Bioclimatic variables affect seed mass and seedling traits of four Gymnocalycium (Cactaceae) species along elevational gradients

Abstract

Differences in climatic factors associated with elevation can lead to natural selection for local adaptation in species with a wide distribution range, with some regenerative characteristics changing along the gradient. Most Cactaceae species occur in heterogeneous environments, mainly in mountains. The increasing severity of environmental conditions along elevational gradients could affect seed size, influencing seedling growth. The main aims of the study were to analyse whether seed mass, and seedling size and shape are related to elevational gradients in different populations of four species of the genus Gymnocalycium and to evaluate the relationship between seed mass and bioclimatic variables. Populations of four species of Gymnocalycium (G. andreae, G. erinaceum, G. monvillei and G. mostii) were sampled; the populations were located along three different elevation gradients, with each population corresponding to an elevational class (extremes and intermediate sites). At each elevational site, mature fruits were collected and seed mass and seedling traits were measured. A shape index was calculated by dividing height by width. A value of 1 represents 'globose' seedlings, while increasing values indicate that the seedlings become 'columnar'. The Pearson correlation coefficient was calculated to analyse the relationship between seed mass and seedling size variables. Linear models were used to analyse seed size and seedling shape. First, with elevation as a predictor and then for seed mass, the 19 bioclimatic variables were extracted from WorldClim. The results show that seed mass was positively correlated with seedling shape index, and with seedling height and width. Differences in seed mass among populations were explained by the species and the gradient where they lived, as well as by the environmental variables mean temperature of the coldest quarter, precipitation of the wettest month, and precipitation of the driest month. In conclusion, the intraspecific analyses of the four Gymnocalycium species revealed that the seedling shape patterns were similar across all species in relation to elevation. However, seed mass varied with elevation differently for each species. These findings suggest that each species possesses unique characteristics that enable them to thrive in varying climatic conditions along elevational gradients.