Chen X.; Liu W.; Zhang Y.-Y. and Zhang Y. 2023. Functional Ecology 37(5): 1280-90.

1. Increasing evidence suggests that invasive populations adapt to the novel environments rapidly, and the ability of rapid adaptation depends on genetically-based trait variation and covariation. However, few studies have investigated the trait covariance in the native and invasive ranges. Such investigation will give a more comprehensive picture of how historical contingency and adaptation shape invasiveness, contributing to the prediction of future invasion dynamics.

2. Here, we collected seven and nine populations alongside latitudes from invasive and native ranges of a global invasive plant, Spartina alterniflora, and planted them in two common gardens at the southernmost and northernmost sites of the invasive range. We measured plant traits, including the first flowering time, plant height and seed set, and analysed how these traits varied with garden sites and populations' origin latitudes and how their covariance changed between ranges.

3. We found that plants flowered later, grew taller and set more seeds in the high-latitude garden than the low-latitude one. The growth and expression of genetic variation of traits appeared to be limited by high ambient temperature in the low-latitude garden. In the high-latitude garden, the flowering time of populations showed clinal variation for both invasive and native populations, whereas the plant height and seed set showed clinal variation only for native or invasive populations. From the native to the invasive range, the flowering time and seed set developed negative genetic covariance, and flowering time and plant height changed from negative genetically correlated to uncorrelated.

4. Our results suggested that S. alterniflora has experienced rapid adaptation to clinal and local conditions over the 40-year invasion. Such geographic-scale rapid adaptation appeared to have benefited from previously identified genetic admixture that has released the trait covariance. Our study highlights the importance of integrating full-range geographical surveys with introduction history to understand the potential and mechanisms of trait evolution during invasion.

The correlations of population means between the plant height and first flowering day (a), between the seed set and first flowering day (c) and between the seed set and plant height (e) for invasive populations, and such correlations (b, d, and f) for native populations in different common gardens. Circles indicate correlations in the low-latitude garden, and triangles indicate those in the high-latitude garden. Significance levels: ^nsp > 0.1; ^#p < 0.1; ^*p < 0.05. Solid lines indicate significant or marginal significant correlations and dash lines indicate non-significant correlations.