在自然界，多数动物取食多种植物，而一种植物也往往为多种动物所取食。因此，草食动物与植物间的相互作用往往不是严格地一对一的协同进化关系（pairwise coevolution），而是弥散性的（diffuse coevolution）。在脊椎动物与植物之间的相互作用中，弥散性协同进化关系更为普遍，但有关证据却十分有限。在多年从事啮齿动物与森林种子间相互关系的研究基础上，中国科学院动物研究所肖治术博士等科研人员在四川都江堰地区发现：赤腹松鼠将易萌发橡子的胚芽切除后再将其贮藏起来，从而可减少由萌发所造成的能量和营养损失，有利于橡子的长期贮藏利用。松鼠的这种切胚行为曾在北美地区有过报道，而他们首次在北美以外地区的发现为松鼠与橡子之间的协同进化关系提供了进一步的可靠证据，并揭示松鼠切除种子胚芽的行为可能具有普遍的适应意义，为洲际间松鼠类种子贮藏行为的趋同进化提供了有力证据。
在许多森林生态系统中，富含营养的橡子（栎属植物的种子）是啮齿动物和许多其它野生动物的重要食物资源。在长期进化过程中，橡子形成了一些适应动物贮藏（扩散）但能防止其被过度捕食的特征，如萌发和单宁等。在栎属植物中，有的种类（白栎类）橡子在成熟后可迅速萌发，而有的（红栎类和青冈类）则保持休眠到次年春季才萌发。橡子的迅速萌发被认为是逃逸动物捕食（包括切胚）的一种适应，而休眠则可促进橡子的有效扩散。这是因为橡子的萌发和休眠可显著影响动物的行为：动物常偏好贮藏休眠的橡子，而易萌发的橡子常在胚芽被切除后才被贮藏，且被切胚橡子的萌发率极低。橡子的单宁水平是另一个显著影响动物行为的特征：高水平单宁可阻止动物取食，但不影响被动物贮藏。通过调查研究，他们发现动物在贮藏时能有效区分橡子的萌发特征和单宁水平：萌发特征可影响橡子胚芽是否被切除，而单宁水平则对橡子是否被贮藏有决定性影响。这些发现有力地揭示了啮齿动物如何有效利用橡子等资源来满足食物的长期供应，从而顺利度过食物匮乏、气候恶劣的冬季。
上述研究结果在国际动物行为学杂志《行为生态学》（Behavioral Ecology）上在线发表。该研究得到了国家基础规划项目（973）、国家自然科学基金和中国科学院知识创新工程前沿领域项目等的资助。（生物谷Bioon.com）
生物谷推荐原始出处：
Behavioral Ecology, doi:10.1093/beheco/arp096
Behavioral adaptation of Pallas's squirrels to germination schedule and tannins in acorns
Zhishu Xiaoa, Xu Gaoa,b, Mingmin Jianga,c and Zhibin Zhanga
a State Key Laboratory of Integrated Management of Pest Insects and Rodents in Agriculture, Institute of Zoology, Chinese Academy of Sciences, Datun Lu, Chaoyang District, Beijing 100101, China b Anhui Provincial Key Laboratory of the Conservation and Exploitation of Biological Resources, College of Life Sciences, Anhui Normal University, Wuhu 241000, China c Key Laboratory of Bio-resources and Eco-environment, Ministry of Education, College of Life Science, Sichuan University, Chengdu 610064, China
Using acorns from Castanea henryi (CH) and Quercus variabilis (QV) with contrasting germination schedule (related to food perishability) and tannin levels, we conducted field experiments in a subtropical forest in Southwest China to investigate how free-ranging Pallas's squirrels (Callosciurus erythraeus) utilize acorns as long-term storage based on the food perishability and high-tannin hypotheses. Though QV acorns germinated much earlier than CH ones, we found that Pallas's squirrels hoarded more high-tannin QV acorns over low-tannin CH ones, supporting the high-tannin hypothesis (but not the food perishability hypothesis). However, several other predictions derived from the food perishability hypothesis received sound support: nondormant QV acorns had their embryos removed with a higher probability (68.5%) than dormant CH ones (8.8%) and embryo-removed acorns had a much lower germination success but had a higher probability surviving as long-term storage. During the caching-recovery process, hoarding animals actively detected acorn state (dormant or not) and removed acorn embryos with an increasing probability in subsequent hoarding events. In addition, embryo-removed acorns could serve as long-term storage because they had a very low probability being infested by fungi as intact acorns did during the time of storage. We conclude that tree squirrels can differentially respond to acorn germination and remove the embryos of nondormant acorns more frequently as long-term storage, but tannin level is more important in determining whether a given acorn is hoarded or not. Combined with the studies from North America, our results suggest convergent evolution of acorn hoarding behavior in tree squirrels across different continents.
