A Study On The Adaptive Significance Of Heteranthery In Commelina Communis (Commelinaceae)

Abstract:In nectarless flower, pollen is the only reward for pollinators. Thus, it is an evolutionary dilemma for these plants that they need to protect their precious pollen from pollen feeder while maintaining enough attractiveness to pollinators. Heteranthery, the occurrence of two or more distinct types of stamens in the same flower, has been thought to reconcile the evolutionary conflict by allowing different stamens to specialize in ’pollinating’ and ’feeding’ functions, respectively.Here, floral traits, flower types, sexual allocation and natural pollination have been investigated in natural populations of Commelina communis, a trimorphic stamen species. we investigated the functions of three different types of stamens and analyzed the mating systems by SSR in natural populations.In flowers of C. communis, the pistil is polymorphic. According to the length of style, three types of style exist:long styled, short styled and none styled. Long styled flowers are bigger than short styled flowers, occurring most common among natural populations (more than80%). However, the coefficient of variation of style length for long styled flowers was less than short one, suggested long styled flowers were under a stablizing selection pressure. Our data also showed that the serious pollen theft rather than legitimate pollination occurred in the two populations, accounting for77.5%and92.2%of total flower visits, respectively.According to the length of filament, stamens in flower of C. com munis are also divided into three types:Long (L), Middle (M) and Short (S) typed stamen. No significant difference in pollen vigor between M-and L-typed anther in C. communis was found. To further examine the pollination roles of the three stamen types we manipulated flowers in the natural populations. We constructed experimental arrays including intact flower as control, L-anther removed flower, M-anther removed flower and S-anther removed flower to investigate pollinator preference and assess pollen deposition and pollen removal of each flower. S-and M-anther removed flowers received much fewer visitations but had no effect on pollen receipt. L-anther removed flowers received as many visits as intact flowers but received significantly fewer pollen grains. The two types of brightly yellow stamens separately functioned as ’deceptive food’ and ’feeding’ for the pollinators. However, the potential role of brown inconspicuous stamens in offering pollen for cross-pollination was disrupted by pollen thieves, significantly impairing pollen dispersal and deposition from the pollinating anthers in C. communis and decreasing the levels of outcrossing (tm=0.23～0.32) in wild populations. These findings indicated that contemporary pollen theft severely weakened the function of heteranthery in C. Communis. In this thesis, a total of12...