Evolution and ecology of extractive foraging in birds and mammals

提取性觅食是定位和加工嵌入或包裹的食物的行为，例如地下植物储存器官，钻木节肢动物，贝类或被多刺，坚韧或坚硬基质保护的植物部分。它被认为可以提高动物利用资源的效率，使它们能够栖息在不适宜居住的环境中，但其大规模的进化和生态后果却很少被研究。鸟类和哺乳动物进化出了各种各样的专门化，以使其能够进行提取性觅食，包括专门的形态学，如食蚁兽的细长的鼻子和舌头以及弯曲的前爪，以及专门的行为，如在aye-ayes中看到的由洞穴引导的挖掘以及在大猿和新喀里多尼亚乌鸦等分类群中展示的工具使用。类似的觅食适应，如鸟类和灵长类动物的双眼视觉8 - 9似乎在不同的类群中独立进化了多次，但这些潜在的趋同进化案例尚未得到正式研究。我们也不太了解觅食和用途：工具使用之间的进化关系：前者是否倾向于后者，如果是，在什么条件下？尽管有其潜在的优势，但提取性觅食在鸟类和哺乳动物中的遗传分布是零散的，这表明它只在某些条件下进化，并且这种条件在独立的情况下反复出现，在整个生命树中。这些复发提供了一个机会，使用系统发育的比较方法来检查不仅有利于提取觅食，如饮食类型和季节性的生态条件，但也形态诱发因素，其出现的限制，其行为，生态位占用，进化速率和物种形成的进化反馈效应。例如，有利于专门行为的条件，如工具使用与专门形态，目前尚不清楚，对人口动态的影响，分支多样化和进化速度后，它出现。复杂的模式提取觅食行为被认为是认知的要求，并需要扩展的发展，以促进学习，预测复杂的提取觅食，大脑的大小或结构，成熟年龄，青少年时期和非社会性游戏所花费的时间之间的关联。提取觅食可以缓冲个人对环境扰动，预测提取觅食和环境的不可预测性或季节性之间的关联。我们将测试“提取觅食假说”的大脑大小的演变，这表明，提取觅食在没有专门的形态与感觉运动技能和大脑大小。我们将在两个分支中研究这些问题，在这两个分支中，提取觅食已经进化了多次，鸟类和哺乳动物，并研究在每个分支中观察到的模式的相似性和差异。这个项目将使用最近开发的系统发育方法，可以推断进化变化的模式和过程，使我们能够解决四个主要问题：（一）性状之间的相关进化，包括行为，神经解剖学和认知;（ii）使用方向方法的进化序列，来检验因果假设，并检查诸如是否提取觅食和/或或工具使用行为在系统发育分支上获得和失去的可能性相同，以及这些行为在最初出现后是否倾向于增加复杂性;（三）进化变化率及其与采掘觅食和工具使用有关的可变性（例如，这些行为的出现是否增加或减少了形态和/或行为的变化率）;（iv）萃取觅食的出现、种群密度、新生态位的入侵和物种形成之间的关系

Extractive foraging is the act of locating and processing embedded or encased foods such as underground plant storage organs, wood-boring arthropods, shellfish or plant parts protected by a thorny, tough or hard matrix. It is assumed to enhance the efficiency with which animals can exploit resources, enabling them to inhabit otherwise inhospitable environments, but its large-scale evolution and ecological consequences have been surprisingly little studied. A variety of specializations have evolved in birds and mammals to enable extractive foraging, including both specialised morphologies such as the elongated snouts and tongues and curved foreclaws of anteaters, and specialised behaviours, such as the auditorily-guided excavation seen in aye-ayes and tool-use displayed by taxa such as great apes and New Caledonian crows. Similar adaptations for extractive foraging, such as binocular vision in birds and primates8-9 appear to have evolved multiple times independently in different taxa, but these potential cases of convergent evolution have not been formally studied. We also know little about the evolutionary relationship between extractive foraging and tool use: does the former predispose to the latter, and if so under what conditions? Despite its potential advantages, extractive foraging is phylogenetically patchily distributed across birds and mammals, suggesting that it evolves under only certain conditions, and that such conditions have recurred repeatedly in independent cases, across the tree of life. These recurrences provide an opportunity to use phylogenetic comparative methods to examine not only the ecological conditions favouring extractive foraging, such as diet type and seasonality, but also morphological predisposing factors, constraints on its emergence, and its evolutionary feedback effects on behaviour, niche occupancy, evolutionary rates and speciation. For example, the conditions favouring specialised behaviours such as tool-use versus specialised morphologies are currently unknown, as are the effects on population dynamics, clade diversification and evolutionary rates after it appears. Complex patterns of extractive foraging behaviour are thought to be cognitively demanding and require extended development to facilitate learning, predicting associations between complex extractive foraging, brain size or structure, age at maturity, juvenile period and amount of time spent in non-social play. Extractive foraging may buffer individuals against environmental perturbations, predicting associations between extractive foraging and environmental unpredictability or seasonality. We will test the "Extractive foraging hypothesis" for brain size evolution, which suggests that extractive foraging in the absence of specialised morphology is associated with sensory-motor skills and brain size. We will examine these questions in two clades within which extractive foraging has evolved multiple times, birds and mammals, and examine the parallels and differences in the patterns observed within each. This project will use recently developed phylogenetic methods that permit inference of the patterns and processes of evolutionary change, allowing us to address four major questions: (i) Correlated evolution between traits, including behaviour, neuroanatomy and cognition; (ii) Evolutionary sequences, using directional methods, to test causal hypotheses and examine questions such as whether extractive foraging and/or tool using behaviour is equally likely to be lost as gained on phylogenetic branches and whether these behaviours tends to increase in complexity after their initial emergence; (iii) Rates of evolutionary change and their variability in relation to extractive foraging and tool use (e.g. does the emergence of such behaviours increase or decrease rates of change in morphology and/or behaviour); (iv) Relationships between emergence of extractive foraging, population density, invasion of new niches, and speciation