetic variance–covariance matrix (G) and the matrix of (co)variance among population means (D), which were 79.8% (95% C.I. 77.7–82.9%) similar. These results suggest that population divergence during invasive spread of L. salicaria in eastern North America has been constrained by strong genetic correlations among life-history traits, despite large amounts of standing genetic variation for individual traits.生物入侵（biological invasion）过程中的演化可发生在当代时间尺度上，但生态相关性状的现存遗传变异（standing genetic variation）匮乏，以及性状间的适合度权衡（fitness trade-offs），可能会抑制演化改变的速率。这些遗传约束在多大程度上限制生物入侵过程中的本地适应（local adaptation）演化，目前尚鲜有研究。为探究生活史性状（life-history traits）所受的遗传约束，我们对北美东部沿纬度气候梯度（latitudinal climatic gradient）采样的20个入侵植物千屈菜（Lythrum salicaria）种群展开测定：所有种群均在温室（glasshouse）统一环境下栽培，据此测量了其现存遗传方差与协方差。所有性状的种群内及种群间遗传方差均显著；然而，幼苗生长速率、生殖成熟时间与成年植株体型的测量值间存在强相关，表明适合度权衡约束了种群分化。支持该假说的证据来自遗传方差-协方差矩阵（genetic variance–covariance matrix，简称G矩阵）与种群均值间（共）方差矩阵（matrix of (co)variance among population means，简称D矩阵），二者的相似性达79.8%（95%置信区间77.7–82.9%）。上述结果表明，尽管单个性状拥有大量现存遗传变异，但北美东部入侵扩散过程中千屈菜的种群分化，仍受到生活史性状间强遗传相关的约束。