1. Control Supplemented
If you want something done right, do it yourself: Estimating autonomous self-
fertilization in a native, self-compatible wildflower, Sabatia angularis.
Curtis Harrity and Dr. Rachel Spigler
Biology Department, Temple University
Introduction
Results
A majority of plant populations face pollen limitation, reductions in seed
production when pollinators or mates are scare, with critical implications for
population viability (Knight et al, 2005). Because most flowering plants
produce flowers containing both pollen and ovules, the opportunity to self-
pollinate exists. The ability to self-fertilize in wild flowers can provide
reproductive assurance against pollen limitation. For most species, however,
just how capable they are at self-pollinating without the aid of pollinators, i.e.
their “autofertility” is unknown.
An important consideration when measuring autofertility and similar
metrics of pollination success is that differences in seed production among
flowers may be exaggerated if plants disproportionately allocate resources to
flowers (and subsequent developing fruits) that received more or better
quality pollen. Complementary experiments should therefore be conducted to
evaluate this possibility, but have not yet been conducted within the same
species (Knight, Steets, Ashman, 2006).
The objectives of this project were therefore to:
(1) Experimentally evaluate and quantify autofertility in a native wild flower.
(2) Experimentally evaluate the potential for differential resource allocation to
influence autofertility estimates.
1. Can Sabatia angularis self-pollinate autonomously, i.e. without the help of
pollinators?
2. How does seed set from autonomous selfing compare to maximum seed
production resulting from outcross pollination (“autofertility”)?
3. How do autofertility estimates evaluated at the whole plant versus partial
plant level compare?
4. Does autofertility vary across populations?
Control Treatment (N=5 flowers/plant)
Supplemented Treatment (N=5
flowers/plant)
Experimental Approach
References
Conclusions
Sabatia angularis is a self-compatible plant capable of autonomous self-fertilization. This ability may be adaptive if it boosts seed production when pollinators or mates are scarce; however, the mechanism enabling autonomous self-pollination is currently
unknown in Sabatia angularis. The difference in autofertility estimates between the whole and partial plant studies can be attributed to the modular nature of plants. The flowers that were supplemented with outcross pollen received more pollen and thus
likely more resources than the flowers that relied on self-pollen. This together indicates that approaches should be consistent across studies in order to make quantitative comparisons.
Knight, T. M., Steets, J. A., & Ashman, T. (2006). A quantitative synthesis of pollen supplementation experiments highlights the contribution of resource reallocation to estimates of pollen
limitation. American Journal of Botany, 93(2), 271-277.
Knight, T. M., Steets, J. A., Vamosi, J. C., Mazer, S. J., Burd, M., Campbell, . . . Ashman, T. (2005). Pollen limitation of plant reproduction: Pattern and process.Annual Review of Ecology, Evolution and
Systematics, 36, 467-497.
We raised plants in a pollinator-free growth chamber and performed the following experiments:
Experiment 1: Autofertility at the whole-plant level (N=28 plants, 1 population)
Differences in autofertility estimates from whole-plant vs. partial-plant level would reveal reallocation among fruits.
Prediction: If plants reallocate resources to flowers that receive more pollen, then AFwhole-plant > Afpartial-plant
Experiment 2: Autofertility at the partial-plant level (N=30plants, 2 populations)
Because the same treatments are applied to ALL flowers on a plant,
reallocation of resources based on pollen treatment should NOT occur.
Sabatia angularis: Common Rose Pink
- Hermaphroditic, self-compatible, biennial, native
wildflower
- Protandrous: Pollen released first, then stigma
becomes receptive
- Blooms from mid-July through late-August
- Found in Serpentine Grasslands which are globally
rare environments
To calculate autofertility:
• We determined seed set as fruit mass (g) for 5-10 fruits/treatment Autofertility (AF) =
Mean Control Seed Set
Mean Supplemented Seed Set
1. Sabatia angularis is able to self-pollinate autonomously to achieve seed production (See ‘Control’ fruit mass in Figs. 1 & 2).
2. Seed production is significantly lower in control than supplemented treatments indicating self-fertilization is unable to achieve complete reproductive assurance (Figs. 1 & 2)
3. Comparisons between the whole-plant and partial-plant experiments reveal that approach matters when estimating autofertility or similar pollination metrics (Fig. 3).
Differences between treatments under the partial-plant method can be exaggerated by resource allocation within the plant. This is further reflected by elevated fruit mass
of supplemented fruits in the partial-plant experiment compared to the whole-plant (Figs. 1 & 2).
4. There was no difference in the autofertility across S. angularis populations (Fig 4).
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
Control Supplemented
AverageFruitMass(g)
Whole-Plant Pollination
t-test
P < .0001
N = 140 N = 142
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
Control Supplemented
Partial-Plant Pollination
Paired t-test
P < .0001
N = 145 N = 145
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Whole Plant Partial Plant
Autofertility
Autofertility Estimates
N = 282 N = 290
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
GFR UB5
Autofertility Between Populations
t-test
P = 0.32
N = 141 N = 149
Questions
Study species
Acknowledgements
Because only a few flowers/plant receive supplemental pollen, reallocation of
resources based on pollen treatment could occur.
Special thanks to A. Woodard, J. Hart, H. Dashnaw for helping to conduct crosses.
Figure 1 Figure 2 Figure 3 Figure 4
AverageFruitMass(g)
Autofertility
Cressler, Alan. Sabatia Angularis Crystal Cave Ridge Mammoth Cave National
Park Edmonson Co Ky 2. Digital image. Flickr. N.p., 21 July 2007. Web.