Maximal Caudal Autotomy in Podarcis hispanica (Lacertidae): The Caudofemoralis Muscle Is Not Sundered
In recent years, the pattern of maximal caudal autotomy in lizards has come under consideration, with attention being focused on how nonsegmental muscles in the tail base, specifically the m. caudofemoralis longus and the m. retractor penis magnus, may limit autotomy where they cross autotomy planes or, alternatively, how they may be ruptured if maximal autotomy is practiced. In this paper, we demonstrate that in the lacertid lizard Podarcis hispanica a number of autotomic vertebrae are spanned by the m. caudofemoralis longus, that maximal caudal autotomy does occur, and that the caudofemoralis muscle dissociates from its vertebral attachments but is not torn in the process. Anatomical and histological data reveal that this muscle has a specialized structure and relationship with surrounding muscles, skeletal elements, and connective tissues that result in minimal damage upon maximal autotomy. Furthermore, upon caudal regeneration, the m. caudofemoralis longus reestablishes contact with the newly formed cartilaginous axial skeleton of the tail.Abstract
Autotomy planes and the extent of the m. caudofemoralis longus in Podarcis hispanica. In all cases, the more anteriorly placed of the two pins is inserted at the level of the cloaca, and the more posteriorly placed one indicates the distalmost point of origin of the m. caudofemoralis longus. (A) The original tail of a male (H77; see Table 1) showing the nonautotomic caudal vertebrae (1–5), one vertebra with an incomplete fracture plane (6), and a series of autotomic vertebrae (7–11). Note that the distalmost point of origin of the m. caudofemoralis longus occurs on the proximal half of vertebra 9, indicating an overlap of 2.5 autotomic vertebrae by this muscle. (B) The original tail of a female (H75). The numbering convention is as for (A), above. Note that the distalmost point of origin of the m. caudofemoralis longus coincides with the proximal part of vertebra 8. (C) A male (H86) showing maximal autotomy without regeneration. Vertebral numbers as in (A). The conelike projections of the exposed m. caudofemoralis longus are evident (arrows). They are somewhat retracted, but the cavity from which one of these has been withdrawn is evident on the detached tail (arrowhead). (D) A female (H83) showing maximal caudal autotomy and conelike projections (arrowhead) of the m. caudofemoralis longus. Vertebral numbers as in (A). (E) The regenerated tail of a male (H91) that had experienced maximal autotomy. Vertebral numbers as in (A). The pin marking the distalmost origin of the m. caudofemoralis longus intersects the cartilaginous rod of the regenerated tail an appreciable distance beyond the remaining vertebrae. (F) The regenerated tail of a female (H95) that had experienced maximal autotomy. Vertebral numbers as in (A). The distalmost origin of the m. caudofemoralis longus traverses less of the regenerated portion of the tail than is the case in (E)
Histological details of frontal sections of the tail base of Podarcis hispanica with reference to the m. caudofemoralis longus and m. retractor penis magnus and their relationship to each other and the caudal skeleton in original and regenerated tails. (A) The ventral pattern of origin of the m. caudofemoralis longus (mc) from vertebral chevrons (cv) and the vertical skeletogenous septum (vcs) in an original tail, male (H77). One hemipenis (hp) is shown with its connection to the m. retractor penis magnus (rpm). (B) A more dorsal site of origin of the m. caudofemoralis longus (mc) from the connective tissue (ct) ensheathing the caudal vertebrae, male specimen (H91) with a regenerated tail. (C) Shared origin of the m. caudofemoralis longus (mc) and the m. retractor penis magnus (rpm) from an intervening connective tissue sheath (cts), male (H77) with an original tail. (D) Dorsal region of origin of the m. caudofemoralis longus (mc) in relation to the segmental muscles (sm) of the tail, male (H77) with an original tail. (E) Thickened connective tissue sheath (cts) of the m. retractor penis magnus (rpm) providing a modified pattern of origin for this muscle and the m. caudofemoralis longus (mc) in a male (H91) with a regenerated tail. (F) Reinsertion of the m. caudofemoralis longus (mc) onto the cartilaginous rod (cr) of the regenerated tail in a male (H91) via connective tissue strands (cts) passing between clusters of adipose tissue cells (at). Scale bar for all panels = 0.5 mm