Dispersal constraints and fine-scale spatial genetic structure in two earthworm species

Abstract

The limited dispersal ability of earthworms is expected to result in marked genetic isolation by distance and remarkable spatial patterns of genetic variation. To test this hypothesis, we investigated, using microsatellite loci, the spatial genetic structure of two earthworm species, Allolobophora chlorotica and Aporrectodea icterica, in two plots of less than 1 ha where a total of 282 individuals were collected. We used spatial autocorrelation statistics, partial Mantel tests of isolation-by-distance (IBD) and isolation-by-resistance (IBR), and Bayesian test of clustering to explore recent patterns involved in the observed genetic structure. For A. icterica, a low signal of genetic structure was detected, which may be explained by an important dispersal capacity and/or by the low polymorphism of the microsatellite loci. For A. chlorotica, a weak, but significant, pattern of IBD associated with positive autocorrelation was observed in one of the plots. In the other plot, which had been recently ploughed, two genetically differentiated clusters were identified. These results suggest a spatial neighbourhood structure in A. chlorotica, with neighbour individuals that tend to be more genetically similar to one another, and also highlight that habitat perturbation as a result of human activities may deeply alter the genetic structure of earthworm species, even at a very small scale.

Shedding Light on the Grey Zone of Speciation along a Continuum of Genomic Divergence

“…Of the 35 pairs of recognized populations from the same species, 6 with D a > 0.02 were inferred to be isolated cryptic species. Genetic isolation has been previously suspected between northern and southern populations of Pectinaria koreni (trumpet worms) [38], between the blue and purple morphs of Cystodytes dellechiajei (colonial ascidians) [39], and between the L1 and L2 lineages of Allolobophora chlorotica (earthworms) [40], but genetic isolation is here newly revealed between Morrocan and European populations of Melitaea cinxia (Glanville fritillary), between Spanish and French populations of A . chlorotica L2, and between Mediterranean and tropical populations of Culex pipiens .…”

Worldwide earthworm research: a scientometric analysis, 2000–2015

“…The first trend highlighted the impact of human activities on earthworm, like agricultural activities (Crittenden et al 2015;Lopez-Hernandez et al 2015), soil reclamation and restoration (Hlava et al 2015;Grumiaux et al 2015), organic waste mixtures (Zibetti et al 2015), pesticide (Pelosi et al 2014;Wang et al 2015), veterinary drug (Gao et al 2015), as well as engineered nanoparticles, like CuO and ZnO nanoparticles (Alandadi and Behboudi 2015), Ag, Co, Ni and TiO2 nanoparticles (Antisari et al 2015). The impacts mostly focused on growth, reproduction, population and community of earthworms, even genetic structure change of earthworm species (Dupont et al 2015). The second trend was the research focus on the effect of climate issues on earthworm, like climate type (Hackenberger and Hackenberger 2014), acid rain (Zhang et al 2015),floods and floodplain rehabilitation (Thorion and Klok 2007).…”

Landscape features impact connectivity between soil populations: a comparative study of gene flow in earthworms

“…For instance, Costa et al (2013) found only sixteen different species among the collembolans, earthworms and isopods groups of soil invertebrates for which a population genetics study was carried out. Some of these papers investigated the spatial genetic structure of soil organisms at a fine scale (Sullivan et al 2009;Novo et al 2010;Dupont et al 2015), but none addressed the effect of landscape features on genetic variation. However, terrestrial habitat heterogeneity is known to affect the diversity of soil species' assemblages by producing variation in the diversity of plant and litter (Vanbergen et al 2007).…”

“…Here, we were interested in landscape features impacting genetic variation and functional connectivity in earthworms. Dispersal by passive mechanisms, such as zoochory, wind, water and human activities, is believed to be implicated in their long-distance movement (Eijsackers 2011;Costa et al 2013;Dupont et al 2015), while their active dispersal is dependent on habitat quality, conspecific density and habitat modification by conspecifics in endogeic (i.e. species living in the upper organo-mineral soil layers and forming horizontal nonpermanent burrows, Bouch e 1977) and anecic (i.e.…”

“…A. chlorotica typically lives between soil surface and the upper 60 mm soil layer (Sims & Gerard 1999) and is theoretically able to travel over 167 m per year in constant suitable conditions (Caro et al 2013). However, in the field, dispersal distances ranging from 6.82 to 7.56 m per year were estimated in a recent population genetics study at fine spatial scales (Dupont et al 2015). A. icterica is found deeper in soils and is considered to be more mobile, being theoretically able to travel up to 500 m year À1 under constant artificial conditions (Mathieu et al 2010;Caro et al 2013).…”