192 S.·Afr. Tydskr. Dierk. 1993,28(4) Skin mechanics and morphology of two species of Pachydactylus (Reptilia: Gekkonidae)

A.M. Bauer' John Ellerman Museum, Department of Zoology, University of Stellenbosch, Stellenbosch, 7600 Republic of South Africa A.P. Russell Vertebrate Morphology Research Group, Department of Biological Sciences, University of Calgary, 2500 University Dr., N. W.. Calgary, AB, Canada T2N 1 N4 R.E. Shadwjck Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093, USA

Recejved 17 Novemher 1992; accepted 21 May /993

The southern African species Pachydactylus namaquensis is one of only a few mainland species of geckos that exhibits the escape strategy of regional integumentary loss. The skin morphology and mechanics of this species were compared to the same parameters in the sympatric congener P. bibronii. The tensile strength and modulus of elasticity of the skin of both species fall in the middle range of values for geckos as a whole. Skin of P. namaquensis, however, has approximately half of the tensile strength 01 that of p, bibromi. As in other skin·losing forms, the morphological basis for weakness lies in the bilayering of the dermis and the presence of zones of weakness within the upper layer of the dermis. Field experience suggests that P. namaquensis does not lose the skin as easily as most geckos exhibiting regional integumentary loss. In this species this escape strategy has probably evolved in response to the prey subjugation mode employed by rock-dwelling lizard predators.

PachydactyJus namaquensis van suidelike Afrika is een van slegs 'n paar vasteland-geitjies wat die ontsnap­ pingstrategie van regionale velverlies vertoon. Ole moriologie en meganika van die vel van hierdie spesie is vergelyk met die van P. blbronii, 'n simpatriese lid van dieselfde genus. Die spansterkte en modulus van elas­ tisiteit van die vel van albei spesies val in die middelgebied van waardes vir geitjies in geheeL Die vel van P. namaquensis het ongeveer die helfte van die spansterkte van die van P. bibron;;. Net soos in ander vorme .

) wat die vel verloor, IS die morfologiese basis vir swakheid gelee in die tweelagigheid van die dermis en die

9 aanwesigheid van sones van swakheid in die boonste laag van die dermis. Ondervinding in die veld dui daar­ 0

0 op dat P. namaquens;s nie so maklik die vel verloor soos ander geitjies wat regionale velverlies toon nie. In 2 hierdie spesies het hierdie ontsnappingstrategie waarskynlik ontwikkel in reaksie op prooi-onderwerpings­ d e metodes wat deur rotsbewonende akkedisvreters gebruik word. t a d

( * To whom correspondence addressed al: Deparlment, Villanova UniversilY, ViHaoova. PA 1909S,

should be Biology r

e USA h s i l b u Regional integumentary loss is an cseape strategy pmctised overlying tissues, remains intact and apparently serves as a P by a wide variety of gekkonine and sphaerodaetyline geekos barrier lO water loss. infeclion and solar radiation (Bauer e{ e h

t (Bauer, Russell & Shadwick 1989, 1992; Bauer & Russell al. 1989).

y 1992) and by at least some representatives of the family The high incidence of healed wounds in wild-caught b

d Scincidae (Mertens 1960; Greer 1986). Lizards utilizing this liz.ards indicates that this strategy is employed extensively in e t means of defence 'permit' the loss of portions of thcir skin natural populations (Baucr er al. 1989). Skin loss may be the n a 10 attackers in order lO effect escape, in a manner somewhat result of cither predatory or intraspecific encounters (McKe­ r g

analogous to the shedding of the tail in caudal aUlOtomy. own & Miller 1985), and app""rs to be dependent on the e c Skin loss is facilitated by thc architccture of the dennis, application of tensile or shear stress on the skin by external n e which is chamcterized by a discontinuity of collagen fibers agents. Schuben & Christophers (1985) and Schuben, c i l

within the stratum compactum of the dcnnis and the Steffen & Christophers (1990), however, have identificd r e presence of preformed zones of weakness within that myofibroblasts in transmission electron micrographs of the d n portion of the dermis superficial to the discontinuity (Bauer dermis of the Madagascan gekkonine gecko Geckolepis u 1989, 1992). At least in some geckos, the main resting y er al. rypica, and have postulated that the mechanism of skin a alignment of collagen fibers is perpendicular to the body fmcture involves an endogenously regu lated rupture of the w e

t long a~is and further serves to weaken the skin with respect skin. a 10 tensile stresses applied longitudinally (Bauer er al. 1989). The phenomenon of regional integumentary loss has G

t As a result of these properties, integumentary damage evolved a minimum of cight times among gekkonid lizards e n results in the loss of the skin e~ternal to the dermal (Bauer & Russell 1992), although the precise number of i b discontinuity (all of the epidermis and approximately 90% independenl dcrivations is uncertain, owing to poor resolu­ a S

of the dennis) at the wound site. A thin layer of the stratum tion in the phylogeny of gekkonine geckos. Most of the y b

compactum, which has a higher tensile strength than the originations of regional integumentary loss have occurred in d e c u d o r p e R S. Afr. 1. Zool. 1993.28(4) 193

lineages that arc principally in sular in their distribution. This of the California Academy of Sciences, San Francisco. Four has been related to the mode of prey sUbju gation empl oyed spec imens of each species were euthani zed by injecti on with by island versus mainland predators (Bauer & Russell pentobarbitol and their skin removed and placed in reptilian 1992). Guilds of saurophagous predators on islands where Ringer's solution (Rogers 1938). Width and length of each skin·losing geckos occur are dominated by snakes (West sample was measured wi th vernier calipers between the Indies). primates (Madagascar) and non-raptorial birds clamps of the tensometer. Mechanical testi ng was carried (Seychell es, Micronesia). In comparison with carnivores and out on a Monsanto no tensometer and samples were raptors, which usuall y deliver a killing bite or puncture to stretched at a rate of 20 mm min" , giving strain rates of prey items during the subjugation phase of prey capture, 0,02..{),04 , '. Force versus displacement was recorded on these predators typically have extensiv e handling times an x,y pl otter and normalized into stress (a ; force per during which the prey is pinned or held before being killed. cross·sectional area) measured in pascals (1 Pa ; 1 N m-') Under such circumsl1lnCes, regional integumentary loss may and siiain (0 ; the increment in length di vided by the initial ha ve a selective advantage (Bauer & Russell 1992). Similar length), a unilless quantity. Loading was applied to samples selective pressures may exist in mainland habitats where of both dorsal and ventral skin in a longitudinal direction lizards are preyed upon primarily by snakes or arthropods only. Bauer el al. (1989) demonstrated that streng th in this (Bauer el al. 1992; Bauer & Ru ssell 1992). direction was minimal and that it correspond ed to naturally In southern Africa. skin weakness ha s been reponed occu rrin g wound orientations in another skin-losi ng species, anecdotally in onl y two species, both representati ves of the Ailuronyx seychellensis. Samples were stretched to their genus Paclrydacrylus. P. scuta IU S. endemic to nonh-westem break point and the va lu es for fa ilure strain (or) and tensile Namibia and adjacent Angola, ha s large imbricati ng scales, strength (a m) were determined. The modulus of elasticity and integumentary loss is probably the result of dermal (E), a val ue representing the material stiffn ess, was deter­ zones of weakness occurring in the hinge regions at the base mined as the tangent modulus of the linear ponion of the of the scales, as has been demonstrated in the Puen o Rican stress- strain curve. Toughness (W) is the work necessary to Sphaerodacrylus roosevelli (Bauer el al. 1992). P. nama· break a unit volume of material and is expressed in ) m-' quensis, distributed from th e Cape Fold Mountains nonh to Uoules per cubic meter), and is equal to the area under the southern Namibia, has been widely reponed as a sk in loser stress- strain curve. Manual separati on of the lower dermis (FitzSimons 1943; Greene 1988; R.B. Hu ey. pers. comm .). of P. namaqu£nsis from the more superficial dermis and However, this species lacks the sca le morphologies typical epidermis was possible for one sample, and the inner dermis of the other geckos capable of regional integumentary loss alone was subjected to mechanical testin g. that have thus fa r been investigated. Furthermore, personal Following mechanical testing, specimens were fixed in

. fi eld experience with thi s species suggests that skin loss is 10% neutral buffered formalin, decalcified, embedded in )

9 not as easil y or as often initiated as in many other ski n· paraffin, and sectioned at 8-10 fl-m on a rotary microtome. 0

0 losing taxa. In thi s paper we examine the morphological In order to prevent di stortion of the skin, sections included 2 basis for regional integumentary loss in this species and underl ying body wall muscu lature. Sections were stained d e t present biomechanical data on skin strength in P. nama· with haematoxylin and eosi n. Mallory's and Mason's trio a d quensis wi th respect to its sympatric and syntopic congener chromes and Verhoeff's elastin stain (Humason 1979). Pho­ (

r P. bibronii, and with respect to other species of fragi le­ tomicrographs were taken on a Nikon OptiphOl microscope. e h ski nned geckos. Measurements for skin thickness, necessary for the standard­ s i l iza tion of mechanical data, were obtained from these b u MaterIals and Methods sec tions using ocular and stage mi crometers. The mean skin P

e Pachydacrylus namaquensis and P. bibronii were coll ected thi ckness val ues reponed (Table I) are the average of h t in rocky habitat at Anysberg Nature Reserv e, Cape measurements of 20 secti ons. Whole skin thicknesses were y

b measured from the base of the dermis to the outer surface of

Province, South Africa (33°44'S /20027'E) on 19 October d the epiderm is in the hinge region of dorsal body scales. e 199 \. These specimens hav e been deposited in the collection t n a r Results g

e Mechanical testing c n e .. ~.. ~ ~~ 1 The skin of both species of Pachydacrylus was found to be c i l

weak, although that of P. namaqu£nsis had onl y about one­ r e ;I; J! third to one·half of the strength of th at of P. bibronii. In all

d ,;,~.r ' ,

n "(f.' ,0., . .".." samples of the former species, failure occurred within the u l , , .. larger tubercles while in the latter fracture occurred at the y

a ...... ' p. . i. ' 'J',.. I~{... " periphery of enlarged tubercles. Force-length load curves w e t ... ':",' . , / . for P. bibronii were characteri zed by a steadily increasing • \ ~ &' .. ' a ...... , ," -.' ... .. slope up to the point of failure, followed by a sudden drop G

t in force to zero, or a more gradual drop in force over a e n

i Figure I Freshly wounded Pachydaclylus namaquensis fro m the length change equal to or sli ghtly greater th an that of initial b

a Richtersveld National Park showi ng the extensive (but nOI ex tension. Similar force-length curves typified P. nama· S exceptional) integumentary damage (arrows). The eXJXlsed areas quensis, although in no instance was there an abrupt cata· y b

remain covered by a thin portion of the lower dermis . strophic fail ure of the skin as renectcd by a sudden drop to d e c u d o r p e R 194 S.-Afr. Tydskr. D;erk. 1993,28(4)

Table 1 Mechanical properties of the skin of Pachy­ When considered separately, there was a drastic differ­ dactylus namaquensis, P. bibronii and representative ence between the perfonnance of inner dermis and the skin weak- (Ailuronyx, Sphaerodactylus) and normal­ of P. namaquensis as a whole. The inner layer comprises skinned (Gekko) geckos (data for Pachydactylus spp. approximately 12% of the tOlal skin thickness (Table 1). [ts from this study, data for other taxa from Bauer et al. failure Slrain was slightly lower than that of whole skin 1989,1992) (0,48). Tensile strength, however, was 2,30 MPa, more than three times greater than that of the whole skin. The modulus Skin Failure Failure of elasticity was 15,80 MPa, also considerably higher than thickness strain stress (J'm Modulus Toughness 3 that of the whole skin. Toughness of P. namaquensis dorsal Species (mm) E:f (MPa) E (MPa) W (M) m- ) and veniral whole skin averaged 0,14 :!: 0,08 MJ m-' and PachydaClylus Nlmaqu£n.sis 0,09 :!: 0,05 MJ m-' and 0,33 MJ m-' for the inner dermis dorsal skin (whole) alone. Values for P. bibronii were 0,44 :!: 0,26 and 0,37 + n = 7 0,145 0.54 0.74 2,55 0,14 0,14 MJ m-'. (SD) (0,13) (0,25) (0,42) (0,08) dorsal skin (inner layer) Histology 0'1= 1 0,018 0,48 2,30 15,&0 0,33 venlral skin (whole) The morphological basis for skin fracture in Pachydactylus n ~ 8 0,190 0,50 0,58 2,40 0.1l9 namaquensis lies within the vacuolated tissue in the (SD) (0,10) (0.15) (0.49) (0,05) enlarged tubercles of the dorsum (Figure 3C) and the imbri­ PachydaClylus bibronii cating plates of the venirum (Figure 3B). The collagen fibres

dor~al ~kin of the Slratum compactum are discontinuous at points within n=4 0,200 0,60 1,27 5,24 0,44 the tubercles where extensions of the vacuolated tissue (SD) (0,33) (0,37) (3,70) (0,26) project toward the inner dennis (Figure 3D). [n freshly ventral skin wounded individuals, skin rupture can be seen to have ,,= 5 0,151 0,45 1.84 8,50 0,37 occurred at such inira-tubercular discontinuities (Figure 3E). (SD) (0,18) (0,47) (4,30) (0,14) As in other skin-losing geckos examined to date, the deepest Sphaerodnclylus roosevelti layer of the dermis ;s separated from the upper region (and whole skin the epidermis) by a gap filled with loose connective tissue. II. = 4 0,122 0,38 0,19 0,58 0,04 Another, more dense aggregation of connective tissue binds inner layer the deep dennis to the underlying somatic musculature. n=1 0,005 0,61 4,82 20,30 [ndividual scales of Pachydactylus namaquensis are

. outer layer

) variable in size and consist of rounded, flattened tubercles

9 n=! 0,117 0,44 0,16 0,42 0,06

0 interspersed among granular scales. The epidennal layer is

0 Ailuronyx seychellensis

2 quite thin. Most of the dermis is composed of collagen

d whole skin fibres oriented parallel to the body surface (as determined e t It = 8 0,36 0.31 1,28 7,20 0.27

a by histology rather than polarizing light analysis; Figure 3).

d inner layer

( Slaining revealed the presence of only small amounts of

r 11=6 0,Q2 0,85 21,0 52 6,5

e elastin. Near the dermal-epidennal interface the fibre direc­ outer layer h s tions become less uniform and the dennis has a woven ap­ i

l 1t=6 0,30 0,29 0,9 4,6 0,13

b pearance. Tala I dermal thickness is minimal in the regions u GekJw gecko between scales, but these areas do not exhibit discontinuities P whole skin e in the outer dermal layer. Only a namJw gap filled with h n = 10 0,22 0,57 11,5 42 2,4 t

loose connective tissue separates the epidermis/outer dennis y b complex from a thin inner layer of parallel-fibred collagen d

e that constitutes the 'inner dermis' (sensu Bauer el al.. 1989). t force zero. The inner dermis of this species, tested alone, n This inner dermis is unbroken and unsegmented, even below a r yielded a similar curve, with a gradual return to zero. When the regions of outer dermal discontinuity. g converted to siress-strain relationships the linear portion of e The skin of P. bibronii likewise iliuSirates a dermal split­ c the stress-strain Curve for P. bibronii possesses a much n ting into inner and outer zones. However, the large, pointed e c higher' slope (i.e. modulus of elasticity) than that of P. i tubercles of this species conlain largely solid masses of con­ l namaquensis (Figure 2), although the inner skin of the latter r nective tissue that are firmly attached 10 the adjacent e d yields a modulus of elasticity that is much higher still. collagen fibres and there is no evidence of any prefonned n Failure strain (Ef) for dorsal and venlral skin averaged 0,54 u zones of weakness (Figure 3A). Comparable tubercular y :!: 0,042 and 0,50 :!: 0,10, and 0,60 :!: 0,33 and 0,45 :!: 0,18 morphology has been demonslrated histologically in the a for P. namaquensis and P. bibronii, respectively. Tensile w Mediterranean gckkonine species, Tarentola mawilanica e t sirength (rr m) averaged 0,74 :!: 0,25 MPa and 0,58 :!: 0,15

a (Schmidt 1912). MPa, and 1,27 :!: 0,37 MPa and 1,84 :!: 0,47 MPa for the G t whole skin samples. The modulus of elasticity (E) was also e n Discussion i very low, with mean values of 2,55 :!: 0,42 MPa and 2,40 :!: b

a 0,49 MPa for dorsal and veniral skin of P. namaquensis and The strength of the entire skin of both species of S 5,24 :!: 3,7 MPa and 8,50 :!: 4,3 MPa for comparable Pachydactylus falls in the middle range of that of other y b

samples of P. bibronii (Table I). geckos thus far tested (Table I). Sirength, stiffness, and for d e c u d o r p e R S. AfT. 1. Zoo\. 1993,28(4) 195

A B " " -;;1.5""r-- ~, , V'i 1.0 .:;:; 1.1) "'" /\

o() ,-, , -,--,- 1 OJ) ~r-.---r~ -, II n n 2 IIA (j,G 11.11 (10 11.2 '" 11./, ,--I(I,H c o

;; In

IL~ O,.~ _ I Oil ,-,­ \-~--"--. I),n -J.=- ILl! '" IIA " " 1111

Figure 2 Representative stress-strain curves of (A) ventral whole skin of Pachydaclylu5 bibronji, (B) ventral whole skin of P. namaquensis, (C) dorsal whole skin of P. namaquensis and (0) dorsal inner dermis of P. namaquensis.

P. bibronii, toughness, arc significantly greater than for respective values for fresh material. On this basis it would . ) Sphaeroriacrylus roosevelti (Bauer et al. 1992). These appear that the skin of this species is moderately weak, but 9

0 parameters arc significantly lower than those for Gekko far stronger, stiffer and tougher than those species which arc 0 2

gecko and other species regarded as non-fragile-skinned known to utilize regional integumentary loss as an escape d e (Bauer et al. 1989). Dorsal skin of P. hihronii has similar strategy. t a tensile strength to that of Ailuronyx seychel/ensis (Bauer et The relatively small difference between the strength and d (

al. 1989). However, the measurements of the latter were stiffness of the skin of Pachydaerylus namaquen.,is, a skin­ r e made on preserved skin rather than fresh tissue, and the loser, and P. bibronii, which docs not exhibit this strategy, h s i significance of the usc of fresh versus preserved gecko skin is somewhat surprising. However, the mechanical l b in material testing remains uncertain, Bauer et al. 1992) parameters of the whole skin reflect the combination of u P

found that the fresh skin of the Puerto Rican species those of its functional components, the inner dermis and the e

h Sphaeroriacrylus roosevelti was considerably weaker than outer dermis plus epidermis. The slrength of the inner t

y any of the formalin-fixed skins previously tested (Bauer et dermis of P. namaquensis, and especially its stiffness, arc b al. 1989). This result is predictahle, but is confused by the high relative to those of P. bibronii whole skin, and the d e

t findings that there were not appreciable mechanical loughnesses of the two are comparable. Because of the n differences between fresh and preserved skin of the tokay, relative thickness of the inner dennis in P. namaquensis (> a r

g Gekko gecko (Bauer et al. 1989). The similarity may be 12% vs 4% in Sphaerodactylus roosevelti and 6% in e

c attributable to the planar arrangement of the collagen fibres Ailuronyx seyehel/ensis) the conlribution of this layer to n

e in reptile skin (Lange 1931: Meyer, Bartels & Neurand whole skin values is especially significant. The biologically c i l 1989) and the paucity of elastin in geckos and other reptiles, significant comparison is actually octwccn the outer skin of r

e as evidenced both empirically by histology and inferentially the skin-losing species and the entire skin of the typical d

n by the more nearly linear stress-strain curve of gcckos in species, the res~ctive mechanical units that are impinged u

comparison with that of mammals (Veronda & Westmann upon by externally applied loads. Unfortunately the outer y a 1970). The effect of fixation may be more pronounced in skin of P. namaquensi.1 could not be isolated intact because w

e taxa with weak skin than in those (like G. gecko) with an of its absolute thinness and relative weakness. The high t a integument of high tensile strength, That fixation is mechanical parameter values of the inner dermis are typical G significant in this case is supported by the comparison of of all other skin-losing geckos studied thus far (Bauer et al. t e 1989,1992). n fresh P. bibronii skin with that of preserved material as i b reported by Bauer et al. 1989). In the preserved material The mechanisms of skin shedding seen in all geckos exa­ a

S tensile slrength was recorded as 7,3 MPa and the modulus mined 10 rlatc are dependent on the presence of a discontinu­ y

b (E) as 23,7 MPa, or approximately six and 4,5 times the ity within the stratum compaclum and the existence of d e c u d o r p e R 196 S. -Afr. Tydskr. Dierk. 1993. 28(4)

Figure 3 Histological sections through the skin of PachydaClylus bibronii and P . namaquensis. All sections suined with hematoxylin and eosin. (A) Dorsa l skin of P. bibronii illustrating the compact core of tubercles. (B) Ventral and (C) dorsal skin of P. rsamaqu.ensjs illusrrating the vacuolated. [i ss ue of tubercles and the bi layering of the stratum compacLUm. (D) Detail of a sm all dorsal tubercle of P. namaquensis showning the zo ne of weakness formed by the collagen discontin ui ry in th e outer dermal layer. (E) Freshly fractured skin of Pachydaclylus namaquensis illustrating the retentio n of the inner layer of dermi s and !.he point at which mechanical fail ure has occurred. .

) Abbrev iations: d = dermis. de = vacuolated dermal core of tu bercle, c = epidermis. il = inner layer of suatum compacturn of dermis. 01 = 9

0 outer layer of SlTatUm compactum of derm is. z = l one of weakness in outer layer of SlTatum compactum. Scale bar (at lower left of B) = 0 2

125 ..,..01 (except for C. where the same un it = 250 Il-m). d e t a d preformed zones of weakness in th e OU ler layer of the sis. and another utilizing the hinge regions of imbricating (

r dermis. Al leaSl lwo differenl scale archilectures produce th e scales in P. sculalus (Bauer & Ru ssell 1992). e h

s required breaks in the ou ler dermis. The imbricating dorsal The evolution of regional integumentary loss in geckos in i l scales of Sphaerodactylus rooseveili, and probabl y other general has been related 10 the subju galion mode of lite b u geckos capable of regional integumentary loss (Bauer el al. predalors encoumered. O n the basis of lite facl Lltal mOSl P

e 1992). exhi bil zones of weakness or coll agen discontinuities sk in -los ing lineages are island fonns. Bauer & Russell h t

in the hinge regions of the scales. The zones of weakness in ( 1992) ha ve hypothesized thal the stralegy has evolved in y b th e skin of Pachydactylus namaquensis lie in the vacuolaled response LO fealures of prey subjugalion Lltal are mOSl

d com mon in insular predators. the pinning or immobilization e lubercles of the dorsum and Ih ickened ventral scales . This is t

n similar to the condition seen in Ailuronyx seychellensis, of prey prior LO lite delivery of a killing punclure. The a r although the tubercles of this species are much larger and hypoLlt esis is diflicullLO assess on the basis of field data, bUl g

e more conspic uous than those of mOSl Pachydactylus. In P. if il is correcl, mainland geckos ex hibiting regional integu­ c n bibronii there are no discominuilies wilhin the lU bereles. mentary loss require some special explanation. In the case of e c i which are filled with dense connective liss ue. Ralher. the some very small geckos. such as lite New World sphaero­ l

r thinnesl point in the collagen matrix of the dermis lies althe daclylines. in which mainland as well as insular fonns have e d edges of th e tubercles, and il is lhere th al fraclure occurs fragile sk in (Hoogmoed 1973; Bauer el al. 1992). some of n u under test condition s. Ihe mosllikely predaLOrs are anhropods (Bauer 1990). These y The essenlial differences belween the morphological me­ would be expecled lo require fairly lengthy handling times a w c hanisms of regional imegum enlary loss among geckos is a when preying upon small venebrales and would nonnally e t

a reflecti on of the independenl origin of lhis Stralegy in require immobilizalion of the prey by legs or mouLltpans G

several lineages. A review of the laxa known 10 utilize lite before a killing wound or injeclion could be delivered. In t e strategy reveals a minimum of eighl origins among gekko­ lhe case of Pachydactylus namaquensis no preda LO rs ha ve n i

b nine geckos (Bauer & Ru ssell 1992). Even wiLltin Pachy­ been recorded in the lilerature. However, lite typical relrcal a

S dactylus. Iwo independem ori gi ns are implicated, one of Lltese lizards in rock crevices suggeslS thal snakes are

y dependenlon lubercular scale morph ology in P. namaquen- likely predators. Many saurophagous colubrid snakes Iypi- b d e c u d o r p e R S. AfT. J. z.,ol. 1993,28(4) 197

cally pin their prey with parts of their body before ingestion Biology of lhe Reptilia. vol. 16. (cds) C. Gans & R.B. Huey. (Jones & Whitford 1989) and thus provide an opportunity pp. 1-152. Alan R, Liss. New York. for skin-losing lizards to escape. In comparison with some GREER, A.E. 1986. Diagnosis of the Lerisla bipes species-group other gcckos employing lhe mechanism, P. namaquensis (Lacertilia: Scincidae), with a description of a new species does not part as readily with its integument (pers. obs., and an updated diagnosis of the genus, Rec. W. Ausl. Mus. AMB). This may be due, in part, to the reliance on alterna­ 13: 121-127. tive modes of non-mutilatory defence, such as biting and HOOGMOED, M.S. ]973. Notes on the herpetofauna of Surinam vocalization, which are ably employed by this spe.:ies. IV. The lizards and amphisbaenians of Surinam. Junk, The Alternatively, the relatively weak expression of regional Hague. integumentary loss in this gecko may be an exaptation, the HUMASON, G.L. 1979. Animal tissue techniques. W.H. fortuitous byproduct of unrelated selective pressures Freeman, San Francisco. favouring the vacuolated tubercular morphology of the JONES, K.B. & WHITFORD, W.G. 1989. Feeding behavior of dermis. free-roaming Maslicophis flagellum: an efficient ambush predator. SouJhwesl. Nat. 34: 460-467. Acknowledgements LANGE. B, 1931. Integument der Sauropsiden. In: Handbuch der vergleichenden Anatomie der Wirbcltiere. vol. 1. (005) L. We thank the Chief Directorate Nature and Environmental Bolk, E. Gapen, E. Kalliu, & W. LUbosch. pp. 150-193. Conservation, Cape Province, for permission to collect the Urban & Schwarzenberg, Berlin. specimens used in this study. This project was completed MCKEOWN, S. & MILLER, M.J. 1985. A brief note on the while the senior author was supported by the John R. natural history, captive maintenance and propagation of Lhe Ellerman Scholarship in Zoology at the University of Seychelles gian[ skin sloughing gecko, Ail"ronyx sechelleflsis. Stellenbosch. Data collection was supported by Villanova Ann. Internall. lIerpelOl. Symp. Captive Propagalion and University (AMB) and NSERC grant OGPOO09745 (APR). Husbandry 8: 96-102. S.F. Milone coordinated much of the laboratory work and MERTENS, R. 1960. The world of amphibians and reptiles. W.R. Branch and M. Burger made the field work possible. McGraw-Hili, New York. P. Ie F. N. Mouton kindly prepared the Afrikaans abstract. MEYER, W., BARTELS, T. & NEURAND, K. 1989. Anmerkungen zur Faserarchitekturder Vertebraten-Dermis. Z. References 7..001. Syst. Evolul.-Jorsch. 27: 115-125. BAUER. A.M. 1990. Gekkonid lizards as prey of invertebrates ROGERS, C.G. 1938. Textbook of comparative physiology. and predators of vertebrates. Herpelol. Rev. 21: 83--87. McGraw-Hill. New York.

. SCHMIDT, WJ. 1912. Sludien am Integumentder Reptilien. I.

) BAUER, A.M. & RUSSELL, A.P. 1992. The evolutionary 9 Die Haul der Geckoniden, Z. Wiss. Zool. 51: 139-258.

0 significance of regional integumentary loss in island gcckos: a 0 10 2 complement caudal autotomy. Ethology, Ecology & SCHUBERT, C. & CHRISTOPHERS, E. 1985. 'Dermolytische

d Evalwioft 4: 343-358. Schreckhautung' - ein besonderes Autotomievcrhalten von e t & Geckolepis lypica (Reptilia. Geckonidae). Zool. Am. 214: a BAUER, A.M., RUSSELL, A.P. SHADWICK, R.E. 1989. d

( Mechanical properties and morphological correlates of fragile 129-141. r

e skin in gckkonid lizards. 1. Exp. Bioi. 145: 79-102. SCHUBERT, C., STEFFEN, T. & CHR1STOPHERS, E. 1990. h s BAUER, A.M .. RUSSELL, A.P. & SHADWICK, R.E. 1992. Weiterc Bcobachtungen l.ur 'dermolytischen Schreckhautung' i l

b Skin mechanics and morphology in Sphaerodaclylus bei Geckolepis Iypica (Reptilia. Gekkonidae). Zool. Ant. 224: u roost!ueJli (Reptilia: Gekkonidae). fierpeloJogica 48: 124-133. 175-192. P

e FITZSIMONS, V.F. 1943. The lizard, of South Africa. Mem. VERONDA, D.R. & WESTMANN, R.A. 1970. Mechanical h t rransuaal Mus. I: xV + 1-528 + 24 pis. + map, characterization of skin finite deformations. J. Biomech, 3: y b

GREENE. H.W. 1988. Antipredator mechanisms in reptiles. In: 111-124. d e t n a r g e c n e c i l r e d n u y a w e t a G t e n i b a S y b d e c u d o r p e R