Many hoarding animals such as tree squirrels rely on plant seeds (e.g. acorn masting from oaks) as food reserves for their survival and reproductive success. As important defensive strategies, germination schedule and tannins in acorns could largely influence feeding and hoarding preferences of hoarding animals. However, it is poorly understood how hoarding animals utilize acorns as long-term food supply in response to these defensive strategies. Dr. Zhishu Xiao, Xu Gao, Mingmin Jiang and Zhibin Zhang from the Institute of Zoology, the Chinese Academy of Sciences, first demonstrated that Pallas’s squirrel (Callosciurus erythraeus), like several Sciurus squirrels reported in North America, displays embryo removal behavior to acorns in China. Their first record on acorn-embryo removal behavior by Pallas’s squirrels provides significant evidence that the evolution of acorn-embryo removal behavior in tree squirrels is a counter-adaptation to deal with non-dormant phenotype in white oaks worldwide. They found that that tree squirrels can differentially response to acorn germination and remove the embryos of non-dormantacorns more frequently as long-term storage, but tannin level is more important in determining whether a given acorn is hoarded or not. Their foundings suggest convergent evolution of acorn hoarding behavior in tree squirrels across different continents, and also provide sound evidence for diffuse coevolution between tree squirrels and oaks.

The results of this work were recently published online in Behavioral Ecology (Xiao Z-S, Gao X, Jiang M-M, Zhang Z-B. 2009. Behavioral adaptation of Pallas’s squirrels to germination schedule and tannins in acorns. Behavioral Ecology, doi:10.1093/beheco/arp096). This work was supported by National Basic Research Program of China, NationalNatural Science Foundation of China and the Knowledge Innovation Program of Chinese Academy of Sciences.