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Dryad

Introduction pathways and evolutionary mechanisms of the spread of alien species of Lolium on sandy coasts in Japan

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Sep 26, 2023 version files 238.24 KB

Abstract

1. Estimating the role of specific processes in the spread of alien species necessitates the determination of introduction pathways and source populations of invaded areas. Alien grasses in the genus Lolium that have become widely invasive in Japan provide provides a unique opportunity to estimate the expansion process through a direct comparison between source and naturalised populations because the introduction pathways, contaminants in grain commodities and commercial cultivars for fodder crops or revegetation materials are well-known. Therefore, by directly comparing between source and naturalised populations, we estimated the introduction pathways and whether adaptative evolution occurred in Lolium species on sandy coasts in Japan.

2. Lolium individuals sampled from naturalised populations in croplands, seaports and sandy coasts were compared with those from two introduction sources for morphological and genetic variations based on a genome-wide single nucleotide polymorphism analysis and a common garden experiment. Furthermore, we conducted a reciprocal sowing experiment between a cropland and sandy coast.

3. Populations naturalized in croplands were closely related to the cultivars, whereas those naturalized in seaports and sandy coasts were associated with contaminants. This pattern is common in western Japan. Therefore, these results indicate that the cropland and sandy coast populations are derived from cultivars and contaminants, respectively. The reciprocal transplant experiment clearly demonstrated the home site advantage; populations derived from croplands yielded higher floret numbers than those derived from other habitats at the cropland site; however, such an advantage was not detected with the coastal site population. Sandy coast populations had higher survival rates than those from croplands at coastal sites. Port populations exhibited a similar tendency as sandy coast populations, indicating that contaminants may be originally adapted to salty and dry environments, such as that in sandy coasts.

4. Synthesis. We demonstrated that two congeneric species with different ecological characteristics were introduced through multiple introduction pathways and spread into different habitats. A direct comparison between source and naturalised populations can greatly advance our understanding of the patterns and processes of biological invasions.