Contrasting patterns at interspecific and intraspecific levels in scorpion body size across a climatic gradient from rainforest to dryland vegetation

Body size is believed to be one of the most fundamental functional traits in animals and is evolutionarily conserved in order to guarantee the survival of the species. Besides the phylogenetic backgrounds, body size patterns might be a product of environmental filters, especially within fine taxonomic levels (i.e., within species or geographical lineages). Here, we evaluated the responses of scorpion body size at different organizational levels (inter and intraspecific) along a dry-wet climatic gradient in Brazilian forests. Scorpions were collected from 20 localities in northeastern Brazil, covering 12 sites of dry forests and eight sites in rainforest environments. As a proxy for body size, we measured the carapace length of 368 adult scorpions belonging to 11 species and applied linear mixed-effects models to investigate the potential effects of climatic features and geographical tendencies in this trait at inter- and intraspecific levels. Our findings suggest the existence of a longitudinal pattern of body size in scorpions with species becoming larger in an east-west direction (i.e., towards the continent); such geographical tendency was also detected for one of the three species analyzed at the population level. In addition, the warmer temperature had a negative effect on body size in scorpions at inter- and intraspecific levels. Based on these findings, we assert that body size in scorpions is not affected solely by their phylogenetic history, but also by the physiological constraints imposed by the environment, which becomes more evident across climatic gradients.