Presence and properties of cellulase and hemicellulase enzymes of the gecarcinid land crabs Gecarcoidea natalis and Discoplax hirtipes.

Digestive juice from the herbivorous gecarcinid land crabs Gecarcoidea natalis and Discoplax hirtipes exhibited total cellulase activity and activities of two cellulase enzymes; endo-ß-1,4-glucanase and ß-1,4-glucosidase. These enzymes hydrolysed native cellulose to glucose. The digestive juice of both species also contained laminarinase, licheninase and xylanase, which hydrolysed laminarin, lichenin and xylan, respectively, to component sugars. The pH optima of ß-1,4-glucosidase, endo-ß-1,4-glucanase and total cellulase from G. natalis were 4–5.5, 5.5 and 5.5–7, respectively. In the digestive juice from D. hirtipes, the corresponding values were 4–7, 5.5–7 and 4–9, respectively. The pH of the digestive juice was 6.69±0.03 for G. natalis and 6.03±0.04 for D. hirtipes and it is likely that the cellulases operate near maximally in vivo. In G. natalis, total cellulase activity and endo-ß-1,4-glucanase activity were higher than in D. hirtipes, and the former species can thus hydrolyse cellulose more rapidly. ß-1,4-glucosidase from G. natalis was inhibited less by glucono-D-lactone (Ki=11.12 mmol l-1) than was the ß-1,4-glucosidase from D. hirtipes (Ki=4.53 mmol l-1). The greater resistance to inhibition by the ß-1,4-glucosidase from G. natalis may contribute to the efficiency of the cellulase system in vivo by counteracting the effects of product inhibition and possibly dietary tannins. The activity of ß-1,4-glucosidase in the digestive juice of D. hirtipes was higher than that of G. natalis.

Reviving growth in the Fiji islands : are we swimming or sinking?

The Fiji government’s 2008 'budget for hope' rests on some fundamental assumptions: political stability, the recovery of key sectors of the economy from the effects of the 2006 coup, as well as the recovery of the tourism industry, an industry which in the past has been resilient to coups. With 34 per cent of the population already living below the poverty line, low economic growth could push significantly more people into poverty. If the increases in global food and fuel prices persist, creating even more difficulties for the poor, the prospect of social instability could heighten. In the absence of the expected recovery of these key sectors and the loss of skilled workers, achieving economic and social recovery will require political consensus to resolve the political impasse that has gripped the country. The Interim Government also needs to revisit its fiscal austerity package.

Functional morphology of the gastric mills of carnivorous, omnivorous, and herbivorous land crabs

Terrestrial decapods consume a wide variety of plant and animal material. The potential adaptations of carnivorous, omnivorous, and herbivorous terrestrial crustaceans were studied by examining the functional morphology of the gastric mill. Two closely related species from each feeding preference group were examined to identify which features of the mill were due to phylogeny and which were due to adaptation. The morphology of the gastric mill matched the diet well; the gastric mills of the carnivorous species (Geograpsus grayi and Geograpsus crinipes) possessed a blunt, rounded medial tooth and flattened lateral teeth with a longitudinal grinding groove. These features make them well suited to a carnivorous diet of soft animal tissue as well as hard material, such as arthropod exoskeleton. In contrast, the mill of the herbivorous gecarcinids (Gecarcoidea natalis and Discoplax hirtipes) consisted of a medial tooth with sharp transverse ridges and lateral teeth with sharp interlocking cusps and ridges and no grinding surface. These features would efficiently shred fibrous plant material. The morphology of the mill of the omnivorous coenobitids (Coenobita perlatus and Birgus latro) was more generalized toward a mixed diet. However, the mill of B. latro was more adapted to deal with highly nutritious food items, such as nuts and heavily calcified decapods. Its mill possessed lateral teeth with extended ridges, which sat close to the calcified cardiopyloric valve to form a flattened floor. Hard items trapped in the mill would be crushed against this surface by the medial tooth.

Analysis and implementation of swimming backward for biomimetic carangiform robot fish

The swimming backward for biomimetic carangiform robot fish is analyzed and implemented in this paper. The swimming law of the carangiform robot fish is modified according to the European Eel swimming mode based on the multiple-link structure to implement the backward motion. The motion mode difference between the eel and carangiform fish is discussed, and a qualitative kinematic analysis of the carangiform swimming in water is given to analyze the propulsion produced by the undulation of the multi-links tail. The experiments conducted demonstrate the good performance of the proposed method, and the results are given.

Spermatogenesis in the blue swimming crab, Portunus pelagicus, and evidence for histones in mature sperm nuclei

Spermatogenesis in the blue swimming crab, Portunus pelagicus, is described by light and electron microscopy. The testis is composed of anterior (AT) and posterior (PT) lobes, that are partitioned into lobules by connective tissue trabecula, and further divided into zones (germinal, transformation and evacuation), each with various stages of cellular differentiation. The vas deferens is classified into three distinct regions: anterior (AVD), median (MVD), and posterior (PVD), on the presence of spermatophores and two secretions, termed substance I and II. Based on the degree and patterns of heterochromatin, spermatogenesis is classified into 13 stages: two spermatogonia (SgA and SgB), six primary spermatocytes (leptotene, zygotene, pachytene, diplotene, diakinesis, and metaphase), a secondary spermatocyte (SSc), three spermatids (St 1–3), and a mature spermatozoon. Spermatid stages are differentiated by chromatin decondensation and the formation of an acrosomal complex, which is unique to brachyurans. Mature spermatozoa are aflagellated, and have a nuclear projection and a spherical acrosome. AUT-PAGE and Western blots show that, during chromatin decondensation, there is a reduction of most histones, with only small amounts of H2B and H3 remaining in mature spermatozoa.

Why do Gull-billed Terns Gelochelidon nilotica feed on fiddler crabs Uca tangeri in Guinea-Bissau?

Gull-billed Terns Gelochelidon nilotica wintering in Guinea Bissau mainly fed on fiddler crabs Uca tangeri and were occasionally seen feeding on fish and locusts. As fiddler crabs have a low energy content, terns need a large gross intake to meet daily energy demands. Fiddler crabs also have a low ratio of digestible flesh to exoskeleton, and therefore tern food intake may be limited by gut capacity. Activity budgets of Gullbilled Terns feeding on fiddler crabs showed that a considerable part of the time was spent resting. The duration of resting intervals increased with energy intake and was positively correlated with the metabolisable energy content of the crab eaten, suggesting that resting periods were required for a proper digestion. The poor quality of fiddler crabs was offset by high capture rates. So daily energy expenditure of the terns could easily be met by feeding on fiddler crabs. Even when resting pauses were included in foraging time, foraging for only 1.5 hours on fiddler crabs satisfied the terns’ daily energy demands. Instead, feeding on energy-rich fish would require about 2.5 hours to satisfy daily energy demands. Compared to the more specialised piscivorous Little Tern Sternula albifrons and Sandwich Tern Sterna sandvicensis, capture rate of fish was poor in Gull-billed Terns. From an energetic point of view, wintering Gull-billed Terns feeding on fiddler crabs seem to have an easy living in Guinea Bissau.