Altered trait covariances between invasive and native ranges of a global plant invader

Increasing evidence suggests that invasive populations adapt to novel
environments rapidly, and the ability to rapidly adapt 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. 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 analyzed how these traits varied with garden
sites and populations’ origin latitudes and how their covariance changed
between ranges. We found that plants flowered later, grew taller, and set
more seeds in the high-latitude garden than in 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.
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.