Invasive lumbricid earthworms in North America - different life-histories but common dispersal?

Andreas Klein,Ina Schaefer,Nico Eisenhauer

doi:10.1111/jbi.13744

Abstract

Lumbricid earthworms are invasive across northern North America, causing notable changes in forest ecosystems. During their range expansion they encountered harsher climatic conditions compared to their native ranges in evolutionary short time. This study investigated if (1) dispersal barriers, (2) climatic selection, or (3) anthropogenic activities, such as fishing bait disposal, structure the dispersal of free-living earthworm populations. North America, forest habitats along former Wisconsinan glaciation line. Lumbricus terrestris, L. rubellus. Lumbricus terrestris and L. rubellus co-occur in the same habitats but differ in ecology and use Conservation approach for goblin species were sampled in five transects ranging from the east to the west coast of northern North America, including major dispersal barriers, three different climate zones, and bait shops near sampling locations. Genetic diversity and structure were compared between the two species, and the presence of free-living bait shop genotypes was assessed using four markers (COI, 16S rDNA, 12S rDNA, H3). Populations of both species were genetically diverse with some geographic structure, which was more pronounced in L. terrestris than in L. rubellus. Common haplotypes were present in all regions, but locally restricted haplotypes also occurred. Further, two distinct genetic clades of L. terrestris co-occurred only in the two most distant transects (Alberta and Minnesota). Genotypes identical to bait individuals were omnipresent in field populations of L. terrestris. Genetic diversity was high in both species, and invasive populations represented a genetic subset of European earthworms. Geographic and climatic dispersal barriers affected the less mobile species, L. rubellus, resulting in differences in genetic structure between the two species. Our results indicate common long-distance dispersal vectors and specific vectors affecting only L. terrestris. The roles of climate and anthropogenic activities are discussed, providing additional explanations of dispersal and new insights into establishment of invasive earthworms.

Highlights

European lumbricid earthworms are among the most successful in‐ vasive species in North America (James & Hendrix, 2004)
During their expansion across northern North America, European earthworms established in distinct climate zones that differ in the amount and distribution of precipitation across the year, as well as frost intensity and duration, two abiotic factors that are known to drive earthworm distribution (Curry, 2004; Fisichelli et al, 2013; Holmstrup, 2003; Uvarov, Tiunov, & Scheu, 2011)
This study shows that northern North American populations of the two earthworm species L. rubellus and L. terrestris share the same genetic lineages with populations of their native range in Europe

Summary

| INTRODUCTION

European lumbricid earthworms are among the most successful in‐ vasive species in North America (James & Hendrix, 2004). The pronounced ecological consequences of earthworm invasions in North America are well documented, making earthworms one of the best‐studied invasive animal species living below the ground (Wardle, Bardgett, Callaway, & Putten, 2011) and a unique model system for biological inva‐ sion and accompanying effects (Hendrix et al, 2008) During their expansion across northern North America, European earthworms established in distinct climate zones that differ in the amount and distribution of precipitation across the year, as well as frost intensity and duration, two abiotic factors that are known to drive earthworm distribution (Curry, 2004; Fisichelli et al, 2013; Holmstrup, 2003; Uvarov, Tiunov, & Scheu, 2011). To account for human‐ mediated dispersal by dumping of fishing baits, which is a severe problem in northern North America (Hale, 2008; Holdsworth et al, 2007; Seidl & Klepeis, 2011), we purchased earthworms from bait shops near sampling locations in all transects to test if bait genotypes contribute to free‐living populations, thereby increas‐ ing local diversity

| MATERIALS AND METHODS

| DISCUSSION

Findings

| CONCLUSIONS