Differential Performances And Invasion Patterns In Aquatic Plant Eichhornia Crassipes (Pontedriacae) Populations

Eichhornia crassipes (Mart.) Solms, an aquatic plant native to the Amazon Plain of South America, has a mating system of three floral morphs (L, M, and S) - tristyly. However, only individuals of morph M and L have been found in the invaded regions of the species, often with M individuals dominant in a population, and lead to substantially lowered sexual reproduction. In order to explain why the frequencies of floral morphs change during the invading process and the effect of such changes on the adaptive evolution of the species, the author conducted field experiments in two populations located in South-Western China in two consecutive years to compare the patterns of clonal growth, biomass accumulation, and sexual reproduction of M and L individuals. Levels of genetic variation of the two morphs were also compared by random amplified polymorphic DNAs (RAPDs) and inter- simple sequence repeats (ISSRs). Moreover, the author cloned and sequenced the fragments likely linked to the loci controlling tristyly in this plant.The comparison of clonal growth (measured by number of ramets per individual) found that in year 2004 and under the floating condition in a pond, M individuals produced 25.37 ramets and L had 21.20 ramets (t=2.252, P< 0.05). The same pattern was also found in 2005 (19.83 for M vs. 15.53 for L). On an average, M individuals produced nearly 24% more clones than L individuals.In the wetland habitat, however, L individuals showed a relatively higher potential of clonal growth than M (16.20 ramets vs. 10.17 ramets, t=4.788, p<0.001). These different growth patterns in adjacent habitats implied a likely niche differentiation between the two morphs. The differentiation may either be developed during the invasion process or reflect the within-species adaptation of the two floral morphs to the alternating growth conditions of floating and fixing found during water- rising and drying along the Amazon River, respectively.The comparison of biomass showed that M individuals have a significantly higher biomass accumulation (measured by dry weight of experimental individuals) under both floating and fixing growth conditions (floating growth: t=6.173, p<0.005 for year 2004, and t=6.99, p<0.001 for 2005; fixing growth: t=4.029, p<0.001 for year 2004). Higher accumulation of biomass indicates a better competitive ability and overwintering potential, therefore a higher biomass accumulation may render M individuals to persist longer in newly invaded regions and could be the consequence of local adaptation in the new environment.The experiments on the sexual reproduction included surveys of the number of inflorescences per plant and total number of flowers per inflorescence, hand-pollination, seed production, and germination of seeds collected from M and L individuals. The results show that although M and L plants generated a similar amount of flowers, more seeds were produced on M individuals than on L individuals, and the pattern was particularly clear for self-pollination (139.8 vs. 76.2 seeds per capsule). Among M individuals, more seeds were produced from selfing than from outcrossing (139.8...