Morphological clines in reduced areas. The case of Henrotius jordai (Reitter), cave-dwelling beetle from Majorca Island

The present paper shows a statistically significant correlation between the geographical latitude and the morphological variation of the pronotum of Henrotius jordai (Reitter) (Col. Caraboidea), cave-dwelling beetle from Majorca island, after studying the linear and curvilinear regression between these two variables. The existence of specimens situated at different heights of the regression lines leads to the conclusion that morphological variation is clinal. The phenomenon of “semi-isolation” to which the studied populations are subjected, because of their cavernicolous character, allows to explain the existence of a cline in such a restricted area as that occupied by this beetle (ca. 500 Km2). It is worth pointing out the interest in the study of these reduced clines of cavernicolous populations, because they can provide a restricted “observation field” - easier to deal with - to investigate these genetic phenomena and their evolutive implications