@phdthesis{Pietsch2005,
  author    = {Pietsch, Christof},
  title     = {The genetics of species differences within the genus Nasonia ASHMEAD 1904 (Hymenoptera: Pteromalidae)},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-14348},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2005},
  abstract  = {The genetics of species differences is an outstanding question in evolutionary biology. How do species evolve to become phenotypically distinct and how is the genetic architecture organized that underlie species differences? Phenotypic diverged traits are supposed to be frequently involved in prezygotic isolation, i.e. they prevent the formation of hybrids, whereas postzygotic isolation occurs when hybrids experience a fitness reduction. The parasitic wasp genus Nasonia represents an appropriate model system to investigate the genetics of species differences as well as the genetics of postzygotic isolation. The genus consists of three species N. vitripennis, N. longicornis and N. giraulti that differ particularly in male traits that are assumed to posses an adaptive significance: courtship behaviour and wing size differences. The courtship behaviour consists of cyclically repeated series of head nods that are separated by pauses. The stereotypic performance allowed to split up the display into distinct courtship components. Males of N. vitripennis bear vestigial forewings and are incapable of flight, whereas N. longicornis wear intermediate sized wings and N. giraulti is fully capable of flying. Nasonia species can produce interspecific hybrids after removing Wolbachia bacteria induced hybrid incompatibilities with antibiotics. Postzygotic isolation occurs to different extent and is asymmetric among reciprocal crosses, e.g. inviability is stronger in the N. vitripennis (\&\#9792;) x N. longicornis (\&\#9794;) cross than in the N. longicornis (\&\#9792;) x N. vitripennis (\&\#9794;) cross. The formation of hybrids allow to study the genetic of species differences in QTL (quantitative trait locus) analyses as well as the genetics of postzygotic isolation causing hybrid inviability. The aim of the study was to investigate the genetic architecture of differences in courtship behaviour and wing size between N. vitripennis and N. longicornis and to assess the genetics of postzygotic isolation to gain clues about the evolutionary processes underlying trait divergence and establishment of reproductive isolation between taxa. In a QTL analysis based on 94 F2-hybrid individuals of an LV cross only few QTL for wing size differences have been found with relatively large effects, although a large proportion of the phenotypic variance remained unexplained. The QTL on courtship behaviour analysis based on 94-F2 hybrid males revealed a complex genetic architecture of courtship behaviour with QTL of large phenotypic effects that explained more than 40 \% of the phenotypic variance in one case. Additionally, an epistatic analysis (non-additive interlocus interaction) of courtship QTL revealed frequent genetic interchromsomal relations leading in some instances to hybrid specific effects, e.g. reversion of phenotypic effects or the transgression of phenotypes. A QTL analysis based on a threefold sample size revealed, however, an overestimation of QTL effects in the analysis based on smaller sample size pointing towards a genetic architecture of many loci with small effects governing the phenotypic differences in courtship behaviour. Furthermore, the the study comprised the analysis of postzygotic isolation in the reciprocal crosses N. vitripennis (\&\#9792;) x N. longicornis (\&\#9794;) versus N. longicornis (\&\#9792;) x N. vitripennis (\&\#9794;) located several loci distributed over different chromosomes that are involved in hybrid incompatibility. The mapping of hybrid incompatibility regions reproduced for the first time the observed asymmetries in the strength of postzygotic isolation in reciprocal crosses of between the more distant related taxa within the genus Nasonia. Stronger postzygotic incompatibilities in the VL cross are supposed to result from the superposition of nuclear-nuclear incompatibilities with nuclear-cytoplasmic incompatibilities, whereas the coincidences of these to types of incompatibilities were found to be much weaker in the reciprocal LV cross.},
  subject      = {Pteromalidae},
  language  = {en}
}