The influence of age and size on temporal mate signalling behaviour

I investigated how male size, condition and age influence both time spent calling and how signals are apportioned throughout the night (i.e. temporal calling pattern) in the Texas field cricket, Gryllus integer. I quantified male calling time and temporal calling pattern using an electronic apparatus that continuously monitored male calling/noncalling behaviour throughout the night. Male condition, measured using the residuals from an allometric regression of male mass on overall body size, did not explain any variation in either time spent calling or temporal calling pattern. However, some intrapopulation variation in time spent calling and temporal calling pattern was explained by differences in male size and age. Large males called more often than small males. Young and very old adult males called significantly less often than middle-age males. As males aged they initiated calling earlier in the evening, probably increasing their susceptibility to parasitism by the tachinid parasitoid Ormia ochracea. Overall, age and size differences explained 10-40% of signalling variation in male G. integer. Copyright 2000 The Association for the Study of Animal Behaviour.     

The influence of aging on androgen dynamics in the male rat

Androgen assimilation was investigated in a variety of accessory sex organs (seminal vesicles and anterior, dorsal, lateral, and ventral prostates) and in several nonaccessory sex organs in male Wistar rats. After administration of a pulse dose of [³H]testosterone in vivo to intact young (3–4 months old) rats, [³H]testosterone was the primary radioactive steroid recovered from most organs examined, except for the secondary sex glands where the reduced metabolites, [³H]5α-dihydrotestosterone (DHT) and [³H]5α-androstanediol(s), predominated. At longer postinjection times, [³H]DHT was preferentially retained in the accessory sex glands, presumably reflecting intracellular metabolism of [³H]testosterone to this compound and subsequent specific binding of [³H]DHT to receptor proteins. At the longest postinjection interval investigated, the ventral prostate retained greater concentrations of [³H]DHT than the lateral prostate which in turn had a higher [³H]DHT concentration than the seminal vesicles or anterior or dorsal prostates. The latter three glands retained approximately equal concentrations of [³H]DHT. Scatchard plot analyses of cytosol binding in 24-h castrates indicated that with one exception, the level of high affinity DHT binding sites was generally correlated with the retention of [³H]DHT in vivo in intact rats. Specifically, while the affinity for DHT binding in all accessory sex organs was the same, the number of high affinity binding sites per mg wet tissue weight was on the order of ventral prostate > anterior prostate ≥ seminal vesicles ≥ dorsal prostate > lateral prostate. Studies of the influence of aging to 22–26 months revealed no apparent differences in the affinity of the DHT receptor for its ligand in any of the accessory sex glands from 24-h castrates when the receptors were present in levels sufficiently high to quantify. The concentration of available DHT receptors with advancing age remained constant in the anterior and dorsal prostates, increased in the seminal vesicles, and declined in the ventral and lateral prostates. The decreases observed in the ventral prostate were only partial, but the receptors of the lateral prostate declined to nondetectable levels.     

The influence of social norms on the dynamics of vaccinating behaviour for paediatric infectious diseases

Mathematical models that couple disease dynamics and vaccinating behaviour often assume that the incentive to vaccinate disappears if disease prevalence is zero. Hence, they predict that vaccine refusal should be the rule, and elimination should be difficult or impossible. In reality, countries with non-mandatory vaccination policies have usually been able to maintain elimination or very low incidence of paediatric infectious diseases for long periods of time. Here, we show that including injunctive social norms can reconcile such behaviour-incidence models to observations. Adding social norms to a coupled behaviour-incidence model enables the model to better explain pertussis vaccine uptake and disease dynamics in the UK from 1967 to 2010, in both the vaccine-scare years and the years of high vaccine coverage. The model also illustrates how a vaccine scare can perpetuate suboptimal vaccine coverage long after perceived risk has returned to baseline, pre-vaccine-scare levels. However, at other model parameter values, social norms can perpetuate depressed vaccine coverage during a vaccine scare well beyond the time when the population''s baseline vaccine risk perception returns to pre-scare levels. Social norms can strongly suppress vaccine uptake despite frequent outbreaks, as observed in some small communities. Significant portions of the parameter space also exhibit bistability, meaning long-term outcomes depend on the initial conditions. Depending on the context, social norms can either support or hinder immunization goals.     

The influence of spatio-temporal resource fluctuations on insular rat population dynamics

Local spatio-temporal resource variations can strongly influence the population dynamics of small mammals. This is particularly true on islands which are bottom-up driven systems, lacking higher order predators and with high variability in resource subsidies. The influence of resource fluctuations on animal survival may be mediated by individual movement among habitat patches, but simultaneously analysing survival, resource availability and habitat selection requires sophisticated analytical methods. We use a Bayesian multi-state capture-recapture model to estimate survival and movement probabilities of non-native black rats (Rattus rattus) across three habitats seasonally varying in resource availability. We find that survival varies most strongly with temporal rainfall patterns, overwhelming minor spatial variation among habitats. Surprisingly for a generalist forager, movement between habitats was rare, suggesting individuals do not opportunistically respond to spatial resource subsidy variations. Climate is probably the main driver of rodent population dynamics on islands, and even substantial habitat and seasonal spatial subsidies are overwhelmed in magnitude by predictable annual patterns in resource pulses. Marked variation in survival and capture has important implications for the timing of rat control.     

The influence of insulin on the metabolism of glucosamine in the isolated rat diaphragm muscle

1. The influence of insulin on the metabolism of [1-¹⁴C]glucosamine by diaphragm muscle from normal rats and rats rendered diabetic with streptozotocin has been studied. 2. The glucosamine was converted into glucosamine 1-phosphate, glucosamine 6-phosphate, glycogen, lactate and small amounts of other unidentified intermediates. 3. Insulin increased the incorporation of ¹⁴C into glycogen in both the normal and diabetic muscle, but did not increase the formation of the glucosamine phosphate esters. 4. The ¹⁴C content in the glycogen was present partly as glucose and partly as glucosamine; there was significantly more [¹⁴C]glucose in the glycogen of the diabetic muscle than in that of the normal muscle.     

The influence of coumestrol,zearalenone, and genistein administration on insulin receptors and insulin secretion in ovariectomized rats

The influence of phytoestrogens (genistein and coumestrol) and mycoestrogen (zearalenone) on insulin secretion, liver insulin receptors and some aspects of lipid and carbohydrate metabolism were investigated in this study. Ovariectomized rats were injected s.c. with the above mentioned compounds in the amount of 1 mg for three days. Coumestrol and zearalenone caused a significant increase in uterus weight, similar to the effects observed after estrone action, while this effect was not observed after the genistein injection. Blood insulin level was not changed after phyto- or mycoestrogen treatment. However, coumestrol and genistein significantly decreased the binding capacity of liver insulin receptors. These changes corresponded with alterations in glucose and free fatty acids profiles in blood, as well as with glycogen content in liver. The effects observed after genistein and coumestrol injections differed from those noticed in rats treated with zearalenone or estrone. On the basis of these results we conclude that metabolic effects of high doses of coumestrol and genistein in ovariectomized rats are partly mediated by changes in insulin sensitivity of the liver and that the action of plant estrogens on metabolism is, at least to the some degree, independent of their estrogen activity.     

Role of 17beta-estradiol administration on insulin sensitivity in the rat: implications for the insulin receptor

The role of 17beta-estradiol in the early steps of insulin action is only partially known, although its effect on glucose homeostasis has been reported. In this paper, we attempt to prove the influence of 17beta-estradiol on the insulin receptor of ovariectomized rats treated with different hormonal doses. Our results show that high doses of estradiol impair insulin sensitivity while low doses improve it. We think that these results are the consequence of changes at a molecular level, because high doses of estradiol produced lower expression of the insulin receptor gene, lower content of this receptor in target tissues, and lower phosphorylation of insulin receptor in these tissues. However, low doses of estradiol seem to produce just the opposite. The possible existence of consensus response elements in the insulin receptor gene promoter to estradiol could be controlling the expression of this gene, this control being dose and timing dependent. Moreover, we cannot discard a possible effect of estradiol on the activity of protein tyrosine phosphatases, and therefore, on the activity of the insulin receptor. These new findings improve knowledge about the possible risk for insulin resistance in women taking oral contraceptives or receiving hormonal replacement therapy around the menopause, but could also open the door towards the possible utilization of 17beta-estradiol in some diabetes cases.     

The influence of fluoride administration on the structure of proteoglycans in the developing rat incisor.

1. 35S-labelled chondroitin 4-sulphate proteoglycan was isolated from the mineralized elements of the developing incisor teeth of Harvard rats receiving intraperitoneal administration of Na235SO4. 2. The chondroitin 4-sulphate proteoglycan underwent a decrease in molecular size in fluorotic teeth as judged by gel filtration on Sepharose 2B. 3. When examined by anion-exchange chromatography on DEAE cellulose-52, the proteoglycan from fluorotic teeth resolved into four peaks in comparison with the material from non-fluorotic teeth, which exhibited only a single major peak. 4. Both the single peak from non-fluoridated teeth and the four peaks from the fluorotic teeth were further resolved on cellulose acetate electrophoresis. 5. Isolated chondroitin 4-sulphate chains obtained from fluorotic teeth also were of smaller molecular size as judged by gel filtration on Sephadex G-150. 6. Some possible influences of fluoride on the metabolism of these connective-tissue components in the developing rat incisor are discussed.     

The influence of insulin administration after weaning the first litter on ovulation rate and embryo survival in sows

Primiparous crossbred sows (n = 43), lactating for an average of 21.1 +/- 0.1 d and weaning 8.7 +/- 0.1 pigs, were used to evaluate the influence of insulin on ovulation rate and embryo survival. The sows were maintained on 2.3 kg/head/d of a 14% protein gestation diet during pregnancy, fed ad libitum during lactation, given 2.7 kg/head/d from weaning until re-breeding and fed 2.3 kg/head/d after mating. Beginning the day after weaning (Day 0) sows were treated with 0.4 IU/kg body weight (BW) insulin (n = 21) or were administered an equivalent volume of saline (n = 22) for 4 d. Beginning on Day 3 and continuing until Day 14 after weaning, the sows were checked for estrus twice daily and were artificially inseminated using pooled semen from 2 fertile boars. At slaughter (days 30 to 40 of gestation), ovaries and uteri were collected, and the ovulation rate, embryo number and viability, and uterine weight and length were evaluated and recorded. Use of insulin decreased the average interval from weaning to estrus compared with saline by increasing percentage in estrus by Day 14 after weaning (5.0 +/- 0.57 vs 6.9 +/- 0.56 d, respectively; P < 0.03). Ovulation rate, number of embryos, embryo survival, and average uterine length and weight were not influenced by insulin treatment. Overall, insulin affected reproductive efficiency in primiparous sows by increasing the percentage of sows in estrus.     

The influence of insulin on circulating ghrelin

Ghrelin is a novel peptide that acts on the growth hormone (GH) secretagogue receptor in the pituitary and hypothalamus. It may function as a third physiological regulator of GH secretion, along with GH-releasing hormone and somatostatin. In addition to the action of ghrelin on the GH axis, it appears to have a role in the determination of energy homeostasis. Although feeding suppresses ghrelin production and fasting stimulates ghrelin release, the underlying mechanisms controlling this process remain unclear. The purpose of this study was to test the hypotheses, by use of a stepped hyperinsulinemic eu- hypo- hyperglycemic glucose clamp, that either hyperinsulinemia or hypoglycemia may influence ghrelin production. Having been stable in the period before the clamp, ghrelin levels rapidly fell in response to insulin infusion during euglycemia (baseline ghrelin 207 +/- 12 vs. 169 +/- 10 fmol/ml at t = 30 min, P < 0.001). Ghrelin remained suppressed during subsequent periods of hypoglycemia (mean glucose 53 +/- 2 mg/dl) and hyperglycemia (mean glucose 163 +/- 6 mg/dl). Despite suppression of ghrelin, GH showed a significant rise during hypoglycemia (baseline 4.1 +/- 1.3 vs. 28.2 +/- 3.9 microg/l at t = 120 min, P < 0.001). Our data suggest that insulin may suppress circulating ghrelin independently of glucose, although glucose may have an additional effect. We conclude that the GH response seen during hypoglycemia is not regulated by circulating ghrelin.     

Effect of glucocorticoid administration in vivo on insulin binding in rat testis

We have studied the effects of adrenalectomy and glucocorticoid injections on insulin binding in membranes from rat testis and liver. Glucocorticoids were administered for 7 days to adrenalectomized rats at daily doses of 30 or 300 micrograms for dexamethasone and 100 or 1000 micrograms for prednisolone. Glucocorticoids, at the selected doses, were associated with 5- to 10-fold increases in basal insulin levels with no significant changes in glucose concentrations. As previously shown by other studies, down-regulation of insulin receptors was observed in liver membrane particularly at the higher dose of steroids. Such an effect was not found in the testis. By contrast, the number of high-affinity sites in the testis was slightly increased with the higher doses of dexamethasone and prednisolone. However, percent 125I-labelled insulin binding was not significantly changed after corticotherapy. These results are in accord with our previous studies and suggest that the testicular receptor for insulin is not affected by mild to moderate changes of insulin concentrations, but that it can be modulated by glucocorticoids through other mechanisms.     

Human influence on the temporal dynamics and spatial distribution of forest biomass carbon in China

Global carbon cycles are impacted by human activity primarily via fossil fuel combustion and forest carbon budget alterations. In this study, the temporal dynamics and spatial distribution of forest biomass carbon (FBC) stock and density in China were analyzed to assess the large‐scale effects of humans on FBC. The results indicated that from 1977 to 2013, the FBC stock increased by 62.9%, from 4,335 to 7,064 Tg C, owing to human‐driven forestation and ecological restoration programs. Because of intensive human impacts, 44.2%–54.6% of the FBC stock was concentrated in four provinces (Heilongjiang, Yunnan, Inner Mongolia, and Sichuan) and the FBC density increased from the densely populated southeastern provinces to the sparsely populated northeastern and western provinces. On a spatial scale, the FBC density was significantly negatively related to population density, and the degree of the dependence of the FBC density on population density has been declining since 1998. This improvement in human–forest relations is related to economic development and programs in China that have promoted forestation and reduced deforestation. These results suggest that human impacts, including forestation, deforestation, population density, and economic development, have played significant roles in determining the temporal and spatial variations of FBC in the anthropogenic era. Moreover, our findings have implications for forest management and improvement of the forest carbon sink in China.     

The influence of insulin on various enzyme activities in human and rat hepatoma cells.

1. Incubation of human and rat hepatoma cells with insulin (1 mU/10(6) cells) decreases their content of adenosine 3':5'-monophosphate by more than half after 1 h and by about a quarter after 4 h. 2. The activities of the ATP-metabolising enzymes, adenylate kinase and Mg2+-adenosine triphosphatase are significantly increased by insulin within 1 h and after 4 h. Activity of succinate dehydrogenase and lactic dehydrogenase showed no change at either time interval. 3. Insulin markedly stimulated glucose 6-phosphate dehydrogenase activity within 1 h but by 4 h the increase was less apparent. Glutamate dehydrogenase activity by contrast was not increased by 1 h but was elevated at 4 h.