Journal Article

Corolla morphology influences diversification rates in bifid toadflaxes (Linaria sect. Versicolores)

Mario Fernández-Mazuecos, José Luis Blanco-Pastor, José M. Gómez and Pablo Vargas

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 112, issue 9, pages 1705-1722
Published in print December 2013 | ISSN: 0305-7364
Published online October 2013 | e-ISSN: 1095-8290 | DOI: https://dx.doi.org/10.1093/aob/mct214
Corolla morphology influences diversification rates in bifid toadflaxes (Linaria sect. Versicolores)

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Background and Aims

The role of flower specialization in plant speciation and evolution remains controversial. In this study the evolution of flower traits restricting access to pollinators was analysed in the bifid toadflaxes (Linaria sect. Versicolores), a monophyletic group of ∼30 species and subspecies with highly specialized corollas.

Methods

A time-calibrated phylogeny based on both nuclear and plastid DNA sequences was obtained using a coalescent-based method, and flower morphology was characterized by means of morphometric analyses. Directional trends in flower shape evolution and trait-dependent diversification rates were jointly analysed using recently developed methods, and morphological shifts were reconstructed along the phylogeny. Pollinator surveys were conducted for a representative sample of species.

Key Results

A restrictive character state (narrow corolla tube) was reconstructed in the most recent common ancestor of Linaria sect. Versicolores. After its early loss in the most species-rich clade, this character state has been convergently reacquired in multiple lineages of this clade in recent times, yet it seems to have exerted a negative influence on diversification rates. Comparative analyses and pollinator surveys suggest that the narrow- and broad-tubed flowers are evolutionary optima representing divergent strategies of pollen placement on nectar-feeding insects.

Conclusions

The results confirm that different forms of floral specialization can lead to dissimilar evolutionary success in terms of diversification. It is additionally suggested that opposing individual-level and species-level selection pressures may have driven the evolution of pollinator-restrictive traits in bifid toadflaxes.

Keywords: Convergence; flower specialization; trait-dependent diversification; species selection; pollination; speciation; reversal; nectar spur; flower tube; toadflax; Linaria sect. Versicolores

Journal Article.  11228 words.  Illustrated.

Subjects: Plant Reproduction and Propagation

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