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Asymmetries of reproductive isolation are reflected in directionalities of hybridization: Integrative evidence on the complexity of species boundaries


Keller, Barbara; Ganz, Rita; Mora-Carrera, Emiliano; Nowak, Michael D; Theodoridis, Spyros; Koutroumpa, Konstantina; Conti, Elena (2020). Asymmetries of reproductive isolation are reflected in directionalities of hybridization: Integrative evidence on the complexity of species boundaries. New Phytologist:Epub ahead of print.

Abstract

The complex nature of species boundaries has been a central topic in evolutionary biology ever since Darwin. Despite numerous separate studies on reproductive isolation and hybridization, their relationship remains underinvestigated. Are the strengths and asymmetries of reproductive barriers reflected in the extent and directionalities of interspecific genetic exchange?
We combined field, experimental, and molecular data to quantify strengths and asymmetries of sympatric reproductive barriers and hybridization between florally heteromorphic primroses. We also assessed whether generalist pollinators discriminate between different floral cues and contribute to reproductive isolation, a long‐debated topic.
Sympatric reproductive isolation is high but incomplete, and most phenotypic intermediates are genetic F1 hybrids, whereas backcrosses are rare, revealing low interspecific gene flow. Species integrity rests on multiple barriers, but ethological isolation is among the strongest, demonstrating that even generalist pollinators crucially contribute to the maintenance of species boundaries. Furthermore, reproductive barriers are weaker for Primula veris and short‐styled plants, results corroborated by molecular data. Thus, in florally heteromorphic systems, both species‐ and morph‐dependent asymmetries affect permeability of species boundaries.
Our study illustrates how the interactions between complex floral syndromes and pollinators shape species boundaries in unique, previously undescribed ways.

Abstract

The complex nature of species boundaries has been a central topic in evolutionary biology ever since Darwin. Despite numerous separate studies on reproductive isolation and hybridization, their relationship remains underinvestigated. Are the strengths and asymmetries of reproductive barriers reflected in the extent and directionalities of interspecific genetic exchange?
We combined field, experimental, and molecular data to quantify strengths and asymmetries of sympatric reproductive barriers and hybridization between florally heteromorphic primroses. We also assessed whether generalist pollinators discriminate between different floral cues and contribute to reproductive isolation, a long‐debated topic.
Sympatric reproductive isolation is high but incomplete, and most phenotypic intermediates are genetic F1 hybrids, whereas backcrosses are rare, revealing low interspecific gene flow. Species integrity rests on multiple barriers, but ethological isolation is among the strongest, demonstrating that even generalist pollinators crucially contribute to the maintenance of species boundaries. Furthermore, reproductive barriers are weaker for Primula veris and short‐styled plants, results corroborated by molecular data. Thus, in florally heteromorphic systems, both species‐ and morph‐dependent asymmetries affect permeability of species boundaries.
Our study illustrates how the interactions between complex floral syndromes and pollinators shape species boundaries in unique, previously undescribed ways.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Systematic and Evolutionary Botany
07 Faculty of Science > Zurich-Basel Plant Science Center
Dewey Decimal Classification:580 Plants (Botany)
Uncontrolled Keywords:Plant Science, Physiology
Language:English
Date:6 August 2020
Deposited On:09 Sep 2020 15:04
Last Modified:09 Sep 2020 15:04
Publisher:Wiley-Blackwell Publishing, Inc.
ISSN:0028-646X
Additional Information:This is the peer reviewed version of the following article: Keller, B., Ganz, R., Mora‐Carrera, E., Nowak, M.D., Theodoridis, S., Koutroumpa, K. and Conti, E. (2020), Asymmetries of reproductive isolation are reflected in directionalities of hybridization: integrative evidence on the complexity of species boundaries. New Phytol., which has been published in final form at https://doi.org/10.1111/nph.16849. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. (http://www.wileyauthors.com/self-archiving)
OA Status:Closed
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1111/nph.16849

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