Structural and mechanical aspects of the skin of Bufo marinus (Anura, Amphibia)

Specific biomechanical characters and some structures possibly related to t hem were investigated in the skin of the toad Bufo marinus using tensile te sting techniques (at constant strain till rupture) as well as morphological methods (histological, immunohistochemical and electronmicroscopical). Mec hanical parameters of the native skin varied considerably according to sex, individual variability and/or site of specimen collection. In skin strips of males and females excised from different parts of the body thickness ran ged from 0.45 to 0.87 mm, strain (epsilon (f)) from 96.52 to 211.03, tensil e strength (sigma (m)) from 5.72 to 9.38 MPa, and stiffness (E-modulus) fro m 5.76 to 6.73. The dermis of B. marinus is provided with a collagenous str atum compactum of considerable thickness, a stratum spongiosum with loosely arranged fibres and a marked calcified layer (substantia amorpha). Collage n appears to be the main determinant of skin mechanics. However, the slope of the J-shaped static stress-strain curves indicates elastin to be respons ible for the high values of strain. Contrary to van Gieson and orcein stain ing, immunostaining with a monoclonal antibody against elastin revealed ver y few elastic fibers between collagen bundles and in the vertical fiber tra cts (perforating bundles), but a considerable amount in the tela subcutanea . This was partly confirmed at the ultrastructural level by tannic acid sta ining. (C) 2001 Harcourt Publishers Ltd.