Brain Size Plasticity in Anamniote Vertebrates

大脑在大小、细胞密度和连通性方面差异很大。我的长期研究目标是了解大脑结构和大小的变化如何影响生物体功能，以帮助确定驱动神经系统进化和可塑性的因素。鱼类和两栖动物（即羊水脊椎动物）具有广泛和终生产生新脑细胞的能力，因此是研究决定大脑大小因素的良好模型。在这里，我们将使用实验室和现场方法研究大脑大小灵活性的细胞机制及其对认知的影响。关于脊椎动物成年脑尺寸灵活性的令人信服的证据尚缺乏，但我们去年获得的初步证据表明，成年鱼在不同季节和从圈养环境中逃到野外后，其相对脑尺寸会发生变化。与鸟类和哺乳动物不同，成年鱼类和两栖动物具有广泛的产生新脑细胞的能力，因此是展示大脑大小灵活性的良好候选者。我们将首先调查解释成年羊膜动物大脑大小季节性变化的竞争性假说：“能量节约”、“感觉重组”和“繁殖努力”假说。为了验证节能假说，将在实验室条件下使用火腹蟾蜍的人工冬眠来测量模拟季节变化期间相对脑大小和能量消耗的变化。感官重组和繁殖努力假说将通过评估具有已知功能的脑区大小在不同季节在成熟状态不同的野生鱼类中的变化来研究。其次，我们将阐明大脑大小变化的细胞机制。脑大小的变化可能涉及神经干细胞出生速率的调节，新神经元和胶质细胞从干细胞分化，和/或细胞死亡。这些过程的标记将通过对不同季节取样的鱼和不同人工冬眠阶段取样的蟾蜍的脑切片进行立体学分析来测量。此外，将使用细胞计数方法获得神经元和非神经元细胞的数量和密度。最后，将测试大脑大小变化与认知和行为的相关性。对脑组织的投资应该会提高认知能力，这将提高动物在涉及认知能力的行为任务中的表现。我们将使用火腹蟾蜍捕捉猎物的条件反射任务来研究与学习和行为灵活性相关的认知能力。这项提议的工作将解决大脑大小、神经元数量和认知能力之间有争议的关系。此外，它将支持与许多利益攸关方有关的更多应用问题，例如帮助制定用于加拿大流域环境监测的水生野生动物的行为表现和精力状况指标。

Brains vary enormously in size, cell density and connectivity. My long-term research goal is to understand how variation in brain structure and size influences organismic function to help identify the factors that drive evolution and plasticity of the nervous system. Fishes and amphibians (i.e. anamniote vertebrates) have a widespread and lifelong ability to produce new brain cells and thus are good models to study the factors determining brain size. Here, we will investigate the cellular mechanisms underlying brain size flexibility and its impacts on cognition using both lab- and field-based approaches. Compelling evidence of adult brain size flexibility in vertebrates is lacking, but our preliminary evidence acquired in the past year suggests that adult fish show changes in relative brain size across seasons and upon escape from captivity into the wild. Unlike birds and mammals, adult fish and amphibians have a widespread ability to produce new brain cells and thus are good candidates to display brain size flexibility. We will first investigate competing hypotheses explaining seasonal changes in brain size in adult anamniotes: the `energy savings', `sensory reorganization', and `reproductive effort' hypotheses. To test the energy savings hypothesis, artificial hibernation of fire-bellied toads under laboratory conditions will be used to measure variation in relative brain size and energy expenditure during simulated seasonal change. The sensory reorganization and reproductive effort hypotheses will be investigated by assessing variation in the size of brain regions with known functions across seasons in wild fish differing in maturation status. Second, we will elucidate the cellular mechanisms responsible for change in brain size. Changes in brain size could involve modulation of the rates of birth of neural stem cells, differentiation of new neurons and glia from stem cells, and/or cell death. Markers for these processes will be measured by stereology analysis on brain sections of fish sampled across seasons and toads sampled across phases of artificial hibernation. Additionally, the number and density of neurons and non-neuronal cells will be obtained using cell counting methods. Finally, the relevance of changes in brain size to cognition and behaviour will be tested. Investment in brain tissue should increase cognitive performance, which will improve the performance of animals tested in behavioural tasks that engage cognitive abilities. We will use prey catching conditioning tasks with fire-bellied toads to study cognitive abilities related to learning and behavioural flexibility. The proposed work will tackle the controversial relationship between brain size, neuron number, and cognitive capacity. Additionally, it will support more applied concerns relevant to many stakeholders, such as helping to develop indicators of behavioural performance and energetic status in aquatic wildlife for environmental monitoring of Canadian watersheds.