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

Abstract

Numerous studies have examined the genetic diversity and genetic structure of invading species, with contrasting results concerning the relative roles of genetic diversity and phenotypic plasticity in the success of introduced populations. Increasing evidence shows that asexual lineages of aphids are able to occupy a wide geographical and ecological range of habitats despite low genetic diversity. The anholocyclic aphid Melanaphis sacchari is a pest of sugarcane and sorghum which originated in the old world, was introduced into the Americas, and is now distributed worldwide. Our purpose was to assess the genetic diversity and structuring of populations of this species according to host and locality. We used 10 microsatellite markers to genotype 1333 individuals (57 samples, 42 localities, 15 countries) collected mainly on sugarcane or sorghum. Five multilocus lineages (MLL) were defined, grouping multilocus genotypes (MLG) differing by only a few mutations or scoring errors. Analysis of a 658 bp sequence of mitochondrial COI gene on 96 individuals revealed five haplotypes, with a mean divergence of only 0.19 %. The distribution of MLL appeared to be strongly influenced by geography but not by host plant. Each of the five MLL grouped individuals from (A) Africa, (B) Australia, (C) South America, the Caribbean and the Indian Ocean including East Africa, (D) USA, and (E) China. The MLL A and C, with a wide geographic distribution, matched the definition of superclone. Among aphids, M. sacchari has one of the lowest known rates of genetic diversity for such a wide geographical distribution.

Recruitment of aphidophagous arthropods to sorghum plants infested with Melanaphis sacchari and Schizaphis graminum (Hemiptera: Aphididae)

“…Originally described as Aphis sacchari from specimens collected on sugarcane in Java, Indonesia (Zehntner, 1897), it was first reported in North America on sugarcane in Belle Glade, Florida in 1977 (Mead, 1978). Blackman and Eastop (2006) considered Melanaphis sorghi as a distinct species, but the morphological distinctions from M. sacchari are ambiguous and recent analyses of population genetics revealed clones defined by geography, rather than by host plant utilization (Nibouche et al, 2014). Thus M. sorghi is likely a synonym, as argued by Remaudiere and Remaudiere (1997), and M. sacchari appears to have arrived in the USA on infested sugarcane material from Hawaii (Nibouche et al, 2014).…”

A Sugarcane Aphid “Super‐Clone” Predominates on Sorghum and Johnsongrass from Four US States

“…], sorghum, and Johnsongrass, the distribution of multilocus lineages was influenced by geography but not host plant (Nibouche et al, 2014). Previously, in a study examining SCA on a worldwide scale where samples were collected from 2007 to 2013 on sugarcane, pearl millet [Pennisetum glaucum (L.) R.…”

“…For SCAs collected on sorghum and Johnsongrass, the observed heterozygosity was higher than the expected heterozygosity for three loci, which indicates an excess of heterozygosity at these loci ( Supplemental Table S3). An excess of heterozygosity at many loci is common in aphids that are continuously parthenogenetic (Figueroa et al, 2005;Harrison and Mondor, 2011;Nibouche et al, 2014). The reason for this excess of heterozygosity is that neutral allele sequence divergence can accumulate to a high degree in asexual lineages (Birky, 1996).…”

“…and in Louisiana from sugarcane and Johnsongrass (Nibouche et al, 2014). In 2007, SCAs were collected in Hawaii from sugarcane (Saccharum spp.)…”

“…In 2007, SCAs were collected in Hawaii from sugarcane (Saccharum spp.) and in Louisiana from sugarcane and Johnsongrass (Nibouche et al, 2014). These samples were genotyped with 10 simple sequence repeat (SSR) markers.…”