Resource partitioning between black-backed jackal and brown hyeana in Waterberg Biosphere Reserve, South Africa

Understanding resource partitioning by predators is important for understanding coexistence patterns, with this becoming more relevant as historical food webs are altered through human impacts. Using scat analysis, we investigated the diet overlap of two sympatric meso-carnviores, the black-backed jackal Canis mesomelas and brown hyaena Hyaena brunnea, in Waterberg Biosphere Reserve, South Africa. Scats (n = 30 jackal, 42 brown hyaena) were collected in April 2012 from game and livestock farms. When comparing main prey categories (medium-large mammal, small mammal, fruit, invertebrate, reptile, and bird) we found little difference in diets, with both carnivores consuming predominantly medium-large mammals (10-100kg). Bushbuck Tragelaphus scriptus was the most commonly consumed large mammal species for both predators. Jackal and brown hyaena had, on average, 1.3 and 1.4 main prey categories per scat respectively which resulted in diet diversities of 3.9 for jackal and 2.5 for brown hyaena. Only jackal consumed livestock (which may have been scavenged), albeit in small amounts (< 5% frequency of occurrence). The high level of resource overlap was consistent with previous jackal–brown hyaena resource partitioning studies. Across a range of studies, resource overlap was higher when apex predator densities were lower. Thus, lower apex predator densities may restrict brown hyaena populations through the lack of carrion. At these lower brown hyaena densities, large mammal carrion, which brown hyaena rely on, may persist for longer. This persistence may enable jackals to increase their consumption of larger mammals, thereby reducing their reliance on rodents and small-medium sized mammals. Our results support the prediction that lower apex predator densities allow jackals to consume more medium to large mammals. However, diet overlap is only one of many niche axes that can assist in species co-occurrence, and further work is required to understand how jackal and brown hyaena interact at spatial, temporal and behavioural scales

Suppression of Na+/K+-ATPase activity during estivation in the land snail Otala lactea

Entry into the hypometabolic state of estivation requires a coordinated suppression of the rate of cellular ATP turnover, including both ATP-generating and ATP-consuming reactions. As one of the largest consumers of cellular ATP, the plasma membrane Na+/K+-ATPase is a potentially key target for regulation during estivation. Na+/K+-ATPase was investigated in foot muscle and hepatopancreas of the land snail Otala lactea, comparing active and estivating states. In both tissues enzyme properties changed significantly during estivation: maximal activity was reduced by about one-third, affinity for Mg.ATP was reduced (Km was 40% higher), and activation energy (derived from Arrhenius plots) was increased by ∼45%. Foot muscle Na+/K+-ATPase from estivated snails also showed an 80% increase in Km Na+ and a 60% increase in Ka Mg2+ as compared with active snails, whereas hepatopancreas Na+/K+-ATPase showed a 70% increase in I50 K+ during estivation. Western blotting with antibodies recognizing the alpha subunit of Na+/K+-ATPase showed no change in the amount of enzyme protein during estivation. Instead, the estivation-responsive change in Na+/K+-ATPase activity was linked to posttranslational modification. In vitro incubations manipulating endogenous kinase and phosphatase activities indicated that Na+/K+-ATPase from estivating snails was a high phosphate, low activity form, whereas dephosphorylation returned the enzyme to a high activity state characteristic of active snails. Treatment with protein kinases A, C or G could all mediate changes in enzyme properties in vitro that mimicked the effect of estivation, whereas treatments with protein phosphatase 1 or 2A had the opposite effect. Reversible phosphorylation control of Na+/K+-ATPase can provide the means of coordinating ATP use by this ion pump with the rates of ATP generation by catabolic pathways in estivating snails

Regulation of sarcoendoplasmic reticulum Ca2+-ATPase (SERCA) in turtle muscle and liver during acute exposure to anoxia

The freshwater turtle Trachemys scripta elegans naturally tolerates extended periods of anoxia during winter hibernation at the bottom of ice-locked ponds. Survival in this anoxic state is facilitated by a profound depression of metabolic rate. As calcium levels are known to be elevated in anoxic turtles, and ion pumping is an ATP-expensive process, we proposed that activity of the sarcoendoplasmic reticulum Ca2+-ATPase (SERCA) would be reduced in muscle and liver of T. s. elegans during acute (up to 20 h) exposure to anoxia. SERCA activity decreased ∼30% in liver and ∼40% in muscle after 1 h anoxia exposure and was ∼50% lower after 20 h of anoxia exposure in both tissues, even though SERCA protein levels did not change. SERCA kinetic parameters (increased substrate Km values, increased Arrhenius activation energy) were indicative of a less active enzyme form under anoxic conditions. Interestingly, the less active SERCA in anoxic turtles featured greater stability than the enzyme from normoxic animals as determined by both kinetic analysis (effect of low pH and low temperatures on Km MgATP) and conformational resistance to urea denaturation. The quick time course of deactivation and the stable changes in kinetic parameters that resulted suggested that SERCA was regulated by a post-translational mechanism. In vitro experiments indicated that SERCA activity could be blunted by protein phosphorylation and enhanced by dephosphorylation in a tissue-specific manner

In cold-hardy insects, seasonal, temperature, and reversible phosphorylation controls regulate sarco/endoplasmic reticulum Ca 2+-ATPase (SERCA)

Winter cold hardiness of insects typically involves one of two major strategies for survival below 0°C: freeze avoidance and freeze tolerance. The two strategies have some common features, including the accumulation of high concentrations of cryoprotectant polyols and the frequent occurrence of diapause. Entry into the hypometabolic state of diapause requires coordinated suppression of major ATP-consuming metabolic processes, and ion motive ATPases are important targets for regulation. This study documents the suppression of sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) activity in the overwintering larvae of two cold-hardy species, the freeze-avoiding gall moth Epiblema scudderiana and the freeze-tolerant gall fly Eurosta solidaginis. Activity was reduced despite a lack of change in SERCA protein levels in E. solidaginis larvae over the winter and a six- to eightfold increase in SERCA protein in E. scudderiana. This implicated posttranslational modification as the mechanism of SERCA suppression, and in vitro incubations indicated that enzyme phosphorylation by protein kinases A, G, or C strongly reduced enzyme activity. A stable reduction in SERCA activity was also seen in cold-acclimated larvae of both species compared with 15°C controls, with significant changes in the kinetic parameters of the E. scudderiana enzyme (e.g., Km ATP was 3.2-fold higher in - 20°C-acclimated larvae) that were consistent with reduced enzyme function at low temperature. Epiblema scudderiana SERCA was also subject to regulation by differential temperature effects (Arrhenius activation energy increased by approximately threefold below 10°C) and by seasonal changes in the levels of a SERCA inhibitor protein, phospholamban

Regulation of global protein translation and protein degradation in aerobic dormancy

We hypothesized that protein turnover would be substantially suppressed during estivation in the land snail, Otala lactea, as part of a wholesale move to conserve ATP in the hypometabolic state, and that decreased rates of protein synthesis and degradation would be mediated by altering the phosphorylation state of key proteins. Rates of protein translation, measured in vitro, decreased by ∼80% in extracts of foot muscle and hepatopancreas after 2 days of estivation, and this reduction was associated with strong increases in the phosphorylation of ribosomal factors, eIF2α and eEF2, as well as decreased phosphorylation of 4E-BP1. Reductions in levels of markers of ribosomal biogenesis and a tissue-specific reduction in the phosphorylation state of eIF4E and eIF4GI were also evident after 14 days of estivation. Activity of the 20S proteasome decreased by 60-80% after 2 days of estivation and this decrease was mediated by protein kinase G in vitro, whereas protein phosphatase 2A activated the proteasome. Levels of protein carbonyls did not change in snail tissues during estivation whereas the expression heat shock proteins increased, suggesting that protein resistance to damage is enhanced in estivation. In conclusion, protein synthesis and degradation rates were coordinately suppressed during estivation in O. lactea and this is associated with the phosphorylation of ribosomal initiation and elongation factors and the 20S proteasome