Small-scale spatial resource partitioning in a hyperparasitoid community

peer reviewe

An Evolutionary Perspective on Linoleic Acid Synthesis in Animals

The diet of organisms generally provides a sufficient supply of energy and building materials for healthy growth and development, but should also contain essential nutrients. Species differ in their exogenous requirements, but it is not clear why some species are able to synthesize essential nutrients, while others are not. The unsaturated fatty acid, linoleic acid (LA; 18:2n-6) plays an important role in functions such as cell physiology, immunity, and reproduction, and is an essential nutrient in diverse organisms. LA is readily synthesized in bacteria, protozoa and plants, but it was long thought that all animals lacked the ability to synthesize LA de novo and thus required a dietary source of this fatty acid. Over the years, however, an increasing number of studies have shown active LA synthesis in animals, including insects, nematodes and pulmonates. Despite continued interest in LA metabolism, it has remained unclear why some organisms can synthesize LA while others cannot. Here, we review the mechanisms by which LA is synthesized and which biological functions LA supports in different organisms to answer the question why LA synthesis was lost and repeatedly gained during the evolution of distinct invertebrate groups. We propose several hypotheses and compile data from the available literature to identify which factors promote LA synthesis within a phylogenetic framework. We have not found a clear link between our proposed hypotheses and LA synthesis; therefore we suggest that LA synthesis may be facilitated through bifunctionality of desaturase enzymes or evolved through a combination of different selective pressures

Ecomorphological adaptations in Collembola in relation to feeding strategies and microhabitat

Some of the most important functional traits in animals are related to the potentially vast array of feeding strategies and microhabitat use. Correlated evolution of diet and habitat specialization with ecomorphological traits has been described in vertebrates, but such functional trait variation in soil in vertebrates is less well-studied. In this study, we explore the evidence for ecomorphological adaptations in Collembola, an important group of soil invertebrates, and place this in the context of their feeding biology, vertical stratification in soil and reproduction mode. For this purpose, we compiled a database of functional traits, including mouthparts structures (mandibula, maxilla), feeding guilds (microbivores, herbivores and scavengers/carnivores), vertical habitat stratification (epigeic, hemiedaphic, euedaphic) and reproduction mode (bisexual, parthenogenetic). We used phylogenetic reconstructions and Pagel's discrete method to test for correlations between various traits. We found a correlation between diet and mandibulae structure, with scavengers/predators possessing scratching/piercing mandibulae without a molar plate, while chewing mandibulae with a molar plate were associated with herbivores and microbivores. Vertical habitat stratification did not correlate to diet or to reproduction mode. No phylogenetic signal was found in the structure of the maxillae, although maxillae in the scavenger/predatory diet group differed structurally from herbivores and/or microbivores. The correlated evolution seen between scavengers/predators and scratching/piercing mandibulae indicate selective pressures linking different morphological traits related to the biology of Collembola, and shed new light on the broader context of diet evolution in soil arthropods

Short-term seasonal habitat facilitation mediated by an insect herbivore

In nature some organisms may facilitate others by creating shelter or other niches that they use for variable periods. We describe a natural multitrophic-species complex in the Netherlands involving a plant, the common hogweed (Heracleum sphondylium) a specialist chewing herbivore, the parsnip webworm (Depressaria pastinacella) and various arthropods associated with them. Larvae of D. pastinacella feed on H. sphondylium seeds and, after they have finished feeding, chew holes in the hollow stems where they pupate. In some areas of the country almost 50% of plants are attacked by webworms. The holes are used by other arthropods to gain access to the stems including herbivores, omnivores, predators and decomposers. The duration of plant occupancy varies between 3 and 4 months, until the plants die. Plants without moth-produced holes were always free of other arthropods, whereas plants with holes, in addition to pupae (and/or mummified-parasitized webworm larvae), often contained many woodlice, earwigs and/or spiders. Earwigs and woodlice perform important ecological functions as predators (in orchards) and decomposers respectively. Our results show that the simple biological activity of one herbivore species can have at least short-term effects on the local arthropod community. In der Natur können manche Organismen andere begünstigen, indem sie Refugien oder andere Nischen erschaffen, die sie für unterschiedliche Zeiträume nutzen. Wir beschreiben einen natürlichen multitrophischen Artenkomplex in den Niederlanden, der den Wiesen-Bärenklau (Heracleum sphondylium), die Pastinakmotte (Depressaria pastinacella) und verschiedene mit ihnen assoziierte Arthropoden umfasst. Die Larven der Pastinakmotte fressen an Bärenklausamen und beißen später Löcher in die hohlen Stengel, um sich darin zu verpuppen. Die Löcher werden von anderen Arthropoden genutzt, um Zugang ins Stengelinnere zu erhalten. Die Pflanze wird für etwa drei bis vier Monate besiedelt bis sie abstirbt. Pflanzen ohne Mottenlöcher wurden niemals von anderen Arthropoden besiedelt, während Stengel mit Löchern zusätzlich zu den Mottenpuppen bzw. parasitierten Larvenmumien häufig viele Asseln, Ohrwürmer und/oder Spinnen enthielten. Ohrwürmer und Asseln erfüllen wichtige ökologische Funktionen als Räuber in Obstplantagen bzw. als Zersetzer. Unsere Ergebnisse zeigen, dass die einfache biologische Aktivität einer Herbivorenart zumindest kurzfristige Auswirkungen auf die lokale Arthropodengemeinschaft haben kann

Functional characterisation of two Δ12-desaturases demonstrates targeted production of linoleic acid as pheromone precursor in Nasonia

Insect pheromones are often derived from fatty acid metabolism. Fatty acid desaturases, enzymes introducing double bonds into fatty acids, are crucial for the biosynthesis of these chemical signals. Δ12-desaturases catalyse the biosynthesis of linoleic acid by introducing a second double bond into oleic acid, but have been identified in only a few animal species. Here, we report the functional characterisation of two Δ12-desaturases, Nvit_D12a and Nvit_D12b, from the parasitic wasp Nasonia vitripennis. We demonstrate that Nvit_D12a is expressed in the rectal vesicle of males where they produce a linoleic acid-derived sex pheromone to attract virgin females. C-labelling experiments with Urolepis rufipes, a closely related species belonging to the ‘Nasonia group’, revealed that females, but not males, are able to synthesise linoleic acid. U. rufipes males produce an isoprenoid sex pheromone in the same gland and do not depend on linoleic acid for pheromone production. This suggests that Δ12-desaturases are common in the ‘Nasonia group’, but acquired a specialised function in chemical communication of those species that use linoleic acid as a pheromone precursor. Phylogenetic analysis suggests that insect Δ12-desaturases have evolved repeatedly from Δ9-desaturases in different insect taxa. Hence, insects have developed a way to produce linoleic acid independent of the omega desaturase subfamily which harbours all of the eukaryotic Δ12-desaturases known so far.F.S. was supported by a doctoral fellowship from the Konrad-Adenauer-Stiftung; J.E. and M.M. were supported by the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NOW; VICI grant 865.12.003)

De novo Synthesis of Linoleic Acid in Multiple Collembola Species

Many ecological interactions in communities take place between consumers and the organisms they feed on. Continuous surplus of specific nutritional compounds in the diet may lead to evolutionary changes in the metabolic capacity of the consumer, leaving the biosynthesis of such compounds prone to genetic decay and render organisms auxotrophic. A nutrient that is essential to many organisms is the unsaturated fatty acid, linoleic acid (LA; 18:2n-6), which is important in the maintenance of cell membrane fluidity and as a precursor for signaling molecules. LA is readily synthesized in bacteria, protozoa and plants, but it was long thought that all animals lack this ability. Although the majority of animals lack the ability for LA biosynthesis, an increasing number of studies have shown that LA is commonly synthesized in arthropods. Here, we investigated a basal hexapod group, Collembola, to shed light on early evolution of LA synthetic ability in arthropods and its relation to dietary composition. We use stable isotope labeling to detect biosynthesis of LA in Collembola fed with C-13-OA oleic acid (OA; 18:1n-9), a precursor of LA. Our data demonstrate that LA biosynthesis is common among Collembola with 10 out of 16 tested species being able to synthesize LA and 4 species lacking this ability. However, we did not find clear evidence for a relationship between LA synthetic ability and the natural diet of species. Thus, the selective pressures underlying LA biosynthesis might be species-specific and further research will shed new light on understanding this evolutionary process