Abstract
During the regeneration of the tail in the arboreal New Zealand gecko (Hoplodactylus maculatus) a new set of tail scales, modified into pads bearing setae 5-20 μm long, is also regenerated. Stages of the formation of these specialized scales from epidermal pegs that invaginate the dermis of the regenerating tail are described on the basis of light and electron microscopic images. Within the pegs a differentiating clear layer interfaces with the spinulae and setae of the Oberhäutchen according to a process similar to that described for the digital pads. A layer of clear cytoplasm surrounds the growing tiny setae and eventually cornifies around them and their spatular ends, later leaving the new setae freestanding on the epidermal surface. The fresh adhesive pads help the gecko to maintain the prehensile function of its regenerated tail as together with the axial skeleton (made of a cylinder of elastic cartilage) the pads allow the regenerated tail to curl around twigs and small branches just like the original tail. The regeneration of caudal adhesive pads represents an ideal system to study the cellular processes that determine setal formation under normal or experimental manipulation as the progressive phases of the formation of the setae can be sequentially analyzed.
Highlights
The regeneration of the tail in lizards involves the regrowth of a variety of tissues, of which the skin with its regenerated scales is one type (Alibardi & Meyer-Rochow, 1988, 1989; Bellairs & Bryant, 1985; Maderson et al, 1978)
We focus on the regenerating tail skin, which allows us to find some stages of setal regeneration and to conclude that this is a promising experimental system to analyze details of setal formation in lizards generally
The available stages of regeneration in the adhesive caudal pads were incomplete to describe the entire process of setal differentiation, the combination of light and electron microscopic observations revealed the novel finding that the formation of setae in the caudal pads largely resembled that of the digital pads earlier described by Hiller (1972), Alibardi (1999, 2009) and Alibardi et al ( 2011)
Summary
The regeneration of the tail in lizards involves the regrowth of a variety of tissues, of which the skin with its regenerated (neogenic) scales is one type (Alibardi & Meyer-Rochow, 1988, 1989; Bellairs & Bryant, 1985; Maderson et al, 1978). In some geckos, specialized scales are regenerated like, for instance, the large, dorsal plate-like scales in Teratoscincus (Werner, 1967), or the caudal adhesive pads in Lygodactylus (Maderson, 1971) and various Carphodactyline geckos (Bauer, 1998) In the latter scales, especially present on the ventral side of the tail, the external layer exhibits micro-ornamentation, brought about by the so-called Oberhäutchen, and features long bristles like those present in the digital pads that allow caudal adhesion and permit arboreal climbing in these geckos (Hiller, 1972; Maderson, 1966). During scale regeneration these stages are repeated and the new scales pass through similar differentiating stages to those normally occurring during the shedding cycle, forming an external corneous wound epidermis (lacunar cells), followed by a clear layer, the Oberhäutchen, and a beta-, meso- and alpha-layer (Figure 1A, B)
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