The Reproductive Strategies Of Two Sympatric Eremurus Species

Eremurus inderiensis (M. Bieb) Regel and E. anisopterus (Kar. et Kir) Regel are herbaceous perennial spring ephemeral of Liliaceae, and in China they only distribute in Gurbantunggut Desert of Xinjiang. There are discernible differences between two sympatric Eremurus species in floral characters. In this study, we had chosen the location where two Eremurus species distributed sympatric to focus on the questions as follow: (1) the reproductive isolation mechanism between them; (2) the evolutionary implication of two kinds of pollen presentation patterns; (3) adaptive advantages of size-dependent gynomonoecious on E. anisopterus; (4) patterns and limitation factor on fruit set and seed set of E. inderiensis. Over few years'field observations and manual experiments, we have drawn some results as follows:1. There was different degree of overlap on flowering period between two E. anisopterus and E. inderiensis in different years. Two species with different floral design have different pollination syndrome. Variation in floral design indicated that two Eremurus species suit for different type of pollinators although they were visited by almost the same series of insects. There was not any seed yield under the control of artificial hybridization. Thorough the observation under the fluorescence microscope, the pollens from E. anisopterus and E. inderiensis did not germinate on each other's stigmas. The results indicated that temporal isolation and floral isolation are important to prevent the gene exchange between taxa, but the two external isolation mechanisms were uncompleted, and combined with internal isolation mechanism was the essential way to maintain sympatric related species boundary in Eremurus .2. Several mechanisms were evolved to control the pollen presentation in E. anisopterus and E. inderiensis. The similarity lies in the fact that two species dispensing pollen by unzipping the anthers. What the distinction between two species were: (1) the peak of flower opening time of E. anisopterus appeared at 12:00, whereas two peaks arose at 12:00 and 18:00 in E. inderiensis; (2) the six anthers within a flower of E. anisopterus shed the pollens at almost the same time, but six anthers within a flower of E. inderiensis presented pollens one by one during about 30h; (3) the flowers of E. anisopterus do not secret the nectar, but the flowers of E. inderiensis provide the nectar to the pollinators as rewards. The volume of nectar accumulated constantly during the flowering course, and related with the length of a flower visit.3. To the E. inderiensis, E. anisopterus was visited by rare pollinators , but pollinated in high efficiency. E. anisopterus has wet stigma and the pollen presentation and stigma presentation occurred at the same time. This species is self-compatible and the pollen could be autonomously transferred to the stigma within flowers. High fruit set by hand cross pollination showed E. anisopterus had the mixed mating system. E. inderiensis has a special type of'wet'stigma, where a secretion accumulates under the cuticle. When the cuticle rupture, the secretion was released and the stigma acquired the receptivity. This species has the outcrossing mating-system and the fertilization depend on the insect pollination. Synchronous pollen presentation of E. anisopterus should be a strategy to insure reproductive success under the early spring in desert where the pollinators are unreliable and efficient at delivering the pollen they remove. The gradual pollen presentation of E. inderiensis should be related with the abundant pollinator and inefficient at delivering the pollen they remove. The results supported PPT (Pollen presentation theory).4. There were two kinds of individual plants in population of E. anisopterus, individual plants had both female and hermaphrodite flowers and individual plants only hermaphrodite flowers. Gynomonoecy sexual system in E. anisopterus was size-dependent, and the number of female flowers in an individual plant was positive correlate with number of leaves, dry weights of leaves, length inflorescence, and total flowers in an inflorescence. The female flowers located at the base, bloomed earliest in an inflorescence and were significant bigger than hermaphrodite flowers. There was non significant difference on the fruit-set percentage between female flowers and hermaphrodite flowers, but seed-set percentage of female was significant higher than that of perfect flowers. Hand cross-pollination could improve the fruit-set ratio and S/O significantly. Adaptive advantages of size-dependent gynomonoecious in E. anisopterus might be a strategy to enhance fitness of individuals by allocated more resources to female function and sired more outcrossing offspring under ensuring certain number of offspring.5. The fruit-set pattern of E. inderiensis was studied and the results showed: (1) fruit-set percentage was highest for ?owers opened in the beginning of the blooming season, followed by the flowers in the middle of flowering season, and the lowest fruit-set was the flowers in the late blooming season. (2) the floral display size was largest in middle blooming season and small in both early and late blooming season. Fruit-set percentage was positively correlated with floral display size. (3) the weather condition influenced the floral display size and frequency of insect visitation, and therefore exerted an influence on fruit-set. (4) fruit-set percentage had no significantly correlated with length of inflorescence and total number of flowers in an inflorescence. (5) the number of pollens, P/O, fruit-set percentage and seed-set percentage between flowers at bottom and in the middle of the inflorescence did not exist the significant differences, but significant higher than those of the flowers at top of the inflorescence. These results indicated that the fruit set of the flowers on the top of the inflorescence were limited by resources more easily. The low fruit-set of the flowers on the top of the inflorescence might be the result of selective abortion and one of strategies to desert environment.