Cognitive systems of obligate brood parasites

动物的思维(认知)或行为方式会影响其生存和繁殖(健康)。然而，直到最近，才在非模式生物体中显示出行为、认知和大脑之间的明确联系。空间记忆是证明这些联系的最强大的认知系统之一，因为(I)空间记忆在动物运动中与资源相关的作用，以及(Ii)海马体在空间记忆中的作用，最终是健康。 专性幼虫是完全依靠其他物种抚养后代的物种，是研究大脑和认知特化的理想系统，因为雌性比雄性使用更复杂的空间，这与我们看到有利于雄性的性别差异的其他系统(例如一夫多妻制的哺乳动物)形成了鲜明对比。在一些孵化的寄生虫中，如褐头牛鸟(Molothus Ater)，只有雌性才会寻找并寄生每个季节多达50个寄主巢。我展示了雌性牛鸟在空间记忆任务上的表现优于雄性，这一任务类似于在野外访问寄主巢。此外，行为和认知的差异与大脑的差异有关；雌性牛鸟的海马神经发生水平(新神经元被招募到海马区)比雄性更高，在非寄生亲属中没有性别差异。对野生动物的性别在空间记忆中的作用进行强有力的测试，需要一个既有明确的性别特定空间记忆需求，又有性别角色颠倒这些需求的系统(以避免许多混淆的性别特定因素)，专性繁殖寄生就是这样的系统之一。 在这里，我建议使用系统发育、发育、机制和功能的方法来研究几种孵化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，(I)在海马神经发生方面的性别偏见是否在不同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，幼虫在海马体属性中进化出了适应能力，最大限度地提高了它们记忆宿主巢穴位置的能力，从而增加了它们终生繁殖的成功。为了验证这一假说，我将结合实验室中的认知测试、野外工作，以及使用免疫组织化学对海马体进行精细测量，以及通过荧光原位杂交(CATFISH)对时间活动进行细胞室分析。 在认知神经科学领域，研究幼体寄生虫提供了一个独特的机会来研究这样一个系统，在这个系统中，女性而不是男性拥有更复杂的空间使用，从而使我们能够表明，空间需求而不是性别本身是否可以塑造这些参数。利用这个系统，我将对野生动物空间记忆中的形式和功能之间的联系提供一个整体的视角。

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.