Sources
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Pollen tube attrition (Poster) 060713 copy

Published on: Mar 4, 2016
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Transcripts - Pollen tube attrition (Poster) 060713 copy

  • 1. Sources  of  varia-on  in  pollen  deposi-on  and  pollen  tube  a4ri-on  in  two  Clarkia  species:  the  effects  of  style  length  and  seasonal  -ming   Arrash  Moghaddasi,  Brandon  Wallace,  Alexandra  Bello,  Alisa  Hove,  and  Susan  J.  Mazer   Department  of  Ecology,  Evolu-on  and  Marine  Biology,  UCSB   Introduction Due to their sessile nature, plants differ from animals in that plants cannot actively choose their mates. Nevertheless, after pollination, male gametophytes may compete with each other to reach the base of the style, and male-female interactions may influence which pollen tubes are most likely to succeed in reaching the ovary and in fertilizing the ovules. Pollen tube attrition — or rate of failure of pollen grains or pollen tubes to reach the ovary — may be the result of interference among competing pollen grains (and pollen tubes) or the result of poor environmental conditions within the maternal flowers. In either case, following pollen germination, it is unlikely that all pollen grains that land on a stigma will be successful in fertilizing an ovule. In this study, we examined several intrinsic and extrinsic factors that may influence pollen attrition rates in natural populations of the annual wildflower species, Clarkia unguiculata and C. xantiana subspecies xantiana. Sources of variation were explored by asking the following questions: 1. Does style length have a significant effect on the amount of pollen received? 2. Does time of floral sampling affect the amount of pollen received or the rate of pollen tube attrition? 3. Do species differ in the patterns observed? Results The effects of style length on pollen load The relationship between pollen deposition and style length differed between species and sampling dates. Where style length predicted the number of pollen grains deposited on stigmas, however, the relationship was always positive; flowers with relatively long styles received more pollen than those with shorter styles. In C. unguiculata, style length did not have a statistically significant effect on pollen load among styles sampled in 2009 (Fig. 1A) (n = 70, r 2 = 0.0103, P = 0.403) or in early 2010 (Fig. 1B) (n = 213, r 2 = 0.0119, P = 0.112). Style length did have a significant and positive effect, however, in late 2010 (Fig. 1C) (n = 213, r 2 = 0.344, P < 0.001*). In C. xantiana ssp. xantiana, style length had a significant and positive effect on pollen load in 2009 (Fig. 1D) (n = 239, r 2 = 0.0515, P < 0.004*). In 2010, style length did not have a significant effect on pollen load early in the season (Fig. 1E) (n = 90, r 2 = 0.0211, P = 0.172), but did have a significant positive effect late in the season (Fig. 1F) (n = 172, r 2 = 0.0715, P < 0.004*). Conclusion In both taxa style length was found to have a significant positive effect on pollen load late in the season in 2010; in 2009, the relationship was positive in C. xantiana ssp. xantiana. This correlation may be due to pollinator preference for (and greater visitation of) larger flowers or by more frequent contact between floral visitors and the stigmas of longer-style flowers. Timing of style harvest was found to influence attrition rate in C. unguiculata, in which flowers harvested later in the season had higher rates of attrition from the stigma to the stigma-style junction and from the stigma to the style base. No effect on pollen tube attrition rates was found in response to the timing of style harvest in C. xantiana ssp. xantiana. To our knowledge, this is the first study to demonstrate a consistent effect of style length on pollen deposition and to detect seasonal changes in pollen attrition rate. Temporal differences in pollen tube attrition Pollen tube attrition from the stigma to the SSJ: The rate of pollen tube attrition during germination and early pollen tube growth differed between styles sampled Early vs. Late in C. unguiculata but not in C. xantiana. In C. unguiculata, the attrition rate increased significantly between samples collected Early and Late in the season (early mean = 0.579, late mean = 0.663; n = 299, r 2 = 0.0243, P = 0.0069*) (Fig 4A). There was no significant effect of harvest date on the attrition rate in C. xantiana ssp. xantiana (early mean = 0.584, late –mean = 0.554; n = 261, r 2 = 0.00309, P = 0.371) (Fig. 4B). Pollen tube attrition from the SSJ to the style base: The timing of style harvest had no significant effect on the mean attrition rate from the SSJ to the style base on either taxon (Fig. 5). There was no significant effect seen in C. unguiculata (early – mean = 0.407, late – mean = 0.372; n = 300, r 2 = 0.00374, P = 0.291) (Fig. 5A) or C. xantiana ssp. xantiana (early – mean = 0.335, late – mean = 0.318; n = 260, r 2 = 0.00108, P = 0.598) (Fig. 5B). Pollen tube attrition from the stigma to the style base: The timing of style harvest had a significant effect on pollen tube attrition over the entire length of the style in C. unguiculata (early – mean = 0.771, late – mean = 0.811; n = 299, r 2 = 0.0198, P = 0.0149*) (Fig. 6A) but not in C. xantiana ssp. xantiana (early – mean = 0.721, late – mean = 0.673 ; n = 261, r 2 = 0.00422, P = 0.2956) (Fig. 6B). Clarkia unguiculata Clarkia xantiana spp. xantiana Images courtesy of Google Dyed callose plugs at SSJ of C.x.x. sample Dyed callose plugs at style base of C.x.x. sample Considering that this was my Senior thesis project, my role was to oversee that all pollen deposition and pollen tube counts were performed. Describe your experience as a research assistant - I learned techniques that I would have never learned outside of the Mazer lab including: fluorescence microscopy, style dissection, and pollen tube staining and visualization. - I am deeply indebted to Professor Susan J. Mazer and my colleagues for committing their time to revise my thesis. - I can apply organizational and time management skills for future research endeavors. Since this was my first time performing a research project on my own, I was allowed to set my own time schedule. I think this helped me make good use of my time in the lab. Writing a thesis taught me how to write all the components that go into a real article.

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