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Summary1. Predation has been proposed to be a selective agent in the evolution of morphological antipredator strategies in prey. Among vertebrates, one of the morphological traits that evolved multiple times is body armour, including carapaces, thickened keratinized scales and plates of dermal bone. 2. It has been generally assumed that body armour provides protection against a predatory attack; yet, few explicit tests of the hypothesis exist. Cordylidae, a relatively small family of southern African lizards, show considerable variation in the degree of body armour. Hence, this family provides an opportunity to test the hypothesis that body armour serves as protection against predators. 3. Experiments were conducted to test whether the bite forces of four species of mammalian predators were high enough to penetrate the skins of Karusasaurus polyzonus, Namazonurus peersi, Cordylus cordylus and Cordylus macropholis, as well as those of Ouroborus cataphractus individuals originating from three localities that differed in their predator diversity. Furthermore, histological techniques were used to test whether variation in skin toughness was associated with concomitant changes in the degree of epidermal (i.e. b-keratin) and dermal (i.e. osteoderm) armour. 4. The skin toughness values for four out of five cordylid lizards tested in this study were well below the bite forces of the mammalian predators. In contrast, the thick osteoderms in the dermis of O. cataphractus can withstand bites from several mongoose species. However, the significant variation in body armour that is present between the three populations of O. cataphractus does not seem to be related to predator diversity. 5. It is concluded that body armour can serve as protection against predation in O. cataphractus, but that alternative selection pressures, such as thermoregulation or predation by snakes, presumably underlie variation in defensive morphology in the other cordylid lizards.

Investigations of aggregation behaviour in five lizard species (three diurnal rockdwelling species, one nocturnal rock-dwelling species, and one diurnal terrestrial species) occurring in the arid western regions of South Africa revealed that there is no single set of causal factors explaining this behaviour. Aggregating behaviour in Cordylus macropholis is simply the result of environmental constraints, namely a shortage of preferred shelter sites. Individuals of Ouroborus cataphractus aggregate to benefit from the early predator detection effect. In Platysaurus broadleyi and Chondrodactylus bibronii aggregation behaviour appears to be the result of environmental constraints as well as possible benefits from the dilution effect. At present there is no conclusive information on the reasons for aggregation in Namazonurus peersi. In the rock-dwelling species investigated, the extent of adaptation to counter the effects of intra-group competition appears to be correlated with the proportion of activity time spent at the communal shelter. The proportion of time spent at the shelter, in turn, appears to be determined by the morphology of the species and whether it is diurnal or nocturnal.

The epidermal glandular structures in lizards belonging to the family Cordylidae are described. In addition to the large tubulo-follicular holocrine glands in the femoral region, "glandular scales" in the femoral, pre-cloacal, dorsal body and anterior antebrachial regions resembling epidermal "generation" glands are for the first time described histologically. In contrast to generation glands described in other lizards, a sequential buildup of glandular generations occur in these structures. Based on histological features, two types of cordylid generation glands are recognized, depending on whether the sequential buildup of the glandular generations is above ("protruding" type) or below ("pit" type) the stratum germinativum profile of the normal epidermis.

1993. Sexual dimorphism in cordylid lizards: a case study of the Drakensberg crag lizard, Pseudocordylus melanotus. Can. J . Zool. 71: 17 15 -1723. In a high-altitude population of the Drakensberg crag lizard, Pseudocordylus melanotus, most adult males, unlike adult females, are brightly coloured, and they are larger in body size and have relatively larger heads than females. Three basic colour phases can be distinguished among the brightly coloured adult males. No apparent differences in reproductive activity, number and differentiation state of the generation glands and femoral pores, or scar frequency were noted among the three colour phases. In males the development of bright colours and the differentiation of the epidermal glands coincide with the onset of sexual maturity. Sexual dimorphism in head size of adults is due to a decrease in female head size relative to juvenile head size as well as an increase in relative head size of males. Preliminary data indicate a social structure of territorial polygyny in P. melanotus and suggest that the dimorphism can partly be ascribed to sexual selection. There are also, however, indications of altitudinal variation in the expression of sexual dimorphism, which may be explained in terms of differential energy allocation by females at different altitudes. MOUTON, P. LE EN., et VAN WYK, J.H. 1993. Sexual dimorphism in cordylid lizards: a case study of the Drakensberg crag lizard, Pseudocordylus melanotus. Can. J . Zool. 71 : 17 15 -1723. Chez une population de haute altitude du lezard Pseudocordylus melanotus, la plupart des miles adultes, contrairement aux femelles, sont trks colores et ils sont aussi plus gros et ont la ttte relativement plus grosse. I1 existe trois types de coloration chez les miles adultes trks colores, mais il ne semble pas y avoir de differences entre ces trois types quant B l'activite reproductrice, quant au nombre ou au stade de differenciation des glandes genitales ou des pores femoraux, ou quant B la frkquence des cicatrices. Chez les mQles, l'apparition des couleurs vives et la differenciation des glandes Cpidermiques coincide avec l'avknement de la maturite sexuelle. Le dimorphisme sexuel de la taille de la tCte chez les adultes est attribuable B la fois B une reduction de la taille de la tCte chez les femelles comparativement B celle des juveniles et B une augmentation de la taille relative de la tCte chez les miles. D'aprks des donnees preliminaires, il semble que la structure sociale de P. melanotus soit basee sur la polygynie territoriale et que le dimorphisme soit attribuable en partie B la selection sexuelle. Cependant, il existe aussi des indices d'un gradient altitudinal dans l'expression du dimorphisme sexuel qui peut peut-etre s'expliquer par une variation dans la repartition de la depense Cnergetique chez les femelles B differentes altitudes.[Traduit par la redaction]

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