Journal Article

Decrease of sexual organ reciprocity between heterostylous primrose species, with possible functional and evolutionary implications

Barbara Keller, Jurriaan M. de Vos and Elena Conti

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 110, issue 6, pages 1233-1244
Published in print November 2012 | ISSN: 0305-7364
Published online September 2012 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcs199
Decrease of sexual organ reciprocity between heterostylous primrose species, with possible functional and evolutionary implications

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  • Ecology and Conservation
  • Evolutionary Biology
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Background and Aims

Heterostyly is a floral polymorphism that has fascinated evolutionary biologists since Darwin's seminal studies on primroses. The main morphological characteristic of heterostyly is the reciprocal placement of anthers and stigmas in two distinct (distyly) floral morphs. Variation in the degree of intermorph sexual reciprocity is relatively common and known to affect patterns of pollen transfer within species. However, the partitioning of sexual organ reciprocity within and between closely related species remains unknown. This study aimed at testing whether intermorph sexual reciprocity differs within vs. between primrose species that hybridize in nature and whether the positions of sexual organs are correlated with other floral traits.

Methods

Six floral traits were measured in both floral morphs of 15 allopatric populations of Primula elatior, P. veris and P. vulgaris, and anther–stigma reciprocity was estimated within and between species. A combination of univariate and multivariate approaches was used to test whether positions of reproductive organs were less reciprocal between than within species, to assess correlations between sexual organ positions and other corolla traits, and to quantify differences between morphs and species.

Key Results

The three species were morphologically well differentiated in most floral traits, except that P. veris and P. vulgaris did not differ significantly in sexual organ positions. Overall, lower interspecific than intraspecific sexual organ reciprocity was detected. This decrease was marked between P. elatior and P. vulgaris, intermediate and variable between P. elatior and P. veris, but negligible between P. veris and P. vulgaris.

Conclusions

Differences in anther and stigma heights between the analysed primrose species were of the same magnitude or larger than intraspecific differences that altered pollen flow within other heterostylous systems. Therefore, it is possible to suggest that considerable reductions of sexual organ reciprocity between species may lower interspecific pollen flow, with potential effects on reproductive isolation.

Keywords: reciprocal herkogamy; sexual organ reciprocity; Primula; primrose; distyly; heterostyly; floral morphology; hybridization; reproductive isolation; pollen flow; pre-mating barriers; speciation

Journal Article.  8975 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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