Abstract
Invasive species pose significant challenges to local biodiversity and ecosystem function, especially on islands. Understanding the factors affecting the establishment of invasive species and how these relate to their genetic background is crucial to improve our ability to manage biological invasions. Here, we performed a phylogeographic study of two cosmopolitan megascolecid earthworms of Asian origin: Amynthas gracilis and Amynthas corticis at 38 localities on São Miguel Island in the Azores archipelago (Portugal). Samples from putative source populations in China, Taiwan, Malaysia, as well as ‘outlier’ populations in USA, Mexico, Brazil and Spain were also included, resulting in a total of 565 earthworms genotyped at the mitochondrial cytochrome oxidase I (COI) and 16S ribosomal RNA genes. Soils were characterised for elemental composition, water holding capacity, organic matter content, texture and pH, and some habitat features were recorded. Both species showed a wide distribution across São Miguel and their abundances were negatively associated, suggesting spatial segregation/competition, with the parthenogenetic A. corticis being relatively more successful. The presence of multiple mitochondrial lineages within each species, one of them found exclusively in the Azores, suggests a complex invasion history. Environmental factors affected the establishment of the different lineages, with metal concentrations, topographical elevation and the degree of human influence being differently linked to their abundances. Lineage diversity was negatively correlated with metal concentrations. These results emphasise the importance of genetically characterising invasive species to better understand their invasion patterns.
Highlights
Invasive species can adversely affect local biodiversity due to alterations of recipient ecosystems, impacts on native species, such as competition, predation or hybridisation, or as carriers of disease (Pejchar and Mooney, 2009)
The studied Amynthas species are successful invaders in the Azores due to their inherent biological and ecological characteristics and enhanced by the fact that their presence is the result of multiple introductions
The relatively higher success of A. corticis may be due to parthenogenesis and higher plasticity
Summary
Invasive species can adversely affect local biodiversity due to alterations of recipient ecosystems, impacts on native species, such as competition, predation or hybridisation, or as carriers of disease (Pejchar and Mooney, 2009). Invasive species have shown rapid adaptations to new biotic and abiotic environments and much of this evidence has been observed on islands, highlighting them as evolutionary hotspots (Mooney and Cleland, 2001). M. Novo et al / Soil Biology & Biochemistry 85 (2015) 89e100 structure by earthworms can cause a cascade of ecological effects (Frelich et al, 2006). A well-documented case concerns the invasion of European earthworms (Lumbricidae) in North America, which has resulted in a change in forest floor litter dynamics with resulting effects on ecosystem processes (e.g., Bohlen et al, 2004; Hale et al, 2005; Frelich et al, 2006). Less understood are the effects of megascolecid species, Burtelow et al (1998) showed that Amynthas gracilis in particular has impacted C and N fluxes in soils of the northeastern United States
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