Limited genetic exchanges between populations of an insect pest living on uncultivated and related cultivated host plants

Abstract

Habitats in agroecosystems are ephemeral, and are characterized by frequent disturbances forcing pest species to successively colonize various hosts belonging either to the cultivated or to the uncultivated part of the agricultural landscape. The role of wild habitats as reservoirs or refuges for the aphid Sitobion avenae that colonize cultivated fields was assessed by investigating the genetic structure of populations collected on both cereal crops (wheat, barley and oat) and uncultivated hosts (Yorkshire fog, cocksfoot, bulbous oatgrass and tall oatgrass) in western France. Classical genetic analyses and Bayesian clustering algorithms indicate that genetic differentiation is high between populations collected on uncultivated hosts and on crops, revealing a relatively limited gene flow between the uncultivated margins and the cultivated part of the agroecosystem. A closer genetic relatedness was observed between populations living on plants belonging to the same tribe (Triticeae, Poeae and Aveneae tribes) where aphid genotypes appeared not to be specialized on a single host, but rather using a group of related plant species. Causes of this ecological differentiation and its implications for integrated pest management of S. avenae as cereals pest are discussed.

Maintaining genetic diversity and population panmixia through dispersal and not gene flow in a holocyclic heteroecious aphid species

“…Previous genetic studies on aphids have reported deviation from Hardy-Weinberg Equilibrium because of heterozygosity excess (Papura et al, 2003;Vialatte et al, 2005). Michel et al (2009a) observed similar levels of heterozygote excess with the soybean aphid, with more deviation present in early collected populations.…”

“…However, in some cases, especially with late populations, genotypic diversities were close or at maximum, that is, every individual was represented by a different clonal genotype. In these instances, we also included common population genetic statistics used in previous aphid genetic studies (Miller et al, 2003;Vialatte et al, 2005;Klueken et al, 2011), as data mirrored randomly admixed populations atypical of clonal reproduction. The probability of two individuals that share a MLG (that is, clones) resulting from a sexual reproduction event was calculated using P sex using GenClone (ArnaudHaond et al, 2007).…”

“…Species can be heteroecious (alternating between primary and secondary hosts) or autoecious (complete life cycle on a single host), holocyclic (undergoing sexual and asexual reproduction) or anholocyclic (asexual only), with populations of the same species exhibiting different strategies. Any adaptation that evolves during the asexual stage can quickly become common and spread, as the generation time can be as little as a few days and selection in the form of clonal amplification markedly increases favored clones (Halkett et al, 2005;Vialatte et al, 2005;Harrison and Mondor, 2011). Through holocycly, favored clones have a better opportunity to transfer favorable genetic variation into new combinations through sexual reproduction, increasing genetic diversity and potentially the adaptation response.…”

Crop domestication, global human-mediated migration, and the unresolved role of geography in pest control

“…Native herbivore populations that shift onto agricultural crops can become genetically differentiated from populations that remain on the original host plant (Vialatte et al, 2005;Michel et al, 2010;Lavandero et al, 2011 Midamegbe et al, 2011;Barman et al, 2012;Bourguet et al, 2014). Because host shifts create new ecological opportunities for herbivores, population can diverge via ecological speciation in sympatry (Bush, 1969;Berlocher and Feder, 2002).…”

Evolution of Soybean Aphid Biotypes: Understanding and Managing Virulence to Host-Plant Resistance

“…Diversity is then a result of the interplay between genetic drift (including random mortality from environmental conditions or natural enemies), and selection through clonal amplification. Clonal amplification refers to the rapid increase in frequency in certain asexual clones through selection which is quite common in many aphid species during the asexual phase (Vorburger et al 2003;Vialette et al 2005), and likely occurs in soybean aphid . Currently, the use of soybean aphid resistant varieties is limited, therefore selective pressure and clonal amplification of specific virulent biotypes is not likely to occur.…”