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Relationships between morphological variation trends in individuals of the genus Hegeter and several environmental variables of altitudinal sites were investigated. Classification (UPGMA) and ordination (PCA) techniques were used to examine these data. Several grouping trends showing high taxonomic variability were observed, although some dominance by individuals of certain species was found in each group. The major trend was related to body size (robust bodies) especially with the dimensions of the abdomen (subelytral capsule) and legs (ambulation) and was conditioned by temperature and broad soil types (xeric habitats). The second trend (broad bodies) was related to burrowing habits and was influenced by rainfall, vegetational parameters and soil carbon and organic matter content (moist habitats). Climatic and edaphic variables are factors limiting both growth of populations and evolutionary change in these detritivorous darkling beetles and co-occurring individuals of these species show the same adaptations to the environment. (C) 2000 Academic Press.