Electrophoretic study of enzymes from cereal aphid populations. III. Spatial and temporal genetic variation of populations ofSitobion avenae(F.) (Hemiptera: Aphididae)

Abstract

Ninety-two individuals of Sitobion avenae (F.) collected throughout Britain in 1979 and, were cloned and investigated genetically by electrophoresis of 14 enzymes representing 26 loci. Percentage polymorphism (P) differed considerably between years, 64% (16/25 loci) in 1979 and 19% (5/26) in 1980, whereas average heterozygosity (H) was low (ca. 2%) in both years and confined mainly to one locus, EST-1. The prevalence of homozygous allozyme variation supports ecological findings suggestingS. avenae to be largely anholocyclic in Britain. In 1981 and 1982, large populations, sampled from 11 sites in Britain and Spain, were examined at 13 loci. H ranged from 2 to 7 • 6%, with heterozygosity restricted again mainly to EST-1. Some alleles were unique to certain geographical regions (including Britain or Spain); others showed significant spatial, and in two British populations examined in successive years, temporal frequency differences. Calculating Nei's genetic identity (/) and distance (D) coefficients for each population pair mostly gave 7>0-8, Z?<0-2 with overall means (± s.e.m.) of 0-896 ± 0-006 and 0-111 ± 0-006, respectively, which are comparable with geographical population values for other insects. D was poorly correlated with geographical distance, although values were slightly greater (ca. 0-025) for international population comparisons and did not overlap on a principal coordinates plot. The overall population similarity suggests substantial inter-population gene flow; geographical barriers may have restricted movements but seemingly have not led to allopatric race formation. P and H values resemble those for many other aphids, but H values are lower than typically found in other insects. Possible causes of this heterozygote deficiency are discussed.

Patterns of genetic variation among Canadian populations of the bird cherry-oat aphid, Rhopalosiphum padi L. (Homoptera: Aphididae)

“…'n rosae, Rhomberg et a!., (1985) found large heterozygote deficits and suggested that they were a direct consequence of clonal prolif eration and the diffusion of a small number of genotypes. Similar 11W deviations in Sitobion avenae were attributed to its complete loss of sexual reproduction (Loxdale et al, 1985) whereas those noted for the sumac aphid Melaphis rhois were linked to inbreeding (Hebert et a!., 1991). In this study 13W deviations were found only at the PEP locus in two populations from the primary host and three from secondary hosts.…”

“…The most striking feature to emerge from these studies is the very low level of genetic variation (as measured by allozyme analysis) among aphid populations. While most other invertebrates show an average heterozygosity of 10 per cent (Nevo, 1978;Ayala, 1982;Graur, 1985), heterozygosities in aphids average only 1.5 per cent (Tomiuk & Wdhrmann, 1980;Loxdale et a!., 1985;Loxdale & Brookes, 1990;Hebert et a!., 1991). An effort has been made to link this unusually low level of variation to those biological characteristics of aphids which differentiate them from other invertebrate groups.…”

Genetic variation and phylogenetic relationships among worldwide collections of the Russian wheat aphid, Diuraphis noxia (Mordvilko), inferred from allozyme and RAPD-PCR markers

“…Isozyme electrophoresis has been useful in identifying markers for studies of aphid breeding structure (Tomiuk Ct at., 1979;Singh & Cunningham, 1981; Loxdale et a!., 1983; Tomiuk & Wohrmann, 1983;Steiner et a!., 1985a). However, polymorphisms are typically detected at a few loci (Wool ci' at., 1978;Loxdale et at., 1985;Rhomberg et aL, 1985;Steiner et at., 1985b) and in several aphid species no variation has been found (May & Holbrook, 1978;Tomiuk & Wohrmann, 1980;Loxdale et a!., 1983;Beregovoy & Starks, 1986). Substantially more genetic variation has been detected using mitochondrial DNNrestriction fragment length polymorphisms (mtDNA-RFLPS) (Powers et at., 1989;) and DNA fingerprinting probes (Carvalho et at., 1991;Shufran et a!., 1991).…”

Characterization and discrimination of three Rhopalosiphum species (Homoptera: Aphididae) based on isozymes

“…Considerable differences in percentage of polymorphism from one year to the next and low average heterozygosity in populations of Sitobion avenae (Fabricius, 1775) were reported by LOXDALE et at. (1985a).…”