Metapopulation structure of the specialized herbivoreMacrosiphoniella tanacetaria(Homoptera, Aphididae)

Abstract

We investigated population dynamics, genetic diversity and spatial structure in the aphid species Macrosiphoniella tanacetaria, a specialist herbivore feeding on tansy, Tanacetum vulgare. Tansy plants (genets) consist of many shoots (ramets), and genets are grouped in sites. Thus, aphids feeding on tansy can cluster at the level of ramets, genets and sites. We studied aphid population dynamics in 1997 and 2001 and found that within sites: (i). at any time, aphids used only a fraction of the available ramets and genets; (ii). at the level of ramets, most aphid colonies survived only one week; (iii). at the level of genets, mean survival time was less than 4 weeks; and (iv). colonization and extinction events occurred throughout the season. We sampled aphids in seven sites in the Alsace region, France (4-45 km apart) and two sites in Germany in 1999 to study genetic structure within and between populations. Genetic analyses using nine microsatellite loci showed that: (i). genotypic variability was high, (ii). none of the populations was in Hardy-Weinberg equilibrium, (iii). heterozygote deficits and linkage disequilibria were frequent, and (iv). all populations were genetically differentiated, even at a small geographical scale. Renewed sampling of the Alsace sites in 2001 showed that three populations had become extinct and significant genetic changes had occurred in the remaining four populations. The frequencies of extinction and colonization events at several spatial scales suggest a hierarchical metapopulation structure for M. tanacetaria. Frequent population turnover and drift are likely causes for the genetic differentiation of M. tanacetaria populations.

Founder events as determinants of within-island and among-island genetic structure of Daphnia metapopulations

“…Patterns of isolation by distance in highly structured metapopulations are often highly scattered and, consequently, large samples are needed for its detection (eg, Nurnberger and Harrison, 1995;Giles and Goudet, 1997;Roach et al, 2001;Charbonnel et al, 2002;Massonnet et al, 2002). This is due to the highly stochastic effect of turnover on the distribution of genetic diversity so that observed correlations can be weak, even if migration rate is strictly negatively correlated with geographic distance (Whitlock, 1992a;.…”

Host-associated genetic structure of Mexican populations of the cabbage aphid Brevicoryne brassicae L. (Homoptera: Aphididae)

“…The existence of host-mediated genetic differentiation is relevant for the analysis of the ecological causes that promote differentiation (Nason et al, 2002). The genetic structure of aphid species is maintained by selection adjusting populations to the local environmental conditions (Tomiuk and Wö hrmann, 1984;EggersSchumacher and Sander, 1988;Tomiuk et al, 1991), by reduced gene flow (Loxdale and Brookes, 1990;Loxdale et al, 1998;Johnson et al, 2002;Massonnet et al, 2002), itself a function of species-specific flight behaviour dependent on their tendency and their ability to fly (see Loxdale et al, 1993, for a review), and by genetic drift (De Barro et al, 1995a). Perhaps, as in the case of the aphid Methopolophium dirhodum, differentiation between hosts in the localities of Mitzitón and Balú n could be better explained if founder effects or genetic drift have occurred (see De Barro et al, 1995a).…”

Evidence for gene flow and local clonal selection in field populations of the grain aphid (Sitobion avenae) in Britain revealed using microsatellites

“…Similar studies have also revealed differences in the genetic structuring of natural aphid populations, relating to lifecycle strategy and clonal selection (eg Simon et al, 1999;Guillemaud et al, 2003). The genetic structuring reflects flight behaviour (eg low genetic differentiation over a wide area for highly migratory species), although selection for lifecycle types better adapted to the climate in particular regions is also apparent (eg Massonnet et al, 2002;Guillemaud et al, 2003).…”