Genomic Footprints of Selfing, Introduction History, and Long-Distance Dispersal in an Invasive Alien Plant

Area of Science:

• Evolutionary Biology
• Ecology
• Genomics

Background:

• Biological invasions offer insights into evolutionary and ecological processes.
• Cotula coronopifolia, an invasive annual plant, was introduced to Europe from South Africa ~300 years ago.

Purpose of the Study:

• Investigate the colonization history and spread of invasive buttonweed (Cotula coronopifolia).
• Analyze genome-wide data to understand its evolutionary trajectory and genetic structure in Europe.

Main Methods:

• Genotyping-by-sequencing (GBS) was used to analyze genome-wide data from 30 populations.
• Phylogenomic dating and mating-system inference were employed.
• Genetic clustering and simulations were used to assess admixture dynamics.

Main Results:

• Three distinct lineages of Cotula coronopifolia were identified in Europe, diverging >2,000 years ago.
• The species exhibits a facultative mating system, with ~70% self-fertilization, leading to low heterozygosity and strong genetic structure.
• Rare inter-lineage outcrossing results in admixture, but diversity decays rapidly under subsequent selfing.

Conclusions:

• The flexible mating system, particularly self-fertilization, aids reproductive assurance and colonization success.
• Baker's "ideal weed" concept is supported, demonstrating how predominant selfing shapes the genomic landscape of invasive species.
• Introduction history and dispersal by waterbirds explain the scattered distribution of lineages.