Effects of floral diversity and pollinator behaviour on the persistence of hybrid zones between plants sharing pollinators

Abstract

Background: Plant hybrid zones often display a large diversity in floral traits due to segregation and recombination occurring in the second and later hybrid generations. Such diversity can have important effects on pollinator behaviour.

Aims: We hypothesised that the number of floral types and their relative densities may influence pollinator preferences and level of flower constancy.

Methods: To test the influence of floral diversity on the number of visits to inflorescences of the most common type and on the level of flower constancy, we monitored bumblebees’ behaviour in experimental arrays of artificial inflorescences with a common (‘parental’) floral type mixed with either one or three uncommon (‘hybrid’) floral types.

Results: We found that pollinators preferentially visited the most common flower colour and showed slightly greater constancy when the number of uncommon floral types was increased.

Conclusions: We conclude that diversity in flower colour could promote moderate pollinator constancy in some types of hybrid zones. Segregation of floral phenotypes due to hybridisation may result in small levels of pollinator-mediated assortative mating and contribute, to a small extent, and most probably in combination with other factors, to the persistence of some hybrid zones.

Keywords:

• Antirrhinum
• artificial flowers
• ethological isolation
• flower colour diversity
• flower constancy
• hybrid zone

Acknowledgements

The research was funded by CNRS and French Ministry of Research core funding to UMR 5174 CNRS - Université Paul Sabatier. The authors thank Nicolas Juillet for his help with the experimental design, Antonina Internicola for her assistance with data analyses and for providing some spectral reflectance data, Beverley Glover for interesting discussions, Martin Giurfa, Jacqui Shykoff and Nick Waser for useful comments on the manuscript. ET was supported by a MESR (Ministère de l’Enseignement Supérieur et de la Recherche) PhD scholarship. CT furthermore acknowledges support from the French Embassy in London through an overseas fellowship of Churchill College, Cambridge.

Additional information

Notes on contributors

Emmanuelle Tastard

Emmanuelle Tastard obtained her Ph.D. focussing on pollinator behaviour in response to floral environments. Her current research addresses the relation between the activity of transposable elements and environmental stresses in microalgae.

Christophe Andalo

Christophe Andalo is a plant evolutionary ecologist interested in pollination biology and the effects of global change on pollinator networks.

Monique Burrus

Monique Burrus is a plant biologist interested in population biology, insect pollination, and plant conservation.

Luc Gigord

Luc Gigord is an evolutionary ecologist interested in the evolution and functional significance of floral polymorphisms. He is currently the Director of Science at the Mascarin Botanic Garden on Réunion.

Christophe Thébaud

Christophe Thébaud is an evolutionary biologist interested in a broad range of questions relative to population differentiation and speciation.