DIFFERENTIAL SELECTION FOR CARNIVORY TRAITS ALONG AN ENVIRONMENTAL GRADIENT IN PINGUICULA MORANENSIS

E-ISSN： 1939-9170|86|10|2652-2660

ISSN： 0012-9658

Source： Ecology, Vol.86, Iss.10, 2005-10, pp. : 2652-2660

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Abstract

The evolution of carnivory in plants is generally interpreted as an adaptation to colonize nutrient‐poor environments. Because the photosynthetic costs associated with this habit are elevated, the selective advantages of carnivory should vary depending on the balance between light, moisture, and nutrient (prey) availability. Here we test whether the patterns of selection operating on the carnivorous habit of Pinguicula moranensis change among four populations located along an environmental gradient for soil nitrogen and prey availability, photosynthetically active radiation, and moisture, and whether or not these changes are in accordance with adaptive expectations. We characterized the phenotypic variation in two carnivory‐related attributes (the densities of capture and digestive glands) and their relationship with the efficiency and the fitness benefit of prey capture along the environmental gradient. Finally, we compared the selective dynamics operating on the carnivorous habit along the environmental gradient by means of path analyses. Both the efficiency and the benefit of carnivory varied among populations and peaked at habitats characterized by a marked nutrient limitation and high levels of irradiance. We also found evidence of adaptive differentiation among populations. Natural selection favored the allocation to capture glands in nitrogen‐poor (soil or prey derived) environments, while investment in digestive glands was more advantageous in nitrogen‐rich habitats. Carnivory was subject to a heterogeneous regime of selection along the environmental gradient that was tightly associated with both abiotic factors and prey availability.