Temporal sampling helps unravel the genetic structure of naturally occurring populations of a phytoparasitic nematode. 2. Separating the relative effects of gene flow and genetic drift.

Cécile Gracianne,Pierre-Loup Jan,Sylvie Bardou-Valette,Sylvain Fournet,Marie-Christine Denis,Jean-François Arnaud,Catherine Porte,Eric Olivier,Eric J Petit

doi:10.1111/eva.12401

Abstract

Studying wild pathogen populations in natural ecosystems offers the opportunity to better understand the evolutionary dynamics of biotic diseases in crops and to enhance pest control strategies. We used simulations and genetic markers to investigate the spatial and temporal population genetic structure of wild populations of the beet cyst nematode Heterodera schachtii on a wild host plant species, the sea beet (Beta vulgaris spp. maritima), the wild ancestor of cultivated beets. Our analysis of the variation of eight microsatellite loci across four study sites showed that (i) wild H. schachtii populations displayed fine‐scaled genetic structure with no evidence of substantial levels of gene flow beyond the scale of the host plant, and comparisons with simulations indicated that (ii) genetic drift substantially affected the residual signals of isolation‐by‐distance processes, leading to departures from migration–drift equilibrium. In contrast to what can be suspected for (crop) field populations, this showed that wild cyst nematodes have very low dispersal capabilities and are strongly disconnected from each other. Our results provide some key elements for designing pest control strategies, such as decreasing passive dispersal events to limit the spread of virulence among field nematode populations.

Highlights

Agrosystems are highly homogenous artificial environments that are amenable to the emergence and development of pathogens (Stukenbrock & McDonald, 2008)
Our analysis of the variation of eight microsatellite loci across four study sites showed that (i) wild H. schachtii populations displayed fine-scaled genetic structure with no evidence of substantial levels of gene flow beyond the scale of the host plant, and comparisons with simulations indicated that (ii) genetic drift substantially affected the residual signals of isolation- by-distance processes, leading to departures from migration–drift equilibrium
(i) we investigated the levels of genetic differentiation in local wild populations of H. schachtii to examine what hierarchical scale should be considered to define a population in the wild, (ii) we examined the spatial genetic structure of nematode populations to identify signatures of dispersal events and the scale over which they occur, and (iii) we separated the respective effects of gene flow and genetic drift in observed population genetic structure

Summary

Separating the relative effects of gene flow and genetic drift

To cite this version: Cécile Gracianne, Pierre-Loup Jan, Sylvain Fournet, Eric Olivier, Jean-François Arnaud, et al. Temporal sampling helps unravel the genetic structure of naturally occurring populations of a phytoparasitic nematode. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Cécile Gracianne1,2 | Pierre-Loup Jan1,3 | Sylvain Fournet1 | Eric Olivier1 | Jean-François Arnaud4 | Catherine Porte1 | Sylvie Bardou-Valette1 | Marie-Christine Denis1 | Eric J.

| INTRODUCTION

| MATERIALS AND METHODS

Findings

| DISCUSSION

| CONCLUSION