Clonal diversity and population genetic structure of the grain aphid Sitobion avenae(F.) in central Europe

Abstract

The grain aphid, Sitobion avenae (F.), displays a number of different life-cycles. These range from complete asexual viviparous and frost-sensitive lineages (anholocyclic) to those including a single sexual generation and which produce frost resistant eggs (holocyclic). In addition, combinations of both life cycles can occur. The spread of life-cycles in a population is known to be dependent on winter climate and earlier studies have used highly polymorphic DNA-markers (microsatellites) to elucidate the influence of seasonal factors on life-cycle variation. However, to date, no such field studies have been performed in geographic areas were mild and cold winters vary between years. Therefore, the central aim of this project was to analyse populations of S. avenae from four diverse geographic regions, viz. northern Germany, two regions from central Germany and one from southern Hungary in three consecutive years. Changes of clonal diversity and population genetic structure were compared within and between years at 32 locations from central and northern Germany differing in the complexity of their landscape structure. The results revealed that seven asexual clones (= multilocus microsatellite genotypes) of S. avenae were common on wheat (Triticum aestivum) and widespread over locations and regions in Germany, including a single clone that was also present in Hungary over two consecutive years. Furthermore, genotypic diversity was dependent on winter climate in Hungary and central Germany, although the two parameters were apparently not correlated in northern Germany. Beside climate effects, genotypic diversity showed a significant positive relationship to simple structured landscapes in central and northern Germany in 2001, but this effect was outweighed in central Germany by successive colder winters in 2002 and 2003. Analysis of the within-season dynamics of clones revealed contrary development in time and space in a yearly repeating pattern. The change in clonal communities was probably dependent on regional insecticide management, clonal variation in host-plant shifts and a restriction of short distance migration by natural geographic barriers. However, long distance migration was high enough to prevent the genetic isolation of populations from northern Germany to Hungary. Overall, the present results confirmed the homogenising effects of migration at a scale of < 50 km and differentiation in genotypic diversity at regional scales > 100km. This project was part of the project BIOPLEX ( Biodiversität und räumliche Komplexität in Agrarlandschaften unter Global Change , Project ID: 01LC0020), financed by the Federal Ministry of Education and Research.