Johannes H. van Wyk

Thermal benefits of melanism in cordylid lizards: a theoretical and field test

The hypothesis that low skin reflectance (melanism) provides an advantage for thermoregulation under cold conditions has received mixed support in ectothermic vertebrates. We selected a model system, three allopatric closely related species of cordylid lizards that differ in skin reflectance, to test this hypothesis. Cordylus niger and Cordylus oelofseni are melanistic and inhabit peninsular and montane areas, respectively, whereas Cordylus cordylus is more widespread and inhabits low inland areas. By combining theoretical, experimental, and field data on these species, we demonstrate that the difference in body temperature (T(b)) between melanistic and non-melanistic lizards under ecologically relevant climate variation ranged from 0 degrees to 2 degrees C. Despite its small magnitude, however, the faster heating rate and higher T(b) of melanistic species relative to non-melanistic species conferred an advantage under cold conditions. Comparison of habitat thermal quality (d(e)) and thermal accuracy (d(b)) across species indicated that, in winter, melanism conferred the greatest advantage during small windows of thermal opportunity. This finding was most pronounced for C. oelofseni, which is most constrained by cold temperatures in its habitat. By contrast, due to their rock-dwelling habits, melanistic and non-melanistic species benefited from rock refugia in summer, giving similar levels of thermoregulatory effectiveness across species, regardless of skin reflectance. This study therefore demonstrates that skin reflectance variation across cordylids has significant effects on their thermal balance. Furthermore, studies investigating the role of varying skin reflectance in field populations and species should incorporate fine and broad temporal scales (daily, monthly, and seasonal), environmental variability, and cost-benefit trade-offs of thermoregulation.

Pheromonal Detection and Sex Discrimination of Conspecific Substrate Deposits by the Rock-Dwelling Cordylid Lizard Cordylus cordylus

The cordylid lizard Cordylus cordylus, a member of a family in which pheromonal communication was previously unreported, detects conspecific pheromones and responds differently to male and female pheromones. In an arena containing a clean ceramic tile or one marked by a male or female conspecific, males tongue flicked male-labeled and female-labeled tiles more frequently than clean tiles, indicating detection of conspecific stimuli. Females detected female pheromones and tongue flicked at a higher rate in response to female than male pheromones, but tongue flicks elicited by male stimuli were not significantly greater than those elicited by clean tiles. Both sexes are territorial, and each sex is more aggressive to consexuals. Both sexes performed more tongue flicks in response to same-sex than to opposite-sex pheromones. The most likely sources of pheromones detected are secretions of femoral and possibly generation glands. Both occur on the ventral femur where transfer to hard surfaces is facilitated

Lizard Epidermal Gland Secretions I: Chemical Characterization of the Femoral Gland Secretion of the Sungazer, Cordylus giganteus

The giant girdled lizard or sungazer, Cordylus giganteus, is endemic to South Africa. It has been suggested that in this species, as in other lizard species, epidermal glands in the femoral, pre-cloacal regions, and cloacal glands are the main sources of semiochemicals and that these secretions could play an important role at different levels of the social biology of the animals. To gain a better understanding of the nature of the femoral gland secretions of the sungazer, characterization of the constituents of the secretions was carried out. By using GC-MS analysis, in conjunction with auxiliary techniques, such as solventless sample introduction and trimethylsilyl derivatization, 53 relatively involatile compounds, including carboxylic acids, alcohols, ketones, esters, and steroids, were identified in the secretions of both sexes. The study showed that the secretions of male and female sungazers contain only semi-volatile chemicals.

The implementation of a battery of in vivo and in vitro bioassays to assess river water for estrogenic endocrine disrupting chemicals

Previous research has shown that accurate evaluation of environmental water samples for estrogenic activity requires a panel of in vitro and in vivo bioassays, which are based on different molecular and cellular action mechanisms. In the current study, a test battery containing four assays was used to analyze water from the Eerste River, South Africa for estrogenicity. Three sites were used for analysis, namely Jonkershoek (control site situated in the mountains at the origin of the Eerste River), sewage effluent from Stellenbosch sewage treatment works and Spier site (sampling site on the Eerste River downstream from Stellenbosch). Estrogenicity was determined using an estrone enzyme linked immuno sorbent assay (ELISA), estrogen induced proliferation of human breast cancer adenocarcinoma cells (MCF-7) also known as the E-SCREEN, estrogen induced suppression of estrogen receptor alpha protein expression (ER-α) in MCF-7 cells (ERα assay) and by monitoring estrogen induced vitellogenin (VTG) synthesis in juvenile Oreochromis mossambicus (VTG assay). Low concentrations of estrone (ranging between 1.4 and 2.2 ng/l) near the detection limit of the assay were detected in samples collected from Jonkershoek. Water from this site shows no estrogenicity in the E-SCREEN, ERα assay or VTG synthesis bioassay. The estrone concentrations in the sewage effluent extracts, as well as Spier site extracts, ranged between 14.7 and 19.4 ng/l. The assays using ERα induction by the MCF-7 cell line, MCF-7 proliferation and in vivo VTG synthesis by juvenile tilapia showed that these samples are estrogenic. The results obtained for the assays in the battery are comparable.

Lizard epidermal gland secretions. II. Chemical characterization of the generation gland secretion of the sungazer, Cordylus giganteus.

In lizards, the epidermal glands of the femoral and precloacal regions are involved in the production of semiochemicals. In addition to its femoral glands, the giant girdled lizard, or sungazer, Cordylus giganteus, which is endemic to South Africa, has generation glands as an additional potential source of semiochemicals. These epidermal glands are described as glandular scales that overlay the femoral glands and are included in the normal epidermal profile located in the femoral (thigh) and anterior antebrachial (fore-leg) regions of the male sungazer. GC-MS analysis of the generation gland secretions and the trimethylsilyl derivatives of some of the steroidal constituents was employed to identify 59 constituents, including alkenes, carboxylic acids, alcohols, ketones, aldehydes, esters, amides, nitriles, and steroids. The quantitative differences of the volatile constituents of the fore- and hind-leg generation glands were compared between individuals. This is the first report on the chemical composition of generation glandular material of lizards.

Group size and termite consumption in the armadillo lizard, Cordylus cataphractus

We investigated possible differences in the consumption of termites ( Microhodotermes viator ) by individuals in different sized groups of Cordylus cataphractus during different times of the year. Scats, collected once a month from small (2-3 individuals), medium (4-10 individuals) and large C. cataphractus groups (more than 10 individuals), from January to December 2005, were analysed for the presence of termite head material. We found termite consumption to be generally greater in larger than smaller groups throughout the year, but only significantly so during the dry months, March and April. Individuals in all group categories utilized termites throughout the year, but consumption was low at the end of winter, a time when general insect abundance is high. We conclude that termitophagy is important to individuals living in large groups, particularly during the dry period of the year, most probably to reduce intragroup competition for food.

Folliculogenesis and ovarian histology of the oviparous gecko, Hemidactylus mabouia (Sauria: Gekkonidae)

Abstract Histological changes during the ovarian cycle of the oviparous gekkonid lizard, Hemidactylus mabouia are described. The ovaries each contained a single germinal epithelium (bed) with numerous oogonia and primordial follicles. Similar to other squamates, the ovarian stroma was characterized by follicles in different stages of development, and may contain corpora lutea, and corpora atretica. The seasonal study revealed that vitellogenic ovarian hypertrophy commenced in spring (September) and ovulation of the first clutch (two eggs) occurred in summer (November). A second vitellogenic cycle followed, the second clutch being ovulated in late‐summer (January). Ovarian quiescence, marked by predominance of pre‐vitellogenic (hydration stage) follicles, was evident in females collected from February to July. Although oocyte growth was accompanied by changes in the granulosa layer, zona radiata and thecal layers, the zona pellucida remained unchanged throughout. The small cells of the granulosa layer differentiated into three distinct cell types ‐ small, intermediate and the conspicuous large pyriform cells. Similar to most other squamates, the intermediate and pyriform cells at the onset of vitellogenesis regressed to a single cuboidal epithelium. Following ovulation, the granulosa layer hypertrophied forming luteal tissue. The theca layer differentiated into two layers and septal invasion of the corpus luteum took place. At the time of oviposition, corpora lutea regressed to form ovarian scars (corpora albicantia). Follicular artresia occurred in previtellogenic follicles (hydration stage) and seldom in vitellogenic follicles. The highest incidence of atresia occurred in the post‐breeding period (February). The gross morphology, oogenesis and folliculogenesis of the ovaries of H. mabouia correspond to the general squamate pattern described for oviparous reptiles.

Strike-induced chemosensory searching is absent in the cordylid lizard,Cordylus cordylus, a scleroglossan ambush forager

SummaryStrike-induced chemosensory searching (SICS) was not detected experimentally in the cordylid lizard,Cordylus cordylus. Both components of SICS, a post-strike elevation in tongue-flick rate (PETF) and searching movements for attacked and released prey, were absent. The findings are consistent with previous data showing that PETF and/or SICS are lacking in all lizard families yet studied that forage primarily by ambush, but are present in actively foraging scleroglossan families and the herbivorous iguanian family Iguanidae. It is suggested that foraging behavior is a primary determinant of the presence or absence of SICS in lizards. Nevertheless, in most families in the two major clades, Iguania and Scleroglossa, the plesiomorphic foraging mode is retained. The findings agree with the prediction that SICS is absent in families lacking lingually mediated prey chemical discrimination (PCD), presumably due to selection against movement by ambush foragers that avoid being detected by either prey or predators because they remain motionless. Although PETF and SICS were absent, labial-licking and lingual movements similar to those observed after swallowing increased after biting prey, suggesting that the functions of these lingual movements may have been related to grooming. Locomotory movements did not increase following biting and appeared to represent avoidance of the experimenter.

Characterization of evolutionary trend in squamate estrogen receptor sensitivity.

Steroid hormones are a key regulator of reproductive biology in vertebrates, and are largely regulated via nuclear receptor families. Estrogen signaling is regulated by two estrogen receptor (ER) subtypes alpha and beta in the nucleus. In order to understand the role of estrogen in vertebrates, these ER from various species have been isolated and were functionally analyzed using luciferase reporter gene assays. Interestingly, species difference in estrogen sensitivity has been noted in the past, and it was reported that snake ER displayed highest estrogen sensitivity. Here, we isolated additional ER from three lizards: chameleon (Bradypodion pumilum), skink (Plestiodon finitimus), and gecko (Gekko japonicus). We have performed functional characterization of these ERs using reporter gene assay system, and found high estrogen sensitivity in all three species. Furthermore, comparison with results from other tetrapod ER revealed a seemingly uniform gradual pattern of ligand sensitivity evolution. In silico 3D homology modeling of the ligand-binding domain revealed structural variation at three sites, helix 2, and juncture between helices 8 and 9, and caudal region of helix 10/11. Docking simulations indicated that predicted ligand-receptor interaction also correlated with the reporter assay results, and overall squamates displayed highest stabilized interactions. The assay system and homology modeling system provides tool for in-depth comparative analysis of estrogen function, and provides insight toward the evolution of ER among vertebrates.

An evaluation of the endocrine disruptive potential of crude oil water accommodated fractions and crude oil contaminated surface water to freshwater organisms using in vitro and in vivo approaches

Knowledge regarding the potential impacts of crude oil on endocrine signaling in freshwater aquatic vertebrates is limited. The expression of selected genes as biomarkers for altered endocrine signaling was studied in African clawed frog, Xenopus laevis, tadpoles and juvenile Mozambique tilapia, Oreochromis mossambicus, exposed to weathered bunker and unweathered refinery crude oil water accommodated fractions (WAFs). In addition, the expression of the aforementioned genes was quantified in X. laevis tadpoles exposed to surface water collected from the proximity of an underground oil bunker. The (anti)estrogenicity and (anti)androgenicity of crude oil, crude oil WAFs, and surface water were furthermore evaluated using recombinant yeast. Thyroid hormone receptor beta expression was significantly down-regulated in X. laevis in response to both oil WAF types, whereas a further thyroid linked gene, type 2 deiodinase, was up-regulated in O. mossambicus exposed to a high concentration of bunker oil WAF. In addition, both WAFs altered the expression of the adipogenesis-linked peroxisome proliferator-activated receptor gamma in X. laevis. The crude oil and WAFs exhibited antiestrogenic and antiandrogenic activity in vitro. However, O. mossambicus androgen receptor 2 was the only gene, representing the reproductive system, significantly affected by WAF exposure. Estrogenicity, antiestrogenicity, and antiandrogenicity were detected in surface water samples; however, no significant changes were observed in the expression of any of the genes evaluated in X. laevis exposed to surface water. The responses varied among the 2 model organisms used, as well as among the 2 types of crude oil. Nonetheless, the data provide evidence that crude oil pollution may lead to adverse health effects in freshwater fish and amphibians as a result of altered endocrine signaling. Environ Toxicol Chem 2017;36:1330-1342.