オオバコ種内2型(普通型とminima型)の生活史特性  [in Japanese] Variation in Life History Traits of Two Types of Plantago asiatica L. s. l.  [in Japanese]

オオバコ種内2型の生活史特性とその成立過程を検討するために, 京都市北東部の8集団を供試して栽培実験と発芽試験を行い, さらに, 自生地での季節消長を調査した。1) minima 型は普通型よりも全乾物重が小さく, 早く出穂し, 繁殖分配率が大きかった(Fig. 1, 2およびTable 2)。また, 年間の種子生産数は, 栽培1年目では2型間に差異はなかったが, 栽培2年目では普通型がminima型を大きく上回った(Table 2)。2) 普通型では, 明条件下で20℃から30℃までのいずれの温度区でも高い種子発芽率が得られた。一方, minima型では25℃で種子発芽率が最大となり, 20℃では発芽速度が顕著に遅かった(Fig. 3)。3) 普通型が生育する畦畔や農道では, 植生が密で, 成熟個体の死亡することが少なく, 競争が激しかった。一方, minima型が生育する神社の境内では, ストレスが大きく, 乾燥した夏の掃き掃除や不定期な除草, 改修工事などの攪乱が予測不能な死亡要因として作用していた(Fig. 4)。また, 出芽の時期は2型間で異なった(Fig. 4)。以上のことから, オオバコ種内2型の生活史特性は, ストレスや攪乱, 競争の質や程度が異なるそれぞれの自生地の環境に適応して成立したものと推定された。

Life history traits of two types of Plantago asiatica L. s. l., the common and minima type, were compared by using experimental populations raised from the seeds collected from eight natural populations in Kyoto City (Table 1). Remarkable genetic variation was observed in the life history traits between the two types. The minima type produced a smaller plant biomass, headed earlier, and allocated a larger amount of dry matter to reproductive organs earlier in the life cycle (Fig. 1 and Table 2). Although both types produced an equivalent number of seeds in the first year, the common type produced a larger number of seeds than the minima type in the second year (Table 2). High seed germination rates of the common type were obtained at 20, 25 and 30℃ under light conditions, while the minima type showed a high germination rate only at 25℃ under light conditions (Fig. 3). Based on the results of ANOVA for the life history traits, it was considered that some environmental factors of habitats were closely related to the genetic variation of the two types (Table 1 and Fig. 3). Phenological observations were made on eight natural populations of the two types to analyze life history strategies. The habitat of the common type, levee or path between fields, was characterized by a relatively high competition due to the high coverage of vascular plants and low mortality of adult P. asiatica plants. On the other hand, the habitat of the minima type consisting of grounds of shrine, was characterized by stress^<14)> and unpredictable mortality due to disturbances, such as weeding, dry weather and sweeping in summer and repair work of the shrine (Fig. 4). The life history strategies of the two types of P. asiafica seem to have evolved as adaptations to such unique environment and management of their habitats.