The influence of status and the social environment on energy stores in a social fish.

This study explores how muscle and liver energy stores are linked with social status and the social environment in Neolamprologus pulcher, a cooperatively breeding fish that lives in colonies comprised of up to 200 distinct social groups. Subordinate muscle energy stores were positively correlated with the number of neighbouring social groups in the colony, but this pattern was not observed in dominant N. pulcher. Furthermore, liver energy stores were smaller in dominants living at the edge of the colony compared with those living in the colony centre, with no differences among subordinates in liver energy stores. Subordinate N. pulcher may build up large energy stores in the muscles to fuel rapid growth after dispersal, which could occur more frequently in high-density environments. Dominant N. pulcher may use the more easily mobilized energy stores in the liver to fuel daily activities, which could be more energetically demanding on the edge of the colony as a result of the increased predation defence needed on the edge. Overall, this study demonstrates that both subordinate and dominant physiology in N. pulcher varies with characteristics of the social environment. Furthermore, dominant and subordinate energy storage strategies appear to differ due to status-dependent variation in daily activities and variation in the need to prepare for future reproductive or dispersal opportunities.

Variation in social information use: the influences of information reliability and mass on decision making in a group-living fish Gambusia affinis.

The effect of the reliability of available social information was assessed by examining whether the age of social information changes its effects on a foraging decision in a group-living fish Gambusia affinis. Individuals switched their patch preference when faced with social information that conflicted with personal information in general; the age of the social information, however, did not significantly influence preference for feeding patch. The mass of decision makers was positively correlated with their use of available social information, with heavier individuals exhibiting a greater difference in patch preference than lighter individuals, suggesting that large and small G. affinis trade-off the benefits of information acquisition and the costs of competition from conspecifics differently.

A survival and reproduction trade-off is resolved in accordance with resource availability by virgin female mosquitoes.

The first 2-4 days after an Anopheles gambiae female mosquito emerges are critical to her survival and reproductive success. Yet, the order of behavioural events (mating, sugar feeding, blood feeding) during this time has received little attention. We discovered that among female cohorts sampled from emergence, sugar feeding had a higher probability than blood feeding of occurring first, and mating rarely occurred before a meal was taken. The night after emergence, 48% of females fed on sugar in mesocosms, and 25% fed on human blood; in the absence of sugar, 49% of females fed on human blood. After 5 days, 39% of the sugar-supplied females had blood fed and mated, and were fructose negative, whereas only 8% of the sugar-denied females had both blood fed and mated by this time. The model that best explained the transitions suggests that females made use of two distinct behavioural pathways, the most common one being to sugar-feed, then mate, and then seek blood. Other females sought blood first, then mated, and forwent a sugar meal. Lipid levels were higher in females with access to sugar than in females without access to sugar, particularly for those in later gonotrophic stages, while glycogen levels in the sugar-supplied group were higher throughout. In single-night experiments with females having had access to sucrose since emergence, those given a blood meal 1 day before spending a night with males had higher insemination rates than those not receiving the blood meal. These results indicate that the trade-off between survival and immediate reproduction is resolved by young adult females in accordance with availability of resources and gonotrophic state.

The effects of temporal variation in predation risk on anti-predator behaviour: an empirical test using marine snails.

Foraging animals must often balance the conflicting demands of finding food and avoiding predators. Temporal variation in predation risk is expected to influence how animals allocate time to these behaviours. Counterintuitively, the proportion of time spent foraging during both high- and low-risk periods should increase with increasing time exposed to high risk. We tested this prediction using intertidal marine snails (Littorina spp.) that were exposed to temporal variation in perceived predation risk from crabs (Cancer productus and Cancer magister). Our results were consistent with those predicted for high-risk, but not low-risk, periods. During high-risk periods, a greater number of snails foraged (versus those that left the water or remained in their shells) as time at high perceived risk increased. For low-risk periods, there was no relationship between the number of snails foraging and time at high risk. This might be due to snails in all treatments foraging maximally in the low-risk periods. As a consequence, the difference in the number of snails foraging between high- and low-risk periods decreased with increasing time subject to high risk. These results indicate that the commonly used protocol of exposing foragers to a single pulse of heightened risk might tend to overestimate their typical investment in anti-predator behaviour.

Interactions between vitamins C and E in human subjects.

Despite convincing in vitro evidence, a vitamin C-E interaction has not been confirmed in vivo. This study was designed to examine the effects of supplementation with either vitamin C or E on their respective plasma concentrations, other antioxidants, lipids and some haemostatic variables. Fasting blood was collected before and after intervention from thirty healthy adults in a double-blinded crossover study. Baselines for measured variables were established after 2 weeks of placebo supplementation, followed by daily supplementation with 73.5 mg RRR-alpha-tocopherol acetate or 500 mg ascorbic acid, and placebo, for 6 weeks. A 2 month washout preceded supplement crossover. Mean values showed that plasma lipid standardised alpha-tocopherol increased with ascorbic acid supplementation: from 4.09 (sem 0.51) to 4.53 (sem 0.66) micromol/mmol total cholesterol plus triacylglycerol (P < 0.05), and plasma ascorbic acid increased from 62.8 (sem 14.9) to 101.3 (sem 22. 2) micromol/l (P < 0.005). Supplementation with (RRR)-alpha-tocopherol acetate increased plasma alpha-tocopherol from 26.8 (sem 3.9) to 32.2 (sem 3.8) micromol/l (P < 0.05), and lipid-standardised alpha-tocopherol from 4.12 (sem 0.48) to 5.38 (sem 0.52) micromol/mmol (P < 0.001). Mean plasma ascorbic acid also increased with vitamin E supplementation, from 64.4 (sem 13.3) to 76. 4 (sem 18.4) micromol/l (P < 0.05). Plasma ferric reducing (antioxidant) power and glutathione peroxidase (U/g haemoglobin) increased in both groups, while urate, total cholesterol and triacylglycerol levels decreased (P < 0.05 throughout). Results are supportive of an in vivo interaction between vitamins C and E.

Marginal copper deficiency and atherosclerosis.

Copper is an essential trace element in the maintenance of the cardiovascular system. Copper-deficient diets can elicit, in animals, structural and functional changes that are comparable to those observed in coronary heart disease. In this study, the effect of dietary-induced copper deficiency on aortic lesion development was measured by quantitative image analysis in C57BL/6 mice that are susceptible to diet-induced aortic lesions. The diets administered were severely copper deficient (0.2 mg/kg diet), marginally deficient (0.6 mg/kg diet), or copper adequate (6.0 mg/kg diet). Similarly, increased aortic lesion areas and elevated serum cholesterol were demonstrated in both deficient groups, compared with the copper-adequate group. Evidence for graded differences in copper status among the dietary groups was shown by the dose-response increase in liver copper concentration, copper-zinc superoxide dismutase and cytochrome-c oxidase activities, together with serum caeruloplasmin oxidase with increasing intakes of dietary copper. Despite the difference in copper status between the copper marginal and severely deficient groups, similar lesions found in both groups of mice suggest a threshold effect of copper deficiency on lesion formation.

Ontogenetic influences on foraging and mass accumulation by big brown bats (Eptesicus fuscus).

Juvenile flying animals, including bats, often cease increasing, or even decrease in body mass after the onset of flight. The low body mass of juvenile bats may be a result of stresses associated with the initiation of flight, or may be an adaptation to reduce flight costs. To test these hypotheses, the body masses of adults and unknown aged juvenile big brown bats (Eptesicus fuscus) were separately compared in August 1990 through to 1995. It was hypothesized that there should be little variation in the body mass of juveniles from year to year if low body mass is an adaption to reduce flight costs. The foraging behaviour and body masses of bats of known or estimated age were also compared in 1994 and 1995. Ambient temperature at sunset was greater in 1994 than in 1995. It was assumed that prey density and predictability increased with temperature, and hypothesized that if low body mass results from energetic stress, then this should be more apparent in 1995. Using radiotelemetry, the foraging behaviour of juvenile, yearling and adult E. fuscus was compared in 1994 and 1995 to determine whether young bats attempt to compensate for energetic shortfalls by foraging for longer, or emerging earlier, than adults. Unknown-aged juveniles did not differ significantly in body mass in August from 1990 through to 1995. Adults were significantly heavier in August in 1990 and 1994 than in 1991, 1993 and 1995. Known-aged juveniles had lower body mass than adults in 1994, and lower wing loading than adults in 1995. Known-aged juveniles did not differ in mass between 1994 and 1995, while adults were heavier in 1994. The foraging times for juvenile and adult bats were both significantly related to ambient temperature. However, the slope of this relationship was steeper for weaned juveniles than for adults. The foraging times of yearling and adults bats were not significantly different. The emergence times of juvenile and adult bats did not differ, nor did the emergence times of yearlings and adults. Emergence time did not differ significantly between 1994 and 1995. The results of the study suggest that juvenile bats maintain a low body mass even under conditions that permit adults to accumulate greater fat deposits. Juveniles do not forage earlier or for longer to compensate for poor foraging ability and increased energy expenditures resulting from the onset of flight. This suggests that, by maintaining a low body mass, juveniles reduce flight costs and the risk of predation at a time when flight and foraging are still developing.