The distal forelimb musculature in aquatic and terrestrial turtles: phylogeny or enviromental constraint?

ABDALA V., MANZANO A.S. & HERREL A.

JOURNAL OF ANATOMY

Blackwell Publishing

Lugar: Oxford; Año: 2007

0021-8782

Summary In the present study we compare the muscular anatomy of the distal front limb in terrestrial and aquatic chelonians to test whether observed differences between the two groups are associated with their divergent life-styles and locomotor modes. Given the different use of the forelimb in the two environments (body support and propulsion on land vs. mainly propulsion in water) we expect that: 1) aquatic and terrestrial turtles show differences in their muscular anatomy, with aquatic species having more individualized muscle bundles to allow for the complex forearm movements observed during swimming and 2) that terrestrial turtles will have more robust muscles to support their body weight against gravity. To address these questions, we examine the forelimb myology and associated tissues in six aquatic or semi-aquatic (Phyrnops hilarii, Podocnemis unifilis,Trachemys scripta, Sacalia bealei, Cuora amboinensis and Mauremys caspica ) and six terrestrial or semiterrestrial turtles (Geochelone chilensis, Testudo graeca, Cuora galbinifrons, Glyptemys insculpta, Terrapene carolina and Rhinoclemmys pulcherrima). We describethe general structure of the forelimb musculature in all species, and quantify muscle masses in those species with more than five specimens available (Phrynops hilarii, Podocnemis unifilis, and Geochelone chilensis). The general structure of the forelimb muscles in the strictly terrestrial species G. chilensis and T. graeca is notably different from the pattern of the aquatic and semi-aquatic species examined, showing a distinct fusion of the different muscular bodies. Terrapene carolina also show a distinctly terrestrial pattern, but a less extensive tendon development. Rhinoclemmys pulcherrima and Glyptemys insculpta were found to be morphologically intermediate; in the geoemydids the strictly terrestrial bauplan never appears. Quantitative differences in the robustness or mass of the distal forelimb muscles were also observed for the species investigated, and support our prediction that the extensor muscles are more robust in terrestrial turtles. However, in contrast to our expectations, not only the extensor muscles of the distal forelimb (which are crucial in providing both body support and propulsion), but all muscles acting around the wrist are heavier in terrestrial turtles.Phyrnops hilarii, Podocnemis unifilis,Trachemys scripta, Sacalia bealei, Cuora amboinensis and Mauremys caspica ) and six terrestrial or semiterrestrial turtles (Geochelone chilensis, Testudo graeca, Cuora galbinifrons, Glyptemys insculpta, Terrapene carolina and Rhinoclemmys pulcherrima). We describethe general structure of the forelimb musculature in all species, and quantify muscle masses in those species with more than five specimens available (Phrynops hilarii, Podocnemis unifilis, and Geochelone chilensis). The general structure of the forelimb muscles in the strictly terrestrial species G. chilensis and T. graeca is notably different from the pattern of the aquatic and semi-aquatic species examined, showing a distinct fusion of the different muscular bodies. Terrapene carolina also show a distinctly terrestrial pattern, but a less extensive tendon development. Rhinoclemmys pulcherrima and Glyptemys insculpta were found to be morphologically intermediate; in the geoemydids the strictly terrestrial bauplan never appears. Quantitative differences in the robustness or mass of the distal forelimb muscles were also observed for the species investigated, and support our prediction that the extensor muscles are more robust in terrestrial turtles. However, in contrast to our expectations, not only the extensor muscles of the distal forelimb (which are crucial in providing both body support and propulsion), but all muscles acting around the wrist are heavier in terrestrial turtles.