白背叶(大戟科)性系统和传粉生物学研究

Sexual System and Pollination Biology of Mallotus apelta (Euphorbiaceae)

摘要:

为探讨野桐属(Mallotus)雌雄异株的进化和传粉机制,对白背叶(Mallotus apelta)野生居群的性系统和传粉生物学进行了研究。结果表明,所调查的白背叶居群均由雌性(F)、雄性(M)和少数两性(B)个体组成,平均性比为1:0.66:0.18 (F:M:B);3 种性别植株的基径大小差异不显著;雌株与两性植株的单花胚珠数、单果结籽数和自然结实率无显著差异;雄株与两性植株的花粉萌发率、花粉组织化学和花粉微形态特征也无显著差异,但雄株的单花花粉量是两性植株的1.26~1.63 倍,且差异显著;雌株的异交结实率为96.67%,两性植株的异交结实率为76.00%,两者差异显著,说明居群内雌株的潜在种子生产力明显高于两性植株;野外观察到雄株和两性植株上的雄花具有访花者而雌株没有;雌株经套网处理后结实率超过30% 而套袋处理不结实。这些表明白背叶具典型的亚雌雄异株性系统,雌株和雄株的适合度均高于两性植株;雌株以风媒传粉结实,两性植株可能兼有风媒和虫媒传粉特征。

Abstract:

In order to understand the evolution of dioecy and pollination modes in the genus Mallotus, the sexual system and pollination biology of M. apelta were studied in wild populations from Guangdong and Guangxi Provinces in southern China. The results showed that all the investigated populations contained female (F), male (M) and bisexual (B) individuals, and the average sex ratio was 1:0.66:0.18 (F:M:B). There were no significant differences in base diameter of trunk among three sexual individuals. Although the pollen of male flowers from pure male individuals and that from bisexual individuals had the same germination rate, histochemical and micro-morphological characters, the single male flower from male individuals produced 1.26-1.63 times pollen grains more than those of bisexual individuals. Female individuals shared the same ovule numbers per flower, seeds per fruit and fruit setting per inflorescence with bisexual individuals. The control crossing (pollen came from males) significantly increased the fruit setting of pure females (96.67%) comparing to bisexual individuals (76.00%) (P < 0.001), indicating higher potential seed fertility in female individuals than that in bisexual individuals. Insects (fly, beetle) were observed to visit male and bisexual but not female individuals in the field, indicating that insects made no contribution to the fruit production of female individuals. More than 30% of the netted female flowers set fruits, while all the bagged female flowers failed to set fruits. Therefore, these indicate that M. apelta is a typical subdioecious species. The results also demonstrate that the male and female individuals have higher fitness than bisexual individuals in populations. Females are pollinated by wind, while bisexual individuals show a combination of entomophilous and anemophilyous characteristics. More comprehensive investigation of the sexual system and pollination mode in the species and its congeners may shed light on our understanding of the evolution of dioecy and pollination modes in the genus Mallotus.