Hairston N G, Olds E J
Section of Ecology and Systematics, Cornell University, 14853, Ithaca, NY, USA.
Entomology Department, Michigan State University, 48824, East Lansing, MI, USA.
Oecologia. 1987 Feb;71(3):339-344. doi: 10.1007/BF00378705.
The reproductive phenology of the freshwater copepod Diaptomus sanguineus differs markedly between populations residing in two Rhode Island ponds. In a permanent pond the population switches abruptly from making subitaneous (immediately hatching) eggs to diapausing eggs at the end of March each year. In contrast, a temporary pond population switches egg types in May, returns to production of subitaneous eggs in June, and concludes the reproductive season by making diapausing eggs in July. An ESS model suggests that the pattern of diapause expected of a copepod population is a function of annual variation in the onset of harsh conditions (catastrophe date). When variation is relatively low, the superior strategy is for diapause to begin a constant period before the mean catastrophe date. When variation is high, females should make first subitaneous eggs and then diapausing eggs irrespective of the expected catastrophe date. With discrete generations, such a population would alternate between egg types. In the permanent pond, variation of catastrophe date the spring onset of planktivory by sunfish is low, whereas in the temporary pond variation of the catastrophe (pond drying) is high. The model predicts well the phenology of the two copepod populations.In the research reported here, we tested the hypothesis that copepods from the permanent pond, which switch to diapause at the same time every year, are cued by the environment to begin diapause (i.e. by photoperiod, temperature, or both), whereas those from the temporary pond make both egg types regardless of environmental conditions. In opposition to our hypothesis, experimental results indicate that diapause in both populations is cued by the environment. The distinct reproductive phenologies documented in the two populations apparently result from the copepods responding to different environmental cues, rather than one being responsive to the environment while the other is not.
淡水桡足类血红哲水蚤（Diaptomus sanguineus）的繁殖物候在罗德岛两个池塘中的种群间存在显著差异。在一个永久性池塘中，种群每年3月底会突然从产出非滞育（立即孵化）卵转变为产出滞育卵。相比之下，一个临时性池塘的种群在5月切换卵的类型，6月恢复产出非滞育卵，并在7月产出滞育卵来结束繁殖季节。一个ESS模型表明，桡足类种群预期的滞育模式是恶劣条件开始时间（灾难日期）年度变化的函数。当变化相对较小时，最优策略是在平均灾难日期前一段固定时间开始滞育。当变化较大时，雌性无论预期灾难日期如何，都应先产出非滞育卵，然后产出滞育卵。在离散世代的情况下，这样的种群会在卵的类型间交替。在永久性池塘中，太阳鱼开始捕食浮游生物的春季灾难日期变化较小，而在临时性池塘中，灾难（池塘干涸）的变化较大。该模型很好地预测了两个桡足类种群的物候。在本文报道的研究中，我们检验了以下假设：来自永久性池塘的桡足类每年在同一时间进入滞育，是受环境（即光周期、温度或两者）的诱导，而来自临时性池塘的桡足类则无论环境条件如何都会产出两种类型的卵。与我们的假设相反，实验结果表明两个种群的滞育都是由环境诱导的。两个种群记录的不同繁殖物候显然是桡足类对不同环境线索做出反应的结果，而不是一个对环境有反应而另一个没有。
