Mechanisms underlying detection of seed dormancy by a scatter-hoarding rodent.

The mechanism underlying detection of seed dormancy by scatter-hoarding rodents is unclear, although previous work suggests that the pericarp plays an important role in signaling dormancy status. Eastern gray squirrels (Sciurus carolinensis) consume early germinating seeds as they are more likely to perish immediately, whereas dormant seeds tend to be cached. To examine the mechanisms underlying dormancy detection, we characterized physical and chemical differences between germinating and dormant pericarps of northern red oak (Quercus rubra), American chestnut (Castanea dentata) and the BC3 hybrid of Chinese chestnut and American chestnut (Castanea mollissima × C. dentata) using scanning electron microscopy and gas chromatography- mass spectrometry. We found that, as seeds break dormancy, the wax layer on the pericarp degrades and is accompanied by the escape of lower molecular weight kernel compounds or lipid metabolism byproducts. Our field experiments showed that squirrels were 4-8 times more likely to consume seeds that were altered to remove pericarp wax coating or that were sprayed with seed chemicals. We argue that dormancy detection by scatter-hoarding rodents is a complex process involving physical cues such as loss of pericarp wax and chemical cues such as emission of olfactory cues.