Host-based genotype variation in insects revisited

Abstract

Elucidation of the genetic variability of a model insect species, the grain aphid, Sitobion avenae (Fabricius), a predominantly asexual herbivore within the temperate agro-ecosystem tested, was initiated using molecular DNA markers (RAPDs). This revealed genetic profiles that appeared related to host adaptation at the specific level amongst the natural populations colonizing different grasses and cereals (Poaceae) within the same geographic location. These profiles were recorded either as 'specialist' genotypes found on specific grasses, or as 'generalist' genotypes colonizing several host types including cultivated cereals or native grasses. These findings are compared with analogous systems found amongst insect species, including at a higher trophic level, i.e. interactions between hymenopterous aphid parasitoids. As the aphids and their respective plant hosts occur in the same geographical region at the same time, this appears to be a rare example of the evolutionary transition leading to sympatric speciation in insects. Hence, this study highlights the importance of understanding not only the demographic parameters to genetic diversity, but also the more intricate correlation of genetic diversity to host types in agricultural environments.

Host-associated genetic structure of Mexican populations of the cabbage aphid Brevicoryne brassicae L. (Homoptera: Aphididae)

“…Ample evidence of host plant differentiation has recently been found in other aphids (eg De Barro et al, 1995a, b;Sunnucks et al, 1997;Via, 1999;Lushai et al, 2002), supporting the view that this phenomenon is much more widespread than previously realized. Natural selection can contribute to host-related genetic structuring in B. brassicae if intense selection occurs during establishment in different hosts.…”

“…Several studies have revealed greater amounts of genetic variability among aphid populations (eg RAPD-PCR, DNA-microsatellite; Vanlerbergh-Masutti and Chavigny, 1998;Wilson et al, 2002;Llewellyn et al, 2003), and hence offer the potential to further assess host-associated genetic differentiation (Lushai et al, 2002).…”

“…Indeed, several studies have shown evidence that the genetic structure of aphids can be related to their host plants (eg De Barro et al, 1995a, b;Sunnucks et al, 1997;Via, 1999;Haack et al, 2000;Anstead et al, 2002;Lushai et al, 2002).…”

Population genetic structure of the lettuce root aphid, Pemphigus bursarius (L.), in relation to geographic distance, gene flow and host plant usage

“…A recent study of mitochondrial DNA variation has revealed that these biotypes are probably host adapted races (Shufran et al, 2000). Populations of S. avenae, confined to specific host plants, have been identified using RAPD (De Barro et al, 1995;Lushai et al, 2002) and microsatellite (Sunnucks et al, 1997a) markers, as well as generalists occupying several different hosts (Sunnucks et al, 1997a;Lushai et al, 2002). RAPD markers, have also revealed distinct populations of Aphis gossypii (Glover) on curcurbit and non-curcurbit hosts (Vanlerberghe-Masutti and Chavigny, 1998) and, in conjunction with mitochondrial DNA, Therioaphis trifolii (Monell) on clover and lucerne (Sunnucks et al, 1997b).…”

Evidence for gene flow and local clonal selection in field populations of the grain aphid (Sitobion avenae) in Britain revealed using microsatellites

“…Other relevant ecological factors may be more important at smaller spatial scales and, indeed, may be overlooked in studies considering larger-scale movements. Such factors could include the existence of 'generalist' genotypes or those adapted to particular host plants (Haack et al, 2000;Lushai et al, 2002) as well as microclimate, crop density, natural enemy pressures and potentially, resistance to pesticides (although there is no evidence at present that S. avenae is resistant to any of the commonly used insecticides in the UK).…”