In our working groups we use morphology, DNA and optical methods to expedite and facilitate the process of identifying and differentiating units of biological diversity, often species. High-throughput, specimen based integrative taxonomy forms the basis of this work, but we are exploring a variety of innovative imaging technologies with potential for automation. This is especially important to us as we try to extract not only taxonomic information, but also functional information from the treasures lying in museum insect collections.
Example research projects :
The evolution of traits is essential for species diversification and adaptation to changing environmental conditions. Understanding how traits evolved and allowed taxa to diversify ecologically is essential for understanding present-day species and ecological diversity. Phylogenomic methods allow generating very robust assessments of the evolution of ecologically interesting groups, a prerequisite for assessing morphological and ecological diversification patterns and processes.
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Phenotypic variation and changes of this variation in populations are the fundamental basis for evolution. In my working group, we are interested in how environmental changes act as selection pressures in populations and species. Using population genetic and genomic methods in time series data we assess population dynamics of species and communities and how environmental changes drive shifts in genetic and phenotypic variation. We do this in the context of both historic and ongoing environmental change.
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At the LOEWE Centre for Translational Biodiversity Genomics, we are interested in harvesting genomic information from a wide range of organisms to better understand the genomic underpinnings of diversification and making genomic resources available for basic and applied research. In my working group, we specifically use genomic and transcriptomic methods to study the genomic basis of caddisfly silk.
The investigations on the gall making sawflies of the genera Pontania, Euura and Phyllocolpa (Tenthredinidae: Nematinae) is an essential part of research in the section Entomology III since 1981. The species of these genera belong to the most common gall-formers on willows (Salix spp.), the taxonomy of which is highly problematical as morphological characters of galls, larvae, and imagines are scarce or very variable. One of the most reliable distinguishing characters of the gall-formers is their association with the foodplant species. In order to clarify the taxonomic status of the species, detailed morphological investigations have been made on the larvae, adults and galls as well as a series of oviposition experiments. Reared material tested and differentiated biologically, especially according to host plant preference, was used for recording morphological characters and their variability within a gall-former population or between different populations. Considering the combination of morphological and biological characters should ensure success in finding the true status of a species as it was accomplished in the present taxonomical studies.
Since 1981 about 140,000 galls (until 2004) of the sawfly genera Pontania, Euura, and Phyllocolpa were collected from 33 willow species in 250 natural sites of 10 European countries. The rearing of entire galls was conducted in the laboratory under ambient conditions. In order to clarify the host plant specificity of the gall-formers more than 550 oviposition experiments have been carried out, testing 38 Pontania species as well as 20 Euura and 15 Phyllocolpa species. A total of 204 individuals of 33 Salix species were used in these experiments, deriving from 102 willow populations. More than 1000 females were tested, originating from 222 populations. Altogether 500 no-choice tests and 60 multiple-choice tests were conducted until the year 2004, surveying 357 different population combinations of gall-former by Salix species. The oviposition experiments were carried out in spring with freshly emerged females. At first, the suitability of the used host plant was examined by an exclusion procedure: The willow individual was offered to its specific gall-former to confirm the unrestricted acceptance of the plant through successful gall induction and oviposition. Those willows which passed the qualification test successfully were then used in the no-choice as well as mutiple-choice tests (= preference tests in small greenhouses).
The results of the oviposition experiments indicated a much narrower host plant spectrum than that mentioned in the literature for a given species. Thus, e.g. for E. atra which induces spindle like stem galls, a wide range of host plants was postulated for a long time, but, oviposition experiments, supplemented by morphological studies, have proved the existence of several distinct species associated with different willow species. Six species of the E. atra-group could be described as new to science. A similar situation could be ascertained in the Pontania dolichura-group which was considered to be monotypical for a long time. Finally, the results of the oviposition experiments and supplementing morphological studies allowed to clarify the taxonomical confusions within all species-groups of Pontania, Phyllocolpa, and Euura.
Gall induction requires an efficient host plant finding by the sawfly female. Due to her high sensitivity to variations of the host plant quality, the female is able to locate very reliably the plant tissue for oviposition. Gall induction and oviposition occur according to the following pattern: 1. selection of the host plant species, 2. selection of the host plant individual, 3. localization of the plant tissue for oviposition, 4. injection of the cecidogenous fluid, 5. egg deposition (sometimes no egg was laid).
Gall induction and oviposition are not separated temporally from each other in Euura and most Pontania species, occurring shortly after the female has inserted her saw-like ovipositor into the plant tissue. In contrast, females of the Pontania dolichura-group and particularly of the genus Phyllocolpa, perform a more or less complex procedure of gall initiation before oviposition.
Females of Pontania oviposit exclusively on longitudinally folded leaves of the apical bundle of a growing shoot, inserting their saw once through the midrib of the leaf (often side rib in the proxima-group). In general only a single egg is laid into the mesophyll tissue by a simultaneous injection of the cecidogenous fluid. Pontania species induce four different types of closed galls, exclusively on the leaves of their host plants: thick-walled, elongated sausage-shaped galls on the upper surface of the leaf; thin-walled, kidney-shaped spacious galls transected horizontally by the leaf blade; thick-walled, bean-shaped galls with a narrow cavity, transected horizontally by the leaf blade; and thin to thick-walled, pea-shaped galls at the underside of the leaf.
Oviposition of Euura occurs at different organs of their host plants, dependent on the particular gall-type of the species. Bud-gallers oviposit only into new flower buds of the next year, arising in the axis of young leaves. Similar to Pontania leaf-gallers, oviposition of stem gallers occurs at the apical bundle of longitudinally folded leaves. However, the females of this guild insert their long ovipositor through the base of unfolded leaves into the young, very succulent stem. The females of gall-formers which induce petiole- or midrib-galls insert their ovipositor into the suitable plant tissue of one of the longitudinally folded leaves of the apical bundle.
In contrast, the species of the genus Phyllocolpa exhibit the most complex behaviour of gall induction. Oviposition occurs at one of the still folded leaves of the apical bundle or at one of the freshly unfolded young leaves below the apical bundle, depending on the species. The females induce simple or twisted leaf folds along the edge of young willow leaves, resulting from a swelling which is caused by multiple ovipositor insertions.
Gall formations can be induced only at viable plant parts. They can develop either during the entire vegetation period or only in temporally limited phases, depending on the generation sequence of the inducer or his inclination for a certain developmental stage of the plant. Gall formation is indispensable for a successful reproduction, demonstrating the particularly close relationship of the inducer to his host plant.
The species of Pontania, Euura, and Phyllocolpa always select specific, viable plant parts for oviposition, initiating gall formation by secreting the cecidogenous fluid of the accessory glands through the ovipositor. A prerequisite for an unimpaired gall formation is a precise placing and dosage of the cecidogenous fluid by the female, causing specific physiological procedures in the plant which stimulate and control the growth of the gall. The success of the female is primarily based on her ability to locate exactly the plant tissue for gall induction and oviposition. The oviposition mode as well as the composition of the cecidogenous fluid may have a relevant influence on the shape of the gall.
Gall formation of sawflies is normally initiated by the females during (Pontania, Euura) or before oviposition (Phyllocolpa). The sawfly female injects the cecidogenous fluid of its accessory glands into the meristem tissue, in most species inducing a complete development of galls.Sometimes hybrids are accepted by the gall formers. This was documented by galls of Pontania samolad and those of P. arcticornis next to each other on the leaves of the hybrid S. lapponum x phylicifolia.
The ability to induce galls presupposes a functioning interaction of the cecidogenous secretion of the gall-former and the pysiological characteristics of the host plant, i.e. only with suitable host plants an unimpaired gall formation may occur which ensures the development of the sawfly larva. Therefore, the acceptance of the host plant depends on various factors, e.g. certain plant defence reactions, genetic changes, effects of hybridisation, and last but not least the high variabilities of biochemical characteristics (secondary compounds, in particular phenol glycosides).
A distinct host plant specificity can be understood as a prerequisite for successful reproduction, permitting only the attack of a single host plant species and, occasionally, of its hybrids. The latter was documented by galls of Pontania samolad and those of P. arcticornis next to each other on the leaves of the hybrid S. lapponum x phylicifolia. The galls differed clearly by their specific shape which appeared unchanged on the hairy leaves of this willow hybrid: the galls of P. samolad were typically pea-shaped and hairy, whereas the galls of P. arcticornis on the same leaf were often exceptionally bizarre and completely glabrous.
The principal research of the section Entomology III includes the analysis of the biodiversity of different ecosystems. We distinguish between ecosystems of different sizes: macrosystems which are indistinctly delimited from the surrounding area and microsytems (e.g. plant galls or flowers) which normally are well-defined. In connection with the analysis of galls we tried to answer following questions:
The studies which are in progress in the section Entomology III correspond to following subjects: