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   Location:Home > Research > Research Progress
Trade-off strategy in stone oak seeds between physical and chemical defense
Author: CHEN Xi
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Update time: 2012-03-27
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Lithocarpus (Blume), commonly known as stone oaks, range from eastern India through southern China, north to Japan, and extend through Southeast Asia, across the Malayan archipelago to Papua New Guinea. Trees in the beech or oak family (Fagaceae) have a mutualistic relationship with scatter-hoarding rodents. Rodents obtain nutrients and energy by consuming seeds, while providing seed dispersal for the tree by allowing some cached seeds to germinate. Seed predation and caching behavior of rodents is primarily affected by seed size, mechanical protection, macronutrient content, and chemical antifeedants. To enhance seed dispersal, trees must optimize trade-offs in investment between macronutrients and antifeedants.

Prof. Chuck Cannon of Xishuangbanna Tropical Botanical Garden (XTBG) and his students proposed a hypothesis that a trade-off strategy exist in stone oak seed phytochemical investment and mechanical protection.

  The researchers chose two distinct fruit types within the tropical stone oaks (Lithocarpus): acorns and enclosed-receptacle (ER) fruits as their study materials. They examined the important chemical balance in the seeds of tropical stone oak species. They sampled numerous individuals from two pairs of sympatric species with differing fruit morphologies, one each in the lowlands and highlands. They compared the chemical composition of numerous macronutrient and antifeedant in seeds from several Lithocarpus species.

   The study found that the two distinctive fruit morphologies of Lithocarpus, ER fruits and acorns, exhibit a trade-off strategy in seed phytochemical investment and mechanical protection. Seeds of ER fruits, enclosed by awoody and thickened receptacle, invested more in macronutrients, while seeds of acorns, enclosed by a thin and bitter exocarp, invested more in antifeedants as chemical protection from predation. Carbohydrate and lipid were the most important macronutrient fractions in the trade-off, while surprisingly, acorn seeds demonstrated an increased concentration of indigestible fibers, not tannins, as the important antifeedant participating in the evolutionary pattern. The pair-wise comparison of sympatric ER and acorn species revealed a considerably more clear and consistent trade-off in phytochemistry in the lowlands than the highlands, which may be caused by the different degree of the predation pressure between the two forests.

 The study entitled “Evidence for a Trade-Off Strategy in Stone Oak (Lithocarpus) Seeds between Physical and Chemical Defense Highlights Fiber as an Important Antifeedant” has been published in PLoS ONE 7(3): e32890. doi:10.1371/journal.pone.0032890

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Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences. Menglun, Mengla, Yunnan 666303, China
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