Morphometric ratio analyses: Locomotor mode in anurans

Abstract

Current studies of anuran morphology use sacral vertebrae, hindlimbs as main predictor for locomotor modes, while forelimbs and their segments were not analysed in this context. Due the fact that the complex interplay of numerous morphological traits determines the locomotion ability of anurans, we used ratios for both fore- and hindlimbs to obtain useful information of the structural and functional properties of locomotor system. We examined patterns of variation in total length of fore-, and hindlimbs as well as sacral vertebrae width and diapophyseal expansion in order to position two locomotor modes (jumpers and walkers) in a morphological shape space. Further, we investigated patterns of variability in limbs proximal, medial and distal elements to highlight differences in intra- and inter-limb relations in two locomotor modes. Our results showed that the ratios between total hindlimb length and sacral width/diapophyseal expansion, as well as ratio between humerus and tibiofibula relate the most to locomotor modes. This implies that functional specialization in different locomotor modes is attained through modifications of ratios, not only within hindlimbs, but also through modifications of the whole integrated system, which consists of forelimb, hindlimb, and girdle elements.