Evolution of cuticular hydrocarbons in the hymenoptera : a meta-analysis

Chemical communication is the oldest form of communication, spreading across all organisms of life. In insects, cuticular hydrocarbons (CHC) function as the chemical recognition cues for the recognition of mates, species and nest-mates in social insects. Although much is known about the function of individual hydrocarbons and their biosynthesis, a phylogenetic overview is lacking. Here we review the CHC profiles of 241 species of hymenoptera, one of the largest and important insect orders, including the Symphyta (sawflies), the polyphyletic Parasitica (parasitoid wasps) and the Aculeata (wasps, bees and ants). We investigated whether these five major taxonomic groups differed in the presence and absence of CHC classes and whether the sociality of a species (solitarily vs. social) had an effect on CHC profile complexity. We found that the main CHC classes (i.e., n-alkanes, alkenes and methylalkanes) were all present early in the evolutionary history of the hymenoptera, as evidenced by their presence in ancient Symphyta and primitive Parasitica wasps. Throughout all groups within the Hymenoptera the more complex a CHC the fewer species that produce it, which may reflect the Occam's razor principle that insects’ only biosynthesize the most simple compound that fulfil its needs. Surprisingly there was no difference in the complexity of CHC profiles between social and solitary species, with some of the most complex CHC profiles belonging to the Parasitica. This profile complexity has been maintained in the ants, but some specialisation in biosynthetic pathways has led to a simplification of profiles in the aculeate wasps and bees. The absence of CHC classes in some taxa or species may be due to gene silencing or down-regulation rather than gene loss, as evidenced by sister species having highly divergent CHC profiles, and cannot be predicted by their phylogenetic history. The presence of highly complex CHC profiles prior to the vast radiation of the social hymenoptera indicates a 'spring-loaded' system where the diverse CHC needed for the complex communication systems of social insects, were already present for natural selection to act upon rather than evolve independently. This would greatly aid the multiple evolution of sociality in the Aculeata

Canopy light heterogeneity drives leaf anatomical, eco-physiological, and photosynthetic changes in olive trees grown in a high-density plantation

15 p., 8 fig., 2 tab. Available online 26 October 2014. The definitive version is available at: http://link.springer.com/article/10.1007/s11120-014-0052-2In the field, leaves may face very different light intensities within the tree canopy. Leaves usually respond with light-induced morphological and photosynthetic changes, in a phenomenon known as phenotypic plasticity. Canopy light distribution, leaf anatomy, gas exchange, chlorophyll fluorescence, and pigment composition were investigated in an olive (Olea europaea, cvs. Arbequina and Arbosana) orchard planted with a high-density system (1,250 trees ha−1). Sampling was made from three canopy zones: a lower canopy (2 m). Light interception decreased significantly in the lower canopy when compared to the central and top ones. Leaf angle increased and photosynthetic rates and non-photochemical quenching (NPQ) decreased significantly and progressively from the upper canopy to the central and the lower canopies. The largest leaf areas were found in the lower canopy, especially in the cultivar Arbequina. The palisade and spongy parenchyma were reduced in thickness in the lower canopy when compared to the upper one, in the former due to a decrease in the number of cell layers from three to two (clearly distinguishable in the light and fluorescence microscopy images). In both cultivars, the concentration of violaxanthin-cycle pigments and β-carotene was higher in the upper than in the lower canopy. Furthermore, the de-epoxidized forms zeaxanthin and antheraxanthin increased significantly in those leaves from the upper canopy, in parallel to the NPQ increases. In conclusion, olive leaves react with morphological and photosynthetic changes to within-crown light gradients. These results strengthen the idea of olive trees as “modular organisms” that adjust the modules morphology and physiology in response to light intensity.This work was supported by the Spanish Agency of International Cooperation for Development (AECID) Project AP/040397/11 and the Aragón Government (A03 Research Group)Peer reviewe