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Floral isolation is the main reproductive barrier among closely related sexually deceptive orchids


Xu, S; Schlüter, P M; Scopece, G; Breitkopf, H; Gross, K; Cozzolino, S; Schiestl, F P (2011). Floral isolation is the main reproductive barrier among closely related sexually deceptive orchids. Evolution, 65(9):2606-2620.

Abstract

Floral isolation is an important component of pollinator-driven speciation. However, up to now, only a few studies have quantified its strength and relative contribution to total reproductive isolation. In this study, we quantified floral isolation among three closely related, sympatric orchid species of the genus Ophrys by directly tracking pollen flow. Ophrys orchids mimic their pollinators' mating signals, and are pollinated by male insects during mating attempts. This pollination system, called sexual deception, is usually highly specific. However, whether pollinator specialization also conveys floral isolation is currently under debate. In this study, we found strong floral isolation: among 46 tracked pollen transfers in two flowering seasons, all occurred within species. Accounting for observation error rate, we estimated a floral isolation index ≥0.98 among each pair of species. Hand pollination experiments suggested that postpollination barriers were effectively absent among our study species. Genetic analysis based on AFLP markers showed a clear species clustering and very few F(1) hybrids in natural populations, providing independent evidence that strong floral isolation prevents significant interspecies gene flow. Our results provide the first direct evidence that floral isolation acts as the main reproductive barrier among closely related plant species with specialized pollination.

Floral isolation is an important component of pollinator-driven speciation. However, up to now, only a few studies have quantified its strength and relative contribution to total reproductive isolation. In this study, we quantified floral isolation among three closely related, sympatric orchid species of the genus Ophrys by directly tracking pollen flow. Ophrys orchids mimic their pollinators' mating signals, and are pollinated by male insects during mating attempts. This pollination system, called sexual deception, is usually highly specific. However, whether pollinator specialization also conveys floral isolation is currently under debate. In this study, we found strong floral isolation: among 46 tracked pollen transfers in two flowering seasons, all occurred within species. Accounting for observation error rate, we estimated a floral isolation index ≥0.98 among each pair of species. Hand pollination experiments suggested that postpollination barriers were effectively absent among our study species. Genetic analysis based on AFLP markers showed a clear species clustering and very few F(1) hybrids in natural populations, providing independent evidence that strong floral isolation prevents significant interspecies gene flow. Our results provide the first direct evidence that floral isolation acts as the main reproductive barrier among closely related plant species with specialized pollination.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute of Systematic Botany and Botanical Gardens
07 Faculty of Science > Department of Plant and Microbial Biology
Dewey Decimal Classification:580 Plants (Botany)
Language:English
Date:2011
Deposited On:06 Mar 2012 09:49
Last Modified:05 Apr 2016 15:26
Publisher:Wiley-Blackwell
ISSN:0014-3820
Publisher DOI:https://doi.org/10.1111/j.1558-5646.2011.01323.x
PubMed ID:21884059
Permanent URL: https://doi.org/10.5167/uzh-56198

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