1 INTRODUCTION

Climate change is increasing mean temperatures and the frequency of thermal extremes and heatwaves (Easterling et al., 2000; Meehl & Tebaldi, 2004). Therefore, the frequency and severity of summer heatwaves is also increasing in aquatic habitats (Frölicher et al., 2018; Woolway et al., 2021). Because species or populations have specific temperature preferences, increasing temperature will have far reaching consequences on local community composition and ecosystem functioning (e.g. by leading to range shifts in the occurrence of species, Easterling et al., 2000; Pinsky et al., 2020). Longer periods of high temperature may also push organisms closer to their limits of physiological tolerance, which, if crossed, may ultimately cause local extinctions (Ma et al., 2021; Stillman, 2019; Vasseur et al., 2014).

Body temperature of ectotherms is tightly linked to environmental temperature, especially for planktonic organisms due to their small body size. Ectotherms can adapt to changing temperature by a variety of regulatory mechanisms. Ectotherm species have to adapt to elevated temperatures locally by behavioural or physiological means or through phenotypic plasticity or evolutionary adaptation, if not they will be replaced by other, more warm-tolerant species (DeWitt et al., 1998; Kawecki & Ebert, 2004; Pigliucci, 2001; Stillman, 2019; Yampolsky et al., 2014).

Increasing temperature favours growth of cyanobacteria (Jöhnk et al., 2008) and therefore the frequency of harmful cyanobacterial blooms is increasing with global warming (Paerl & Huisman, 2008). Cyanobacterial blooms can have many negative effects in aquatic ecosystems, including the poor usability for secondary production by herbivorous zooplankton (Martin-Creuzburg et al., 2009; Von Elert et al., 2003; Wilson et al., 2006). Cyanobacteria can be toxic, develop colonies or filaments to hinder ingestion, and are of poor nutritional quality for zooplankton due to the lack of specific micronutrients, such as phytosterols and polyunsaturated fatty acids (PUFAs) (Martin-Creuzburg et al., 2009; Von Elert et al., 2003; Wilson et al., 2006). The lack of phytosterols and PUFAs due to high proportions of cyanobacteria in the diet can limit zooplankton growth and reproduction (Martin-Creuzburg et al., 2009; Sperfeld et al., 2012; Sperfeld & Wacker, 2015). The dietary supply of sterols seems to be especially important for physiological adaptation to higher temperatures (Hassett & Crockett, 2009; Sperfeld & Wacker, 2009), whereas PUFAs are more important at colder temperatures (Martin-Creuzburg et al., 2012; Sperfeld & Wacker, 2012).

Daphnia spp. are key freshwater zooplankton linking primary production with higher trophic level consumers such as fish (Ogorelec et al., 2021). Daphnia magna, the largest Daphnia species, is often used as model organism in ecological, evolutionary or ecotoxicological studies (Miner et al., 2012). Daphnia females usually reproduce asexually under favourable conditions, making it a suitable organism to study local genetic adaptation or adaptive phenotypic plasticity by investigating clonal lineages originating from different localities (Yampolsky et al., 2014). Daphnia magna is geographically widely distributed (Benzie, 2005) and different clonal lines can occur across seasons (e.g. Paul et al., 2012). Earlier studies found mixed evidence for genetic temperature adaptation in local D. magna populations (across a geographic gradient, Mitchell & Lampert, 2000; Yampolsky et al., 2014) or for seasonal temperature adaptation of clonal lines (Carvalho, 1987; Mitchell et al., 2004; Paul et al., 2012). A more recent study, using many more D. magna clones, shows strong evidence for local temperature adaption in summer-active populations (latitudes higher than c. 43°), whereas winter-active clones at latitudes lower than c. 43° are not locally adapted to temperature as they endure the very high summer temperatures in a dormant stage (Seefeldt & Ebert, 2019). Daphnia magna also shows strong adaptive phenotypic plasticity by being more heat tolerant when pre-acclimated to higher temperatures, allowing this species to better tolerate suboptimal temperatures (MacIsaac et al., 1985; Yampolsky et al., 2014).

There is limited knowledge about how food quality limitation imposed by cyanobacteria affects life history traits of locally adapted Daphnia populations and their capacity to tolerate high temperatures. In this study, we investigated the effects of cyanobacteria-mediated food quality and warmer temperature on life history traits and heat tolerance of D. magna clones originating from different latitudes. For this, we measured somatic growth and reproduction of five D. magna clonal lineages kept at 20, 24, and 28°C on three food mixtures that differed in their relative abundance of cyanobacteria, resulting in poor, medium, and good food quality. We also measured short-term heat tolerance by knockout time, that is, time until immobilisation when exposed to lethally high temperature (37°C), for two clones differing in thermal sensitivity that have been acclimated to 20, 24, and 28°C and kept on medium and good food quality. We expected that clones from lower latitudes would grow better at higher temperatures than clones from higher latitudes due to local adaptation and that food quality limitation will weaken this effect due to smaller growth responses. We also expected the clone from lower latitude to be more heat tolerant than the clone from higher latitude (due to local temperature adaptation) and that heat tolerance increases with increasing acclimation temperature due to adaptive phenotypic plasticity.

中文翻译：

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食品质量介导大型水蚤生活史特征的反应和对高温的耐热性

1 简介

气候变化正在增加平均温度以及极端高温和热浪的频率（Easterling 等人，  2000 年；Meehl 和 Tebaldi，  2004 年）。因此，水生生境中夏季热浪的频率和严重程度也在增加（Frölicher 等人，  2018 年；Woolway 等人，  2021 年）。由于物种或种群具有特定的温度偏好，温度升高将对当地群落组成和生态系统功能产生深远的影响（例如，通过导致物种发生的范围变化，Easterling 等人，  2000；Pinsky 等人，  2020）。较长时间的高温也可能使生物体更接近其生理耐受极限，如果超过，最终可能导致局部灭绝（Ma et al.,  2021 ; Stillman,  2019 ; Vasseur et al.,  2014）。

变温动物的体温与环境温度密切相关，特别是对于浮游生物，因为它们的体型很小。等温动物可以通过多种调节机制来适应不断变化的温度。变温物种必须通过行为或生理手段或通过表型可塑性或进化适应来适应局部升高的温度，否则它们将被其他更耐温的物种取代（DeWitt et al.,  1998 ; Kawecki & Ebert,  2004 ; Pigliucci，  2001 年；斯蒂尔曼，  2019 年；Yampolsky 等人，  2014 年）。

温度升高有利于蓝藻的生长（Jöhnk 等人，  2008 年），因此随着全球变暖，有害蓝藻水华的频率正在增加（Paerl & Huisman，  2008 年）。蓝藻水华会对水生生态系统产生许多负面影响，包括草食性浮游动物的二次生产可用性差（Martin-Creuzburg 等人，  2009 年；Von Elert 等人，  2003 年；Wilson 等人，  2006 年）。由于缺乏特定的微量营养素，例如植物甾醇和多不饱和脂肪酸 (PUFA)，蓝藻可能有毒，会形成菌落或细丝以阻碍摄入，并且对浮游动物的营养质量较差（Martin-Creuzburg 等人，  2009 年）; Von Elert 等人，  2003 年；Wilson 等人，  2006 年）。由于饮食中蓝藻比例高，植物甾醇和多不饱和脂肪酸的缺乏会限制浮游动物的生长和繁殖（Martin-Creuzburg 等人，  2009 年；Sperfeld 等人，  2012 年；Sperfeld 和 Wacker，  2015 年）。甾醇的膳食供应似乎对于生理适应较高温度尤为重要（Hassett & Crockett,  2009 ; Sperfeld & Wacker,  2009），而 PUFA 在较低温度下更为重要（Martin-Creuzburg et al.,  2012 ; Sperfeld & Wacker, 2009）。瓦克，  2012）。

水蚤属 是关键的淡水浮游动物，将初级生产与鱼类等更高营养级的消费者联系起来（Ogorelec 等人，  2021 年）。Daphnia magna是最大的水蚤物种，经常被用作生态、进化或生态毒理学研究中的模式生物（Miner 等人，  2012 年）。水蚤雌性通常在有利的条件下无性繁殖，使其成为通过研究来自不同地区的克隆谱系来研究局部遗传适应或适应性表型可塑性的合适生物（Yampolsky et al.,  2014）。Daphnia magna在地理上分布广泛（Benzie，  2005) 并且不同的克隆系可以跨季节出现（例如 Paul 等人，  2012 年）。早期的研究发现，本地D. magna种群（跨越地理梯度，Mitchell & Lampert，  2000；Yampolsky 等人，  2014 年）或克隆系的季节性温度适应（Carvalho，  1987 年；Mitchell 等人）的遗传温度适应的混合证据.，  2004 年；保罗等人，  2012 年）。最近一项使用更多D. magna无性系的研究显示了夏季活动种群（纬度高于c . 43°）的局部温度适应的有力证据，而纬度低于c的冬季活动无性系. 43° 不适应当地的温度，因为它们在休眠阶段忍受着非常高的夏季温度（Seefeldt & Ebert，  2019 年）。Daphnia magna还表现出很强的适应性表型可塑性，在预先适应较高温度时具有更高的耐热性，从而使该物种能够更好地耐受次优温度（MacIsaac 等人，  1985 年；Yampolsky 等人，  2014 年）。

关于蓝藻对食品质量的限制如何影响当地适应的水蚤种群的生活史特征及其耐受高温的能力的知识有限。在这项研究中，我们研究了蓝藻介导的食品质量和温度升高对来自不同纬度的D. magna克隆的生活史特征和耐热性的影响。为此，我们测量了五个D. magna的体细胞生长和繁殖克隆谱系在三种食物混合物上保持在 20、24 和 28°C，它们的蓝藻相对丰度不同，导致食物质量差、中等和良好。我们还通过敲除时间测量了短期耐热性，即暴露于致命高温 (37°C) 时直到固定的时间，对于两个已适应 20、24 和 28°C 的热敏感性不同的克隆并保持中等和良好的食品质量。我们预计，由于局部适应，来自低纬度地区的无性系在较高温度下会比来自高纬度的无性系生长得更好，并且由于较小的生长反应，食品质量限制将削弱这种影响。