Running energetics of the North American river otter: do short legs necessarily reduce efficiency on land?

Semi-aquatic mammals move between two very different media (air and water), and are subject to a greater range of physical forces (gravity, buoyancy, drag) than obligate swimmers or runners. This versatility is associated with morphological compromises that often lead to elevated locomotor energetic costs when compared to fully aquatic or terrestrial species. To understand the basis of these differences in energy expenditure, this study examined the interrelationships between limb morphology, cost of transport and biomechanics of running in a semi-aquatic mammal, the North American river otter. Oxygen consumption, preferred locomotor speeds, and stride characteristics were measured for river otters (body mass=11.1 kg, appendicular/axial length=29%) trained to run on a treadmill. To assess the effects of limb length on performance parameters, kinematic measurements were also made for a terrestrial specialist of comparable stature, the Welsh corgi dog (body mass=12.0 kg, appendicular/axial length=37%). The results were compared to predicted values for long legged terrestrial specialists. As found for other semi-aquatic mammals, the net cost of transport of running river otters (6.63 J kg(-1)min(-1) at 1.43 ms(-1)) was greater than predicted for primarily terrestrial mammals. The otters also showed a marked reduction in gait transition speed and in the range of preferred running speeds in comparison to short dogs and semi-aquatic mammals. As evident from the corgi dogs, short legs did not necessarily compromise running performance. Rather, the ability to incorporate a period of suspension during high speed running was an important compensatory mechanism for short limbs in the dogs. Such an aerial period was not observed in river otters with the result that energetic costs during running were higher and gait transition speeds slower for this versatile mammal compared to locomotor specialists.     

Increased glucose uptake promotes oxidative stress and PKC-delta activation in adipocytes of obese,insulin-resistant mice

Increased oxidative stress is believed to be one of the mechanisms responsible for hyperglycemia-induced tissue damage and diabetic complications. In these studies, we undertook to characterize glucose uptake and oxidative stress in adipocytes of type 2 diabetic animals and to determine whether these promote the activation of PKC-delta. The adipocytes used were isolated either from C57Bl/6J mice that were raised on a high-fat diet (HF) and developed obesity and insulin resistance or from control animals. Basal glucose uptake significantly increased (8-fold) in HF adipocytes, and this was accompanied with upregulation of GLUT1 expression levels. Insulin-induced glucose uptake was inhibited in HF adipocytes and GLUT4 content reduced by 20% in these adipocytes. Reactive oxygen species (ROS) increased twofold in HF adipocytes compared with control adipocytes and were largely reduced with decreased glucose concentrations. At zero glucose, ROS levels were reduced to the normal levels seen in control adipocytes. The activity of PKC-delta increased twofold in HF adipocytes compared with control adipocytes and was further activated by H2O2. Moreover, PKC-delta activity was inhibited in HF adipocytes either by glucose deprivation or by treatment with the antioxidant N-acetyl-l-cysteine. In summary, we propose that increased glucose intake in HF adipocytes increases oxidative stress, which in turn promotes the activation of PKC-delta. These consequential events may be responsible, at least in part, for development of HF diet-induced insulin resistance in the fat tissue.     

Ingestion of crude oil: effects on digesta retention times and nutrient uptake in captive river otters

Studies following the Exxon Valdez oil spill in Prince William Sound, Alaska indicated that river otters (Lontra canadensis) from oiled regions displayed symptoms of degraded health, including reduced body weight. We examined the fate of ingested oil in the digestive tract and its effects on gut function in captive river otters. Fifteen wild-caught males were assigned to three groups, two of which were given weathered crude oil in food (i.e., control, 5 ppm day⁻¹, and 50 ppm day⁻¹) under controlled conditions at the Alaska Sealife Center. Using glass beads as non-specific digesta markers and stable isotope analysis, we determined the effects of ingested oil on retention time and nutrient uptake. Our data indicated that oil ingestion reduced marker retention time when we controlled for activity and meal size. Fecal isotope ratios suggested that absorption of lipids in the oiled otters might have been affected by reduced retention time of food. In addition, a dilution model indicated that as much as 80% of ingested oil was not absorbed in high-dose animals. Thus, while the ingestion of large quantities of weathered crude oil appears to reduce absorption of oil hydrocarbons and may alleviate systemic effects, it may concurrently affect body condition by impacting digestive function. Accepted: 18 May 2000     

Chickens fed with biomass of the red microalga Porphyridium sp. have reduced blood cholesterol level and modified fatty acid composition in egg yolk

The biomass of the red alga Porphyridium sp.constitutes a unique combination of soluble sulfatedpolysaccharide that accounts for about 70% of thealgal dry weight, and various polyunsaturatedfatty acids (PUFA) such as arachidonic andeicosapentaenoic acid (AA, 20:4 6 and EPA,20:5 3). In view of earlier results in ourlaboratory showing a reduction in serum cholesteroland triglyceride levels in rodents fed with red algalbiomass, we set out to examine the influence of algalbiomass as a feed additive on the metabolism ofchickens, with an emphasis on blood and eggcholesterol levels. For that purpose, lyophilizedalgal biomass was fed to 12–13, 30-week-old, WhiteLeghorn chickens for 10 days at a proportion of 5% or10% of the standard chicken diet. Twelve chickensfed with unsupplemented diet served as the control. No differences in body weight, egg number, and eggweight were found between the algal-fed chickens (atboth concentrations) and the control. However,chickens fed with algal biomass consumed 10% lessfood for both groups, and their serum cholesterollevels were significantly lower (by 11% and 28% forthe groups fed with 5% and 10% supplement,respectively) as compared with the respective valuesof the control group. Egg yolk of chickens fed withalgae tended to have reduced cholesterol levels (by10%) and increased linoleic acid and arachidonic acidlevels (by 29% and 24%, respectively). In addition,the color of the egg yolk was darker as a result ofthe higher carotenoid levels (2.4 fold higher) forchickens that fed with 5% supplement. Theseresults encourage the development of an improvedchicken feed having dietary fibers and polyunsaturatedfatty acids.     

Little interspecific pollen transfer despite overlap in pollinators between sympatric Aeonium (Crassulaceae) species pairs

It is still unknown what exact role interspecific gene flow and reticulate patterns of gene transfer may play in adaptive radiations. To contribute to a better understanding of gene flow in a morphologically diverse and species-rich lineage, we investigated pollen transfer in the adaptively radiated Macaronesian Crassulaceae-Sempervivoideae. We aimed at comparing pollinator spectra and pollen transfer rates among sympatric species of Aeonium. Field studies were conducted on Tenerife (Canary Islands) including pollinator observations and estimations of pollen transfer using fluorescent dye powder as pollen analogue. Our results indicate an overlap in visiting insects among four sympatric species pairs of Aeonium. However, our dye experiments indicate that on an average about 95% of the detected pollen transfer was infraspecific. Only a small proportion of interspecific pollen transfer could be recorded. We explain these outcomes by specific pollinator behaviour such as floral preference and constancy during a foraging bout. This may be linked to different reward regimes of the studied Aeonium species.     

An isotopic technique to mark mid-sized vertebrates non-invasively

Understanding the basis of habitat choice having important implications for explaining the distribution of organisms, as well as helping to differentiate between habitats of different quality for effective management. In this study, the effects of sex, age and reproductive status on habitat use patterns of cheetahs Acinonyx jubatus in the Serengeti plains were explored using Ecological Niche Factor Analysis (ENFA). Our results showed that gender and territoriality did not affect patterns of habitat use. However, females tended to be more specialized when they were young than when they were older, displaying a more restricted ecological niche. Likewise, older females without cubs were more specialized than the same adult females with young cubs. This result did not hold for younger females. Altogether, the ENFA approach allowed us to (1) use the large amount of incidental sighting data collected over 12 years on cheetah spatial distribution; (2) identify the importance of reproductive status and age on the relationship between animals and their habitat; (3) further demonstrate that ENFA is applicable in a wide range of situations, including for exploring individual variation in niche definition.     

Prospective Large-Scale Field Study Generates Predictive Model Identifying Major Contributors to Colony Losses

Over the last decade, unusually high losses of colonies have been reported by beekeepers across the USA. Multiple factors such as Varroa destructor, bee viruses, Nosema ceranae, weather, beekeeping practices, nutrition, and pesticides have been shown to contribute to colony losses. Here we describe a large-scale controlled trial, in which different bee pathogens, bee population, and weather conditions across winter were monitored at three locations across the USA. In order to minimize influence of various known contributing factors and their interaction, the hives in the study were not treated with antibiotics or miticides. Additionally, the hives were kept at one location and were not exposed to potential stress factors associated with migration. Our results show that a linear association between load of viruses (DWV or IAPV) in Varroa and bees is present at high Varroa infestation levels (>3 mites per 100 bees). The collection of comprehensive data allowed us to draw a predictive model of colony losses and to show that Varroa destructor, along with bee viruses, mainly DWV replication, contributes to approximately 70% of colony losses. This correlation further supports the claim that insufficient control of the virus-vectoring Varroa mite would result in increased hive loss. The predictive model also indicates that a single factor may not be sufficient to trigger colony losses, whereas a combination of stressors appears to impact hive health.