The molecular basis of daily and seasonal migration behaviour in the copepod Calanus finmarchicus in the face of climate change

气候变化引起的海洋温度升高正在导致许多温带海洋生物向极地的分布范围发生变化。这些变化对海洋食物网和海洋碳通量有着深远的影响。浮游动物是海洋生态系统的核心组成部分，它们捕获浮游植物固定的初级碳，并为更高营养水平提供主要碳源，包括商业上重要的鱼类资源。分布广泛且富含脂质的桡足动物Calanus finmarchicus在北大西洋浮游动物生物量中占主导地位，并已成为了解海洋碳循环生物地球化学过程的强大模式生物。Calanus表现出的两种行为对其在海洋食物网和碳泵中的作用至关重要。首先，diel垂直迁移（DVM），这是一种昼夜节律行为，动物在白天潜入深海，晚上迁移到水面觅食。这种行为是一种躲避捕食者的反应，主要由光线驱动。第二，长休眠期（滞育），这是Calanus生命周期的关键部分，在春末的最后一个准成年桡足动物阶段，幼鱼从它们的地表摄食地迁移到更深的上层水域（~400-1000米），在那里它们保持7-8个月的不活动，直到1月。控制滞育进入和退出时间的因素尚不清楚，但怀疑包括日长，温度和脂质储备。DVM和滞育结构种群在空间和时间上以及它们的行为对环境线索的变化都很敏感。气候变化正在促进范围向高纬度地区扩展，在高纬度地区，控制这些行为的线索（光、温度）可能与低纬度地区不同。因此，个体和种群通过表型可塑性和/或适应性对这些物候变化作出反应的能力将是影响北大西洋已实现的范围变化、生物量通量和更广泛的生物地球化学过程的关键因素。预测种群对物候变化的反应的一个主要障碍是缺乏对个体水平上影响行为变异的生理和分子过程的了解。DVM的时间、速度和深度在个体之间有明显的差异，并与光响应性的个体差异（KSL小组未发表的正在进行的工作）和代谢因素（如呼吸速率和脂质储备）有一定的相关性。同样，个体进入滞育的时间也各不相同，尽管滞育退出通常是显著同步的。关于这种个体间变异的分子遗传基础，行为同步性的生理基础，以及Calanus种群间适应性遗传多样性是如何在空间和时间上形成的，我们知之甚少。该项目将研究与DVM和滞育行为变异相关的分子遗传变异以及可能驱动行为同步性的环境因素。主要目的有两个：首先，检查基因表达，行为表型可塑性和环境因素之间的联系，假设触发和同步DVM和滞育。第二，研究从近岸沿海到开阔海洋环境的不同纬度人群的遗传多样性和遗传结构。我们假设，首先，DVM/滞育的环境触发因素导致了与表型可塑性一致的生物节律相关的关键基因的表达变化；其次，这些基因在不同纬度的种群中显示出等位基因频率的差异，这与对范围变化的适应性进化反应一致。

Climate-change-induced increases in oceanic temperatures are causing poleward distribution range shifts in many temperate marine organisms. These shifts have far-reaching effects on marine food webs and oceanic carbon fluxes. Zooplankton are a central component of oceanic ecosystems, where they capture primary carbon fixed by phytoplankton and provide the major carbon source to higher trophic levels, including commercially important fish stocks. The cosmopolitan and lipid-rich copepod Calanus finmarchicus dominates zooplankton biomass in the North Atlantic and has emerged as a powerful model organism for understanding the biogeochemical processes in oceanic carbon cycling.Calanus displays two behaviours that are crucial for its role in the oceanic food web and carbon pump. First, diel vertical migration (DVM), which is a circadian behaviour whereby the animals dive to depth during the day and migrate to the surface to feed at night. This behaviour is a predator avoidance response and is driven primarily by light. Second, long resting stage (diapause), which is a crucial part of the life cycle of Calanus whereby juveniles in their last pre-adult copepodid stage in late spring migrate from their surface feeding grounds down to deeper epipelagic waters (~400-1000m) where they remain inactive for 7-8 months until January. The factors governing timing of diapause entry and exit remain unclear, but are suspected to include daylength, temperature and lipid reserves.Both DVM and diapause structure populations in space and time and both behaviours are sensitive to changes in environmental cues. Climate change is facilitating range expansions into higher latitudes where the cues (light, temperature) governing these behaviours are likely to differ from those at lower latitudes. Therefore, the capacity of individuals and populations to respond to these phenological shifts via phenotypic plasticity and/or adaptation will be a crucial factor in affecting realised range shifts, biomass flux and broader biogeochemical processes in the North Atlantic.A major hindrance in predicting population responses to phenological shifts is a lack of insight into the physiological and molecular processes affecting behavioural variability at the individual level. DVM timing, speed and depth vary measurably among individuals and show some correlation with among-individual variability in photo-responsiveness (unpublished ongoing work in KSL's group) and metabolic factors such as respiration rates and lipid reserves. Similarly, individuals vary in their timing of diapause entry, though diapause exit is often remarkably synchronised. Very little is known about the molecular genetic basis of this among-individual variation, of the physiological basis of behavioural synchronicity, and how adaptive genetic diversity among Calanus populations is structured in space and time.This project will examine the molecular genetic variation associated with variation in DVM and diapause behaviour and environmental factors likely to drive behavioural synchronicity. The principal aims are twofold: First, to examine the links between gene expression, behavioural phenotypic plasticity and environmental factors hypothesised to trigger and synchronise DVM and diapause. Second, to examine genetic diversity and genetic structure among populations from different latitudes from nearshore coastal to open ocean environments. We hypothesise that, first, environmental triggers of DVM/diapause cause changes in expression at key genes involved in biological rhythms consistent with phenotypic plasticity, and, second, that these genes show allele-frequency differences among populations from different latitudes, consistent with an adaptive evolutionary response to range shifts.