title: Genetic structure of earthworm populations at a regional scale: inferences from mitochondrial and microsatellite molecular markers in Aporrectodea icterica (Savigny 1826).
abstract: Despite the fundamental role that soil invertebrates (e.g. earthworms) play in soil ecosystems, the magnitude of their spatial genetic variation is still largely unknown and only a few studies have investigated the population genetic structure of these organisms. Here, we investigated the genetic structure of seven populations of a common endogeic earthworm (Aporrectodea icterica) sampled in northern France to explore how historical species range changes, microevolutionary processes and human activities interact in shaping genetic variation at a regional scale. Because combining markers with distinct modes of inheritance can provide extra, complementary information on gene flow, we compared the patterns of genetic structure revealed using nuclear (7 microsatellite loci) and mitochondrial markers (COI). Both types of markers indicated low genetic polymorphism compared to other earthworm species, a result that can be attributed to ancient bottlenecks, for instance due to species isolation in southern refugia during the ice ages with subsequent expansion toward northern Europe. Historical events can also be responsible for the existence of two divergent, but randomly interbreeding mitochondrial lineages within all study populations. In addition, the comparison of observed heterozygosity among microsatellite loci and heterozygosity expected under mutation-drift equilibrium suggested a recent decrease in effective size in some populations that could be due to contemporary events such as habitat fragmentation. The absence of relationship between geographic and genetic distances estimated from microsatellite allele frequency data also suggested that dispersal is haphazard and that human activities favour passive dispersal among geographically distant populations.
authors.affiliation: University Paris Est Créteil, Institute of ecology and environmental sciences of Paris, Créteil, France; Unité de Zoologie Forestière UR0633, Institut National de la Recherche Agronomique, Orléans, France.
authors.forename: Magally
authors.initials: M
authors.lastname: Torres-Leguizamon
authors.affiliation: University Pierre and Marie Curie, Institute of ecology and environmental sciences of Paris, Paris, France.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Mathieu
authors.affiliation: EA 1293 ECODIV, University of Rouen, Mont Saint Aignan, France.
authors.forename: Thibaud
authors.initials: T
authors.lastname: Decaëns
authors.affiliation: University Paris Est Créteil, Institute of ecology and environmental sciences of Paris, Créteil, France.
authors.forename: Lise
authors.initials: L
authors.lastname: Dupont
mesh_terms: D000483:Alleles; D000818:Animals; D016000:Cluster Analysis; D004272:DNA, Mitochondrial; D005602:France; D005787:Gene Frequency; D014644:Genetic Variation; D005828:Genetics, Population; D005843:Geography; D006239:Haplotypes; D018895:Microsatellite Repeats; D008969:Molecular Sequence Data; D009154:Mutation; D009835:Oligochaeta / Q000145:classification / Q000235:genetics*; D011157:Population Dynamics
chemical_list: D004272:DNA, Mitochondrial