Title Transcriptionコニシキソウ ニオケル アリ ニヨル シュシ サンプ ノ イギ ト アリ ニトッテノ シュシ ノ カチ
Degree Type博士(農学)
Doctor of Philosophy in Agricultural Science
Note (General)学位論文の要旨, 学位論文全文
連合農学研究科博士論文(農学) ; 学位取得日: 平成21年9月18日
Although efficient dispersal of seeds bearing an elaiosome has been reported in many plant species, ants also carry seeds without an elaiosome in other many species (leftover seed dispersal). In the leftover seed dispersal, most of seeds that have been carried by harvester ants or omnivorous ants are consumed as foods, but seeds lost by ants during the seed carry to their nest or leftover seeds in the nest have been consequently dispersed. In this case, ants’ behaviors such as seed transport, seed loss, seed predation, and seed abandon are important for determining the seed fate. In this mode of seed dispersal by ants, the efficiency of dispersal has been considered to be extremely low. However, the quantitative investigation for
the efficiency of seed dispersal has been hardly carried out, and the significance of this mode of dispersal is less well elucidated.
Chamaesyce maculata (L.) Small is a prostrate annual weed. Plants that emerged in June commenced sexual reproduction from late July, and thereafter both vegetative growth and sexual reproduction continued together until early November. Seeds produced in the summer germinated without dormancy, resulting in overlapping multiple generations within a year. Consequently, the competition between parents and offspring would occur. Seeds produced in the autumn germinated from early summer of the next year, and the competition among offspring seedlings would occur. Therefore, in C. maculata, the seed dispersal is important for escaping from the sib-competitions.
In this study, in order to elucidate modes of seed dispersal in C. maculata, we carried out (1) the examinations of seasonally different modes of seed dispersal, (2) the investigations on the characteristics of seed dispersal by two ant species and their efficiencies, (3) the investigations on the defense of pre-dispersal seeds, the exclusion of pre-dispersal seed predators, and the preferential removal of noninjured seeds by ants, (4) the examinations of ant’s preferences to the seed coat and the effects of the seed coat on the seed dispersal by ants.
In the summer when the competition between parents and offspring would occur, the competition between parents and offspring was weakened by the
autochory. On the other hand, in the autumn the autochory did not occur because no competition between parents and offspring occurs, but the seed dispersal by ants of Tetramorium tsushimae Linnaeus and Pheidole noda Smith. F. was observed. The seed dispersal by ants is likely to contribute to escape from the competition among offspring in the next year.
In P. noda, although the proportion of seeds lost during the seed carry to their nest was high, the seeds carried into the nest were hardly carried out of the nest, and almost of them were consumed in the nest. Thus, although the dispersal range of the seeds by P. noda expanded, seedlings did not emerged around the nest of P. noda. Therefore, it is expected that P. noda contributes to the seed dispersal of C. maculata by the seed loss during the seed carry to their nest. In T. tsushimae, although the proportion of seed loss by ants during the seed carry to their nest was low, about half of the seeds carried into the nest were carried out of the nest without 110 consumption by ants. Thus, the proportion of seeds consumed was conspicuously low, and many seedlings emerged around the nest of T.tsushimae. Therefore, it is expected that T. tsushimae greatly contributes to the seed dispersal of C. maculata by the low seed consumption rate.
When two ant species existed on the plants of C. maculata, the density of stinkbugs was low on the plants. Therefore, the pre-dispersal seeds seem to be defended by ants. Moreover, when both injured and non-injured seeds were provided to ants at the same time, T. tsushimae carried non-injured seeds more quickly into the nest than injured seeds. Therefore, T. tsushimae seems to be the efficient seed disperser.
Ants of T. tsushimae showed the preference to the seed coat of C. maculata, and they consumed only the seed coat in the nest without the consumption of the body of seeds. On the other hand, ants of P. noda showed no preference to the seed coat, and only the consumption of the seed coat was not found. The difference in seed consumption modes between two ant species seemed to be influenced by their food habits.
Consequently, C. maculata would acquire new habitats resulting from the seed dispersal by ants, and would be able to expand their distribution range. The value of seeds differed between T. tsushimae and P. noda, resulting in different patterns of the seed dispersal between two ant species. It is considered that T. tsushimae and P. noda contribute to the seed dispersal of C. maculata by the low proportion of seed consumption and the high proportion and dispersion of seed loss during the 111 seed carry to their nest, respectively.
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