Seasonal Changes In Sensitivity Research Articles

Seasonal differences in larval sea lamprey (Petromyzon marinus) sensitivity to the pesticide TFM

Invasive sea lamprey (Petromyzon marinus) are controlled in the Great Lakes with 4-nitro-3-(trifluoromethyl)phenol (commonly 3-trifluoromethyl-4-nitrophenol or TFM). The proper amount of TFM must be applied during treatments to effectively kill larval sea lamprey while minimizing impacts to non-target species. In this study, bioassay tests were conducted in May, July, and September in a portable test trailer at six larval sea lamprey infested rivers in Michigan to determine potential seasonal changes in sensitivity of larval sea lamprey to TFM. Larvae greater than 60 mm were collected from each stream and exposed for 12 h in TFM-treated stream water using two independent continuous-flow diluter systems. A suite of water chemistries and larval physiological parameters were collected during the tests and modeled as potential predictors of seasonal changes in the sensitivity of larval sea lamprey to TFM. The observed minimum lethal concentrations to larval sea lamprey were 0–40% lower (May), 8% lower–59% higher (July), and 49–117% higher (September) than sea lamprey control personnel treatment prediction charts. Water temperature, liver glycogen content, and time of year were strongly associated with seasonal differences in TFM sensitivity, offering sea lamprey control personnel more exact predictions to limit potential residual lamprey surviving future treatments.

Tissue-specific gene regulation corresponds with seasonal plasticity in female testosterone

Testosterone (T) is a sex steroid hormone that often varies seasonally and mediates trade-offs between territorial aggression and parental care. Prior work has provided key insights into the ‘top-down’ hypothalamic control of this seasonal plasticity in T, yet mechanisms acting outside of the brain may also influence circulating T levels. We hypothesized that peripheral mechanisms may be especially critical for females, because peripheral regulation may mitigate the costs of systemically elevated T. Here, we begin to test this hypothesis using a seasonal comparative approach, measuring gene expression in peripheral tissues in tree swallows (Tachycineta bicolor), a songbird with intense female-female competition and T-mediated aggression. We focused on the gonad and liver for their role in T production and metabolism, respectively, and we contrasted females captured during territory establishment versus incubation. During territory establishment, when T levels are highest, we found elevated gene expression of the hepatic steroid metabolizing enzyme CYP2C19 along with several ovarian steroidogenic enzymes, including the androgenic 5α-reductase. Despite these seasonal changes in gene expression along the steroidogenic pathway, we did not observe seasonal changes in sensitivity to upstream signals, measured as ovarian mRNA abundance of luteinizing hormone receptor. Together, these data suggest that differential regulation of steroidogenic gene expression in the ovary is a potentially major contributor to seasonal changes in T levels in females. Furthermore, these data provide a unique and organismal glimpse into tissue-specific gene regulation and its potential role in hormonal plasticity in females.

Valoración de la dosis efectiva media y sensibilidad estacional en el bufo spinulosus, usando standard internacional de gonadotrofina corionica

Usando por primera vez en nuestro país standard internacional de gonadotrofina coriónica, hemos observado modificaciones estacionales de la sensibilidad al desprendimiento de espermatozoides en el sapo común de Lima, en forma similar a la que presentan diversas especies de batracios en otros países. Los resultados hemos apreciado por la dosis efectiva teórica en U.I. para cada estación, encontrando valores D. E. 50 ó D.E.M. entre 9 y 15 U.I., con sensibilidad máxima en primavera, decreciente en verano y mínima en otoño, para volver a aumentar en invierno. Aplicando estos informes, como se comprende, se facilita en nuestro medio la determinación cuantitativa de la gonadotrofina coriónica en unidades internacionales, usando el Bufo spinulosus y con ayuda de las curvas dosis-respuestas para cada estación representadas en un diagrama, sin importar la época del año en que se trabaje. Con todo, creemos oportuno establecer que sólo es válido el método para las titulaciones en sangre y orina que se realicen en Lima; si hay la intención de aplicarlo en otras regiones del país, previamente conviene valorar en cada zona la sensibilidad específica del animal reactivo del lugar para evitar un posible error de cálculo. Por otra parte, nuestro animal de laboratorio ha resultado más sensible que sus congéneres de otros países y comparable a la que presenta la coneja, aunque menor a la rata impúber. Por ello, juzgamos conveniente usar el Bufo spinulosus para determinaciones cuantitativas cuando se busquen niveles altos de gonadotrofinas coriónicas, en tanto que no es apropiado para niveles bajos.

千岛湖陆桥岛屿鸟类集团对栖息地片段化的敏感性及其季节变化

PDF HTML阅读 XML下载 导出引用 引用提醒 千岛湖陆桥岛屿鸟类集团对栖息地片段化的敏感性及其季节变化 DOI: 10.5846/stxb201406261319 作者: 作者单位: 浙江大学生命科学学院,广东省昆虫研究所 华南濒危动物研究所,浙江大学生命科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目(31170397,31210103908) Seasonal changes in sensitivity of bird guilds to habitat fragmentation on land- bridge islands in the Thousand Island Lake, China Author: Affiliation: College of Life Sciences, Zhejiang University,,College of Life Sciences, Zhejiang University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为探究千岛湖陆桥岛屿不同鸟类集团对栖息地片段化敏感性的差异和季节变化,于2009年4月-2012年1月鸟类繁殖季(4、5、6月)和冬季(11、12、1月)对千岛湖41个陆桥岛屿鸟类集团进行了研究。结果表明,冬季杂食鸟对片段化敏感性高于食虫鸟,繁殖季时二者无显著差异,繁殖季和冬季时下层鸟对片段化敏感性均高于林冠鸟,冬季留鸟对片段化敏感性高于候鸟,繁殖季则无显著差异。杂食鸟和留鸟对片段化敏感性存在季节差异,而食虫鸟、林冠鸟、下层鸟和候鸟对片段化敏感性均无季节差异。不同鸟类集团对栖息地片段化敏感性的差异和季节变化规律,有助于人们在栖息地管理和保护区设计时采取更有针对性的鸟类保护措施。 Abstract:Habitat loss and fragmentation seriously threaten global species diversity. Understanding the impact on species and communities is a core issue for ecology and conservation biology. A guild acts as a functional unit within a community. Bird guild research can help to analyze relationships among different species and evaluate their responses to habitat fragmentation. Much research has focused on bird guilds in terrestrial fragments, while other fragmented systems, such as land-bridge islands, draw relatively less attention. Because different systems tend to display different geological and ecological patterns, we needed to verify whether terrestrial fragments and land-bridge islands share common patterns of response to habitat fragmentation. The land-bridge islands in the Thousand Island Lake, which were created by dam construction, are an ideal platform for the study of habitat fragmentation. To test bird sensitivity to habitat fragmentation across seasons, we conducted bird guild studies on 41 land-bridge islands in the Thousand Island Lake during the breeding season (April-June) and winter season (November-January) of each year between April 2009, and January 2012. We classified birds into guilds according to dietary type, foraging strata, and migratory status. We used an equation with logarithmic transformation from island biogeography, S=CAz, to clarify the relationship between bird guild species richness and island fragment area. In this equation, S represents species richness of each bird guild, A represents island area, C is a constant, and z is the slope of the species-area curve. This variable can be considered a measurement of sensitivity to habitat fragmentation. The bigger the value of z, the greater the sensitivity of the bird guild. We extracted and compared the slope of each species-area relationship curve (z value) to determine whether there exists significant variation in sensitivity to habitat fragmentation among the different bird guilds. Our research indicated that omnivorous birds were more sensitive to habitat fragmentation than insectivores during the winter season, while no significant difference was found for the breeding season. Understory birds were more sensitive to habitat fragmentation than canopy birds, both in breeding and winter seasons. Resident birds were more sensitive than migrants in winter, while no significant difference between them were observed in the breeding season. Both omnivorous and resident birds showed seasonal changes in their sensitivity to fragmentation. Other guilds, including insectivorous birds, canopy birds, understory birds, and migratory birds, showed no significant seasonal changes. Previous studies conducted in terrestrial fragments support our findings that responses of bird guilds to habitat fragmentation differ and that seasonal changes in the responses to habitat fragmentation do exist. These results may aid in the effective management of bird habitats and in the design of nature reserves. Future studies may focus on other bird guild types and determine if differences in responses to habitat fragmentation occur at a larger temporal scale. 参考文献 相似文献 引证文献

Photic Sensitivity for Circadian Response to Light Varies with Photoperiod

The response of the circadian system to light varies markedly depending on photic history. Under short day lengths, hamsters exhibit larger maximal light-induced phase shifts as compared with those under longer photoperiods. However, effects of photoperiod length on sensitivity to subsaturating light remain unknown. Here, Syrian hamsters were entrained to long or short photoperiods and subsequently exposed to a 15-min light pulse across a range of irradiances (0-68.03 µW/cm(2)) to phase shift activity rhythms. Phase advances exhibited a dose response, with increasing irradiances eliciting greater phase resetting in both conditions. Photic sensitivity, as measured by the half-saturation constant, was increased 40-fold in the short photoperiod condition. In addition, irradiances that generated similar phase advances under short and long days produced equivalent phase delays, and equal photon doses produced larger delays in the short photoperiod condition. Mechanistically, equivalent light exposure induced greater pERK, PER1, and cFOS immunoreactivity in the suprachiasmatic nuclei of animals under shorter days. Patterns of immunoreactivity in all 3 proteins were related to the size of the phase shift rather than the intensity of the photic stimulus, suggesting that photoperiod modulation of light sensitivity lies upstream of these events within the signal transduction cascade. This modulation of light sensitivity by photoperiod means that considerably less light is necessary to elicit a circadian response under the relatively shorter days of winter, extending upon the known seasonal changes in sensitivity of sensory systems. Further characterizing the mechanisms by which photoperiod alters photic response may provide a potent tool for optimizing light treatment for circadian and affective disorders in humans.

Cholecystokinin activation of central satiety centers changes seasonally in a mammalian hibernator

Hibernators that rely on lipids during winter exhibit profound changes in food intake over the annual cycle. The mechanisms that regulate appetite changes in seasonal hibernators remain unclear, but likely consist of complex interactions between gut hormones, adipokines, and central processing centers. We hypothesized that seasonal changes in the sensitivity of neurons in the nucleus tractus solitarius (NTS) to the gut hormone cholecystokinin (CCK) may contribute to appetite regulation in ground squirrels. Spring (SPR), late summer (SUM), and winter euthermic hibernating (HIB) 13-lined ground squirrels ( Ictidomys tridecemlineatus) were treated with intraperitoneal CCK (100 μg/kg) or vehicle (CON) for 3 h and Fos expression in the NTS was quantified. In CON squirrels, numbers of Fos-positive neurons in HIB were low compared to SPR and SUM. CCK treatment increased Fos-positive neurons in the NTS at the levels of the area postrema (AP) and pre AP during all seasons and at the level of the rostral AP in HIB squirrels. The highest absolute levels of Fos-positive neurons were found in SPR CCK squirrels, but the highest relative increase from CON was found in HIB CCK squirrels. Fold-changes in Fos-positive neurons in SUM were intermediate between SPR and HIB. Thus, CCK sensitivity falls from SPR to SUM suggesting that seasonal changes in sensitivity of NTS neurons to vagally-derived CCK may influence appetite in the active phase of the annual cycle in hibernating squirrels. Enhanced sensitivity to CCK signaling in NTS neurons of hibernators indicates that changes in gut–brain signaling may contribute to seasonal changes in food intake during the annual cycle.

Seasonal variation in ecophysiological patterns in macroalgae from an Arctic fjord. I. Sensitivity of photosynthesis to ultraviolet radiation

Marine macroalgae inhabiting Arctic coastal ecosystems are exposed to pronounced seasonal variations in the radiation regime, including harmful UVB radiation. This study presents the first data on the seasonal changes in the sensitivity of macroalgal photosynthesis towards UV exposure by comparing under-ice, clear-water and turbid-water conditions characteristic for late winter, spring and summer. Various brown (Laminariasaccharina, L. digitata, L. solidungula, Saccorhizadermatodea, Desmarestiaaculeata), red (Palmariapalmata, Devaleraearamentacea) and one green macroalgal species (Monostroma aff. arcticum) were collected at the same water depth throughout the seasons in the Kongsfjord (Spitsbergen, Svalbard, Norway). Maximum quantum yield (Fv/Fm) and maximum photosynthetic electron transport rates (ETRmax) were determined immediately after collection, after 2 h exposure to artificial UV radiation and after 18 h recovery in dim white light. Photosynthesis of the studied species showed different responses depending on their morpho-functional and physiological characteristics, their life strategies, phenology and depth distribution. Within the genus Laminaria, maximum quantum yield of adult specimens of the deep-water species L. solidungula was most strongly UV sensitive. Adult L. saccharina exhibited a lower UV sensitivity than a 6-month-old specimen. Inhibition of photosynthesis after UV exposure remained at the same level throughout the study period, both in adult L. saccharina and S. dermatodea. However, adult specimens of L. saccharina collected in May showed partial recovery only, whereas photosynthesis of specimens from both species collected later recovered fully. D. aculeata exhibited a remarkable decrease of UV sensitivity during the study period. Photosynthesis of specimens collected under the ice was strongly inhibited by UV, but the degree of inhibition decreased during spring and summer. Concomitantly ETRmax values were low after UV exposure in specimens collected in June, but increased later in the season. P. palmata exhibited a relatively flexible response. Photosynthesis in specimens collected under the ice in June or in turbid water in July/August was relatively strongly inhibited; specimens collected during sunny periods and in clear water in spring showed a much lower degree of photoinhibition after UV exposure. The seasonal pattern of low/high ETRmax values in spring/summer is probably a characteristic of the life strategy of this species. The UV sensitivity of D. ramentacea exhibited a similar seasonal pattern. In M. aff. arcticum, UV sensitivity increased and ETRmax values decreased during the study period, reflecting the life strategy of this annual late winter/spring species. The physiological basis for the seasonal changes in UV sensitivity of photosynthesis is presented in a companion paper (this issue).

Rapid freezing injury in red spruce: seasonal changes in sensitivity and effects of temperature range.

On calm, cold days in winter, sun-exposed needles of red spruce (Picea rubens Sarg.) may warm 10 to 20 degrees C above ambient air temperature, and undergo rapid (>/= 1 degrees C min(-1)) fluctuations in temperature as light breezes or passing clouds alter the energy balance of the foliage. It has been proposed that the resulting rapid freeze-thaw cycles (freezing stress) cause a type of winter injury in montane red spruce that is characterized by necrosis of sun-exposed foliage. In autumn and winter, we monitored rapid freezing stress response of needle sections from 10 montane red spruce trees by subjecting needles to rapid freezing over the temperature span typically recorded in the field. In autumn, experimental rapid freezing stress produced severe injury only at temperatures considerably lower than expected for that time of year. In winter, rapid freezing caused occasional, moderate injury in fully hardened foliage of trees susceptible to both slow and rapid freezing. Seasonal changes in sensitivity to rapid and slow freezing were correlated, suggesting that environmental factors that are known to affect sensitivity to slow freezing may also affect sensitivity to rapid freezing. Experimental manipulation of the start and end temperatures of rapid freezing stress events showed that moderate to severe needle injury can occur in susceptible trees at temperature spans slightly more extreme than those typically recorded in the field. The extent of injury was similar at different starting temperatures if rapid freezing occurred over the same temperature span. Year-old foliage was consistently less sensitive to rapid freezing stress than current-year foliage, but some year-old foliage was damaged when the rapid freezing stress regime caused severe injury in current-year foliage. We conclude that rapid freeze-thaw cycles can explain light to moderate injury of current-year foliage, but they do not explain the more severe and widespread pattern of foliar damage that has occurred intermittently over at least the last 18 years.

Effect of inhaled budesonide on seasonal changes in sensitivity and maximal response to methacholine in pollen-sensitive asthmatic subjects

The aim of this study was to investigate the effect of inhaled budesonide on modifications of the provocative concentration of agonist causing a 20% fall in forced expiratory volume in one second (FEV1) (PC20) and maximal response plateau to inhaled methacholine during the pollen season in pollen-sensitive subjects with mild asthma. The effects of inhaled budesonide (800 micrograms.day-1) on the threshold value (PC20) and maximal response plateau to inhaled methacholine were studied in 28 pollen-sensitive subjects with mild asthma during a pollen season in a randomized, double-blind, placebo-controlled parallel fashion. They were challenged with methacholine (up to 200 mg.ml-1) in February (preseasonal assessment) and during the middle of the pollen season (in May and again in June). Subjects treated with budesonide (n = 13) were protected from the decrease in PC20 seen in the placebo (n = 15) group (geometric mean PC20 placebo group: preseasonal = 8.51, May = 2.19 and June = 1.78 mg.ml-1; budesonide group: preseasonal = 3.71, May = 3.23 and June = 2.40 mg.ml-1; intergroup differences in doubling concentrations, p < 0.05). Among 10 subjects in the placebo group who reached plateau during the preseasonal assessment, seven lost the plateau in May and six in June. In the budesonide group, among seven subjects who reached plateau during the preseasonal assessment, three lost the plateau in May and four in June. Between-group differences were not significant. We conclude that in pollen-sensitive subjects with mild asthma, inhaled budesonide blocks the effects of natural allergen exposure on the methacholine threshold value.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative analysis of oestrous behaviour through the breeding season in two breeds of sheep

Intact ewes (11 Ile-de-France, IF, and 11 Préalpes du Sud, PA) were used to study the quantitative changes in two parameters of sexual behaviour, the receptivity and the proceptivity, through the breeding season. Behaviour was quantified during the first and second cycles of the season, in the midbreeding season and during the last cycle, using standardized procedures at daily intervals during oestrus and 3 to 5 days per week between oestrous periods. Receptivity (R) and proceptivity (P) generally varied in parallel. They markedly increased on the days of oestrus but receptivity was displayed more regularly than proceptivity, in particular in IF ewes (respectively 94 and 60% for IF versus 100 and 93% for PA). The maximum level for both parameters did not vary during the season. It was often higher in PA than in IF (mean R index around 90% in PA and 80% in IF; mean time near male around 120 s in PA and 70 s in IF). During anoestrus or between oestrous days, the level of receptivity and proceptivity was very low, with the exception of receptivity in IF at the time of transition from anoestrus to breeding season where it was significantly higher. These changes are related to known seasonal changes in sensitivity to oestradiol, and a role of both progesterone and oestradiol at the beginning of the breeding season is proposed.

Changes in pulsatile LH secretion after ovariectomy in Ile-de-France ewes in two seasons.

Two experiments were conducted in Ile-de-France ewes to study changes in pulsatile LH secretion in ewes ovariectomized during anoestrus or during the midluteal phase of the oestrous cycle. In Exp. 1, blood samples were taken every 20 min for 12 h the day before ovariectomy (Day 0). After ovariectomy, samples were taken every 10 min for 6 h (10 ewes per group), on Days 1, 3, 7 and 15. In Exp. 2 samples were taken every 10 min for 6 h (10 ewes per group) on Days 7, 15, 30, 60, 90, 120, 150 and 180 after ovariectomy. Further samples were taken (5 ewes per group) at 9 and 12 months after ovariectomy. There were significant interactions between season and day of sampling for the interval between LH pulses in both experiments. LH pulse frequency increased within 1 day of ovariectomy and the increase was more rapid during the breeding season. There were clear seasonal differences in pulse frequency in Exp. 2. Compared with ewes ovariectomized in anoestrus, pulse frequency was significantly higher for ewes ovariectomized in the breeding season, from Day 7 until Day 120. Once pulse frequency had increased in ewes about the time of the normal breeding season, pulse frequency remained high and subsequent seasonal changes were greatly reduced. Pulse amplitude increased immediately after ovariectomy to reach a maximum on Day 7 and there were no differences between season of ovariectomy in the initial changes in amplitude. In Exp. 2, changes in amplitude followed changes in pulse interval and there was a significant interaction between season and day of sampling. There were no significant effects of season on nadir LH concentrations which increased throughout the duration of the experiments. These results show that, in ovariectomized ewes, LH pulse frequency observed on a given day depends on time after ovariectomy, season at the time of sampling and on previous exposure of ewes to stimulatory effects of season. The direct effects of season on LH pulse frequency and seasonal changes in sensitivity to steroid feedback may contribute to control of the breeding season and their relative contributions to the beginning and end of the breeding season may differ.

Diurnal and seasonal changes in sensitivity of plants to short exposures of hydrogen chloride gas

Increasing the concentration of hydrogen chloride (HCl) gas during single 20-min exposures from 13 to 27 mg m −3 significantly increased amounts of visible foliar injury recorded after 48 h on pinto beans and radishes. These two species were equally sensitive to HCl gas. Fumigations made between 08.00 and 14.00 h were more damaging than those made earlier or later in the day. No clear effect of season was noted although injury from fumigations made in August was greater than that occurring in February. In addition to being related to concentrations of HCl, amounts of foliar injury were positively correlated with ambient temperatures and amounts of light, these relationships possibly explaining the greater sensitivity of plants in the period 08.00–14.00 h.

Lowered sensitivity to acetylcholine in hearts from cold-acclimated rats and frogs.

AbstractThe sensitivity of the heart to the negative chronotropic effect of acetylcholine (ACh) was measured in vivo from denervated hearts of the rat and frog before and after they were acclimated to cold. In the frog the possible seasonal changes in sensitivity were also observed. In the rat, cold acclimation lowered the sensitivity to ACh. This change was significant already at 3 days after cold exposure. Cold acclimation lowered the sensitivity to ACh also in the frog, but only during the winter. On the other hand, summer frogs were much niore sensitive to ACh than winter frogs. It was concluded that it is the increased parasympathetic activity in the cold‐acclimated rat and in the winter frog which results in the lowering of sensitivity to ACh.

Seasonal changes in the sensitivity of spayed ewes to progesterone and oestrogen.

Seasonal variation in the incidence and duration of behavioural oestrus in spayed ewes treated with progesterone and oestrogen has been attributed to changes in the sensitivity of ewes to oestrogen (Reardon & Robinson, 1961; Fletcher & Lindsay, 1971). This interpretation is open to question, however, in view of suggestions from Lamond & Bindon (1962) and Lamond (1964) that intact ewes showed seasonal changes in sensitivity to progesterone. The investigation reported here was designed to determine whether changes in sensitivity to progesterone contributed to seasonal variation in the expression of oestrous behaviour in spayed ewes. The experiment was of factorial design with three different doses of progesterone for priming, two breeds of ewe and two seasons of observation. Sixty spayed Merino and 60 spayed Border Leicester × Merino cross-bred ewes were each allotted at random to three groups of 20. They were injected daily with 5, 10 or 20 mg progesterone