Effects of acute stress on aggression and the cortisol response in the African sharptooth catfish Clarias gariepinus: differences between day and night

African sharptooth catfish Clarias gariepinus were housed under continuous dim light (1 lx) or 12L:12D (350–0 lx) cycles. The number of skin lesions, as indicator of aggressive acts, and plasma cortisol levels, as indicator of stress‐axis activity, were measured at baseline as well as following a stressor (given in the light or dark phase). Results showed that (1) baseline plasma cortisol levels were not different between photoperiods, (2) the number of baseline skin lesions was highest for C. gariepinus housed under continuous dim light, (3) stressor‐induced peak levels of plasma cortisol were highest in the light phase and (4) the number of skin lesions following a stressor was highest in the dark phase. The higher number of stressor‐related skin lesions in the dark (active) phase suggests increased stressor‐induced aggression while in the active phase. In addition, the data suggest that housing under continuous dim light does not result in higher stress‐axis activity, as measured by baseline levels of cortisol, but does result in more stressor‐induced aggression, as measured by the higher number of skin lesions. The latter may be related to the fact that the continuous dim light photoperiod has twice the number of dark‐phase (active) hours in which stressor‐induced aggression is stronger compared to the 12L:12D photoperiod, which has a light phase in which stressor‐induced aggression is lower.     

野牛草克隆分株酶促活性氧清除系统对差异光周期的响应

以盆栽野牛草克隆分株为材料,将克隆分株分别标记为O(姊株)和Y(妹株),设置连接组和断开组两种处理,其中,连接组中O分株和Y分株通过节间子相连,断开组则剪断分株节间子;两组处理的O分株光周期均设置为光照12h/黑暗12h,Y分株光周期均设置为黑暗12h/12h光照(恰好与O分株相反),经过7d的差异光周期处理后进行72h全光照稳定培养,并于全光照条件下在48h内连续测定各分株叶片超氧化物歧化酶(SOD),过氧化物酶(POD),过氧化氢酶(CAT),抗坏血酸过氧化物酶(APX)的活性以及丙二醛(MDA)的含量,探讨野牛草叶片酶促活性氧清除系统对差异光周期的响应特征。结果表明,差异光周期处理1周后,全光照条件下,断开状态的野牛草克隆分株O和Y间叶片中SOD、POD、CAT、APX活性以及MDA含量在24h内基本呈现相反的变化趋势,而野牛草相连克隆分株O和Y间叶片中以上指标在24h内呈现趋于一致的变化规律。研究发现,野牛草酶促活性氧清除系统活性在一天内呈现节律性表达模式,且差异光周期处理下的野牛草相连克隆分株的活性氧清除系统的活性的节律性变化趋于同步。     

Patterns of diapause frequency and emergence in swede midges of southern Ontario

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