Pollen limitation in a dioecious seagrass: evidence from a field experiment

Abstract

Pollen limitation is relatively common in plants pollinated by animals, but whether pollen availability may limit the reproduction of water-pollinated plants is much less known. We investigated pollen production and possible limitation of pollen availability in the hydrophilous dioecious seagrass Thalassia testudinum in an area where flowering was abundant (20 to 33% of the shoots produced flowers annually). Fruit production decreased from 86 to 60% after experimental removal of half of the male flowers (estimated pollen:ovule ratio of 6.7 × 10 4 :1) during April 2008. In late April to May 2009, when male flowers were less abundant than in the previous year (at a pollen:ovule ratio of 3.7 × 10 4 :1), artificial pollination resulted in an increase in fruit production from 65% in control flowers to 91% in the treated flowers in the same plot. This study is the first experimental evidence of pollen limitation in a dioecious plant with hydrophilous pollination.

Meso-fauna foraging on seagrass pollen may serve in marine zoophilous pollination

“…Negative consequences of the pollen consumption for the reproductive success of the seagrass were most likely insignificant. Thalassia testudinum suffered from pollen limitation after experimental reduction of male flowers at this site (Van Tussenbroek et al 2010). However, the flowers produced a large number of pollen grains (on average 1.6 × 10 5 grains flower −1…”

Where a male is hard to find: consequences of male rarity in the surfgrass Phyllospadix torreyi

“…Although the pollen load required for fertilization in Phyllospadix torreyi is unknown, it has one of the largest pollen:ovule ratios among plants (1.8 × 10 4 to 2.5 × 10 4 :1; Williams 1995). For comparison, Van Tussenbroek et al (2010) found that 6.7 × 10 4 pollen per ovule were required for optimal fertilization of the dioecious aquatic angiosperm Thalassia testudinum. Also, 1000 to 10 000 pollen grains were needed to fertilize 1 Zostera marina ovule (Ackerman 2002).…”

“…Among plants with abiotic pollination, nearly all reports address anemophilous plants. How aquatic plants adjust to pollen-limited conditions is an area that has received little attention to date; to our knowledge, only a few studies have examined the causes and consequences of reproductive failure in dioecious hydrophilous, or water-pollinated, plants (Shelton 2008, 2010c, Van Tussenbroek et al 2010). …”

“…They are highly specialized plants with uniquely evolved functional morphologies such as reduced flowers that facilitate submarine pollination (Ackerman 2006). While such adaptations promote pollination and fertilization, reproductive success and outcrossing rates in hydrophilic plants are also influenced by physical factors (depth and currents; Ackerman 2000) and density of flowering shoots (Reusch 2003, Van Tussenbroek et al 2010. Reproductive success of some dioecious seagrass species, measured as fraction of fertilized ovules, is well below the potential maximum of 1.0 (Shelton 2008, Van Tussenbroek et al 2010.…”

“…While such adaptations promote pollination and fertilization, reproductive success and outcrossing rates in hydrophilic plants are also influenced by physical factors (depth and currents; Ackerman 2000) and density of flowering shoots (Reusch 2003, Van Tussenbroek et al 2010. Reproductive success of some dioecious seagrass species, measured as fraction of fertilized ovules, is well below the potential maximum of 1.0 (Shelton 2008, Van Tussenbroek et al 2010. Much of seagrass reproduction is clonal, yet sexual reproduction appears to be important based on evidence of high outcrossing rates for a variety of seagrass species (Reusch 2000, Waycott et al 2006).…”