Ecology and Genetics of Pityogenes chalcographus

Since the 1970ies, the spruce bark beetle Pityogenes chalcographus poses a unique case in European forest entomology as populations were classified into two major geographic groups (Central and Northern Europe) revealing crossing incompatibility. Recently, the genetic divergence of these two groups was confirmed by analyzing mitochondrial markers. Further, four other mitochondrial entities within European P. chalcographus populations were found - three closely related ones situated in the Apennines and one located in the Dinaric Alps. For these entities no information on their phenotypes exists. In the proposed project, the first objective will be to elucidate the semiochemical system of the mitochondrial defined P. chalcographus entities. The enantiomeric forms of chalcogran and the geometric isomers of methyl decadienoate will be analyzed using gas chromatography and mass spectrometry. The quantitative variation of the pheromone components and their ratios from different attack phases, considering also body weight and fat content of the individuals, will be considered. The second objective involves use of the mitochondrial defined P. chalcographus entities for crossing and mate choice experiments in order to quantify the strength of prezygotic and postzygotic incompatibility. Crossings will be performed until the F2 as this will give insight into whether the hybrid generation (F2) is viable or whether hybrid breakdown can be observed. The third objective will be the analysis of the European populations by AFLP to obtain an insight into the nuclear genome. This project will enable syntheses of evolutionary forces that cause phenotypic divergence and speciation in P. chalcographus.

Since the 1970ies, the spruce bark beetle Pityogenes chalcographus poses a unique case in European forest entomology as populations were classified into two major geographic groups (Central and Northern Europe) revealing incompatibility if crossed with each other. The genetic divergence of these two groups was confirmed by maternal genetic markers. The aims of the project had to be changed after rearing problems and were thereupon: 1. Nuclear confirmation of the P. chalcographus entities 2. Compare the evolutionary histories of P. chalcographus and Ips typographus and 3. Detecting parameters influencing the maternal DNA like bacterial endosymbionts or nuclear copies of the maternal DNA (numt). The analysis of European P. chalcographus specimens with known maternal genotype by highly polymorphic loci revealed a homogenous nuclear genome. This incongruent nuclear and maternal data can be explained by their different evolution and differences between male and female biology. I. typographus and P. chalcographus have a similar biology, life history, and habitat.