Social play does not reduce aggression in wild meerkats

Of the numerous hypotheses advanced to explain the adaptive significance of play, several assert that social play increases social harmony, cementing alliances and reducing aggression between group members or littermates. These hypotheses are frequently cited, but their validity remains unknown. We examined the relation between social play and aggression in juvenile meerkats, Suricata suricatta, living in a wild population in the southern Kalahari Desert. We tested the hypothesis that social play reduces aggression, by examining rates of play, play partner choices, the structure of social play and rates of aggressive interactions during foraging. We found no relation between frequency of play and level of aggression, either between individuals or during the course of development. Pups that played together frequently were just as aggressive towards one another as pairs of pups that played infrequently, and play interactions had no subsequent effect on the likelihood of aggression. In contrast, aggressive interactions during foraging inhibited the subsequent likelihood of play, and high levels of aggression during foraging changed the structure of social play, with victimized pups avoiding play wrestling. We conclude that social play does not reduce aggression in young meerkats. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.      

Halofuginone does not reduce fibrosis in bleomycin-induced lung injury

Halofuginone, a coccidiostatic alkaloid, has anti-fibrotic properties, and may be useful as a therapeutic agent in lung fibrosis. To test this hypothesis we investigated the effect of halofuginone on bleomycin-induced lung fibrosis in Sprague-Dawley rats. Treatment groups included: (1) a single intratracheal (IT) instillation of 1.2U bleomycin, and intraperitoneal (IP) injection of halofuginone (0.5 mg/dose), every other day; (2) IT 1.2U bleomycin and IP distilled water (D.W.), every other day; (3) IT 0.8U bleomycin and daily IP halofuginone (0.5 mg/dose); (4) IT 0.8U bleomycin and daily IP D.W.; (5) IT saline and IP halofuginone, every other day; (6) IT saline and daily IP D.W.; (7) IT 0.625U bleomycin and oral halofuginone (10 mg/kg rodent lab chow); (8) IT 0.625U bleomycin and standard lab chow. Animals were studied 14 days after IT instillation. Lung injury was evaluated by total and differential cell count in bronchoalveolar lavage fluid, by a semi-quantitative morphological index of lung injury, and by biochemical analysis of lung hydroxyproline content. Overt signs of lung injury were apparent in bleomycin-treated rats by all measures. These changes were not affected by treatment with halofuginone, irrespective of the treatment regimen used. This study does not support the use of halofuginone to prevent or ameliorate lung fibrosis.     

Intragametophytic selfing does not reduce reproduction inDryopteris filix-max

Gametophytes ofDryopteries filix-mas (L.) Schott were grown as isolates and as pairs of related and unrelated individuals. Reproductive efforts were generally highest among isolates, which reproduce by intragametophytic selfing only. Reproductive success ofD. filixmas may depend on the abundance of resources rather than the actual mating system employed. The estimates of the amount of genetic load for the two populations examined were low, 10% and 16%, respectively. The great numbers and the high viability of sporophytes produced by intragametophytic selfing indicate thatD. filix-mas does not experience serious inbreeding depression.     

Diurnal variation around an optimum and near‐critically high temperature does not alter the performance of an ectothermic aquatic grazer

The growing threat of global climate change has led to a profusion of studies examining the effects of warming on biota. Despite the potential importance of natural variability such as diurnal temperature fluctuations, most experimental studies on warming are conducted under stable temperatures. Here, we investigated whether the responses of an aquatic invertebrate grazer (Lymnaea stagnalis) to an increased average temperature differ when the thermal regime is either constant or fluctuates diurnally. Using thermal response curves for several life‐history and immune defense traits, we first identified the optimum and near‐critically high temperatures that Lymnaea potentially experience during summer heat waves. We then exposed individuals that originated from three different populations to these two temperatures under constant or fluctuating thermal conditions. After 7 days, we assessed growth, reproduction, and two immune parameters (phenoloxidase‐like activity and antibacterial activity of hemolymph) from each individual. Exposure to the near‐critically high temperature led to increased growth rates and decreased antibacterial activity of hemolymph compared to the optimum temperature, whilst temperature fluctuations had no effect on these traits. The results indicate that the temperature level per se, rather than the variability in temperature was the main driver altering trait responses in our study species. Forecasting responses in temperature‐related responses remains challenging, due to system‐specific properties that can include intraspecific variation. However, our study indicates that experiments examining the effects of warming using constant temperatures can give similar predictions as studies with fluctuating thermal dynamics, and may thus be useful indicators of responses in nature.     

Density-dependent natural selection does not increase efficiency

Summary Populations ofDrosophila melanogaster kept at high population density (K-selected) for 125 generations have higher larval viability than populations kept at low densities (r-selected) when both are raised under crowded conditions. In additionK-selected adults that emerge from crowded cultures are larger than theirr-selected counterparts. These differences cannot be explained by differences in efficiency of food use. The minimum food required for successful pupation is actually greater in theK-selected populations. I conjecture that there may be a trade-off between minimum food requirements and competitive ability, which has changed substantially in theK-selected populations. The possibility thatK-selected larvae can dig more more deeply and gain access to unused food is examined and rejected as a possible explanation of the viability differences. Evidence is provided supporting the hypothesis that the differences in viability may be due to an increased tendency of theK-selected larvae to pupate off the surface of the medium.     

Inhaled nitric oxide does not reduce systemic vascular resistance in mice

Inhaled nitric oxide (NO) is a highly selective pulmonary vasodilator. It was recently reported that inhaled NO causes peripheral vasodilatation after treatment with a NO synthase (NOS) inhibitor. These findings suggested the possibility that inhibition of endogenous NOS uncovered the systemic vasodilating effect of NO or NO adducts absorbed via the lungs during NO inhalation. To learn whether inhaled NO reduces systemic vascular resistance in the absence of endothelial NOS, we studied the systemic vascular effects of NO breathing in wild-type mice treated without and with the NOS inhibitor N(omega)-nitro-l-arginine methyl ester and in NOS3-deficient (NOS3(-/-)) mice. During general anesthesia, the cardiac output, left ventricular function, and systemic vascular resistance were not altered by NO breathing at 80 parts/million in both genotypes. Breathing NO in air did not alter blood pressure and heart rate, as measured by tail-cuff and telemetric methods, in either awake wild-type mice (whether or not they were treated with N(omega)-nitro-l-arginine methyl ester), or in awake NOS3(-/-) mice. Our findings suggest that absorption of NO or adducts during NO breathing is insufficient to cause systemic vasodilation in mice, even when endogenous endothelial NO production is congenitally absent.     

Ruminal fermentation and fill change with season in an arctic grazer: responses to hyperphagia and hypophagia in muskoxen (Ovibos moschatus)

We studied castrated adult muskoxen fed a standard diet of grass hay and supplement throughout the year to determine seasonal changes in digesta passage, fill, and fermentation without the confounding effects of reproductive demands or changes in food quality. Although food intake increased by 74% between spring and autumn, mean retention times of fluid and particulate digesta markers were maintained between seasons in both the rumen (9-13 h) and the intestines (27-37 h). The rumen contained 84.5% of digesta and accounted for 79% of dry matter digestion in the whole digestive tract. Ruminal fluid space and whole-gut digesta fill increased by 31%-34%, while ruminal rates of in situ degradation increased by more than 100% between spring and autumn for cellulose and hemicellulose. Hyperphagia in autumn was accompanied by increased bacterial counts in ruminal fluid (30%), declines in ruminal pH, and increases in the concentration of fermentation acids (16%) when compared with spring hypophagia. Consumption of fresh hay and supplement increased the concentrations of acids most markedly during winter and spring when bacterial counts were low. Low food intakes in winter and spring may limit the microbial population, whereas hyperphagia in autumn may foster a much more active microflora that requires consistent supplies of substrate. Plasticity of fill and fermentation in muskoxen minimizes winter costs and maximizes nutrients and energy gained from coarse forages in small home ranges throughout the year.     

Prepartum peripherally-induced hyposmia does not reduce postpartum anoestrus duration in nursing goats

Parturient goats rapidly develop exclusive nursing of their own litter that relies on olfactory recognition of the young. They also show a period of postpartum anoestrus whose duration depends on the presence of the kid. In cattle, maternal selectivity is one of the factors that delays the recovery of sexual activity. To investigate the possible influence of maternal selectivity on the duration of postpartum anoestrus in goats, we compared the recovery of estrus behavior by daily estrus detection with an active buck in intact and selective nursing goats (n = 24) with that of dams rendered non-selective by peripheral hyposmia with ZnSO4 (n = 18). Postpartum anoestrus duration was shorter in intact (68+/-7 days) than in hyposmic mothers (93+/-7 days; P < 0.05). However, the cycles of normal duration were less frequent in intact goats (P = 0.03). We conclude that in nursing goats, preventing the establishment of selective nursing by prepartum peripheral hyposmia does not reduce postpartum anoestrus duration. Our results suggest that daily exposure to the buck may result in an earlier recovery of ovarian activity in intact mothers.     

Systemic adenosine deaminase administration does not reduce active hyperemia in running rats

The importance of adenosine in controlling the magnitude and distribution of blood flow among and within skeletal muscles in rats during slow locomotor exercise was tested by systemic infusion of adenosine deaminase (ADA). Blood flows were measured using labeled microspheres before exercise and at 0.5, 15, and 30 min of fast treadmill walking at 15 m/min. An initial infusion of ADA (1,000 U/kg) was given 30 min before the first blood flow measurement and a second injection (1,000 U/kg) was given 5 min into exercise. These infusions maintained ADA activity above 5 U/ml blood throughout the experimental period. This plasma concentration of ADA was shown to be sufficient to result in a 64% decrease in muscle adenosine levels during ischemic contraction. Blood flows were measured in all of the muscles of the hindlimb (28 samples) and in various nonmuscular tissues in ADA-treated and control rats. Preexercise blood flows were primarily directed to slow-twitch muscles and exercise blood flows were highest in muscles with fast-twitch oxidative fibers. ADA treatment did not reduce total muscle blood flow or exercise blood flows in any of the muscles at any time. These findings do not support the hypothesis that adenosine plays an essential role in controlling muscle blood flow in skeletal muscles during normal locomotor activity.     

Group hibernation does not reduce energetic costs of young yellow-bellied marmots

We investigated mechanisms of energy conservation during hibernation. The amount of time torpid was significantly less for groups of three young marmots than for marmots hibernating singly. Mean daily mass loss (DML; as mg d(-1) g(-1) immergence mass) averaged 1.33 for single marmots and 1.46 for grouped young. Animals were active 17.3% of the time, which used 82.4% of the energy, and were torpid 82.7% of the time, which used 17.6% of the energy expenditure. During longer torpor bouts, more time was spent in deep torpor, which decreased the hourly cost of a complete bout. Bout oxygen consumption V dot o2, percent time in deep torpor, and body temperature (T(B)) during deep torpor changed seasonally and were curvilinearly related to when in the hibernation period the measurements were made and probably represent a stage in the circannual metabolic cycle. The decrease of environmental temperature (T(E)) to 2 degrees C significantly increased metabolism. Potential costs of low T(E) were reduced by allowing T(B) to decrease, thereby reducing the T(B) to T(E) gradient. Average monthly metabolic rate was high early and late in the hibernation period when time spent euthermic was greater and when VO2 was higher. Over the hibernation period, energy saved averaged 77.1% and 88.0% of the costs for winter and summer euthermic metabolism, respectively. Hibernation costs were reduced by the seasonal changes, the high percentage of time in torpor, the rapid decline in V dot o2 following arousal, and allowing T(B) to decline at lower T(E). Asynchrony in the torpor cycles increased energy expenditures in group hibernators, which negated possible beneficial effects of group hibernation.     

Damage to sagebrush attracts predators but this does not reduce herbivory

Emissions of volatiles increase following herbivory from many plant species and volatiles may serve multiple functions. Herbivore‐induced volatiles attract predators and parasitoids of herbivores and are often assumed to benefit plants by facilitating top‐down control of herbivores; this benefit of induced emissions has been tested only a few times. Volatile compounds released by experimentally clipped sagebrush shoots have been shown to reduce levels of chewing damage experienced by other shoots on the same plant and on neighboring sagebrush plants. In this study, I asked whether experimental clipping attracted predators of herbivorous insects to sagebrush shoots. I also evaluated aphid populations and chewing damage on clipped and unclipped shoots and whether predators were likely to have caused differences in aphids and chewing damage. Shoots that had been clipped recruited more generalist predators, particularly coccinellids and Geocoris spp. in visual surveys conducted during two seasons. Clipping also caused increased numbers of parasitized aphids in one season. Ants were common tending aphids but were not significantly affected by clipping. Despite the increase in generalist predators, clipped plants were more likely to support populations of aphids that increased during both seasons compared to aphids on unclipped control plants. Clipped shoots suffered less damage by chewing herbivores in the 1‐year in which this was measured. Chewing damage was not correlated with numbers of predators. These results suggest that predators and parasitoids were attracted to experimentally clipped sagebrush plants but that these predators were not effective at reducing net damage to the plant. This conclusion is not surprising as much of the herbivory is inflicted by grasshoppers and deer, herbivores that are not vulnerable to the predators attracted to sagebrush volatiles. More generally, it should not be assumed that predators that are attracted by herbivore‐induced volatiles necessarily benefit the plant without testing this hypothesis under field conditions.     

Inhibition of prostaglandins does not reduce the cardiovascular changes during endotoxemia in rats

Vasodilatory prostanoids, such as prostacyclin and PGE2, and pro-inflammatory cytokines are known to play a central role in the pathogenesis of endotoxemia. This study was undertaken to elucidate whether indomethacin (INDO), a non-selective COX inhibitor, has protective effects against the cardiovascular alterations that occur during endotoxemia. Sprague-Dawley rats were injected intraperitoneally with 15 mg/kg lipopolysaccharide (LPS). LPS injection led to a prominent decrease in cardiac left ventricular end diastolic area (LVEDA) and increased LV fractional shortening (FS), as measured by echocardigraphy. LPS also led to a significant increase in plasma and myocardial TNF-alpha and IL-1beta levels, and elevated plasma and hypothalamic levels of PGE2. Neither the decrease in LVEDA and the increase in FS, nor the elevation in plasma and myocardial cytokine levels were altered by INDO (10 mg/kg). On the other hand, pretreatment with INDO significantly reduced the elevation in PGE2 and the hypothermia induced by LPS. Taken together, this study demonstrates that solely inhibiting the production of PGE2 is not sufficient to reduce the cardiovascular alteration seen in endotoxemia.