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AERODYNAMICS AND POLLEN ULTRASTRUCTURE IN EPHEDRA
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
2015 (English)In: American Journal of Botany, ISSN 0002-9122, E-ISSN 1537-2197, Vol. 102, no 3, 457-470 p.Article in journal (Refereed) Published
Abstract [en]

Premise of the study: Pollen dispersal is affected by the terminal settling velocity (U-t) of the grains, which is determined by their size, bulk density, and by atmospheric conditions. The likelihood that wind-dispersed pollen is captured by ovulate organs is influenced by the aerodynamic environment created around and by ovulate organs. We investigated pollen ultrastructure and U-t of Ephedra foeminea (purported to be entomophilous), and simulated the capture efficiency of its ovules. Results were compared with those from previously studied anemophilous Ephedra species. Methods: U-t was determined using stroboscopic photography of pollen in free fall. The acceleration field around an average ovule was calculated, and inflight behavior of pollen grains was predicted using computer simulations. Pollen morphology and ultrastructure were investigated using SEM and STEM. Key results: Pollen wall ultrastructure was correlated with U-t in Ephedra. The relative proportion and amount of granules in the infratectum determine pollen bulk densities, and (together with overall size) determine U-t and thus dispersal capability. Computer simulations failed to reveal any functional traits favoring anemophilous pollen capture in E. foeminea. Conclusion: The fast U-t and dense ultrastructure of E. foeminea pollen are consistent with functional traits that distinguish entomophilous species from anemophilous species. In anemophilous Ephedra species, ovulate organs create an aerodynamic microenvironment that directs airborne pollen to the pollination drops. In E. foeminea, no such microenvironment is created. Ephedroid palynomorphs from the Cretaceous share the ultrastructural characteristics of E. foeminea, and at least some may, therefore, have been produced by insect-pollinated plants.

Place, publisher, year, edition, pages
2015. Vol. 102, no 3, 457-470 p.
Keyword [en]
anemophily, entomophily, Gnetales, granular infratectum, pollen morphology, pollination, scanning electron microscopy, scanning transmission electron microscopy, Welwitschia
National Category
Biological Sciences
Research subject
Plant Systematics
Identifiers
URN: urn:nbn:se:su:diva-116636DOI: 10.3732/ajb.1400517ISI: 000351208000015PubMedID: 25784479OAI: oai:DiVA.org:su-116636DiVA: diva2:807177
Note

AuthorCount:3;

Available from: 2015-04-22 Created: 2015-04-22 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Pollen and pollination in Ephedra (Gnetales)
Open this publication in new window or tab >>Pollen and pollination in Ephedra (Gnetales)
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Ephedra (Gnetales) is a gymnosperm genus with a long evolutionary history; the first dispersed pollen grains with affinity to the group are known already from the Permian. This thesis focuses on the evolutionary history of the group and different aspects of its pollination mechanisms. Despite the limited number of extant species of the genus (50-60), and a low morphological and genetic divergence among species, there is variation in pollination syndrome in the genus. The prevailing state in Ephedra, and most gymnosperms, is wind pollination. It is therefore surprising that one species, E. foeminea, is insect-pollinated. Together with co-workers I documented the pollination syndromes of E. foeminea and a sympatric species, E. distachya, based on long term field experiments in north-eastern Greece and aerodynamic investigations and calculations. Placing the results into an evolutionary framework reveals that the insect-pollinated species E. foeminea is sister to the remaining (mostly wind-pollinated) genus, and indicates that insect pollination is the ancestral state in the Gnetales. During the course of evolution of the group there has been a shift to wind pollination, which may have played a crucial role for the diversification of the crown group in the Paleogene. Pollination biology is often correlated with the morphology of the pollen such that pollen grains of anemophilous plants are small with a smooth surface, whereas pollen grains of entomophilous plants are larger with an ornamented surface and a covering of pollenkitt. The pollen morphology of Ephedra can be broadly divided into two types: an ancestral type with an unbranched pseudosulcus between each pair of plicae, and a derived type with a branched pseudosulcus between each pair of plicae. Further, the pollen morphology and ultrastructure of the pollen wall in Ephedra are to some degree correlated with the pollination syndrome and capability of long distance dispersal. Pollen of E. foeminea has a denser ultrastructure, as a result a higher settling velocity and is therefore capable of flying shorter distances than does pollen of the anemophilous E. distachya, and other investigated anemophilous species that show a more spacious ultrastructure of the pollen grain. These results can be useful in the reconstruction of the pollination mechanism of extinct taxa of the Ephedra-lineage in the future.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University, 2017. 46 p.
Keyword
aerodynamics, evolution, moonlight, pollination, pollen morphology, ultrastructure
National Category
Evolutionary Biology Botany
Research subject
Plant Systematics
Identifiers
urn:nbn:se:su:diva-140771 (URN)978-91-7649-774-6 (ISBN)978-91-7649-775-3 (ISBN)
Public defence
2017-05-19, Vivi Täckholmsalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20, Stockholm, 10:00 (English)
Opponent
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Available from: 2017-04-26 Created: 2017-03-16 Last updated: 2017-04-03Bibliographically approved

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