Study On The Adaptive Significance Of Flexistyly In Alpinia (Zingiberaceae)

This thesis investigates a distinct plant sexual dimorphism, flexistyly, and its adaptive significance and possible evolutionary pathway in animal-pollinated plant populations. Flexistyly is characterized by the variation in style movement direction with anther dehisce time and stigma receptivity in flowers of anaflexistylous (ana)- and cataflexistylous (cata)-morphs. The reciprocity in pollen presence and stigma receptivity between morphs is similar to the well known sexual polymorphism heterodichogamy. The spatio-temporal separation of male and female function promote disassortative mating.I examined the morph frequency and mating system in natural population of four flexistylous Alpinia species. Flexistyly is widespread in the genus Alpinia, making it valuable for studying questions related to the evolution and function of the dimorphism. Natural populations of Alpinia had morph ratios ranging from isoplethy (1:1) in large populations (N > 25) to either ana- or cata-biased in small populations.There were no morph-specific differences in the species in multilocus outcrossing rates suggesting that no difference exist in pollen transfer and levels of disassortative mating contribute to the equal morph frequencies. Most populations are largely outcrossed at population level, only 7 population showed inbreeding depression.The adaptive significance of flexistyly has been interpreted as a floral mechanism which promote outcrossing, but alternatively it may also function to reduce sexual interference in which styles and stigmas impede the pollen export. To test the hypothesis, I conducted manipulative studies on the cata-morph plants of Alpinia blepharocalyx. My sequential manipulative pollination demonstrated that self-pollen largely affected seed production per flower, although outcrossing rate was slightly lower compared to natural treatment. Experimental pollination revealed that pollen tube growth rate depends upon the position of the stigma, regardless of the pollination treatments and floral morphs. When stigma is located at the receptive position, the pollen grains begin to germinate and the tubes penetrate into the style just one hour after pollination. However, the stigma is at the non-receptive position it takes more time for pollen grains to germinate and pollen tube to grow. It is showed that heterodichogamy and reciprocal herkogamy may be two distinct features of flexistyly which unlikely to evolve simultaneously.