Population genetic structure of Ascaridia galli re-emerging in non-caged laying hens

Johan Höglund,Désirée S Jansson,Peter Nejsum,Annie Engström,David A Morrison

doi:10.1186/1756-3305-5-97

Abstract

BackgroundThe poultry roundworm Ascaridia galli has reappeared in hens kept for egg production in Sweden after having been almost absent a decade ago. Today this is a frequent intestinal nematode parasite in non-caged laying hens. The aim of this study was to investigate the genetic diversity (Fst) in A. galli collected from different poultry production sites in southern Sweden, to identify possible common routes of colonization.MethodsAdult parasites (n = 153) from 10 farms, including both broiler breeder parents and laying hens, were investigated by amplified restriction fragment length polymorphism analysis (AFLP). Worms from a Danish laying hen farm were also included for comparison. Most of the farms were represented by worms from a single host, but on two farms multiple samples from different hosts were assessed in order to study flock variation.ResultsA total of 97 fragments (loci) were amplified among which 81% were variable alleles. The average genetic diversity was 0.13 (range = 0.09-0.38), which is comparable to other AFLP studies on nematodes of human and veterinary importance. Within-farm variation showed that worms harboured by a single hen in a flock covered most of the A. galli genetic variation within the same flock (Fst = 0.01 and 0.03 for two farms). Between-farm analysis showed a moderate population genetic structure (Fst = 0.13), along with a low mutational rate but high gene flow between different farms, and absence of strong genetic selection. Network analysis showed repeated genetic patterns among the farms, with most worms on each farm clustering together as supported by high re-allocation rates.ConclusionsThe investigated A. galli populations were not strongly differentiated, indicating that they have undergone a genetic bottlenecking and subsequent drift. This supports the view that the investigated farms have been recently colonized, and that new flocks are reinfected upon arrival with a stationary infection.

Highlights

The poultry roundworm Ascaridia galli has reappeared in hens kept for egg production in Sweden after having been almost absent a decade ago
Organisms vary genetically as a reflection of their evolutionary history and, information about the population genetic structure is basic to the understanding of biodiversity
We describe here for the first time the genetic diversity and population genetic structure of 154 worms of Ascaridia galli, a parasitic nematode of poultry, applying the whole genome fingerprinting technique AFLP

Summary

Introduction

The poultry roundworm Ascaridia galli has reappeared in hens kept for egg production in Sweden after having been almost absent a decade ago Today this is a frequent intestinal nematode parasite in non-caged laying hens. Organisms vary genetically as a reflection of their evolutionary history and, information about the population genetic structure is basic to the understanding of biodiversity. Quantifiable components of this structure include: genetic diversity, population hierarchical structure, population mutation rate, rate of gene flow, and selective neutrality [1]. Direct sequencing of PCR-amplified mitochondrial DNA is the most frequently used molecular-based strategy, which has been used to infer the population genetic structure and diversity of a number of animal nematodes, for a review: [4]. Few AFLP based studies have been conducted on nematodes of domesticated animals: Dictyocaulus viviparus, a trichstrongylid lungworm of ungulates [9], Ascaris suum, an Ascarid intestinal parasite of pigs [10], and Haemonchus contortus, a trichostrongylid abomasal parasite of ruminants [11]; as well as for Necator americanus, a strongylid intestinal nematode of humans [12]

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