Evidence map›Paper›PMID 42466848›Full record

ArticleAnnals of botany2026

Breakdown of dimorphic enantiostyly is linked to reduced herkogamy and increased self-pollination.

Sam McCarren, Spencer C H Barrett, Alice L M Fairnie, Sinéad Watchorn, Bruce Anderson, Nicola Illing, Robert A Ingle

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Article in Annals of botany, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.

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4 · The record

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5 · Who and what money

Authors and funding

7 authors.

Sam McCarrenDepartment of Molecular and Cell Biology, University of Cape Town, Cape Town 7701, South Africa.ORCID 0000-0002-3861-0811
Spencer C H BarrettDepartment of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario M5S 3B2, Canada.ORCID 0000-0002-7762-3455
Alice L M FairnieDepartment of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario M5S 3B2, Canada.
Sinéad WatchornPaleo-Research Institute, University of Johannesburg, Johannesburg 2092, South Africa.
Bruce AndersonDepartment of Botany and Zoology, Stellenbosch University, Stellenbosch 7602, South Africa.ORCID 0000-0002-7264-4505
Nicola IllingDepartment of Molecular and Cell Biology, University of Cape Town, Cape Town 7701, South Africa.ORCID 0000-0002-7322-4713
Robert A IngleDepartment of Molecular and Cell Biology, University of Cape Town, Cape Town 7701, South Africa.ORCID 0000-0002-8362-3777

Funding

Memorial Botanical Fellowshipthe International Human Frontiers Science Programme
6 · The paper itself

Abstract

BACKGROUND AND

aimsThe evolutionary breakdown of outcrossing mechanisms has occurred repeatedly across angiosperm lineages. Stylar polymorphisms are of particular interest because their floral morphs exhibit discrete variation with pronounced spatial separation between reproductive organs (herkogamy), a trait strongly influencing outcrossing. These polymorphisms are typically maintained by negative frequency-dependent selection resulting from disassortative (between-morph) mating. In contrast, biased morph ratios and homostylous variants with anthers and stigmas adjacent to one another often signal transitions towards self-fertilization and erosion of the polymorphism. Here, we investigate this transition in three Wachendorfia species that exhibit dimorphic enantiostyly. Based on observations of biased morph ratios, we predicted the breakdown of enantiostyly to be associated with reduced herkogamy and an increased likelihood of self-pollination.

methodsTo test this hypothesis, we quantified morph ratios and reproductive-organ separation across 42 populations spanning the three species. In a subset of populations, we also measured flower width, pollinator visitation, seed set and pollen transfer to examine their association with floral polymorphism breakdown. KEY

resultsPopulations with equal morph ratios typically exhibited well-developed herkogamy, consistent with disassortative mating. In contrast, reduced herkogamy, increasing the potential for autonomous self-pollination, was characteristic of populations with biased ratios or those that were monomorphic. Homostylous variants occurred in all three species and were characteristic of populations with low herkogamy and biased morph ratios as expected during early stages in the evolutionary modification of stylar polymorphism.

conclusionsOur investigation revealed that the breakdown of outcrossing polymorphisms is not restricted to heterostylous species but also occurs in species with mirror-image flowers. In both cases of breakdown, the proximate mechanism causing increased self-pollination involves changes in herkogamy, emphasizing the importance of this key reproductive trait in influencing mating-system evolution.

Indexed as

FlowersPollinationSelf-FertilizationBiological EvolutionPolymorphism, GeneticReproductionDisassortative pollinationhomostylymirror-image flowersquantum dotreproductive assuranceselfingstylar polymorphismWachendorfia

Identifiers

PMID42466848
PMCPMC13595285

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