Abiotic factors may explain the geographical distribution of flower colour morphs and the maintenance of colour polymorphism in the scarlet pimpernel

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Summary

  1. Flower colour polymorphism is traditionally attributed to pollinator selection although other factors, such as indirect selection on correlated traits, can play an important role.
  2. Lysimachia arvensis is a widespread annual species with two colour morphs differing in anthocyanin composition. We explored the hypothesis that colour polymorphism is maintained by selection related to environmental heterogeneity. Morph frequencies and environmental traits were recorded in 51 populations along a wide geographical range. To explore the existence of morph-by-environment interactions, we conducted an experimental study comparing the two morphs under treatments differing in water and light availability.
  3. A geographical pattern was found with a negative association between blue frequencies and latitude. The proportion of the blue morph increased with temperature and sunshine hours, but decreased with precipitation. Flowering onset and flower size differed between morphs and scarcely varied across treatments. In contrast, several fitness components such as germination, seedling survival, seedling mass and flower production showed important morph-by-environment interactions. The blue morph showed higher overall male and female fitness in all the treatment combinations excepting in sun-wet conditions where the red morph had higher fitness.
  4. Synthesis. Our results indicate that the mechanism of selection on flower colour seems to be related to differences in fitness of both morphs due to abiotic factors. These differences could explain the geographical distribution of flower colour morphs and the maintenance of the colour polymorphism. The marked difference in flowering time between morphs leaves open the potential for assortative mating and speciation in Lysimachia arvensis.

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