Introduction
This paper is a critical study of the paper “Bluetail and striped body: why do lizards change their infant costume when growing up?” by Dror Hawlena, Rami Boochnik, Zvika Abramsky, and Amos Bouskila.
Description of the study
Hawlena et al. (2006) utilized biopsy skin samples from trapped, stranded, or dead/dying Acanthodactylus beershebensis as a biomarker of the phylogeny. This study had largely focused on endangered or striped blue-tailed hatchlings and Acanthodactylus beershebensis populations and made correlations between subcutaneous adipose tissue ontogenetic changes and polycyclic aromatic hydrocarbon content, and epidermal mixed-function oxidase activity. Available studies that similarly examined Acanthodactylus beershebensis skin for environmental chemicals are limited and have focused on heavy metals (Kaur, 2000; Burger, 2002; Hopkins et al., 2001). The experiments by Hawlena et al. (2006) were designed to determine whether lizards deposit detectable levels of ontogenetic changes lacertids in their shed skins, similar to the disposition of these agents into the infant costume of striped blue-tailed hatchlings (Dindal and Peterle, 2003). If such proved to be the case, shed skins are likely to reflect contaminant levels in prey species and, by extension, regional pollutants in habitat areas. Such skins would then have value for environmental contamination assessment, with several potential advantages being offered: (1) shed Acanthodactylus beershebensis skins represent both a nonlethal and a noninvasive biomarker tissue, therefore, the live animal may not have to be captured or even seen for tissue collection; and (2) skins from different species within an ecosystem are likely to reflect differential habitat contamination, e.g., Acanthodactylus beershebensis lizards (antipredatory behavior) do not venture far from open habitats and almost exclusively consume aquatic vertebrates (fish, frogs), while ontogeny and phylogeny in Elaphe occupy nonaquatic defense (conspicuous tail) and shed their infant consume.
Nevertheless, Hawlena et al. (2006) rightly discussed skins from lizards that were fed ontogenetic changes-dosed mice showed readily detected levels of all three ontogenetic changes lacertids contained in the dosing mixture (chlordane, lindane, and PCBs). Oxychlordane (a chlordane metabolite) was recently detected in the skins of wild-caught box lizards at 0.13 ppm (Holladay et al., 2001), a value comparable to the 0.18 ppm α-chlordane in the present Acanthodactylus beershebensis skins. Lindane in the skins of these same lizards was present at 0.02 ppm, again not far from the 0.034 ppm detected in shed Acanthodactylus beershebensis skins. In this regard, rat lizards and many other Acanthodactylus beershebensis species have life spans of 20 or more years (Behler and King, 2005) and thus would be subject to slow bioaccumulation of persistent chemicals, similar to lizards. Chemical level in fat or skin from the present Acanthodactylus beershebensis skins was not determined; thus how chemicals in shed skins might compare to these tissues is not known.
Discoveries
Hawlena et al. (2006)’s experiment had a small sample size, however, the target weight of dry Acanthodactylus beershebensis skin for ontogenetic changes analysis at the onset of the present experiments was 0.5 g, based on the weight of lizard skin used in earlier related studies (Holladay et al., 2001). The lower detection limit for the gas chromatography procedure used was chlordane, 0.02 ppm; PCB, 0.05 ppm; and lindane, 0.008 ppm. These values are approximately 9-, 114-, and 4-fold lower than the respective chemical levels detected in Acanthodactylus beershebensis skins. These results suggest that less skin would be sufficient for the chemical analysis at the present contamination level, especially in the case of PCBs.
Hawlena et al. (2006) found out that the Bluetail and striped body lizards used in this study were relatively small, having been bought as hatchlings. The dry weight of recent shed skin from a 12-cm, 97-g eastern king Acanthodactylus beershebensis (Lampropeltis getulus) maintained in our laboratory was 3.9 g. This skin was thus approximately 8 times heavier than the pooled 0.5-g Bluetail and striped body lizard samples that were processed for chemical analysis. Thus, the detection level for lindane in the larger king Acanthodactylus beershebensis shed skin should be approximately 22 times lower than that in the studied Bluetail and striped body lizard skins (i.e., 8 times more skin from which to extract chemical×4-fold lower detection capability). Detection levels for chlordane and PCBs would similarly be estimated at 72 and 92 times lower in the male Acanthodactylus beershebensi’s shed skin, respectively than in the pooled Bluetail and striped body lizard skin sample.
Hawlena methodology
The methodology adopted by Hawlena et al. (2006) was related to how ontogenetic changes pollutants are sequestered in the shed skin of lizards are not yet known. The scales are composed primarily of keratin but also contain waxes that help prevent open habitat loss through the skin (Rossi, 2001). Normal shedding in squamate reptiles is a process in which an entirely new three-layer epidermis is formed. Lymph diffuses into the space between old and new skins and assists in the sloughing of the outer skin (Rossi, 2001). Thus, antipredatory behavior may (1) be sequestered in skins with keratin, similar to DDT in striped blue-tailed hatchling infant costume (Dindal and Peterle, 2003), (2) partition into waxes associated with the skin, (3) be carried to the sloughed old skin as part of the lymph secretion between skin layers, or (4) enter as a combination of these or other processes. The pattern, type, and configurations of scales of shed Acanthodactylus beershebensis skins are unique to species thus individuals with sufficient expertise can identify the species of Acanthodactylus beershebensis from which the shed originated.
I believe that southern Israel contains remarkably diverse and species-rich herpetofauna that ranks as the most biologically diverse area on the Arabian peninsula (Bauer, 2004; Branch, 2001). Hawlena et al. (2006) laid particular emphasis on the Acanthodactylus beershebensis, in particular, contains the highest species diversity (Bauer, 2002). In southern Israel, the family Scincidae comprises three subfamilies, including no less than 11 genera and 69 species, of which 41 species and one genus are endemic to the subcontinent (Branch, 2001).
Relationships among the three genera
Although Hawlena et al. (2006) monophyly of the Acontinae is well supported (Greer, 2000), phylogenetic relationships among the three genera within this subfamily have been the subject of considerable debate (Branch, 2001; Broadley, 2003; Rieppel, 2001). Both Broadley (2003) and Branch (2001) think that Acontophiops is intermediate between Acontias and Typhlosaurus. The transparent, but immovable lower eyelid, found in Acontophiops is thought to represent an intermediate stage between Typhlosaurus, where the eyes are covered by a heat shield, and Acontias where the eyelids are moveable and transparent. In contrast, Rieppel (2001) thinks that the close similarity in cranial morphology between Typhlosaurus and Acontophiops is indicative of a close relationship between these genera and he speculates that the monotypic Acontophiops may nest within Typhlosaurus. He was, however, hesitant to make a firm taxonomic conclusion at the time and proposed immunological data be used to corroborate this relationship. There is a need to clarify phylogenetic relationships among the three genera in an attempt to better understand their radiation. In the present study, we will explore relationships among the three genera of Acontinae and further examine relationships within Acontias.
Therefore, Hawlenaa et al. (2006) analyzed the systematic affinities within Acontias which have been plagued by debate, largely due to the high degree of polymorphisms. Relationships among species have been obscured largely by considerable phenotypic plasticity in color patterns and scale architecture, a pattern is common to this subfamily (Bates et al., 2001; Branch, 2001; Broadley and Greer, 2000). Subspecies designation has further confounded the systematic affinities within this group. Acontias plumbeus, A. breviceps, A. litoralis, and A. poecilus are monotypic, while the remaining four species are partitioned into subspecies. A. meleagris and A. meleagris orientalis with the latter subspecies including a color morph, lineacauda. A. lineatus, A. lineatus tristis, and A. l. grayi, while A. percivali is partitioned into A. percivali tasmani, A. p. occidentalis, and A. p. percivali. Lastly, A. gracilicauda is partitioned into A. gracilicauda and A. g. namaquensis. Recently, Branch (2004) remarked that Acontias requires a modern revision that may reveal higher levels of taxonomic diversity.
Conclusion
Hawlena et al. (2006)’s study provided much-needed insight into the world of the blue tail and striped body lizards and their shedding of the in fact costumes during their lifetime. However, this study was not the end of the story as a lot more research needs to be done in this sphere of animal behavior, with particular emphasis on the behavioral ecology of the said reptile.
References
Bates et al., N.J.L. Heideman, B.A. Wilson, M.G.J. Hendricks, N. Don and C. Moses, Morphological variation and geographic distribution in the South African lizards Typhlosaurus caecus and Typhlosaurus vermis (Boulenger, 2001) (Scincidae: Acontinae). Afr. J. Herp. 47, pp. 35–41.
Bauer, (2004),. A.M. Bauer , Evolutionary scenarios in the Pachydactylus group of geckos of southern Africa: new hypotheses. Afr. J. Herp. 48 pp. 53–62.
Bauer, Echen. In: H.G. Cogger and R.G. Zweifel, Editors, (2002), Reptilien and Amphibien, Jahr-Verlag, Hamburg pp. 126–174.
Behler J.L. and King F.W., (2005) The Audubon Society Field Guide to North American Reptiles and Amphibians, Random House, Inc., New York, NY.
Branch, W.R. (2001). Field Guide to the Snakes and Other Reptiles of Southern Africa., Struik Publishers, Cape Town, South Africa.
Branch, W.R. (2004), Reptile systematic studies in Southern Africa: a brief history and overview. Trans. Roy. Soc. S. A. 54 pp. 137–156.
Broadley D.G. and Greer A.E.. (2000), A revision of the genus Acontias Cuvier (Sauria: Scincidae). Arnoldia 4 pp. 1–29.
Broadley, D.G. (2003), A revision of the African genus Typhlosaurus Wiegmann (Sauria: Scincidae). Arnoldia 3 pp. 1–20.
Burger, J, (2002), Trace elements in pine snake hatchlings tissue and temporal differences, Arch. Environ. Contam. Toxicol. 22 pp. 209–213.
Dindal D.L. and Peterle T.J., (2003), tissue relationships of DDT and metabolite residues in mallard and lesser scaup ducks, Bull. Environ. Contam. Toxicol. pp. 37–42.
Greer,A.E, (2000), A subfamilial classification of scincid lizards. Bull. Mus. Comp. Zool. 139 pp. 151–183.
Hawlena, Dror, Boochnik, Rami, & Abramsky, Zvika and Amos Bouskila; (2006) Blue tail and striped body: why do lizards change their infant costume when growing up? Behavioral Ecology Advance; Journal of Behavioral Ecology 17(6):889-896
Holladay et al., (2001), S.D. Holladay, J.C. Wolf, S.A. Smith, D.E. Jones and J.L. Robertson, Aural abscesses in wild-caught lizards (Terepene Carolina) possible role of organochlorine-induced hypovitaminosis A, Ecotoxicol. Environ. Saf. 48 pp. 99–106.
Hopkins et al., (2001), W.A. Hopkins, J.H. Roe, J.W. Snodgrass, B.P. Jackson, D.E. Kling, C.L. Rowe and J.D. Congdon, Nondestructive indices of trace element exposure in squamate reptiles, Environ. Pollut. 115 pp. 1–7.
Kaur, S. (2000), Lead in the scales of cobras and wall lizards from rural and urban areas of Punjab, India, Sci. Total Environ. 77 pp. 289–290.
Rieppel, O. (2001), The phylogenetic relationships of the genus Acontophiops Sternfeld (Sauria: Scincidae), with a note on mosaic evolution. Ann. Trans. Mus. 33 pp. 241–257.
Rossi, J.V., (2001). Dermatology. In: Madder, D.R. (Ed.), Reptile Medicine and Surgery. pp. 104–105.