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Reproduction in a changing environment: Mussels, impoundments, and conservation.

机译：在不断变化的环境中繁殖：贻贝，蓄水池和保护区。

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As humans alter the environmental landscape, there is an increasing need to understand the relationship between species and the environment, how changes to the environment translate to populations and communities, and how to develop management practices that reduce or reverse our negative impacts. Different animals respond differently to environmental change as do different developmental life stages within the same species. Reproduction, for example, is often the most sensitive time period of an organism's life, yet has been largely ignored in conservation biology, partly due to the difficulties in studying reproduction (e.g. complex life cycles, migration, delayed reproduction). Nonetheless, it is vitally important that we have some basic understanding of the reproductive process in order to facilitate sound management of critically imperiled fauna. Freshwater mussels are one such globally imperiled group of invertebrates with over 70% of species considered threatened. However, very little is understood about their complex life cycle, particularly the portion of reproduction up to and including fertilization. The research detailed in my dissertation broadens our understanding of this portion of the mussel reproductive cycle and how it is being impacted by humans.;My first chapter explores the environmental variables that are important in regulating timing of gametogenesis in mussels. Using a year-long field sampling regime I found that water temperature, and in particular the number of degree days during which growth occurs, is an important correlate for the number of mature gametes present in adult mussel's gonadal tissue. Using a 3-month long laboratory study I confirmed these findings; however, I also discovered the potential for a food quality by temperature interaction in this study as mussels in my experiment were fed high quality food and had substantially more gametes present in their gonads than were ever observed in the field.;My second chapter explores how environmental variables affect the process of fertilization in freshwater mussels. I conducted a sperm viability experiment in which I manipulated water temperature (5, 15, 25, and 35°C) and measured the percentage of viable mussel sperm that were motile over time. I found that mussel sperm are viable for extensive periods of time, but that the highest motility was observed in the 15 and 25°C temperature range. I combined these data with a modeling approach to determine how mussel population dynamics and gene flow could be impacted by different thermal and flow regimes. I discovered that mussel sperm has the potential to move extremely long distances downstream, but that ultimately sperm transport is a function of stream velocity and height above the sediment at which sperm are released. Reproductive success, however, is a function of the proportion of sperm that have remained viable over time.;The research detailed in my third chapter examines the role of impoundments on the reproductive success and population attributes of freshwater mussels. Using data collected in my year-long field study, I found that mussels below a cold-water release impoundment had lower overall mussel densities, higher proportions of hermaphroditic individuals, higher prevalence of sterilizing trematodes, and lower body condition relative to mussels found above the impoundment. I also found that patterns in timing of gamete development were also unusual below the cold-water release dam. I outline a conceptual model by which alterations in temperature, stream flow, light, and food availability caused by impoundments could lead to overall negative density-dependence in mussel populations. These first three chapters illustrate the importance of natural temperature and flow regimes in maintaining healthy reproduction in freshwater mussel communities, information that is critical for managing rivers that provide habitat to mussels.;As humans continue to alter riverine landscapes, we are also likely to impact the evolutionary trajectories of species residing there. Unfortunately, another aspect of mussel biology that is also understudied is the evolution of the great diversity of freshwater mussels, particularly in North America. Several evolutionary hypotheses have been proposed for the evolution of these organisms, yet none have been tested. The goal of my fourth chapter was to address freshwater mussel evolution from the perspective of mechanisms of reproductive isolation, since barriers must exist between species to maintain distinct species identities. I examined the role that habitat use and timing of reproduction may play in isolating co-occurring, closely related mussel species of the genus Quadrula. I found that habitat overlap among closely related species varies (although is often high), but could be one isolating mechanism. Timing of reproduction, however, overlaps almost entirely among these species and is likely not a factor maintaining species identity in this genus. Further research into other isolating mechanisms is required to increase our understanding of reproductive barriers and evolution of freshwater mussels.
机译：随着人类改变环境景观，人们越来越需要了解物种与环境之间的关系，环境变化如何转化为人口和社区，以及如何制定减少或扭转我们负面影响的管理实践。不同的动物对环境变化的反应不同，同一物种内不同的生命发育阶段也是如此。例如，繁殖通常是生物体生命中最敏感的时间段，但在保护生物学中却被很大程度上忽略了，部分原因是研究繁殖困难（例如复杂的生命周期，迁移，繁殖延迟）。然而，至关重要的是我们对生殖过程有一些基本的了解，以促进对严重受害动物的合理管理。淡水贻贝就是这样一种无处不在的无脊椎动物，其中超过70％的物种被认为是受威胁的。然而，人们对它们的复杂生命周期知之甚少，特别是直到受精（包括受精）的生殖部分。在我的论文中进行的详细研究拓宽了我们对贻贝繁殖周期的这一部分及其对人类的影响的理解。我的第一章探讨了对调节贻贝配子发生时间至关重要的环境变量。通过使用长达一年的田间采样方案，我发现水温，特别是生长发生的度数天数，与成年贻贝的性腺组织中存在的成熟配子的数量有着重要的关系。通过为期三个月的实验室研究，我证实了这些发现。但是，在这项研究中，我还发现了通过温度相互作用产生食物品质的潜力，因为在我的实验中，贻贝被喂以优质食物，并且生殖腺中的配子比野外观察到的要多得多。；第二章探讨了如何环境变量影响淡水贻贝的施肥过程。我进行了一个精子生存能力实验，其中我控制了水温（5、15、25和35°C），并测量了随着时间推移运动的贻贝的存活百分比。我发现贻贝精子在很长一段时间内都可以存活，但是在15和25°C的温度范围内观察到了最高的活力。我将这些数据与一种建模方法结合起来，以确定贻贝种群动态和基因流如何受到不同的热力和流动方式的影响。我发现贻贝精子有可能向下游移动很长一段距离，但是最终，精子的运输是溪流速度和释放精子的沉积物上方的高度的函数。然而，生殖成功是随着时间的流逝仍能存活的精子比例的函数。我在第三章中详述的研究考察了水库对淡水贻贝繁殖成功和种群属性的作用。使用我进行的为期一年的野外研究收集的数据，我发现冷水释放蓄水池下方的贻贝相对于上方的贻贝具有较低的总体贻贝密度，较高的两性生殖个体比例，较高的杀菌吸虫性虫病和较低的身体状况。蓄水。我还发现在冷水释放坝下方，配子发育时间的模式也很不寻常。我概述了一个概念模型，据此模型，蓄水引起的温度，水流，光和食物供应量的变化可能导致贻贝种群总体上负密度依赖性。前三章说明了自然温度和水流态势对于维持淡水贻贝群落健康繁殖的重要性，这对于管理为贻贝提供栖息地的河流至关重要。信息随着人类继续改变河流景观，我们也可能会影响居住在那里的物种的进化轨迹。不幸的是，贻贝生物学的另一个方面也得到了研究，这是淡水贻贝的巨大多样性的演变，特别是在北美。对于这些生物的进化已经提出了几种进化假说，但尚未对它们进行检验。我第四章的目的是从生殖隔离机制的角度来解决淡水贻贝的进化问题，因为物种之间必须存在障碍，以保持独特的物种身份。我研究了栖息地的使用和繁殖时间在隔离Quadrula属的同时出现，密切相关的贻贝物种中的作用。我发现密切相关的物种之间的栖息地重叠有所不同（尽管通常很高），但这可能是一种隔离机制。复制的时间，但是这些物种之间几乎完全重叠，并且可能不是维持该属物种同一性的因素。需要进一步研究其他隔离机制，以加深我们对生殖障碍和淡水贻贝进化的了解。

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