Enemy at the gates: Rapid defensive trait diversification in an adaptive radiation of lizards

Adaptive radiation (AR), the product of rapid diversification of an ancestral species into novel adaptive zones, has become pivotal in our understanding of biodiversity. Although it has widely been accepted that predators may drive the process of AR by creating ecological opportunity (e.g., enemy-free space), the role of predators as selective agents in defensive trait diversification remains controversial. Using phylogenetic comparative methods, we provide evidence for an “early burst” in the diversification of antipredator phenotypes in Cordylinae, a relatively small AR of morphologically diverse southern African lizards. The evolution of body armor appears to have been initially rapid, but slowed down over time, consistent with the ecological niche-filling model. We suggest that the observed “early burst” pattern could be attributed to shifts in vulnerability to different types of predators (i.e., aerial versus terrestrial) associated with thermal habitat partitioning. These results provide empirical evidence supporting the hypothesis that predators or the interaction therewith might be key components of ecological opportunity, although the way in which predators influence morphological diversification requires further study

Sexual size dimorphism in montane cordylid lizards: a case study of the dwarf crag lizard, Pseudocordylus nebulosus

The aim of this study was to provide information on sexual size dimorphism (SSD) in Pseudocordylus nebulosus and to discuss the observed variation in SSD among montane cordylids. Data for P. nebulosus were recorded in the Landdroskop area in the Hottentots Holland Mountains, South Africa. The total sample of 87 lizards, consisted of 26 adult males, 49 adult females and 12 juveniles. Size at sexual maturity was determined as 60 mm snout–vent length (SVL) for both sexes. Generation glands were found to be present in males only and the number present was significantly correlated to body size. Both adult males and adult females possessed active femoral glands, but males had significantly more than females. Females were found to reach larger body sizes than males, but adult males had relatively larger heads than females. No significant difference in scar frequency was found between male and female samples. The female-biased SSD in P. nebulosus and its sister species, P. capensis, is tentatively ascribed to fecundity selection for offspring to be large at birth in order to survive in a predictable unfavourable environment at high altitudes. Variation in SSD among montane cordylids is discussed and the need for more comprehensive data is highlighted.Keywords: epidermal glands, body size, head size, melanistic, fecundity selectio

Data from: Proximate causes of variation in dermal armour: insights from armadillo lizards

Although it is widely assumed that body armour in animals evolved to thwart predator attacks, assessing the role that predators may play in shaping defensive morphologies has proven to be difficult. Recent studies suggest that body armour might be influenced by additional factors besides predation, and/or even by sexual selection. We investigated variation in dermal armour in 13 populations of armadillo lizards (Ouroborus cataphractus), spanning the entire distribution range of the species. We obtained thickness measurements of osteoderms – bony plates embedded in dermal layer of the skin – using micro- and nano-computed tomography. Using these data, we examined the effects of predation pressure/risk and climatic variables on dermal armour variation and addressed sexual and ontogenetic influence. Our results show that climate is the only factor affecting variation in dermal armour. Populations inhabiting more arid environments, characterized by low summer precipitation and mild winter temperatures, are relatively more armoured than those present in less arid environments. In contrast to our expectations, predation pressure or perceived predation risk was not associated with osteoderm thickness. The results of our study support the idea that the evolution of defensive traits might not be driven exclusively by predator-prey interactions, but could be moulded by environmental factors. In particular, we highlight the role of dermal armour as a potentially important mechanism to reduce evaporative water loss in arid environments

Climate and the evolution of group-living behaviour in the armadillo lizard (Ouroborus cataphractus)

We evaluated the hypothesis that the regular use of the southern harvester termite, Microhodotermes viator, as food source by the armadillo lizard, Ouroborus cataphractus, originated as an adaptation to survive the summer dry season in a climatic regime where rainfall is highly seasonal. To do so, we determined the most important climatic predictors of the geographical range of this species. Climatic data were obtained for 130 localities where O. cataphractus is known to occur and 168 adjacent localities where it is known to be absent. For each locality, data for 10 climatic variables were extracted from the South African Atlas of  Agrohydrology and Climatology database.We constructed a forward stepwise logistic regression model of the probability of O. cataphractus occurrence, based on the set of 10 climatic variables. The best model included, in order of importance, average monthly summer rainfall, mean annual precipitation, average monthly solar radiation, and the ratio of winter rainfall over summer rainfall as most significant predictors. The selected model predicted 88.80% of the presences correctly and 85.52% of the absences. In essence, O. cataphractus is restricted to the winter rainfall zone of South Africa, excluding the high-rainfall  southwestern section. We postulate that the highly predictable seasonal rainfall and the ameliorating effect of the Atlantic Ocean on climates in the Namaqualand region, in particular, have provided a unique selective regime for the origin of group-living in O. cataphractus. Dependence on M. viator as food source developed to survive the summer-autumn period of low food  availability and resulted in the evolution of heavy armour and group-living behaviour. The moderate winters and early spring temperatures allowed full capitalization on high arthropod abundance during winter–spring, thereby overriding the negative impacts of armour and  groupliving on foraging efficiency at the home crevice.Keywords: Microhodotermes viator, winter rainfall zone, climatic predictors, logistic regression, armour, Namaqualand

Field body temperatures, activity levels and opportunities for thermoregulation in an extreme microhabitat specialist, the girdled lizard (Cordylus macropholis)

The girdled lizard Cordylus macropholis inhabits semi-desert areas along the west coast of South Africa. Unlike many other small diurnal lizards living in open habitats, it exhibits extreme low levels of above-ground activity and does not show overt thermoregulatory behaviours, such as basking or shuttling. It has an extreme low movement rate and confines routine activity to the microhabitat of the succulent Euphorbia caput-medusae. We document this restriction of activity in time and space in relation to aspects of this lizard's thermal biology. Throughout the day, a majority of the lizards was found sheltering (‘covered’) among the branches of E. caput-medusae plants, and surface-active (‘exposed’) individuals were seen during only a restricted time period (i.e. 1100–1700 h). Mean body temperatures (Tbs) of both ‘exposed’ (29.4 °C) and ‘covered’ (28.4 °C) individuals were surprisingly low for a lizard inhabiting a hot and dry climate zone. This similarity of the Tbs of both groups, as well as the correspondence between the ambient temperatures in the plant microhabitat and the Tbs of ‘exposed’ lizards indicate that, for a considerable part of day, thermal conditions under plant cover allow achievement of Tbs at a similar level as that maintained by the ‘exposed’ lizards. Moreover, the absence of sightings of overtly basking lizards supports the view that C. macropholis warm up by adopting the ambient temperature in their shelters thereby reducing the time spent in surface activity. All lizards observed were within the periphery of E. caput-medusae plants, indicating that C. macropholis is an extreme microhabitat specialist. The succulent provides more and safer hiding places than other common shrubs in the environment. In addition, estimates of ambient temperatures indicate that these plants offer superior opportunities for thermoregulation compared with other available shrub microhabitats.Peer reviewe

Bone growth patterns in two cordylid lizards, Cordylus cataphractus and Pseudocordylus capensis

Cross-sections through the midshaft of the femora from an ontogenetic range of individuals were examined for Cordylus cataphractus, a heavily armoured, group-living lizard found in the western parts of South Africa, and Pseudocordylus capensis, an agile, montane lizard, occurring in the Cape Fold Mountains of South Africa. Relative bone thickness was found to be high in C. cataphractus and low in P. capensis. Both species displayed a high incidence of double lines of arrested growth. Endosteal resorption and deposition were extensive in C. cataphractus, occurring around the entire medullary cavity margin, and, except in the smallest juveniles, embryonic bone and the birthline had been completely resorbed. In P. capensis, on the other hand, endosteal resorption and deposition were limited and highly localized. Remnants of embryonic bone and a birthline were present in juveniles of varying size, as well as in several adults. These remnants always occurred in the dorsal half of the femoral midshaft and coincided with endosteal deposits, when present. In both species, maximum endosteal deposition and minimum periosteal deposition characterized the dorsal half of the femoral midshaft, while the ventral half was characterized by maximum periosteal deposition and most intensive endosteal resorption. In C. cataphractus, the correlation between medullary cavity area and total bone area differed significantly between the sexes, but not so in P. capensis. The remodelling process in each species can be explained in terms of the respective lifestyles of the species.Keywords: bone histology, femur, embryonic bone, remodelling, double lines of arrested growt

Solitary individuals in populations of the group-living lizard Ouroborus cataphractus: voluntary or forced?

We compared crevice fidelity among solitary and group-living individuals in a population of the group-living lizard Ouroborus cataphractus. We also compared the incidence of solitary individuals between the sexes and different seasons.We surveyed suitable rocky areas at two sites in the Graafwater district, South Africa, and all O. cataphractus individuals found, whether in groups or solitary, were marked and released back into their crevices. The areas were resurveyed after one month, three months and four months to compare crevice fidelity of solitary and group-living individuals. We found that solitary individuals were significantly less loyal to their rock shelters than individuals living in groups, and that solitary females appeared to be less loyal than solitary males. We found no significant difference in the frequency of solitary adult males in and outside of the mating season. Solitary adult males were significantly smaller in mean body size than group-living adult males, but did not have more scars or other deformities than the latter. We found no significant difference in the frequencies of solitary individuals during the wet and the dry seasons, or in the frequencies of solitary adult males versus solitary adult females recorded during any of the surveys. The significantly lower crevice fidelity displayed by solitary than group-living individuals supports the notion that being in a group must be the optimal situation for individuals of this relatively slow-moving cordylid. Our finding that solitary adult males were significantly smaller in mean body size than group-living adult males also suggests that the exclusion of less competitive males from groups may in part be responsible for the occurrence of solitary males.Key words: Cordylidae, mark-recapture, crevicefidelity, sexual differences, seasonal differences, competitive exclusion

Phylogeny of girdled lizards

10 p. : ill. ; 26 cm.Includes bibliographical references (p. 8-9).Mitochondrial DNA sequences were obtained for 16 species representing all nominal genera of Cordylidae (Platysaurus, Chamaesaura, Cordylus, and Pseudocordylus). Gerrhosauridae and Teiidae were used as first and second outgroups. Results indicate that the oviparous Platysaurus is the sister taxon of the remaining cordylids (all of which are ovoviviparous). Within the ovoviviparous group Cordylus is paraphyletic with respect to Chamaesaura and Pseudocordylus. No evidence of Pseudocordylus monophyly was discovered. The three species of Chamaesaura and the seven species of Pseudocordylus are transferred to Cordylus to render a monophyletic taxonomy