Rapid evolution of multidimensional traits and climate‐driven syndromes in an invasive plant across latitudinal gradients

Rapid adaptive evolution is increasingly recognized as a key driver of plant invasion success. Few studies have simultaneously examined the coevolution of multidimensional traits of growth, reproduction and defence across large geographic scales in invasive plants. Using a 17‐site, 85‐family common‐garden experiment replicated in China, we combined multivariate trait comparisons, herbivore bioassays, climate–trait relationships and phenotypic selection analyses to test whether the saltmarsh grass Spartina alterniflora evolved integrated ‘invasion syndromes’ within 40 years of its introduction from the United States. We identified four distinct syndromes across all families. Overall, introduced Chinese families displayed superior, genetically based trait syndromes that simultaneously enhanced growth, fecundity and defence against two generalist herbivores relative to native US families. Across latitudes, the dominant mid‐latitude Chinese syndrome coupled the most vigorous growth with the strongest defences but was not predominant at any native collection site. Syndrome membership was predicted by provenance temperature and/or precipitation and generated measurable fitness advantages: selection favoured taller, better‐defended phenotypes that maximized both biomass and seed set. Latitudinal variation in eight traits within China further indicates adaptive tracking of climate across 2000 km of coastline. Synthesis. We concluded that since its introduction to China, Spartina has rapidly evolved an integrated ecological strategy to enhance invasiveness under climate‐driven selective pressure, which can explain why this grass became the most successful invader along the country's coast. Our findings highlight the importance of syndrome‐based approaches in understanding the evolutionary dynamics of plant invaders and provide insights to forecast their future range expansion.