Brain Size Plasticity in Anamniote Vertebrates

大脑在大小、细胞密度和连通性方面存在巨大差异。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组织功能，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(即厌羊膜脊椎动物)具有广泛和终身的能力来产生新的脑细胞，因此是研究决定大脑大小的因素的良好模型。在这里，我们将使用实验室和现场两种方法来研究大脑大小灵活性背后的细胞机制及其对认知的影响。 目前还没有令人信服的证据表明脊椎动物成年后大脑大小的灵活性，但我们在过去一年中获得的初步证据表明，成年鱼的相对大脑大小在不同季节和逃离圈养进入野外时会发生变化。与鸟类和哺乳动物不同，成鱼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水动物大脑大小季节性变化的相互竞争的假说：能量节约、感觉重组和生殖努力假说。为了验证能量节约假说，实验室条件下的火腹蛙的人工冬眠将被用来测量在模拟季节变化期间相对大脑大小和能量消耗的变化。将通过评估不同成熟状态的野生鱼类在不同季节具有已知功能的大脑区域大小的变化来研究感觉重组和生殖努力假说。其次，我们将阐明导致大脑大小变化的细胞机制。大脑大小的变化可能涉及调节神经干细胞的出生率，干细胞分化出新的神经元和神经胶质细胞，和/或细胞死亡。这些过程的标志物将通过体视学分析在不同季节采样的鱼和不同阶段的人工冬眠的蟾蜍的大脑切片上进行测量。此外，还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，这将改善动物在参与认知能力的行为任务中的表现。我们将使用火腹蛙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。 这项拟议的工作将解决大脑大小、神经元数量和认知能力之间的有争议的关系。此外，它将支持与许多利益攸关方有关的更多应用关切，例如帮助制定水生野生动物行为表现和精力状况的指标，用于加拿大流域的环境监测。

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.