What question did this study set out to answer?

The research aims to explore how environmental gradients influence adaptation in invasive plants, particularly examining Amaranthus palmeri.

April 22, 2026

Asymmetric adaptation across a core–periphery climate gradient drives rapid phenological evolution and range expansion in an invasive plant

Key Points

The research aims to explore how environmental gradients influence adaptation in invasive plants, particularly examining Amaranthus palmeri.
Conducted a five-year reciprocal transplant common garden experiment across China's invasive range.
Quantified population fitness using asymptotic growth rates and identified trait-fitness relationships through structural equation modeling.
Performed genomic analyses including GWAS and gene-level studies to investigate evolutionary mechanisms.
Northern peripheral populations showed local specialization with earlier flowering by 2.5-18.9 days and longer flowering duration by 5.7-18.2 days, enhancing fitness.
Trait divergence greatly surpassed neutral expectations, indicating strong diversifying selection.
Identified the PTM gene as key in flowering phenology variation in northern populations, showing evidence of recent selective sweeps.

Abstract

Abstract The core–periphery paradigm predicts that asymmetric selection along environmental gradients drives divergent adaptation at range margins, influencing range limits and invasion dynamics. However, empirical tests spanning entire latitudinal gradients and mechanistic explanations for the genetic paradox of invasion—rapid adaptation despite limited genetic diversity—remain rare. We conducted a five‐year reciprocal transplant common garden experiment on the invasive annual Amaranthus palmeri across its entire invasive range in China (21–49° N). Population fitness was quantified using asymptotic growth rates () to test for asymmetric adaptation. We then measured key phenotypic traits and used structural equation modelling (SEM) to identify trait–fitness relationships. Finally, we integrated quantitative genetic () and neutral genomic () comparisons with gene‐level analyses, including genome‐wide association studies (GWAS), a genome‐wide scan and expression validation, to elucidate the evolutionary mechanisms underlying adaptation. We detected pronounced latitudinal asymmetry in adaptation. Northern peripheral populations evolved local specialization through genetic shifts towards earlier flowering (2.5–18.9 days) and prolonged flowering duration (5.7–18.2 days), increasing fitness (| ß | > 0.56, p < 0.01). Trait divergence ( = 0.41–0.62) greatly exceeded neutral expectations ( = 0.0156), indicating diversifying selection on standing genetic variation. Genomic analyses identified PTM as the top GWAS candidate, a single candidate gene associated with flowering phenology variation, ranking in the top 5% of the genome‐wide distribution and showing signatures of recent selective sweeps, with significantly higher expression in northern peripheral populations. In contrast, southern edge populations exhibited consistent maladaptation, revealing a fundamental asymmetry in range‐limiting filters. Synthesis . Climatic extremes at range margins drive rapid genetic adaptation in key phenological traits, facilitating asymmetric range expansion. By linking phenotypic selection, fitness consequences and genomic divergence across spatial scales, our study provides a mechanistic framework for understanding range limits and offers insights for predicting species redistribution and managing biological invasions under climate warming.

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