在自然界，多數(shù)動物取食多種植物,，而一種植物也往往為多種動物所取食,。因此,，草食動物與植物間的相互作用往往不是嚴(yán)格地一對一的協(xié)同進(jìn)化關(guān)系（pairwise coevolution），而是彌散性的（diffuse coevolution）,。在脊椎動物與植物之間的相互作用中,，彌散性協(xié)同進(jìn)化關(guān)系更為普遍，但有關(guān)證據(jù)卻十分有限,。在多年從事嚙齒動物與森林種子間相互關(guān)系的研究基礎(chǔ)上,，中國科學(xué)院動物研究所肖治術(shù)博士等科研人員在四川都江堰地區(qū)發(fā)現(xiàn)：赤腹松鼠將易萌發(fā)橡子的胚芽切除后再將其貯藏起來,，從而可減少由萌發(fā)所造成的能量和營養(yǎng)損失，有利于橡子的長期貯藏利用,。松鼠的這種切胚行為曾在北美地區(qū)有過報道,，而他們首次在北美以外地區(qū)的發(fā)現(xiàn)為松鼠與橡子之間的協(xié)同進(jìn)化關(guān)系提供了進(jìn)一步的可靠證據(jù)，并揭示松鼠切除種子胚芽的行為可能具有普遍的適應(yīng)意義,，為洲際間松鼠類種子貯藏行為的趨同進(jìn)化提供了有力證據(jù)。
在許多森林生態(tài)系統(tǒng)中,，富含營養(yǎng)的橡子（櫟屬植物的種子）是嚙齒動物和許多其它野生動物的重要食物資源,。在長期進(jìn)化過程中,，橡子形成了一些適應(yīng)動物貯藏（擴(kuò)散）但能防止其被過度捕食的特征，如萌發(fā)和單寧等,。在櫟屬植物中,，有的種類（白櫟類）橡子在成熟后可迅速萌發(fā)，而有的（紅櫟類和青岡類）則保持休眠到次年春季才萌發(fā),。橡子的迅速萌發(fā)被認(rèn)為是逃逸動物捕食（包括切胚）的一種適應(yīng),，而休眠則可促進(jìn)橡子的有效擴(kuò)散。這是因?yàn)橄鹱拥拿劝l(fā)和休眠可顯著影響動物的行為：動物常偏好貯藏休眠的橡子,，而易萌發(fā)的橡子常在胚芽被切除后才被貯藏,，且被切胚橡子的萌發(fā)率極低。橡子的單寧水平是另一個顯著影響動物行為的特征：高水平單寧可阻止動物取食,，但不影響被動物貯藏,。通過調(diào)查研究，他們發(fā)現(xiàn)動物在貯藏時能有效區(qū)分橡子的萌發(fā)特征和單寧水平：萌發(fā)特征可影響橡子胚芽是否被切除,，而單寧水平則對橡子是否被貯藏有決定性影響,。這些發(fā)現(xiàn)有力地揭示了嚙齒動物如何有效利用橡子等資源來滿足食物的長期供應(yīng)，從而順利度過食物匱乏,、氣候惡劣的冬季,。
上述研究結(jié)果在國際動物行為學(xué)雜志《行為生態(tài)學(xué)》（Behavioral Ecology）上在線發(fā)表。該研究得到了國家基礎(chǔ)規(guī)劃項(xiàng)目（973）,、國家自然科學(xué)基金和中國科學(xué)院知識創(chuàng)新工程前沿領(lǐng)域項(xiàng)目等的資助,。（生物谷Bioon.com）
生物谷推薦原始出處：
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.
