INSECT PHYLOGENETICS AND PHYLOGEOGRAPHY

Of the various forms of insect herbivory, the most intimate and complex form is gall induction. Galls are plant tissues but their development is largely controlled by insect genes. They represent discrete microhabitats that support relatively closed communities of specialist inhabitants. This property has made galls important model systems in many subject areas ranging from population dynamics to the evolution of communities. In spite of the utility of insect galls in these topics, the high diversity of galling taxa, processes shaping their distribution and evolution are poorly understood. Recent advances of molecular approaches may provide insight into these processes.

Phylogenetics of gall wasps

With around 1400 described species, gall wasps constitute the second largest group of galling insects, and they induce some of the most structurally complex and diverse galls known. They are obligate plant parasites; the most important host plants are oaks. Oak gall wasps (tribe Cynipini) are cyclically parthenogenetic insects including many well-known species distributed mainly in Holarctic. A number of species within Cyinipidae have lost the ability to induce galls themselves but instead develop inside the galls of other cynipids: these are called inquilines (tribe Synergini). Their host specificity varies from species to species. Little is known about this group.

Despite recent advances in Cynipidae phylogenetics, details are to be explored. Early taxonomy was based on wasp morphology and gall structure. For now, the utility of DNA sequence markers in reconstructing phylogenetic relationship at various levels of divergence is well established. Theoretical advances also provide a standard tool to combine datasets collected on levels of morphology and DNA sequences. We revised relationships in Chilaspis - Dryocosmus (Cynipini) and Synophrus (Synergini) genera. Work on Synergus (Synergini) is in progress.

This work is done in collaboration with G. Melika (Pest Diagnostic Laboratory, PPSCD of County Vas, Hungary), G. Stone (Univ. Edinburgh, UK) and J. Pujade-Villar (Univ. Barcelona, Spain).

Genetic diversity of an inquiline gall wasp

Previous work on gall wasps has revealed substantial intra-specific variation, particularly between regions known to represent discrete Pleistocene glacial refuges. Asia Minor is known to be a centre of diversity. It is a potential source for westward range expansion into Europe. By projecting genetic diversity of populations into a geographic map, colonization routes can be reconstructed by the aid of molecular markers in different scales of space and time.

Parasitism may result in accelerated rates of molecular evolution and it may engender bursts of speciation and diversification. Signs of these events can be detected by studying genetic differentiation. The evolution of host-races appears to represent one of the main routes to diversification in phytophagous insects. Closed communities of galls provide unique systems to test this theory.

Synergus umbraculus is a common inquiline species living predominantly in galls of different Andricus species. Our work shows that it is characterized by high genetic diversity. Different wasp hosts are used simultaneously. Multiple colonization events may account for the pattern detected in the Carpathian basin.