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.     

Hostile encounters among spruce-woods warblers (Dendroica: Parulidae)

Intraspecific interactions were initiated with high frequency by four species of sympatric warblers (Dendroica: Parulidae) early in the breeding season. They declined during the incubation and nestling stages and then increased during the fledging stage in two species, the black-throated green (Dendroica virens) and yellow-rumped (D. coronata) warblers. Interspecific interactions occurred infrequently early in the season, but increased during the incubation and nestling stages in the black-throated green and blackburnian (D. fusca) warblers and during the fledging stage in the magnolia warbler (D. magnolia). Fights and chases predominated over supplanting attacks in both intraspecific and interspecific encounters. Male black-throated green and yellow-rumped warblers initiated hostile encounters more frequently than did their females, but male and female blackburnian and magnolia warblers did not differ in this regard. A somewhat equivocal interspecific social dominance hierarchy occurred: magnolia > black-throated green > yellow-rumped > blackburnian. Reversals to this trend were frequent and may have resulted from the strong defences initiated by these species in certain parts of their territories, particularly about their nests.     

AT(1) receptor inhibition does not reduce arterial wall hypertrophy or PDGF-A expression in renal hypertension

To separate the role of ANG II from pressure in hypertrophy of the vascular wall in one-kidney, one-clip (1K1C) hypertension, experimental and sham-operated rats were given the AT(1)-receptor antagonist losartan (20 mg x kg(-1) x day(-1)) or tap water for 14 days. Mean arterial pressure was elevated in both experimental groups compared with controls. Rats were anesthetized with pentobarbital sodium, and the thoracic aorta and carotid, small mesenteric, and external spermatic arteries were harvested and embedded in paraffin. Tissue sections were used for morphological analysis, immunohistochemistry for 5-bromo-2'-deoxyuridine (BrdU) and platelet-derived growth factor (PDGF)-AA, stereological measurements, and in situ hybridization with a (35)S-labeled riboprobe for PDGF-A mRNA. Elevated cross-sectional areas of thoracic, carotid, and small mesenteric artery in 1K1C rats were not reduced by losartan. The internal diameter of the external spermatic artery and microvascular density of the cremaster muscle were reduced in 1K1C rats. The number of BrdU-positive nuclei per cross section did not differ between 1K1C and control arteries. PDGF-A mRNA was elevated in the arterial walls of 1K1C rats compared with controls and was hardly changed by losartan. PDGF-A protein stained strongly in the media of 1K1C arteries and was not inhibited by losartan; it appeared in the adventitia of all aortas and carotid arteries. These observations demonstrate that effects of ANG II mediated through the AT(1) receptor are not necessary for hypertrophy of the vascular wall during 1K1C hypertension or expression of PDGF-A.     

Nitrogen addition does not reduce belowground competition in a salt marsh clonal plant community in Mississippi (USA)

Previous studies have suggested that belowground competition for nutrients influences plant zonation in salt marshes. In this study, I tested the hypothesis that competition for nitrogen structured a clonal plant community in a nitrogen-limited salt marsh in coastal Mississippi, USA. In contrast to most previous field studies that have investigated mechanisms of competition, I examined clonal growth responses of established genets of a nitrogen-demanding low-intertidal species (Spartina alterniflora) to nitrogen addition and the removal of a nitrogen-conserving high-intertidal species (Juncus roemerianus). Nitrogen addition stimulated clonal invasion of the Juncus zone by Spartina but did not reduce the significant competitive effects of Juncus on Spartina. Simulated Juncus shade did not reduce invasion of the Juncus zone by Spartina, indicating that belowground competition reduced clonal invasion. In the last year of the study, the border shifted unexpectedly towards the Spartina zone, resulting in competitive displacement of Spartina by Juncus. Nitrogen addition did not prevent or slow this displacement, further contradicting the nitrogen competition hypothesis. Although growth rates were much more strongly limited by nitrogen in Spartina than in Juncus, nitrogen addition did not cause the displacement of Juncus by Spartina after three growing seasons. I conclude that zonation of Spartina and Juncus is maintained by preemption of space and greater tolerance of low nitrogen supplies by Juncus in the high marsh. These results contrast sharply with findings of reduced belowground competition with nutrient addition in previous studies and highlight the important role of nutrient-mediated competition for space between clonal plants.     

Social status does not affect resting metabolic rate in wintering dark-eyed junco (Junco hyemalis)

Studies of wintering birds have demonstrated a correlation between social rank and energy expenditures. It is assumed that dominance is energetically costly because of increased activity, possibly caused by elevated androgen levels. As winter acclimatization leads to an increase in metabolic rate, maintaining dominance status in a cold climate can be a substantial challenge. We measured resting metabolic rates in dominant and subordinate dark-eyed juncos (Junco hyemalis) living in small groups in a controlled winter environment. We found no significant effect of social rank when controlling for body size. It has been shown previously that high testosterone levels during the nonbreeding season can lead to higher body conductance, fat loss, and higher nocturnal body temperature. A hypothesis explaining our result is that for juncos it is preferable to maintain low androgen levels during winter and to maintain social rank using a mechanism other than higher agonistic activity.     

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.     

Seasonal hyperphagia does not reduce digestive efficiency in an Arctic grazer

Muskoxen (Ovibos moschatus) consume fibrous plants that grow rapidly over the short Arctic summer. We studied responses of eight castrated male muskoxen to a diet of grass hay and mineral supplements during spring, autumn, and winter. Animals gained body mass in spring (239+/-39 kg) as body fat content increased from 26% to 38% of ingesta-free mass in winter without changes in lean mass and protein. Intakes of dry matter (DM) increased by 74% between spring and autumn as digestible energy increased from 554 to 923 kJ kg(-0.75) d(-1) during mass gain. Digestibility of cellulose (72%-76%) was not affected by increasing food intake between spring and autumn but was reduced to 65% in winter. Digestibility of nitrogen compounds was 61%-66%, even though intake increased by 134% between spring and autumn. Excess dietary nitrogen from hay and supplements increased urea concentrations in plasma and urine. High loads of solutes such as potassium did not affect plasma or urinary osmolality but were associated with increased rates of glomerular filtration and urinary excretion. Low intakes of sodium from grasses may limit intake and digestion during summer, but high food intakes can support deposition of nitrogen, calcium, magnesium, copper, and zinc in body tissue even when dietary concentrations are low. Seasonal increases in digestive and metabolic functions allow muskoxen to rapidly accumulate energy and nutrients in body tissue during the short season of plant growth.     

Suppression of prolactin does not reduce infant care by parentally experienced male common marmosets (Callithrix jacchus)

High levels of prolactin have been found to correlate with the expression of paternal care in a variety of taxa. However, in mammals, there is little experimental evidence that prolactin is causally involved in the stimulation or maintenance of paternal care. Here, we suppressed prolactin production in paternally experienced common marmoset fathers in their family groups during the first 2 weeks after their infants were born. Circulating prolactin levels were suppressed using cabergoline (Dostinex: Pfizer), a long acting dopamine (D2) agonist with minimal behavioural side-effects. A within-subject design was used to compare behavioural and hormonal data on 5 paternally experienced fathers during two consecutive births. Cabergoline reduced prolactin to negligible levels in all fathers without effecting testosterone, DHT and cortisol and without adverse side-effects. However, lowering prolactin had no significant effect on the expression of majority of the behaviour patterns associated with paternal care. These included infant carrying, infant grooming and the frequency with which fathers retrieved and rejected infants. The only infant-related behaviour to be affected was the frequency with which fathers touched, licked and investigated infants. We noted a marginally significant increase in this behaviour during cabergoline treatment. Despite the lack of effect on paternal care, cabergoline did exert an effect on the affiliative/sexual behaviour of fathers as there was a significant increase in the grooming behaviour fathers directed at and received from their mates during drug treatment. This study showed that experienced male marmosets can express paternal behaviour in the absence of the high prolactin levels normally seen after infants are born.     

Removal of the glycosylphosphatidylinositol anchor from PrP(Sc) by cathepsin D does not reduce prion infectivity

According to the protein-only hypothesis of prion propagation, prions are composed principally of PrP(Sc), an abnormal conformational isoform of the prion protein, which, like its normal cellular precursor (PrP(C)), has a GPI (glycosylphosphatidylinositol) anchor at the C-terminus. To date, elucidating the role of this anchor on the infectivity of prion preparations has not been possible because of the resistance of PrP(Sc) to the activity of PI-PLC (phosphoinositide-specific phospholipase C), an enzyme which removes the GPI moiety from PrP(C). Removal of the GPI anchor from PrP(Sc) requires denaturation before treatment with PI-PLC, a process that also abolishes infectivity. To circumvent this problem, we have removed the GPI anchor from PrP(Sc) in RML (Rocky Mountain Laboratory)-prion-infected murine brain homogenate using the aspartic endoprotease cathepsin D. This enzyme eliminates a short sequence at the C-terminal end of PrP to which the GPI anchor is attached. We found that this modification has no effect (i) on an in vitro amplification model of PrP(Sc), (ii) on the prion titre as determined by a highly sensitive N2a-cell based bioassay, or (iii) in a mouse bioassay. These results show that the GPI anchor has little or no role in either the propagation of PrP(Sc) or on prion infectivity.     

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.     

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.     

Toxoplasma gondii does not persist in goldfish (Carassius auratus)

Recent reports of toxoplasmosis in marine mammals raise concern that cold-blooded marine animals are a potential source of Toxoplasma gondii infection. To examine the transmissibility of T. gondii to fish, we observed the development of T. gondii tachyzoites inoculated into oviduct epithelial cells of goldfish (Carassius auratus) microscopically in vitro. Further, the survival period of tachyzoites inoculated into goldfish muscle was bioassayed in mice and through PCR analysis. In cell cultures at 37 C, both RH and Beverley strains of T. gondii tachyzoites had penetrated into cells at 6 hr post inoculation, and were multiplying. In cell cultures at 33 C, many tachyzoites of both strains attached to the host cells, but no intracellular tachyzoites were observed at 24 hr post inoculation. In the T. gondii inoculated goldfish kept at 33 C, tachyzoite DNA was detected in the inoculated region on day 3, but not on day 7. When inoculated goldfish were kept at 37 C, live tachyzoites were seen at the inoculation site on day 3, but not on day 7. These results suggest that T. gondii does not persist in fish.