Cognitive systems of obligate brood parasites

动物思考（认知）或行为的方式会影响其生存和繁殖（适应性）。然而，直到最近，在非模式生物中，行为、认知和大脑之间才有了明确的联系。空间记忆是证明这些联系的最有力的认知系统之一，因为(i)空间记忆在动物运动中与资源有关，（ii）海马体在空间记忆和最终的适应性中发挥着明确的作用。******专育寄生物，一种完全依赖其他物种来养育后代的物种，是研究大脑和认知专业化的理想系统，因为雌性比雄性有更复杂的空间使用，这与我们看到的性别差异有利于雄性的其他系统（例如一夫多妻哺乳动物）形成鲜明对比。在一些幼虫中，如褐头牛鹂（Molothrus ater），每个季节只有雌性寻找和寄生多达50个寄主巢穴。我展示了雌鸟在空间记忆任务上的表现优于雄鸟，这类似于在野外拜访宿主巢穴。此外，行为和认知的差异与大脑的差异有关；与雄性相比，雌性牛鹂的海马神经发生（新神经元被吸收到海马体中）水平更高，而在非寄生亲属中没有性别差异。对野生动物空间记忆中性别作用的有力测试，需要一个对空间记忆有明确的性别特异性需求和这些需求的性别角色逆转（以避免许多混淆的性别特异性因素）的系统，而专性幼虫寄生就是这样一个系统。******在这里，我建议使用系统发育、发育、机制和功能方法来检查几种幼虫寄生虫的认知和神经特化。我的目标是确定(I)除了潜在的发育特化外，海马神经发生中的雌性偏向性差异是否在不同分类群的幼虫中持续存在，（ii）海马属性（如神经发生）影响生态相关的空间记忆，以及（iii）海马神经发生影响适应性。我推测，寄生幼虫在海马体属性中进化出了适应性，使它们能够最大限度地记住宿主巢穴的位置，从而提高它们一生的繁殖成功率。为了验证这一假设，我将结合实验室的认知测试、实地工作，以及使用免疫组织化学对海马体进行精细测量，并通过荧光原位杂交（catFISH）对时间活动进行细胞室分析。******研究寄生幼虫为认知神经科学领域提供了一个独特的机会来研究一个系统，在这个系统中，雌性比雄性有更复杂的空间使用，从而使我们能够表明，是否空间需求，而不是性别本身，可以塑造这些参数。利用这个系统，我将提供一个整体的视角来研究野生动物空间记忆的形式和功能之间的联系。* * * * *

The way an animal thinks (cognition) or behaves can influence its survival and reproduction (fitness). However, only recently have clear links been shown between behaviour, cognition and the brain in non-model organisms. Spatial memory is one of the strongest cognitive systems to demonstrate these links because of the clear role of (i) spatial memory in animal movement in relation to resources and (ii) the hippocampus in spatial memory, and ultimately, fitness. ******Obligate brood parasites, species that rely solely on other species to raise their young, are an ideal system to study specializations in the brain and cognition because females have more complex space use than males, which contrasts with other systems in which we see a sex difference favouring males (e.g. polygynous mammals). In some brood parasites, like brown-headed cowbirds (Molothrus ater), only females search for and parasitize up to 50 host nests per season. I showed that female cowbirds outperformed males on a spatial memory task that resembled host nest visits in the wild. In addition, differences in behaviour and cognition were linked to differences in the brain; female cowbirds had higher levels of hippocampal neurogenesis (new neurons recruited into the hippocampus) than males, with no sex difference in a non-parasitic relative. Strong tests of the role of sex in spatial memory in wild animals requires a system with both clear sex-specific demands on spatial memory and sex role reversal of those demands (to avoid the many confounding sex-specific factors), and obligate brood parasitism is one such system. ******Here, I propose to examine cognitive and neural specializations in several species of brood parasites using phylogenetic, developmental, mechanistic, and functional approaches. I aim to determine whether (i) female-biased sex differences in hippocampal neurogenesis persist in brood parasites across taxa, in addition to potential developmental specializations, (ii) hippocampal attributes such as neurogenesis affect ecologically-relevant spatial memory, and (iii) hippocampal neurogenesis affects fitness. I hypothesize that brood parasites have evolved adaptations in hippocampal attributes that maximize their ability to remember the location of host nests to increase their lifetime reproductive success. To test this hypothesis, I will combine cognitive testing in the lab, field work, and fine-scale measures of the hippocampus using immuhistochemistry and cellular compartment analysis of temporal activity by fluorescence in situ hybridization (catFISH).******Examining brood parasites offers a unique opportunity within the field of cognitive neuroscience to study a system in which females, instead of males, have more complex space use, thus enabling us to show whether spatial demands, rather than sex itself, can shape these parameters. Using this system, I will provide a holistic perspective on the link between form and function in spatial memory in wild animals. *****