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PubMed1998

Strategies for migration in the terrestrial christmas island red crab gecarcoidea natalis: intermittent versus continuous locomotion

The terrestrial red crab Gecarcoidea natalis undertakes an annual breeding migration and must sustain locomotion for prolonged periods. The migrating crabs must travel a specific distance in a fixed time and can either walk at a constant speed or walk faster for short periods and then pause to feed or rest. To simulate the potential differences between continuous and intermittent locomotion during the migration, red crabs were sampled after walking at a voluntary speed for 5 or 20 min without pausing or after 20 min of enforced walking intermittently at approximately twice that speed. The respiratory and metabolic status of the crabs was investigated during the different exercise regimes to assess which strategy might be more advantageous during the migration. The gills and lungs appeared to function similarly in gas exchange, and the PO2 in the haemolymph was 8.2 kPa which fully saturated the haemocyanin with O2. The uptake of O2 by red crabs was diffusion-limited and the diffusion coefficient (Ldiff) varied from 0.53 in resting crabs to 0. 8 post-exercise. Post-exercise, red crabs experienced a mixed respiratory/metabolic acidosis which was greatest (0.2 pH units) in crabs walking intermittently, i.e. at a higher speed. Haemolymph l-lactate concentrations peaked at 5 mmol l-1 immediately post-exercise in the intermittent exercise group, whereas after 20 min of continuous exercise haemolymph l-lactate continued to increase, reaching a maximum of 2.5 mmol l-1 at 1 h post-exercise. l-Lactate recovered slowly to basal levels within 5 h. The maximum rate of l-lactate clearance from the haemolymph was only 1.75 mmol l-1 h-1, and short pauses in exercise were insufficient for substantial l-lactate reoxidation. Exercise regimes in the laboratory were within the locomotor speeds determined for migrating red crabs, which overall have a mean walking speed close to their aerobic limit but periodically pause and also exceed this limit by three- to fourfold.

Journal Article↗
PubMed1998

The functioning of the haemocyanin of the terrestrial christmas island red crab gecarcoidea natalis and roles for organic modulators

Gecarcoidea natalis is a land crab that migrates annually several kilometres to breed. The O2-binding properties of haemocyanin in G. natalis were investigated in vitro to test the idea that the O2-binding properties of the haemocyanin of land crabs are not dependent on circulating modulators and to provide a model of haemocyanin functioning during exercise. The affinity of the haemocyanin for O2 decreased with increasing temperature (change in the heat of oxygenation; capdelta H=-59 kJ mol-1). The haemocyanin of G. natalis apparently differs from that of other terrestrial crabs in showing haemocyanin O2 modulation by both organic and inorganic molecules. Haemocyanin O2-affinity was not affected by Mg2+ but was sensitive to changes in Ca2+ concentration ( capdelta logP50/ capdelta log[Ca]=-0.61, where P50 is the partial pressure of O2 required for half-maximal O2 binding). The Bohr factor was modest ( &phgr; =-0.26+/-0.03, N=4, in whole haemolymph at 25 degreesC) and there was no specific effect of CO2 on the O2-binding properties of the haemocyanin. An increase in urate concentration increased haemocyanin O2-affinity, but the effect was linear ( capdelta logP50/ capdelta [urate]=-0.06) and not logarithmic as is the case in other species. The effect of l-lactate on the haemocyanin O2-affinity in G. natalis was unique among the crustaceans, because an increase in l-lactate concentration decreased the haemocyanin O2-affinity. The effect of l-lactate on haemocyanin O2-affinity ( capdelta logP50/ capdelta log[lactate]) was time-dependent and decreased from a maximum of 0.044 on day 1 to 0.001 after 4 days of storage at 4 degreesC. The presence of an unknown dialysable and unstable factor in the haemolymph is postulated to explain the time-dependent effect of l-lactate on haemocyanin O2-binding properties. Model oxygen equilibrium curves constructed for in vivo conditions showed that the reverse effect of l-lactate was advantageous by decreasing the O2-affinity of the haemocyanin beyond that predicted by the Bohr shift alone and assisted in O2 off-loading at the tissues. This effect of lactate can only provide an advantage if the gas-exchange organs maintain arterial O2 loading and thus is dependent on lung function in land crabs and must have occurred coincident with the evolution of these other features.

Journal Article↗
PubMed2005

Haemophilia B: Christmas disease.

Haemophilia B is an inherited bleeding disorder associated with a deficiency of coagulation factor IX. The hallmark of the severe phenotype is recurrent and spontaneous bleeding into joints, which can lead to joint deformity and arthritis at an early age. Recombinant factor IX is now increasingly regarded as the treatment of choice because it does not transmit human pathogens. All patients in the UK now receive this product exclusively. Conventional treatment now consists of the administration of recombinant factor IX concentrate on a prophylactic basis to prevent bleeds and, hence, minimise disability in the long term. Trials of gene therapy are also underway, but these are in the very early stages and will not be a realistic option for at least another 20 years.

Antifibrinolytic Agents↗
PubMedDate not supplied

A Christmas story.

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Adaptation, Psychological↗
PubMed2001

Metabolic status and respiratory physiology of Gecarcoidea natalis, the Christmas Island red crab, during the annual breeding migration.

With the arrival of the monsoonal rains and after months of inactivity during the dry season, the terrestrial crab Gecarcoidea natalis embarks on its annual breeding migration to the coast. The physiological demands of the migration were assessed by determining respiratory gases in the hemolymph, key metabolites, and energy stores in G. natalis during two migratory seasons. At the end of each day of migration the pulmonary hemolymph PO2 decreased by 1-2.5 kPa, but the hemocyanin remained saturated with O2 and the venous reserve was largely unchanged (O2 > 0.4 mmol x l(-1)). The breeding migration of red crabs was accomplished without recourse to anaerobiosis, even though at times walking speeds (up to 6.2 +/- 0.5 m x min(-1)) exceeded those that promoted anaerobiosis in non-migrating crabs and in crabs exercised in the laboratory. In contrast to all previous studies, at the end of each day of migrating, red crabs experienced an alkalosis (up to 0.1 pH units) rather than any acidosis. This alkalosis was removed overnight when the crabs were inactive. Although there were seasonal fluctuations in the glycogen, glucose, and triglyceride stores, crabs engaging in the migration did not draw on these stores and must have fed along the way. In contrast, crabs returning from breeding activities on the shore terraces had significantly depleted glycogen stores. Additionally, in 1993, the male crabs returning from the breeding activities on the terraces were dehydrated and experienced a decrease in muscle tissue water of 11%. In contrast to the breeding migration per se, fighting for burrows in which breeding occurs produced severe anaerobiosis in males, especially the victors: after 135 s of combat, the maximum L-lactate concentration in the hemolymph was 35 mmol x l(-1). It appears that burrowing, courtship, and mating are more demanding than the migration itself. Furthermore, the data provide evidence that the metabolic responses of migrating individuals of G. natalis might be different from those at other times of the year.

Animals↗
PubMed1980

Christmas eye.

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Humans↗