Morphological plasticity of an endemic widespread columnar cactus and its congener

Abstract

The morphological variation among 11 populations belonging to two endemic congener species of Neobuxbaumia, columnar cacti, was studied. One of our hypotheses was that N. mezcalaensis (Bravo) Backeb. with widespread distribution would show a higher variation of morphological characters and geographic–environmental variables compared with N. multiareolata (E.Y. Dawson) Bravo, Scheinvar & Sanchez-Mej. displaying a narrow distribution range, thus N. mezcalaensis will have a higher plasticity in some of its morphological traits. For each population, 41 morphological variables, three geographic, 10 climatic, and six soil properties were generated and analyzed by the simplified relative distance plasticity index, principal component, and regression analyses. The plasticity index across all populations for N. mezcalaensis showed more levels of plasticity than N. multiareolata in 12 variables as we expected. Principal component analysis explained 74% of the total variation. The first principal component, 47.41%, resulted from environmental differences and contributes to species separation. Difference in fruits traits and plant height was correlated with longitude (P < 0.0001) and elevation (P < 0.0001), thereby indicating a steep clinal decrease in fruit size and plant height from east to west as well as with the increase of elevation (P < 0.0001). Moreover, this variation negatively correlated with the mean temperature of the driest quarter (P < 0.0001) and annual precipitation (P < 0.0001), thereby indicating also a steep clinal decrease from east to west in N. mezcalaensis, the species with widespread distribution. The vegetative characters show that plasticity could be influenced by geographic, climatic, and edaphic variables, while the reproductive characters are probably genetically fixed because no significant variation was detected.