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

Abstract

Past allozyme studies have shown a very low level of genetic variation among aphid populations. Attempts have been made to link this lack of diversity to the biological characteristics of aphids. This study examines the effect of host-alternation on genetic diversity in Canadian populations of the aphid Rhopalosiphum padi. Allozyme analysis of 15 populations on the primary host and 14 on the secondary hosts revealed polymorphism at only three of 51 loci. Little geographical differentiation was observed among populations from a single host category. However, gene frequency differences were noted between populations on primary and those on secondary hosts at two of three polymorphic loci and the mean heterozygosity was substantially reduced on secondary hosts. This pattern might result from the admixture on secondary hosts of resident clones and relatively invariant migrants from southern areas. Alternatively, the decreased heterozygosity might result from either a selective disadvantage of heterozygotes on secondary hosts or their selective migration to other hosts.

Genetic diversity and mode of reproduction in French populations of the aphid Rhopalosiphum padi L.

“…In agreement with earlier studies (Loxdale & Brookes, 1988;Simon & Hebert, 1995) on R. padi, Fig. 1 Origins of the 45 populations of Rhopalosiphum padi collected throughout France in spring and summer 1994 and analysed for allozyme variation at four loci.…”

“…Holocyclic populations in France also showed the genetic attributes of bisexual species, such as the congruence of genotypic frequencies to Hardy-Weinberg equilibrium and the absence of linkage disequilibrium (data not shown), as is typical for cyclic parthenogens (Hebert, 1987). These same populations showed little regional differentiation in genotypic frequencies as evidenced by very low FST values, providing further evidence for the high vagility of this species (Loxdale & Brookes, 1988;Simon & Hebert, 1995). The mean heterozygosity of individuals from holocyclic populations in France (H-0.126) was similar to that noted in Canadian populations (H = 0.149) (Simon & Hebert, 1995).…”

“…Populations of R. padi in France possessed higher allelic diversity at the four polymorphic loci (12 alleles vs. seven) than their Canadian counterparts ( Simon & Hebert, 1995), but similar diversity to English populations (Loxdale & Brookes, 1988). Canadian populations also showed differences in allele frequency distribution when compared with European ones.…”

“…Each individual was assayed for variation at four enzymes; Sdh (sorbitol dehydrogenase, EC 1.1.1.44), Pgm (phosphoglucomutase, EC 5.4.2.2), Pep (peptidase, EC 3.4.11-13) and Aat (aspartate aminotransferase, EC 2.6.1.1). These enzymes were chosen for analysis because they were found to be reliably resolved and polymorphic in previous surveys of allozyme variation in R. padi (Loxdale & Brookes, 1988;Simon & Hebert, 1995).…”

“…In this study, we compare allozyme variation at four polymorphic loci (Loxdale & Brookes, 1988;Simon & Hebert, 1995) among spring populations of R. padi from their primary and secondary hosts in order to analyse the influence of the mode of reproduction on genetic diversity and population structure. We also analyse the genetic composition of summer populations of R. padi on its secondary hosts, which should be a mixture of holocyclic and anholocyclic clones.…”