A morphometric approach to the geographic variation of the terrestrial isopod species Armadillo tuberculatus (Isopoda: Oniscidea)

The terrestrial isopod species Armadillo tuberculatus Vogl, 1876 (Crustacea, Isopoda, Oniscidea) is a widely polymorphic species distributed in the south-central Aegean region (Greece) with a different morph on each island. Variation consists in coloration, size of cuticular tubercules, shape of telson and the shape of the male first pleopod exopodite (secondary sexual character of taxonomic importance). We studied the allometric growth of a cuticular tubercule in 17 populations (for both male and female individuals) and the shape variation of the first male pleopod exopodite in 10 populations using Elliptic Fourier Analysis, in order to test for patterns of intraspecific variation and possible relationships between morphs. In addition, Thin Plate Spline analysis was used for the calculation of the minimum bending energy between different exopodite shapes, which was then used for estimating the minimum spanning network (MSN) connecting them. The different allometric growth rates of the tubercule among island groups were significantly related to island latitude and climatic factors. On the other hand, the clustering of islands and the MSN based on male exopodite shape differences were not related to the palaeogeography of the Aegean region or to the present geographic distances of islands. These results are interpreted as evidence for non-adaptive radiation of the morphs.