de Kort Selvino R, Clayton Nicola S
Department of Experimental Psychology, University of Cambridge, Downing Street, Cambridge CB2 3EB, UK.
Proc Biol Sci. 2006 Feb 22;273(1585):417-23. doi: 10.1098/rspb.2005.3350.
A principal finding in the food-caching literature is that species differences in hoarding propensity are positively correlated with species differences in degree of adaptations to caching behaviour, such as performance on spatial memory tasks and hippocampal volume. However, there are examples that do not fit this pattern. We argue that these examples can be better understood by considering the phylogenetic relatedness between species. We reconstruct the ancestral state for caching behaviour in corvids and assess when transitions in caching behaviour occurred within the corvid phylogeny. Our analysis shows that the common ancestor of all corvids was a moderate cacher. This result suggests that corvids followed a bi-directional evolutionary trajectory in which caching was secondarily lost twice and there were at least two independent transitions from moderate to specialized caching. The independent evolution of specialized cachers in the two groups must, therefore, be a case of convergent evolution. This is exemplified by the fact that specialized cachers show structurally different adaptations serving the same function to intense caching, such as different pouches to transport food. Finally, we argue that convergent evolution may have led to adaptations in memory and hippocampus that serve the same function but differ in design, and that these different adaptations may explain the examples that do not fit the pattern predicted by the adaptive specialization hypothesis.
食物贮藏文献中的一个主要发现是，贮藏倾向的物种差异与对贮藏行为的适应程度差异呈正相关，比如在空间记忆任务中的表现以及海马体体积。然而，也有不符合这种模式的例子。我们认为，通过考虑物种之间的系统发育相关性，可以更好地理解这些例子。我们重建了鸦科动物贮藏行为的祖先状态，并评估了在鸦科系统发育中贮藏行为的转变发生在何时。我们的分析表明，所有鸦科动物的共同祖先是适度贮藏者。这一结果表明，鸦科动物遵循了一条双向进化轨迹，即贮藏行为两次次生丧失，并且至少有两次从中度贮藏到专门贮藏的独立转变。因此，两组专门贮藏者的独立进化必定是趋同进化的一个例子。这一点体现在专门贮藏者为了强烈贮藏表现出结构上不同但功能相同的适应，比如用于运输食物的不同嗉囊。最后，我们认为趋同进化可能导致了在记忆和海马体方面具有相同功能但设计不同的适应，并且这些不同的适应可能解释了不符合适应性特化假说所预测模式的例子。
