Investigating Mixotrophic Algal Contribution to Copepod Diet and Reproduction

生物海洋学中感兴趣的一个主要话题是藻类生产力在全球碳循环中的作用。在过去的几十年里，随着对微生物重要性的更好理解，传统的浮游食物网一直在进行修改。海洋食物网底部的许多单细胞生物是混合营养的，这意味着它们能够在单个细胞内进行光合作用和摄取猎物。尽管人们认识到这种营养策略已经有一个多世纪了，但它已经从被认为是一种生理上不利的奇怪现象，变成了一种多样化和广泛的适应。尽管混合营养在海洋系统中很普遍，但很少有实验研究评估混合营养生物如何与摄食它们的浮游动物相互作用和影响。该项目正在帮助确定混合营养对海洋中上层食物网中较高营养水平的贡献。研究人员正在测试在藻类食物质量较差的情况下，混合营养生物是否能够支持桡足类动物的繁殖，并评估混合营养对缅因湾两种丰富的桡足类物种饮食的贡献。此外，最近的建模工作表明，当被纳入生物地球化学和食物链模型时，混合营养对初级生产力和碳循环具有重大影响。为了促进在模型中更广泛地考虑混合营养，研究人员参加了混合营养工作组，并在海洋科学会议上主持了一次会议。此外，调查人员还接待了正在获得实验室工作经验的本科生暑期学生，包括通过伍兹霍尔伙伴关系教育计划(PEP)和从当地社区招募的客座学生，以增加海洋科学的多样性。调查人员还与当地高中教师合作，让学生利用他们的艺术培训为一本图解小说做贡献，这本小说展示了缅因湾的食物网络和气候变化的潜在影响。碳和营养物质有效地转移到海洋环境中的较高营养水平依赖于浮游食物网络。混合营养在食物网模型中的应用表明，混合营养可以稳定微生物猎物营养质量的波动，并可能是向浮游动物转移营养物质的重要途径。然而，缺乏足够的经验数据来对这些模型进行充分的参数描述。到目前为止，关于混合营养生物作为猎物的经验研究受到了测试数量有限的分类群、猎物丰度的混淆影响以及未能表征它们的混合营养状态的影响。同样，很少有现场研究以一种能够识别混合营养生物的方式来评估中浮游动物的饮食，而在实验室研究中，尚未确定猎物来源的混合营养状态。因此，不可能提供真实的参数来描述混合营养生物对通过食物网进行营养转移的贡献，混合营养藻类是否能够缓解劣质光合作用食物的影响的问题在很大程度上仍未得到解决。这项研究描述了混合营养藻类在缓解在桡足类繁殖方面浮游植物食物质量方面的缺陷方面的作用。正在进行的喂养实验包括数量一致的积极混合营养猎物。对不同混合营养藻类的营养成分和脂肪酸组成的分析说明了猎物质量的连续体，这可能有助于为浮游动物模型预测提供信息。该项目正在通过对比细菌和浮游植物饲养的异养生物的营养质量来探索营养可塑性的影响。这项工作有助于了解混合营养生物补充或支持桡足类繁殖的能力，这可能与光营养食物的可获得性差相吻合。最后，通过标记猎物摄取实验，然后对标记的食草动物DNA和环境水样进行扩增序列测定，正在评估野外活跃的混合营养体的存在和身份。这项工作是确定缅因湾桡足类动物在生长季节的就地取食偏好，是否随着生命阶段的变化而变化，以及它是如何影响鸡蛋生产的。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

A primary topic of interest within biological oceanography is the role of algal productivity in the global carbon cycle. Over the past few decades, the traditional planktonic food web has been undergoing revision with a better understanding of the significance of microbes. Many of the single-celled organisms at the base of marine food webs are mixotrophic, meaning they are capable of both photosynthesis and ingestion of prey within a single cell. Though recognized for over a century, this trophic strategy has gone from being considered a physiologically unfavorable oddity to a diverse and widespread adaptation. Despite the prevalence of mixotrophy in marine systems, very few experimental studies have assessed how mixotrophic organisms interact with and impact the zooplankton that ingest them. This project is helping define mixotrophic contributions to higher trophic levels in marine pelagic food webs. The investigators are testing whether mixotrophs can support copepod reproduction under conditions when algal food is of poor quality and assessing mixotrophic contributions to the diet of two abundant copepod species within the Gulf of Maine. Additionally, recent modeling efforts suggest that when incorporated into biogeochemical and food web models, mixotrophy has significant implications for primary productivity and carbon cycling. To facilitate broader consideration of mixotrophy in models, the investigators are participating in a mixotrophy working group and hosting a session at the Ocean Sciences Meeting. In addition, the investigators are hosting undergraduate summer students who are gaining experience with laboratory work, including through the Woods Hole Partnership Education Program (PEP) and guest students recruited from local communities to increase diversity in marine science. The investigators are also partnering with local high school teachers to have students use their art training to contribute to a graphic novel that illustrates the Gulf of Maine food web and potential effects of climate change.Effective transfer of carbon and nutrients to higher trophic levels in the marine environment relies on the planktonic food web. Inclusion of mixotrophy in food web models suggests that it may stabilize fluctuations in the nutritional quality of microbial prey and could be an important pathway for transfer of nutrients into zooplankton However, empirical data have been lacking to parameterize these models adequately. To date, empirical studies of mixotrophs as prey have suffered from testing a limited number of taxa, confounding effects of prey abundance, and a failure to characterize their mixotrophic status. Similarly, few field studies have assessed the diet of mesozooplankton in a way that would allow mixotrophs to be identified, and as in lab studies, the mixotrophic status of prey sources has not been identified. Thus, it has been impossible to provide realistic parameters describing the contribution of mixotrophs to nutrient transfer through the food web, and the issue of whether mixotrophically-growing algae can mitigate the effects of poor-quality photosynthetic food remains largely unresolved. This study is characterizing the role of mixotrophic algae in mitigating deficiencies in phytoplankton food quality with respect to copepod reproduction. Feeding experiments are being conducted that include consistent quantities of actively-mixotrophic prey. Analysis of the nutrient and fatty acid composition of different mixotrophic algae is illustrating a continuum of prey quality that could help inform zooplankton model predictions. The project is exploring effects of nutritional plasticity by contrasting the nutritional quality of heterotrophs reared on bacteria versus phytoplankton. The work is contributing to knowledge of the ability of mixotrophs to supplement or support copepod reproduction, which can coincide with poor phototrophic food availability. Finally, the presence and identity of active mixotrophs in the field is being assessed using labeled-prey ingestion experiments, followed by amplicon sequencing of labeled grazer DNA and environmental water samples. The work is identifying the in situ grazing preferences of copepods in the Gulf of Maine over a growing season, whether it varies with life stage, and how it impacts egg production.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.