| Capparis spinosa L. is a perennial shrub with a typical andromonoecious sexual system. In this study, we compared the sexual system, floral display, pollination characteristics, breeding system and fruit and seed dispersal characteristics of this species in an arid desert of northern Xinjiang. The main results can be summarized as follows.1) The species is andromonoecious, i.e. individual plants possess both male and perfect flowers. Stamens of the two floral morphs were normal and could be divided into long and short ones in each flower. The perfect flowers had well developed pistils, but male flowers had aborted pistils and only functioned as males.2) There were significant differences (P<0.01) among the populations in day-to-day ratios of the two floral morphs in length of filaments and anthers of short stamens in male flowers, in number of long and short stamens of perfect flowers and in size of pollen grains of male flowers; however, no significant differences (P>0.05) occurred in biomass of floral parts. Anthesis was nocturnal; flowers opened in early evening and withered the next morning. Both male and perfect flowers opened about 18:00 (GMT+8) , at which time flowers emitted a spicey fragrance; nectar was secreted in the cavity of sepals. Number of two-floral morphs produced on each plant was indeterminate throughout the flowering period, thus, an individual was temporally androdioecious. However, every day of the flowering period total number of male flowers was greater than that of perfect flowers within the population.3) P/O ratios of perfect flowers in three populations studied were 1.57×10~4, 1.65×10~4 and 1.71×10~4. There was no significant difference (P>0.05) in pollen numbers within population between male and perfect flowers or between long and short stamens. Also there was no significant difference (P>0.05) among the populations in number of pollen grains of male and perfect flower or and in ovule numbers and P/O ratios of perfect flowers. Dynamic curves of pollen viability (i.e., pollen survivorship curve) of long and short stamens in the two floral morphs were similar in three populations. Pollen longevity of both long and short stamens was about 18-20h, and duration of stigmatic receptivity was about 16-18h.4) In both male and perfect flowers, nectar was secreted from the surface of nectary disc at the beginning of anthesis, and then it accumulated as a single drop in the sepal. In both flower types, nectar was visible from 18:00, when flower had just opened, until 10:00, when the flower had just closed. Rate of nectar accumulation increased from 6:00 on the following day and then declined gradually from 11: 00 until 13:00. There was no significant difference (P>0.05) in nectar production at the same time points (same time since flower opened) nor in cumulative nectar production between male and perfect flowers. In both flowers types, variation in sugar concentration in nectar showed similar patterns. Both started at a similar level and then decreased to similar levels at similar times, and they reached their highest points following a similar amount of time.5) Floral visitors to C. spinosa were hymenopterous and lepidopterous insects. There was a total of seven species of floral visitors in the three populations. Activities of these insects were greatly affected by climate of the desert environment. Pollen grains were found on the stigma of all flowers. Dyed pollen grains were not found on the stigma of three of the 11 plants that was more than 25 m away from the pollen source. No clear pattern was revealed for pollen flow, in terms of number of pollen donated and distance of pollen dispersal from the from male and perfect flowers; floral ratio also had no effects on pollen flow pattern. Plants with a large floral display, i.e., more flowers, tend to receive more pollen grains on the stigma of perfect flowers (P< 0.01).6) Perfect flowers produced fruits after self-pollination (autogamy and geitonogamy) and after cross-pollination; thus, they have a mixed mating system. Flowers that were hand-pollinated (either selfed or crossed) with pollen from a male flower produced significantly (P>0.05) more seeds per fruit than flowers hand-pollinated with pollen from perfect flowers.7) The fruits dehisce spontaneously, exposing the red pulp, which covers the seeds. The fruits and the seeds are primarily dispersed by the mouse Meriones meridianus Palls and the ant Messor clivorum Ruzs. Meriones meridianus eats and transports the fruits of C. spinosa, and most fruits were carried to the mouse's holes to a depth of 50-150cm. Messor clivorum transports the seeds, with or without pulp, to their underground nests, and seeds with pulp are transported more quickly to the nests than those without pulp. Ants transported seeds to nests 5-7 m away from the mother plant, that could decreased the degree of collection of the seeds.
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