Effects of climatic variation on field metabolism and water relations of desert tortoises

We used the doubly labeled water method to measure the field metabolic rates (FMRs, in kJ kg^?1?day^?1) and water flux rates (WIRs, in ml H₂O?kg^?1?day^?1) of adult desert tortoises (Gopherus agassizii) in three parts of the Mojave Desert in California over a 3.5-year period, in order to develop insights into the physiological responses of this threatened species to climate variation among sites and years. FMR, WIR, and the water economy index (WEI, in ml H₂O?kJ^?1, an indicator of drinking of free water) differed extensively among seasons, among study sites, between sexes, and among years. In high-rainfall years, males had higher FMRs than females. Average daily rates of energy and water use by desert tortoises were extraordinarily variable: 28-fold differences in FMR and 237-fold differences in WIR were measured. Some of this variation was due to seasonal conditions, with rates being low during cold winter months and higher in the warm seasons. However, much of the variation was due to responses to year-to-year variation in rainfall. Annual spring peaks in FMR and WIR were higher in wet years than in drought years. Site differences in seasonal patterns were apparently due to geographic differences in rainfall patterns (more summer rain at eastern Mojave sites). In spring 1992, during an El Niño (ENSO) event, the WEI was greater than the maximal value obtainable from consuming succulent vegetation, indicating copious drinking of rainwater at that time. The physiological and behavioral flexibility of desert tortoises, evident in individuals living at all three study sites, appears central to their ability to survive droughts and benefit from periods of resource abundance. The strong effects of the El Niño (ENSO) weather pattern on tortoise physiology, reproduction, and survival elucidated in this and other studies suggest that local manifestations of global climate events could have a long-term influence on the tortoise populations in the Mojave Desert.     

Current progress in use of adipose derived stem cells in peripheral nerve regeneration

Unlike central nervous system neurons; those in the peripheral nervous system have the potential for full regeneration after injury. Following injury, recovery is controlled by schwann cells which replicate and modulate the subsequent immune response. The level of nerve recovery is strongly linked to the severity of the initial injury despite the significant advancements in imaging and surgical techniques. Multiple experimental model shave been used with varying successes to augment the natural regenerative processes which occur following nerve injury. Stem cell therapy in peripheral nerve injury may be an important future intervention to improve the best attainable clinical results. In particular adipose derived stem cells(ADSCs) are multipotent mesenchymal stem cells similar to bone marrow derived stem cells, which are thought to have neurotrophic properties and the ability to differentiate into multiple lineages. They are ubiquitous within adipose tissue; they can form many structures resembling the mature adult peripheral nervous system. Following early in vitro work; multiple small and large animal in vivo models have been used in conjunction with conduits, autografts and allografts to successfully bridge the peripheral nerve gap. Some of the ADSC related neuroprotective and regenerative properties have been elucidated however much work remains before a model can be used successfully in human peripheral nerve injury(PNI). This review aims to provide a detailed overview of progress made in the use of ADSC in PNI, with discussion on the role of a tissue engineered approach for PNI repair.     

Foraging behaviour and diet of an ectothermic herbivore: Testudo horsfieldi

Herbivorous vertebrates of arid regions are frequently faced with inadequate food quality, quantity or both. The time and energy devoted to foraging is vital to balancing their energy budgets. For desert ectotherms, a low metabolism should be advantageous, reducing their total energy requirement, but extreme ambient temperatures can strongly constrain these animals' activity periods. We provide the first data on the activity budgets, foraging behaviour and diet of a highly abundant, desert-dwelling, herbivorous ectotherm, the steppe tortoise Testudo horsfieldi . Extreme climatic conditions of Central Asia limit steppe tortoise's activity to only three months per year. They remain inactive most of their "active season" (90%), and spend very little time foraging (<15 min per day). This suggests that steppe tortoises can satisfy their energy requirements with modest feeding efforts. Interestingly, steppe tortoises avoid feeding on grass species and feed mostly on plant species that are usually highly toxic to mammals. This result suggests that steppe tortoises and ungulates do not compete for food.     

Viewing chelonian reproductive ecology through acoustic windows: cranial and inguinal perspectives

Ultrasonography is a powerful new tool in reproductive physiology and ecology but quantitative evaluations of acoustic window efficacies are necessary to assess methodological accuracy. We evaluated the efficacy of the left inguinal, right inguinal and cranial acoustic windows for detecting ovarian follicles and oviducal eggs in three tortoise species. Incorporating cranial results improved upon inguinal efficacies for detecting follicles in the three species, and for detecting eggs in Chersina angulata, which had small inguinal apertures for its body size. The cranial window provided the best follicle results (highest numbers detected) but the left inguinal window provided the best egg results. This asymmetry was probably due to the primarily posterior position of the oviducts (eggs) and the pliable ovarian sheets allowing follicles to move cranially. The left-right asymmetry may result from intestinal asymmetry (i.e., between the cecum and descending colon) in obscuring ultrasound transmission or displacing follicles and eggs. Seasonal influences upon efficacies varied with species, partially due to species differences in a) reproductive cycles and b) size and number of follicles and eggs. We attributed other efficacy differences among species to differences in body size and shell morphology, especially the inguinal apertures. Correlation analyses revealed strong individual influences upon window efficacy, suggesting that individuals varied in the position of follicles and eggs and the degree of obfuscation by nonreproductive structures. The paucity of correlations between efficacies and body size reflects the complex interactions of body size, shell morphology, reproductive structures and reproductive cycles on efficacies.