Gut Cell Cycles and Diel Feeding Patterns in Acartia Tonsa

对桡足动物种群摄食活动的观察揭示了物种之间和物种内部的广泛反应。喂养可能是连续的，在日粮期间肠道饱腹度没有变化，或者喂养可能以周期性的日粮模式发生。在非迁徙的桡足类和没有叶绿素A垂直分层的情况下，都可以看到昼夜模式。最近，研究人员已经证明，Acartia tonsa的夜间放牧与光照条件有关。然而，虽然光可能提示进食反应，光条件本身并不能解释进食周期模式的能量优势。一种假说提出了Calanus finmarchicus，一种垂直迁徙动物，在实验条件下，在喂养过程中，肠道细胞的发育出现了周期性模式。这些结果表明，在摄食过程中，某些类型的细胞被耗尽，需要一段非摄食期来再生。作为一个垂直迁徙者，C. finmarchicus在白天有一个自然的时期来允许这种再生。这项研究将调查暴露于连续食物的非迁徙桡足类动物可能存在的差异。本项目将在实验室对近岸桡足动物Acartia tonsa的肠道细胞进行24小时的形态计量学分析。分析将在光学和电子显微镜水平上进行。实验室条件将模拟自然光和食物条件，这些结果将与从田间采集的样本进行比较。生理速率（消化酶活性、谷氨酸脱氢酶活性和呼吸速率）和肠道饱腹度的模式将同时确定。

Observations of the feeding activity of copepod populations have revealed a wide range of responses both between and within species. Feeding may be continuous, with no change in gut fullness on a diel period, or feeding may occur on a cyclical, diel pattern. A diel pattern may be seen in both non-migratory copepods and in the absence of vertical stratification of chlorophyll a. Recently, researchers have demonstrated that nocturnal grazing in Acartia tonsa was timed to lighting conditions. However, while light may cue a feeding response, light conditions alone cannot explain an energetic advantage for cyclical patterns in feeding. One hypothesis is suggested Calanus finmarchicus, a vertical migrator, where a cyclical pattern is seen in gut cell development during feeding under experimental conditions. These results indicate that during the course of feeding certain cell types are depleted, and require a non-feeding period to regenerate. As a vertical migrator, C. finmarchicus has a natural period during the daylight hours in which to allow this regeneration. This research will investigate differences that might exist in non-migrating copepods, exposed to continuous food. This project will use morphometric analyses of the gut cells of the nearshore copepod Acartia tonsa over a 24-h period in the laboratory. Analyses will be conducted at both the light and electron-microscope level. Laboratory conditions will simulated natural light and food conditions, and these results will be compared to samples taken from the field. Patterns in physiological rates (digestive enzyme activity, glutamate dehydrogenase activity, and respiration rates) and gut fullness will be determined concurrently.