Patterns of Genetic Variation and Host Adaptation in an Invasive Population of Rhopalosiphum padi (Hemiptera: Aphididae)

Abstract

Adaptive changes to local conditions are often thought to be required for successful invasions. However, there are also successful invasive asexual species that may have limited potential for evolutionary change. The bird cherry-oat aphid, Bhopalosiphum padi (L.) (Hemiptera: Aphididae), is thought to have been introduced in Australia 100 yr ago and is now an established pest of cereal crops. Here, we use mitochondrial DNA, cytochrome c oxidase subunit I, and nuclear microsatellites to characterize the genetic diversity in invasive R. padi. Asexual reproduction was detected and clonal diversity was low; with two multilocus genotypes, Rp1 and Rp2, dominating all populations. No geographic or host association was detected between the dominant genotypes on cereals but Rp2 was not found on sweet corn, Zea mays L., crops. The fitness of the predominant multilocus genotypes, Rp1 and Rp2, and an uncommon genotype, Rp26, were investigated on different host types (wheat | Triticum aestivum L. |, barley |Hordeum vulgare L. |, triticale | × Triticosecale Wittm. ex A. Camus. |, and sweet corn | Zea mays L. var. rugosa|) at two temperatures. Rp1 and Rp2 performed similarly on cereals and Rp26 performed poorly on all hosts, patterns that might explain field distributions and abundance of these clones. The results suggest that a high level of clonal diversity is not required for successful invasion and that host associations may develop despite low diversity.

Peer Review #1 of "Asexual reproduction of a few genotypes favored the invasion of the cereal aphid Rhopalosiphum padi in Chile (v0.1)"

“…This situation has also been noted in other introduced aphid species such as Myzus persicae and Sitobion avenae (Vorburger et al, 2003;Loxdale et al, 2017). The presence of one dominant genotype in Australian populations of R. padi was even more striking; a single genotype accounted for 62.7% of the population (Valenzuela et al, 2010). Other studies performed in the Northern Hemisphere (e.g., France and China) have also demonstrated the predominance of superclones (Simon et al, 1996;Duan et al, 2017).…”

“…A comparison between these populations revealed significant genetic differentiation; the cyclic parthenogenetic populations exhibited a larger number of alleles, greater allelic richness, and higher genotypic diversity compared with the asexual populations (Duan et al, 2017). Low levels of genetic diversity and differentiation using mitochondrial DNA were also detected in China (Wang et al, This event, together with mild winters and a low abundance of the primary host, may have resulted in the predominance of asexual reproduction (Figueroa et al, 2018;Valenzuela et al, 2010).…”

“…S1). A lack of host-based differentiation has been described in populations from Australia (Valenzuela et al, 2010) and France (Gilabert et al, 2009); these locales are where most genetic differences are associated with host alternation.…”

Novel bioassay to assess antibiotic effects of fungal endophytes on aphids

“…Studies are already in progress using this cup-based method and a modified version of it with A. lentisci and R. padi to investigate the effects of loline-producing alkaloids and entomopathogenic bacterial seed treatments of perennial ryegrass for each species respectively. The versatility of this cup-based assay means it can be used in other areas of research such as life history studies as seen in [49] where the life history of five R. padi genotypes was tested on four different host plants and two temperatures. All D. noxia and A. lentisci used in this study were sourced from the same clonal populations and therefore lacked genetic variation; however, this bioassay can be applied to multiple aphid populations of different genotypes to determine both inter-and intra-specific differences of endophyte effects on life history [17,50].…”

Effects of aphid feeding and associated virus injury on grain crops in Australia

“…Some clones were efficient vectors of specific BYDV-MAV serotypes while others were not, highlighting the value of recording lineage as well as species. In this review, more than a third of studies on cereals and pulses lacked information about aphid species, and there was no information on clonal lineages of the species despite local evidence for biological differences between lineages (Valenzuela et al 2010). Aphid species identification and genotypic characterisation is possible for all local major aphid pest groups through a combination of morphological traits and various mitochondrial and nuclear markers (Hales et al 1997;Valenzuela et al 2007;Foottit et al 2008).…”