Cumulative effects matter: multi‐brood responses of Daphnia to hypoxia
Cumulative effects matter: multi‐brood responses of Daphnia to hypoxia
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DOI：
10.1111/fwb.12808
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发表时间：
2016-10
影响因子：
2.7
通讯作者：
Kai Lyu;Qianqian Wang;Zhou Yang;D. Montagnes
中科院分区：
文献类型：
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作者：
Kai Lyu;Qianqian Wang;Zhou Yang;D. Montagnes
由于人类活动的影响，目前预计淡水沃茨中的缺氧期可长达数周。然而，缺氧对水蚤的累积影响，在多个育雏，几乎没有得到关注，并建立和评估这样的反应，有必要在很宽的范围内的氧浓度进行测量，可能揭示非线性模式。我们预测缺氧对生长、存活和繁殖力的影响（即，新个体的产生）将在多个窝中增加，并且随着氧气的增加，这些响应将在矩形双曲线响应之后接近渐近最大值。将相似水蚤暴露于1.0、2.0、3.0、4.0、5.0、6.0和8.0 mg氧气L-1。为了确定对第一窝的影响，我们检查了：后代的数量;第一个鸡蛋的时间;第一窝的时间和第一个鸡蛋和第一窝的雌性大小。为了确定多窝（21天内最多8窝）的氧气累积效应，我们测量了：雌性产生的后代总数;存活时间和蜕皮和窝的总数。为了研究累积效应是如何在多个窝中产生的，我们检查了八个窝中每个窝的后代数量。为了评估治疗效果并指示反应，使用反映数据趋势的最简约函数将函数拟合至数据。与一个单一的育雏相关的测量线性响应，或根本没有，随着氧气浓度的变化，而在21天的测量之后的矩形双曲线响应，增加到渐近线的氧气增加。对于第一窝，当氧气浓度从1 mg L−1提高到8 mg L−1时，产生后代的数量和产生后代所需的时间没有受到影响;产生卵子所需的时间减少了0.3倍;而产生卵子和后代时的个体大小增加了0.1倍。在21天的时间里，在1到8 mg L−1之间，后代的总数增加了1.34倍;个体存活率和蜕皮数量增加了1.22倍，育雏数量增加了1.21倍。对于单窝反应，在第一窝中，降低氧水平对后代的数量没有影响，但对第二至第四窝有负面影响;剩余窝中的后代数量与氧水平没有显著相关，因为由于存活率低，低水平的数据较少。我们的结论是，水蚤人口统计的评估不应该依赖于估计的氧气浓度对单窝的影响。相反，研究应该考虑多个育雏的累积变化。根据我们的方法，研究人员现在可以探索缺氧对同源物和其他浮游动物的影响，并研究与多育雏反应相关的机制。
Summary Periods of hypoxia lasting up to weeks are now anticipated in fresh waters, owing to anthropogenic influences. However, the cumulative effects of hypoxia on Daphnia, over multiple broods, have received virtually no attention, and to establish and evaluate such responses there is a need to make measurements over a wide range of oxygen concentrations, potentially revealing non-linear patterns. We predict that the effect of hypoxia on growth, survival and fecundity (i.e., production of new individuals) of Daphnia will increase over multiple broods, and with increasing oxygen these responses will approach asymptotic maxima, following a rectangular hyperbolic response. Daphnia similoides were exposed to 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 and 8.0 mg oxygen L−1. To determine effects on the first brood we examined: number of offspring; time to the first eggs; time to the first brood and size of the female at the first eggs and the first brood. To determine cumulative effects of oxygen over multiple broods (up to 8 broods over 21 days), we measured: total number of offspring produced by a female; survival time and total number of moults and broods. To investigate how the cumulative effects arose over the multiple broods, we examined the number of offspring per brood in each brood over eight broods. To assess treatment effects and indicate responses, functions were fit to data using the most parsimonious function that reflected trends in the data. Measurements associated with a single brood responded linearly, or not at all, with changing oxygen concentration, whereas measurements made over the 21 days followed a rectangular hyperbolic response, increasing to an asymptote as oxygen increased. For the first brood, as oxygen concentration was raised from 1 to 8 mg L−1 the number of offspring produced and the time required to produce the brood were not affected; the time required to produce eggs decreased ˜0.3-fold; and the size of individuals at the time when the eggs and the brood were produced increased ˜0.1-fold. Over the 21 days, between 1 and 8 mg L−1 the total number of offspring increased ˜3.4-fold; individual survival and the number of moults increased ˜2-fold, and the number of broods increased ˜1-fold. For single-brood responses, there was no effect of decreasing oxygen levels on the number of offspring in the first brood, but there were negative effects on the second-to-fourth broods; the number of offspring in the remaining broods was not significantly related to oxygen levels, as there were fewer data at low levels due to poor survival. We conclude that assessments of Daphnia demographics should not rely on estimates of the effect of oxygen concentration on single broods. Instead, studies should consider cumulative changes over multiple broods. Following our approach, researchers may now explore the impacts of hypoxia on congeners and other zooplankton, and investigate the mechanisms associated with multi-brood responses.