The effect of acquired microbial enzymes on assimilation efficiency in the common woodlouse, Tracheoniscus rathkei

Terrestrial crustaceans (Arthropoda, Crustacea): taxonomic diversity, terrestrial adaptations, and ecological functions

Terrestrial crustaceans are represented by approximately 4,900 species from six main lineages. The diversity of terrestrial taxa ranges from a few genera in Cladocera and Ostracoda to about a third of the known species in Isopoda. Crustaceans are among the smallest as well as the largest terrestrial arthropods. Tiny microcrustaceans (Branchiopoda, Ostracoda, Copepoda) are always associated with water films, while adult stages of macrocrustaceans (Isopoda, Amphipoda, Decapoda) spend most of their lives in terrestrial habitats, being independent of liquid water. Various adaptations in morphology, physiology, reproduction, and behavior allow them to thrive in virtually all geographic areas, including extremely arid habitats. The most derived terrestrial crustaceans have acquired highly developed visual and olfactory systems. The density of soil copepods is sometimes comparable to that of mites and springtails, while the total biomass of decapods on tropical islands can exceed that of mammals in tropical rainforests. During migrations, land crabs create record-breaking aggregations and biomass flows for terrestrial invertebrates. The ecological role of terrestrial microcrustaceans remains poorly studied, while omnivorous macrocrustaceans are important litter transformers and soil bioturbators, occasionally occupying the position of the top predators. Notably, crustaceans are the only group among terrestrial saprotrophic animals widely used by humans as food. Despite the great diversity and ecological impact, terrestrial crustaceans, except for woodlice, are often neglected by terrestrial ecologists. This review aims to narrow this gap discussing the diversity, abundance, adaptations to terrestrial lifestyle, trophic relationships and ecological functions, as well as the main methods used for sampling terrestrial crustaceans.

Factors Influencing Damage by the Portuguese Millipede, Ommatoiulus moreleti (Julida: Julidae), to Crop Seedlings

In different parts of the world, the increasing agricultural practice of retaining crop stubble in fields across seasons has led to population increases of soil-dwelling arthropods, primarily detritivorous species. These species typically play a beneficial role in the ecosystem, but some, including the Portuguese millipede (Ommatoiulus moreleti (Lucas)) can be sporadic pests. To assist in better understanding of pest risk, this study examines why O. moreleti feeds on crop seedlings. For lupin, seedling susceptibility appears to be related to plant properties, with greatly different levels of damage caused to the two cultivated species (Lupinus angustinus and Lupinus albus) and particularly between cultivated and wild-type L. angustinus seedlings. Millipedes feeding on lupin (cultivated L. angustinus), but not lucerne (Medicago sativa), gained a similar amount of weight to those feeding on other foods known to be readily consumed. The life-stage and sex of O. moreleti was found to be related to seedling damage. The presence of crop stubbles (as alternate food sources) did not limit the damage O. moreleti caused to lupin, suggesting that the presence of stubble in a field situation may not preclude feeding on crop seedlings. We discuss how results from these controlled environment trials can build a basis for understanding variable crop damage by O. moreleti in the field.

Consumption Performance of Five Detritivore Species Feeding on Alnus glutinosa L. Leaf Litter in a Microcosm Experiment

The present study was performed to assess the feeding performance of five detritivore species in a microcosm design. The test animals were four millipede species, Telodeinopus aoutii (Demange), Epibolus pulchripes (Gerstäcker), Cylindroiulus caeruleocinctus (Wood), Glomeris hexasticha (Brandt), and one isopod species, Porcellio scaber (Latreille), all feeding on Alnus glutinosa L. leaf litter for five consecutive weeks. At the end of each one-week interval, litter consumption, animal fresh weight, and excrement production were measured. Then, the feeding activity parameters for each species were calculated. Between big-size animal species, higher leaf consumption rates of 12.3–30.9 mg dry weight day−1 individual−1 were calculated for T. aoutii compared to those of 3.72–8.25 mg dry weight day−1 individual−1 for E. pulchripes. However, there was no difference in the consumption rates among small-size animals ranging from 0.46 to 1.65 mg dry weight day−1 individual−1. Excrement production rates followed a similar trend, as the consumption rates and the animals’ body weight remained constant during the experiment. Time was an important factor influencing the feeding activity of the animals, especially for the big-size group. Overall, the average assimilation efficiency of these species varied from 13.7% to 53.3%. The results of the present work will be the first step for understanding the ecological needs of these decomposer species in soil ecosystems.

Fungal enzymes transferred by leaf-cutting ants in their fungus gardens

Leaf-cutting ants finely fragment the leaf material that they bring to the nest and place faecal droplets on this substrate before incorporating it in the upper part of the fungus-garden. The faecal droplets contain enzymes of which some have been shown to be of fungal origin. Here we explicitly address the enzymatic activity of faecal droplets in the leaf-cutting ants Acromyrmex echinatior and Atta colombica. We used isoelectric focusing and specific staining to show that faecal droplets of both species contain carboxymethylcellulases, laccases, proteases, and pectinases (both pectin esterases and pectin lysases) and we demonstrate that these enzymes originate from the symbiotic fungus and not from the ants themselves. The level of activity of fungal pectin lyase in faecal droplets indicates that fungal enzymes may be protected and possibly concentrated during their passage through the ant gut. This would imply that enzymes that are transferred by ants from mature parts of the fungus gardens may play an important role for the colonization of new substrate by new mycelium of the same fungal clone.

Nutrition in terrestrial isopods (Isopoda: Oniscidea): an evolutionary-ecological approach

The nutritional morphology, physiology and ecology of terrestrial isopods (Isopoda: Oniscidea) is significant in two respects. (1) Most oniscid isopods are truly terrestrial in terms of being totally independent of the aquatic environment. Thus, they have evolved adaptations to terrestrial food sources. (2) In many terrestrial ecosystems, isopods play an important role in decomposition processes through mechanical and chemical breakdown of plant litter and by enhancing microbial activity. While the latter aspect of nutrition is discussed only briefly in this review, I focus on the evolutionary ecology of feeding in terrestrial isopods. Due to their possessing chewing mouthparts, leaf litter is comminuted prior to being ingested, facilitating both enzymatic degradation during gut passage and microbial colonization of egested faeces. Digestion of food through endogenous enzymes produced in the caeca of the midgut glands (hepatopancreas) and through microbial enzymes, either ingested along with microbially colonized food or secreted by microbial endosymbionts, mainly takes place in the anterior part of the hindgut. Digestive processes include the activity of carbohydrases, proteases, dehydrogenases, esterases, lipases, arylamidases and oxidases, as well as the nutritional utilization of microbial cells. Absorption of nutrients is brought about by the hepatopancreas and/or the hindgut epithelium, the latter being also involved in osmoregulation and water balance. Minerals and metal cations are effectively extracted from the food, while overall assimilation efficiencies may be low. Heavy metals are stored in special organelles of the hepatopancreatic tissue. Nitrogenous waste products are excreted via ammonia in its gaseous form, with only little egested along with the faeces. Nonetheless, faeces are characterized by high nitrogen content and provide a favourable substrate for microbial colonization and growth. The presence of a dense microbial population on faecal material is one reason for the coprophagous behaviour of terrestrial isopods. For the same reason, terrestrial isopods prefer feeding on decaying rather than fresh leaf litter, the former also being more palatable and easier to digest. Acceptable food sources are detected through distance and contact chemoreceptors. The 'quality' of the food source determines individual growth, fecundity and mortality, and thus maintenance at the population level. Due to their physiological adaptations to feeding on and digesting leaf litter, terrestrial isopods contribute strongly to nutrient recycling during decomposition processes. Yet, many of these adaptations are still not well understood.

Do stable isotopes reflect the food web development in regenerating ecosystems?

We evaluated the use of delta15N- and delta13C-values to monitor the development of food web complexity and biodiversity in a regenerating ecosystem. Therefore a model food chain was established feeding cultivated woodlice (Porcellio dilatatus) on a cellulolytic fungus (Chaetomium globosum) grown on cellulose paper. Two diets of different quality (C:N ratios of 54 vs. 200) with different delta15N- (1.3% vs. 3.1%) but identical delta13C-values caused low and high dietary stress in animals of treatment A and B, respectively. After an incubation time of 7 weeks amount, elemental and isotopic composition of collected faeces and exuviae as well as woodlice and remaining food were determined. The increase of delta15N-values of woodlice relative to the diet was 5.7% and 2.5% in treatments A and B, respectively, whereas delta13C-shifts were 1.0% and 1.6%, showing a reverse relationship. Modelling of elemental and isotopic mass balances indicated that faeces recycling explains the unexpected high 15N-enrichments. Moreover, 13C-enrichments were positively correlated to the degree of starvation. Considering the effects of starvation and recycling of faeces, stable isotopes represent a useful tool to elucidate trophic interactions in regenerating food webs.

Purification and properties of the xylanases from the termite Macrotermes bellicosus and its symbiotic fungus Termitomyces sp

Four xylanases were purified, two from the termite Macrotermes bellicosus workers (XIT and X2T) and two from its symbiotic fungus Termitomyces sp. (X1Mc and X2Mc). The analysis of the step required for the purification of X1T and X1Mc and the comparison of their different properties suggested that xylanases X1T and X1Mc were the same enzyme, X1. The determination of the reducing sugars by TLC revealed that X1 was an endoxylanase (EC 3.2.1.8) and X2T and X2Mc were endoxylanases (EC 3.2.1.37). The apparent molecular weights of the three xylanases, determined by SDS-polyacrylamide gel electrophoresis, were 36 kDa for X1, 56 kDa for X2T and 22.5 kDa for X2Mc. The optimal pH of the three xylanases was approximately 5.5, and Km values determined with birchwood xylan as substrate were 0.2% for X1, 0.1% for X2T and 0.3% for X2Mc, showing a high affinity for this substrate. The three enzymes differed also by their thermal stability.

The transformation of Saperda calcarata (Coleoptera: Cerambycidae) into a cellulose digester through the inclusion of fungal enzymes in its diet

The larvae of the aspen borer, Saperda calcarata, which feed on the inner bark and sapwood of living aspen stems, are unable to digest cellulose. However, they can be transformed into cellulose digesters by adding the active cellulase complex of the fungus, Penicillium funiculosum to their diet. S. calcarata larvae are preadapted to exploit the digestive potential of ingested microbial enzymes. We argue that ingested fungal enzymes may be responsible for cellulose digestion in many, perhaps most or even all, cellulose digesting cerambycid beetles.