Adaptive Mechanisms of Plant-Ant Interaction and its Evolutionary-Ecological Implications

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(1) The chemical attractants of seed elaiosomes of the four temperate woodland perennials in Japan, i. e., Erythronium japonicum, Trillium kamtschaticum, Chloranthus japonicus, and C-. serratus, were critically analyzed, and the behavioral bioassays were conducted to chemically identify the attractant responsible for the interaction. Both water-soluble fractions and CHC1_3/MeOH extracts were analyzed.The HPLC analysis of free amino acids revealed that none of the four species' elaiosomes contained amino acids in their water-soluble fractions. No sugars were also contained in,the elaiosomes of Erythronium japonicum and Chloranthus serratus; whereas high amounts of fructose, glucose and saccha rose or maltose were detected from the dlaiosomes of Trillium kamtschaticum and Chloranthus japonicus.The CHC1_3/MeOH extracts proved to contain diglycerides, triglycerides, free fatty acids, phospholipids sterols. sterolesters, and hydrocarbons. The GC-MS analyses of methylesters of fatty acids,sh … More owed that the major fatty acid present is oleit acid, accompanying with palmitic acid, palmitoleic acid, stearic acid, vaccenic acid, linoleic acid and linolenic acid. The present results, as a conclusion, show that there are two types of ant-dispersed seeds with elaiosomes in terms of chemical compositions, i. e., "sugar" seeds in which sterol, sterolester and diglycerides are entirely lacking (e. g., Trillium kamtschaticum, Chloranthus japonicus, etc.), and "lipid" seeds in which sugars are lacking but instead having large quantities of sterol, sterolester and triglycerides (e. g., Erythronium japonicum, Chlo ranthus serratus, etc.). Assays of purified free lipid extracts, diglycerides, sterols and hydrocarbon all revealed that ants are attracted to all fractions mentioned above, and did not demonstrate clear preference for any specific substance. This fact demonstrates that any specific substance is not an attractant eliciting the ant response to seeds with elaiosomes, which is different from what had been previously suggested (Bresinsky, 1963; Marshall et al., 1979).(2) The morphology, anatomical structures, and chemical compositions of extrafloral nectaries that occur at the base of petioles or at each stem node of Polygonum cuspidatum and P. sachalinense were studied, and further visiting insects, including ants, to extrafloral nectaries were critically examined in the field. The extrafloral nectaries of these two Polygonum species are obviously vascularized judging from their shape, size, and inner structures. Three different sugars, i. e., glucose, fructose and saccharose, were detected by HPLC analysis from the nectar of two Polygonum species.Insect predators were also collected in the field and identified. There is no doubt that ants are effectively guarding young shoots of Polygonum in spring to early summer from heavy predation pressure of various phytophagous insects, e. g., such as Callerucida bifasciata, Blitopertha conspurcata, Maladera sp., etc. Less