Figure 21.22 The Effect of Stigma Retraction in Monkeyflowers
The untouched, open stigma of the bush monkeyflower blocks access to the anthers. Upon pollen deposition, the stigma closes, thus providing a path to the anthers. To determine if these stigma responses favor the export of pollen, Elizabeth Fetscher set up experimental arrays. Pollen donors were: 1) control flowers with untouched, open stigmas; 2) flowers with artificially closed stigmas; or 3) flowers with permanently propped open stigmas. Results showed that pollen dispersal from control flowers was nearly twice as much as from flowers whose stigmas were propped open. Consistent with this finding, the flowers whose stigmas were artificially closed exported the most pollen. These data support the conclusion that stigma behavior increases pollen export in the bush monkeyflower. This remarkable behavior is thought to have evolved as a mechanism to reduce self-pollination. While self-pollination can be advantageous in areas where wind or animal pollination vectors are unreliable, it is typically considered to be disadvantageous, as it leads to reduced genetic variation and, consequently, reduced fitness due to the expression of recessive deleterious alleles (inbreeding depression). To directly test how the stigmatic response of the bush monkeyflower affects self-pollination, one could use genetic approaches to compare the percentage of seeds from self versus outcross pollinations between flowers that had stigmas propped open and control flowers that were free to close after being touched. If the percentage of selfed seeds was significantly higher when stigmas were propped open, then the hypothesis that the movement of the stigma reduces self-pollination would be supported.
Original Paper
Fetscher, A. E. 2001. Resolution of male-female conflict in an hermaphroditic flower. Proceedings of the Royal Society B 268: 525–529.
http://dx.doi.org/10.1098/rspb.2000.1395
Links
Fetscher, A. E., and J. R. Kohn. 1999. Stigma behavior in Mimulus aurantiacus (Scrophulariaceae). American Journal of Botany 86: 1130–1135.
http://www.amjbot.org/cgi/content/abstract/86/8/1130
Milet-Pinheiro, P., A. T. Carvalho, P. G. Kevan, and C. Schlindwein. 2009. Permanent stigma closure in Bignoniaceae: Mechanism and implications for fruit set in self-incompatible species. Flora 204: 82–88.
http://dx.doi.org/10.1016/j.flora.2007.11.006
San Diego State University: Video of stigma closure in Mimulus aurantiacus
http://www.sci.sdsu.edu/plants/plantsystematics/mimu_aura.html
UC-Berkeley: CalPhotos: Mimulus aurantiacus
http://calphotos.berkeley.edu/cgi/img_query?where-genre=Plant&where-taxon=Mimulus+aurantiacus
San Diego State University: Plant reproductive biology
http://www.sci.sdsu.edu/plants/plantsystematics/ch13.ppt
United States Department of Agriculture, Forest Service: The Birds and the Bees
http://www.fs.fed.us/wildflowers/pollinators/What_is_Pollination/birdsandbees.shtml
Kimball’s Biology Pages: Self-Incompatibility: Avoiding Inbreeding
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/SelfIncompatibilty.html
UC-Berkeley: Understanding Evolution: Inbreeding Depression
http://evolution.berkeley.edu/evosite/relevance/IIIA1Inbreeding.shtml
Landry, C. 2010. Mighty Mutualisms: The Nature of Plant–pollinator Interactions. Nature Education Knowledge 1(8): 48
http://www.nature.com/scitable/knowledge/library/mighty-mutualisms-the-nature-of-plant-pollinator-13235427