Effect of photoperiod length on body mass and testicular growth in the house sparrow (Passer domesticus) and brahminy myna (Sturnus pagodarum)

Two experiments studied the relative effects on body mass and testicular growth of stimulatory photoperiods applied simultaneously to two photosensitive species, the house sparrow (Passer domesticus) and brahminy myna (Sturnus pagodarum). Experiment 1 on the house sparrow consisted of two parts. In experiment 1A, beginning on 24 March 2002, short day pretreated sparrows were exposed for 12 weeks to 13L: 11D (13 h light: 11 h darkness), 20L: 4D and NDL (control). Experiment 1B was similar to 1A except that it used sparrows that were not treated with short days. This experiment was repeated at three different times in the year. Beginning on 29 December 2002 (for 24 weeks), 26 March 2003 (for 12 weeks) and 16 August 2003 (for 8 weeks), sparrows captured from the wild and acclimated to captive condition for 1 week were exposed to 13L: 11D and 20L: 4D. Each time, a group was maintained in NDL and served as the control. Experiment 2 was performed on myna and used an identical protocol. Beginning on 24 March 2002, myna that were captured from the wild and acclimated to captivity conditions were exposed for 16 weeks to 13L: 11D and 20L: 4D; a group was maintained in NDL and served as the control. There was photostimulation and subsequent regression of the testes on all day lengths except in the August group of experiment 1B. The effect on body mass was variable. Interestingly, however, the response to 20L:4D was relatively smaller as compared to 13L:11D. Taken together, these results confirm that the two species use photoperiods in control of their reproductive cycle, and tend to indicate that exposure to unnatural long photoperiods may in fact be unfavorable and could compromise gonadal growth and development.     

Termination of photorefractoriness in the brahminy myna, Sturnus pagodarum: role of photoperiods and gonadal hormones.

In brahminy myna a photosensitive species, long days caused full gonadal development followed by rapid regression, whereas short days inhibited these responses. Experiments were performed to investigate the effects of duration of photoperiod and gonadal hormones on the recovery of photosensitivity to long photoperiods in male birds. Groups of photorefractory birds were subjected to 8-, 9- or 11-hr daily photoperiods for 45 (6.5 weeks) or 63 (9 weeks) days and then transferred to 15 h daily photoperiods for 60 days to check for the regaining of photoresponsivity. A control group was held under 15L:9D throughout the period of study. Another experiment included three groups of photorefractory males, which were maintained on 9L:15D for 9 weeks and administered with, birth-1day-1 alternately for first 30 days olive oil or different doses (10 or 100 micrograms) of testosterone propionate (TP)/bird/day alternately for first 30 days, and then transferred to 15L:9D for another 30 days to test the recovery of photosensitivity. The results indicated that (i) a period of exposure to short daylengths is required to dissipate photorefractoriness, (ii) termination of photorefractoriness is dependent on the length and duration of photoperiods and (iii) TP inhibits the recovery of photosensitivity in a dose dependent manner.     

Photo-gonadal response of Indian brahminy myna to resonance cycles in different seasons

The role of annual changes in day length in regulation of seasonal breeding is widely investigated in a number of subtropical birds. But, how the seasonal changes in bird’s photosensitivity are involved in regulation of breeding in subtropical myna, Sturnus pagodarum, is less understood. We combined the tool of resonance experiments with the seasonal variability in photo-gonadal responses of myna, to investigate whether exposing myna to resonance cycles for 10–12?months starting four different seasons of the year would alter its gonadal recrudescence-regression cycle. Eight groups (n?=?5) of myna were transferred to either 6L: 18D (6?h of light/18?h of dark) or 6L: 30D starting March, June, September and December, respectively, and held thence for 10 or 12?months. The observations suggest a seasonal transition between photosensitive, photo-stimulated and photo-insensitive states occurs during different seasons in subtropical myna. The photoperiodic clock involved in the regulation of seasonality in myna appears to follow the principle of external coincidence model, used to explain photoperiodism in many birds.     

The development of photorefractoriness in termination of the breeding season in the tropical brahminy myna: role of photoperiod

Gonads of brahminy myna (Sturnus pagodarum) spontaneously regress in July/August when the daylength is still stimulatory. Experiments were conducted to investigate if photoperiod was involved in the timing of gonadal regression and if photorefractoriness terminated the breeding season in this species. The observations obtained in the present study clearly show that: i) increasing photoperiods of spring/summer programmed for eventual gonadal regression in the late summer; ii) the birds developed photorefractoriness to all stimulatory daylengths and consequently the breeding season could not be extended by providing more stimulatory photoperiods; and iii) exposure to short daylength treatment failed to overcome the onset of refractoriness in birds after they had attained full gonadal growth and development. These results suggest that refractoriness is a process used by the brahminy myna to terminate the breeding season, and that this species becomes totally photorefractory.     

The starvation–predation risk trade-off, body mass and population status in the Common Starling Sturnus vulgaris

It is theoretically and empirically well established that body mass variation in small birds reflects a trade-off between starvation risk and predation risk. This occurs because carrying increased fat reserves reduces starvation risk but also results in a higher predation risk due to reduced escape flight performance and/or the increased foraging exposure needed to maintain a higher body mass. In principle, therefore, the theory of mass-dependent predation risk could be used to understand how a bird perceives and responds to the risks in its environment, because its mass will reflect the predictability of foraging opportunities and predation risk. Mass in birds may then provide a relatively straightforward way of assessing the foraging environment of birds and so the potential conservation problems a species faces. This study tests, for the first time for any species, how body mass changes in response to changing starvation risk, changing predation risk and changing population status. Common Starling Sturnus vulgaris mass varies as predicted by starvation–predation risk trade-off theory: mass is lower when foraging conditions are more favourable and when predation risk is increased. The populations that are declining the most strongly have higher mass, which is most likely indicative of a poor foraging environment, leading to lower relative survival. The results suggest that increased mass in Starlings, and possibly in other species, may provide an indication of the poor quality of the foraging environment and/or rapidly declining populations.     

Photoperiod-induced testicular apoptosis in European starlings (Sturnus vulgaris)

To determine the extent to which testicular regression involves apoptotic cell death, photosensitive adult starlings were photostimulated for up to 9 wk by exposure to long-day (18 h of light) photoperiods. Apoptotic activity in recrudescing and regressing testes was assessed by in situ TUNEL labeling. Absolute testis mass in male starlings increased after 2 wk of photostimulation and subsequently decreased with continued long-day exposure. Seminiferous tubule diameter also increased after 1-3 wk of photostimulation, then decreased as photorefractoriness developed. Testosterone concentrations increased significantly by Week 2 of photostimulation and declined with further light exposure. TUNEL labeling was significantly elevated in germ cells with 4 wk of photostimulation. An approximate 7-fold increase in the degree of apoptotic cell death was observed over the course of gonadal regression. Incidences of TUNEL labeling in somatic Sertoli cells also increased. Light and electron microscopy examination confirmed that these somatic cells displayed morphological characteristics of apoptotic death. In rodents, Sertoli cells have not been previously reported to die during gonadal regression. These results suggest that seasonal testicular regression in European starlings is mediated by apoptosis.     

Pinealectomy affects the circannual testicular rhythm in european starlings (Sturnus vulgaris)

Summary Pinealectomized and sham-operated European starlings were maintained for 16 months under a constant 12-h photoperiod and constant temperature conditions. In all birds, testicular width was measured at about monthly intervals and the onset and end of molt was determined. Shortly after the beginning of the experiment, the sham-operated birds went through a cycle of testicular growth and regression which was followed by a complete molt; subsequently most individuals initiated a second testicular cycle. Most of the pinealectomized birds, in contrast, failed to go through a second testicular cycle. Moreover, during the first cycle their testes regressed earlier than in the sham-operated birds and the subsequent molt was relatively advanced. In these respects the pinealectomized birds behaved like intact starlings under a 13-h photoperiod. Since pinealectomy probably changes the phase-relationship between circadian rhythms and the entraining light-dark cycle it is proposed that pinealectomy in the present experiment might have altered the phase-relationship between a circadian rhythm of photosensitivity and the light-dark cycle in such a way that the birds interpreted the 12-h photoperiod as a 13-h photoperiod.This work was supported by the Deutsche Forschungsgemeinschaft SPP Mechanismen biologischer Uhren.     

Stable daily light regimens as inductive factors of endogenous testicular cycles in the European starling,Sturnus vulgaris

European starlings (Sturnus vulgaris ) maintained under chronic 12L:12D exhibit testicular cycles with a periodicity of 9–10 months. These circannual testicular cycles incorporate all of the physiologically distinct phases observed during gonadal cycles in starlings under temperate-zone photoperiods. Starlings maintained under chronic 6L-18D also undergo testicular cycles but these cycles: (a) have a relatively short periodicity (about 6 months); (b) include periods of testicular involution, though not to the minimal quiescent level for this species; and (c) do not include the physiologically distinct photorefractory phase separating testicular cycles in starlings under chronic 12L:12D and under temperate-zone photoperiods. While it is possible that testicular cycles in starlings under certain daily light regimens of fixed duration are a function of an endogenous circannual reproductive rhythm, we believe that the testicular cycles generated under both 12L:12D and 6L:18D are the product of gonadotropin secretion rates controlled by circadian (not circannual) oscillations periodically entrained by these chronic photoperiods.     

Telomerase activity coevolves with body mass not lifespan

In multicellular organisms, telomerase is required to maintain telomere length in the germline but is dispensable in the soma. Mice, for example, express telomerase in somatic and germline tissues, while humans express telomerase almost exclusively in the germline. As a result, when telomeres of human somatic cells reach a critical length the cells enter irreversible growth arrest called replicative senescence. Replicative senescence is believed to be an anticancer mechanism that limits cell proliferation. The difference between mice and humans led to the hypothesis that repression of telomerase in somatic cells has evolved as a tumor-suppressor adaptation in large, long-lived organisms. We tested whether regulation of telomerase activity coevolves with lifespan and body mass using comparative analysis of 15 rodent species with highly diverse lifespans and body masses. Here we show that telomerase activity does not coevolve with lifespan but instead coevolves with body mass: larger rodents repress telomerase activity in somatic cells. These results suggest that large body mass presents a greater risk of cancer than long lifespan, and large animals evolve repression of telomerase activity to mitigate that risk.     

Effects of stochastic food deprivation on energy budget,body mass and activity in Swiss mice

When small animals are faced with an unpredictable food supply,they can adapt by altering different components of their energy budget such as energy intake,metabolic rate,rate of non-shivering thermogenesis(NST)or behaviour.The present study examined the effect of stochastic food deprivation(FD)on body mass,food intake,resting metabolic rate(RMR),NST and behaviour in male Swiss mice.During a period of 4 weeks' FD,animals were fed ad libitum for a randomly assigned 4 days each week,but were deprived of food ...     

Maternal body mass index and risk of testicular cancer in male offspring: A systematic review and meta-analysis

Objectives: To date a number of studies have examined the association between maternal weight and testicular cancer risk although results have been largely inconsistent. This systematic review and meta-analysis investigated the nature of this association. Methods: Search strategies were conducted in Ovid Medline (1950–2009), Embase (1980–2009), Web of Science (1970–2009), and CINAHL (1937–2009) using keywords for maternal weight (BMI) and testicular cancer. Results: The literature search produced 1689 hits from which 63 papers were extracted. Only 7 studies met the pre-defined criteria. Random effects meta-analyses were conducted. The combined unadjusted OR (95% CI) of testicular cancer in the highest reported category of maternal BMI compared with the moderate maternal BMI was 0.82 (0.65–1.02). The Cochran's Q P value was 0.82 and the corresponding I² was 0%, both indicating very little variability among studies. The combined unadjusted OR (95% CI) for testicular cancer risk in the lowest reported category of maternal BMI compared to a moderate maternal BMI category was 0.88 (0.65–1.20). The Cochran's Q P value was 0.05 and the corresponding I² was 54%, indicating evidence of statistical heterogeneity. The combined unadjusted OR (95% CI) of testicular cancer risk per unit increase in maternal BMI was 1.01 (0.97–1.06). The Cochran's Q test had a P value of 0.05 and the corresponding I² was 55% indicating evidence of statistical heterogeneity. Conclusion: This meta-analysis, which included a small number of studies, showed that a higher maternal weight does not increase the risk of testicular cancer in male offspring. Though an inverse association between high maternal BMI and testicular cancer risk was detected, it was not statistically significant. Further primary studies with adjustment for appropriate confounders are required.     

Overweight in urban schoolchildren assessed by body mass index and body fat mass in Dalian, China

In order to assess overweight in urban schoolchildren (298 boys and 298 girls) aged 9-16 years in Dalian, China, their body height, weight, skinfolds at triceps, biceps, subscapular and suprailiac, and body circumferences of mid-upper arm, waist and hip were measured. The results showed that the prevalence of overweight, based on the United States Centers for Disease Control 2000 reference values using body mass index (BMI), was 22.9% in boys and 10.4% in girls, which was higher than that of indicated in Chinese national surveys of recent decades. More boys were overweight than girls due to excessive increase in body fat, although the prevalence of overweight in girls prevalence increased from 13 years. Discussion here focuses on the effects of behavioral patterns on overweight in Dalian schoolchildren, paying attention to gender difference.     

The metabolic output of avian (Sturnus vulgaris,Calidris alpina) adipose tissue liver and skeletal muscle: Implications for BMR/body mass relationships

• 1.1. The oxygen uptake rate of avian adipose tissue, liver and skeletal muscle slices were measured.
• 2.2. The energy consumption of fat was less than one tenth that of liver and muscle.
• 3.3. Thus, interspecific allometric equations for the prediction of basal metabolic rate from body mass will not be accurate throughout the avian annual cycle unless changes in body composition are taken into account.

     

Ethnicity, body mass, and genome-wide data

This article combines social and genetic epidemiology to examine the influence of self-reported ethnicity on body mass index (BMI) among a sample of adolescents and young adults. We use genetic information from more than 5,000 single nucleotide polymorphisms in combination with principal components analysis to characterize population ancestry of individuals in this study. We show that non-Hispanic white and Mexican-American respondents differ significantly with respect to BMI and differ on the first principal component from the genetic data. This first component is positively associated with BMI and accounts for roughly 3% of the genetic variance in our sample. However, after controlling for this genetic measure, the observed ethnic differences in BMI remain large and statistically significant. This study demonstrates a parsimonious method to adjust for genetic differences among individual respondents that may contribute to observed differences in outcomes. In this case, adjusting for genetic background has no bearing on the influence of self-identified ethnicity.     

种子感光的机理及影响种子感光性的因素

种子的萌发或休眠均取决于萌发时种子内所建立起来的Pfr含量和Pfr/(Pr Pfr)比值。种子内的Pfr水平受到诸多因素的影响。光中性种子在成熟时已存在适合萌发的Pfr水平;需光种子在不同程度地接受白光或红光照射后,方可达到适宜的Pfr水平;忌光种子萌发要求的Pfr水平较低,因此萌发需要较长时间的黑暗。种子的感光性不是绝对的,母株的生长条件、种子本身的成熟度、贮藏状况、光质、光流量、光周期、萌发温度、O2供应及某些化合物的处理等都可使种子的感光性发生改变。