Regular or covert sex defines two lineages and worldwide superclones within the leaf‐curl plum aphid (Brachycaudus helichrysi, Kaltenbach)

Abstract

Asexual reproduction occurs widely in plants and animals, particularly in insects. Aphid species usually reproduce by cyclic parthenogenesis, but many species include obligate asexual lineages. We recently showed that the leaf-curl plum aphid, Brachycaudus helichrysi, actually encompasses two lineages, B. helichrysi H1 and H2. Ecological data suggest that these lineages have different life cycles. We conducted a large population genetics study, based on 14 microsatellite loci, to infer their respective life cycles and investigate their population structure and geographical distribution. Brachycaudus helichrysi H1 displayed the genetic signature of cyclical parthenogenesis, using plum trees as primary hosts for sexual reproduction, as classically described for B. helichrysi. This global survey showed that the Central Asian population of H1 was clearly differentiated from American-European populations. By contrast, B. helichrysi H2 displayed the typical signature of obligate asexual reproduction. H2 encompassed at least eight highly successful genotypes or superclones. This lack of ability to undergo sexual reproduction was confirmed for one of the superclones by sex induction experiments. We found only one B. helichrysi H2 population that underwent sexual reproduction, which was collected from peach trees, in Northern India. Our results confirm that H1 and H2 have different life cycles. Brachycaudus helichrysi H1 is clearly heteroecious using plum trees as primary hosts, while B. helichrysi H2 encompasses several anholocyclic lineages, and some heteroecious populations that until now have only been found associated with peach trees as primary hosts. We discuss implications of these findings for the pest status of B. helichrysi lineages.

Low Genetic Diversity in Melanaphis sacchari Aphid Populations at the Worldwide Scale

“…At least two of the five MLLs covered a very wide geographic area and matched the pattern of a single asexual genotype with a high capacity for dispersal which would have spread across a large area: MLL-A was observed in West and East Africa, and MLL-C was observed in South America, the Indian Ocean, East Africa, and the Caribbean. Both MLLs match the definition of “superclone” [7], characterised by geographically and ecologically widespread distribution, which has already been documented in several aphid species [9], [10], [11], [55], [56].…”

“…High genetic diversity and evidence for sexual reproduction was also observed in A. gossypii alate spring migrants in France [54]. Similarly, in the Brachycaudus helichrysi (Kaltenbach) sibling species H2, a sexually reproducing population was identified in India, despite almost exclusively clonal reproduction at the worldwide scale [11]. This shows that sexual admixture can still exist in a local population even in species which are highly clonal at the worldwide scale.…”

“…Organisms with clonal reproduction may exhibit reduced genetic diversity within populations, as better-adapted clonal genotypes expand and dominate available resources [6]. In aphids, the concept of “superclones” emerged [7] when a few asexual genotypes of the same species were able to colonize a wide geographical or ecological range of habitats [8]–[11]. The capacity of these populations to adapt to different conditions could be the result of a preadaptation capacity for phenotypic plasticity rather than local selection acting on genetic diversity [12], [13].…”

Microsatellite Markers Reveal a Predominant Sugarcane Aphid (Homoptera: Aphididae) Clone is Found on Sorghum in Seven States and One Territory of the USA

“…This may be due to a wide range of phenotypic plasticity, as aphids can produce winged or wingless forms in response to host plant quality, crowding, or daylength (Zepeda‐Paulo et al, 2010). Alternatively, the success of an asexual lineage may be that they are not dependent on finding suitable mates or mating sites for their long‐term survival (Piffaretti et al, 2013). Another hypothesis is that aphids that are superclones have the ability to tolerate allelochemicals, which allows high fitness across multiple hosts (Castañeda et al, 2010).…”

Invasion of sorghum in the Americas by a new sugarcane aphid (Melanaphis sacchari) superclone

“…Since the congruence between COI haplotypes and microsatellite MLGs is strong, the lack of matching between AFLP clusters and microsatellite MLGs makes the correspondence between AFLP clusters and COI haplotypes unsubstantiated. MLL-F appears as a ‘superclone’ [ 18 ], a concept used in aphids when a few asexual genotypes of the same species are able to colonize a wide geographical or ecological range of habitats [ 31 , 32 ]. While sexual morphs have been observed in Mexico [ 33 ], our study did not support the occurrence of sexual reproduction events in the geographic range studied, according to the low p sex value observed, which indicates that replicates from the same MLG were unlikely to have derived from distinct reproductive events [ 27 ].…”