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Do visual traits honestly signal floral rewards at community level?

Citation

Ortiz, Pedro Luis et al. (2020), Do visual traits honestly signal floral rewards at community level?, Dryad, Dataset, https://doi.org/10.5061/dryad.pg4f4qrn4

Abstract

1. The high variability observed in floral traits has been interpreted as resulting from the adaptation of plants to pollinators, as the latter present innate preferences for specific floral traits and impose selection over them. However, some pollinators such as bees can learn to associate floral signals with rewards, thus increasing floral constancy on more rewarding flowers. The integration of all these rewards and cues is markedly important at community level, where co-flowering species compete for pollinators. 2. In order to verify the honesty of the above mentioned signals, we examined the association between floral visual signals (size, colour, symmetry and floral display) and rewards (pollen and nectar) for 98 species in a Mediterranean community. The associations between floral traits were analysed considering the phylogenetic relationship between the different species. 3. Flower colour, size, pollen volume, or amount of sucrose exhibited no phylogenetic signal, which suggests an adaptive evolution in response to different conditions in the pollinator community. Flower size was seen to constitute the most honest signal for pollinators, as this was significantly associated with quantities of pollen and nectar. In contrast, nectar concentration was observed to be positively associated with chromatic contrast. We detected no relationship between flower shape and rewards, on the one hand, or between flower display and rewards, on the other. 4. Our study unequivocally demonstrates the correlation between rewards and the visual signals perceived by bees, the most effective pollinators in the Mediterranean Basin. In the community studied, bees employed flower size at longer distances and chromatic contrast at shorter distances to predict rewards. The limited number of studies existing in this sense indicates that this kind of association appears to be community specific.

Methods

The dataset includes measures of floral reward production and visual floral traits of 98 species in a Mediterranean community. For reward production data we profited from two earlier extensive studies on nectar and pollen production in the same community (Ortiz, 1991; Talavera, Herrera, Arroyo, Devesa, & Ortiz, 1988) and, for species not included in those studies, we assessed reward production following the same procedures employed therein in such a way that both datasets were comparable. For data on floral size and symmetry we used the Flora Vascular de Andalucía Occidental by Valdés, Talavera & Fernández-Galiano (1987). We estimated floral display size as the number of flowers at anthesis of a plant at its peak of flowering. For floral colour data, we used a spectrometer to obtain spectral reflection functions of petals, and from those functions, we calculated reflectance amplitude and spectral purity. We also plotted those spectral functions in the bee vision model by Chittka (1992) to calculate the remainders colour parameters: green contrast, brightness contrast, chromatic contrast, X and Y coordinates in the model, and bee colour.

References

- Chittka, L. (1992). The colour hexagon: a chromaticity diagram based on photoreceptor excitations as a generalized representation of colour opponency. Journal of Comparative Physiology A, 5, 533–543. doi: https://doi.org/10.1007/BF00199331.

- Ortiz, P. L. (1991). Melitopalinología en Andalucía Occidental. Tesis Doctoral en Microfichas. Sevilla: Universidad de Sevilla.

- Talavera, S., Herrera, J., Arroyo, J., Devesa, J. A., & Ortiz, P. L. (1988). Estudio de la flora apícola de Andalucia Occidental. Lagascalia, 15(1), 567–592.

- Valdés, B., Talavera, S., & Fernández-Galiano, E. (1987). Flora Vascular de Andalucía Occidental. Barcelona: Ketres Editora.

 

Usage Notes

All figures represent mean values for each species. We assessed floral display size only in a subset of the studied species, and there are some missing data for reward production and flower size.