Phenotypic and reproductive responses of an Andean violet to environmental variation across an elevational gradient

Abstract

Environmental gradients in alpine systems may lead to differences in both abiotic conditions and species interactions in very short distances. This may lead to reproductive and phenotypic changes in plants to enhance fitness in each environment. In this study, we explored how the Central Andean Viola maculata responds to the elevation gradient, where it is distributed, with an expected increase in water availability and a decrease in pollinator availability with elevation. We hypothesized that: (1) plants would be more water-stressed at low elevations; (2) investment in and success of cleistogamous flowers (closed, self-pollinated) would increase with elevation; and (3) correlation patterns between floral and vegetative traits would vary along the gradient according to changes in biotic/abiotic selection pressures across sites. We partially confirmed the inverse gradient of water stress with elevation, with V. maculata populations in the lowest site experiencing lower soil moisture and showing thicker leaves and lower stomatal conductance. Cleistogamy was more prevalent and successful at the highest site, thus confirming the hypothesis of maintenance of a mixed-mating system as reproductive assurance. Correlation patterns between flower and leaf size differed across sites, with stronger vegetative–floral correlation at the lower sites and a weak correlation at the highest site. This finding disagrees with the notion of pollinators as drivers of correlation between floral and vegetative traits. Our study shows how a narrow gradient in an alpine system may affect not only reproductive and physiological responses in plants, but also floral and vegetative covariances.