Chemosystematics Using Cuticular Compounds: A Powerful Tool to Separate Species in Mediterranean Dung Beetles (Coleoptera: Geotrupidae)

The use of chemical characters to infer a phylogeny is known to be promising to ascertain phylogenetic relationships in controversial groups. Dung beetle classifications containing the Geotrupidae family, based on morphological characters and genes, are debated with respect to the subfamilies, such as the Bolboceratids. In our study, we used different approaches to generate and compare the Geotrupidae phylogenies based on genetics and chemotaxonomy. Cuticular compounds were analyzed for 12 species of Mediterranean dung beetles to build a chemical phylogeny. In addition, mitochondrial and nuclear marker concatenation have been used to elaborate the molecular phylogeny. Using the cuticular compound continuous data, our results showed that each species was associated with a specific chemical pattern and that all individuals belonging to the same species displayed a similar chemical blend. The most distant species was Bolbelasmus gallicus, with an evident distinction from the other species due to several compounds. The maximum parsimony tree showed that all genera belonging to a Geotrupidae subfamily were grouped in the same clade, with B. gallicus species isolated in another clade, similar to the chemotaxonomy grouping. A strong positive correlation between chemotaxonomy and genetic phylogeny has been demonstrated, underlying a genetic basis for cuticular hydrocarbon variations. Our results are congruent with previous studies using morphological or genetic data. Our results also showed that only 10 compounds can be used to distinguish at least six species of dung beetle and that chemotaxonomy could become a useful and affordable tool to determine phylogenetic relationships in insects.

Olfactory selection of Plantago lanceolata by snails declines with seedling age

BACKGROUND AND AIMS

Despite recent recognition that (1) plant-herbivore interactions during the establishment phase, (2) ontogenetic shifts in resource allocation and (3) herbivore response to plant volatile release are each pivotal to a comprehensive understanding of plant defence, no study has examined how herbivore olfactory response varies during seedling ontogeny.

METHODS

Using a Y-tube olfactometer we examined snail (Helix aspersa) olfactory response to pellets derived from macerated Plantago lanceolata plants harvested at 1, 2, 3, 4, 5, 6 and 8 weeks of age to test the hypothesis that olfactory selection of plants by a generalist herbivore varies with plant age. Plant volatiles were collected for 10 min using solid-phase microextraction technique on 1- and 8-week-old P. lanceolata pellets and analysed by gas chromatography coupled with a mass spectrometer.

KEY RESULTS

Selection of P. lanceolata was strongly negatively correlated with increasing age; pellets derived from 1-week-old seedlings were three times more likely to be selected as those from 8-week-old plants. Comparison of plant selection experiments with plant volatile profiles from GC/MS suggests that patterns of olfactory selection may be linked to ontogenetic shifts in concentrations of green leaf volatiles and ethanol (and its hydrolysis derivatives).

CONCLUSIONS

Although confirmatory of predictions made by contemporary plant defence theory, this is the first study to elucidate a link between seedling age and olfactory selection by herbivores. As a consequence, this study provides a new perspective on the ontogenetic expression of seedling defence, and the role of seedling herbivores, particularly terrestrial molluscs, as selective agents in temperate plant communities.