Effects Of Wild Apricot (Armeniaca Sibirica) Seed Odor On Hoarding Behavior In Rodents

Scatter-hoarding rodents play a significant role in seed dispersal and plant regeneration through hoarding seeds. Although the importance of scatter hoarding rodents to seed dispersal of plants is considered, those advantages for plants have often viewed as incidental to the imperfect behavior of rodents, whereby seeds were deposited into favorable situations and fail to retrieve completely, and the plants had little or no control over the seed movement and fate when a seed left from its mother tree. Recently, it was argued that mutualistic interactions between plants and animals have been developed during the long history of coevolution. On one hand, rodents have evolved a series of strategies of searching, feeding, hoarding and retrieving seeds to maximize energy rewards. On the other hand, plants have also developed many strategies to improve seed dispersal and regeneration. In this study, we studied the odor attenuation hypothesis that seed odor will reduce to a minimum in a short time once the seeds are cached in soil; as a result, the cached seeds will not be retrieved by animals easily, benefiting to plant regeneration.The subjects were the seed dispersal system between wild apricot (Armeniaca sibirica) and small rodents, such as Chinese white-bellied rats (Niviventer confucianus), large field mice (Apodemus peninsulae) in Donglingshan area, northwestern Beijing city. We used Gas chromatography-mass spectrometry (GC-MS) analytical method,and conducted several experiments in the field and within controlled enclosures to look at the questions:(1) what chemical odors are there in the focal seed species? (2) Will seed odors degrade in short time after caching by small rodents? (3) Will odor attenuation of seeds affect seed-hoarding behaviors of small rodents? And (4) will rodents with different hoarding pattern have different responses to odor attenuation of seeds?Our results showed that:(1) benzaldehyde and benzyl alcohol were the main volatile chemicals of seed odors of A. sibirica; (2) Contents of benzaldehyde decreased, while contents of benzyl alcohol did not change greatly with the increasing of burying time of seeds. Both of the two chemicals affected hoarding and retrieving behavior of small rodents. (3) When the focal seeds were buried in soil till to 60 days (buried seeds) or stored at 4℃ till to 60 days (cool-stored seeds), and then buried under same conditions, more buried seeds were hoarded and retrieved by small rodents in the field, and by A. peninsulae and N. confucianus under enclosure conditions than the cool-stored seeds. (4) A. peninsulae preferred to hoard lOppm-benzene methanol seeds and 40ppm-benzaldehyde seeds, whereas N. confucianus has no significant preference for these seeds.These results suggest that seed odors will decrease when the seeds were buried in soil, and subsequently reduce seed retrieving by small rodents, benefiting to seed survival and seedling establishment of plants. This founding largely supports the odor attenuation hypothesis that seed odor will reduce to a minimum when the seeds are buried in soil, and thus preventing small rodents from retrieving these seeds. Furthermore, this manipulation of seed odor attenuation of plants to small rodents mainly acts upon seed dispersers (scatter hoarders) rather than purely seed consumers (larder hoarders and consumers). Our results emphasize that plants have evolved strategies to manipulate their seed dispersers to behave a way to improve seed dispersal and seed survival, benefiting to seedling recruitment and regeneration. More studies are needed to look at how these strategies act, and how these plant-animal interactions affect the coevolution between plants and animals, and sustainablility of community.