Nephrurus

Abstract: Each of the 14 genera now referred to the subfamily Diplodactylinae (Naultinus, Hoplodactylus, Heteropholis, Bavayia, Rhacodactylus, Eurydactylodes, Pseudothecadactylus, Carphodactylus, Phyllurus, Nephrurus, Oedura, Diplodactylus, Rhynchoedura, and Crenadactylus) is characterized on the basis of its internal and external morphology. The type species, referred species, and distribution are given for each genus. The Diplodactylinae are divided into two tribes primarily on the basis of differences in the arrangement and number of preanal pores and the size and shape of the nasal process of the premaxilla. The Carphodactylini includes Naultinus, Hoplodactylus, Heteropholis, Bavayia, Rhacodactylus, Eurydactylodes, Carphodactylus, Pseudothecadactylus, Phyllurus, and Nephrurus. The Diplodactylini includes Diplodactylus, Oedura, Rhynchoedura, and Crenadactylus. The Carphodactylini appear to be more primitive than the Diplodactylini. Carphodactylus may be close to the ancestral stock of the subfamily. Phyllurus and Nephrurus seem to be closely related to Carphodactylus. Pseudothecadactylus is considered to be closely related to the New Caledonia-Loyalty Islands radiation, which consists of Eurydactylodes and Rhacodactylus, and probably Bavayia. The New Zealand genera Hoplodactylus, Heteropholis, and Naultinus seem to form a natural group which is related to the New Caledonian genera. Crenadactylus is probably only distantly related to the other genera of the Diplodactylini. Rhynchoedura seems to be related to the stenodactylus group of Diplodactylus, while Oedura shows an affinity to the strophurus group of that genus. Geographically, the Diplodactylinae is restricted to the Australian Region (Australia, New Caledonia, Loyalty Islands, and New Zealand). The ancestral stock of the subfamily probably originated in south-east Asia and dispersed toward Australia by way of the Indo-Australian Archipelago during the upper Cretaceous. It is postulated that the subfamily reached Australia (and continental New Guinea) by Palaeocene- Eocene time.

Abstract: Unusually among lizards, Australian thick-tailed geckos (Nephrurus milii) aggregate in their diurnal retreat-sites. They continue to do this in the laboratory, even when excess shelters are available. We manipulated cues available to captive lizards to investigate three putative advantages to aggregation: enhanced social interactions, avoidance of predators, and control over rates of heat or water flux. Trials in which we prevented physical contact with conspecifics eliminated the aggregative response, suggesting that chemical and visual cues alone do not stimulate aggregation. Adding the scent of a predatory snake did not modify the degree of aggregation, nor did changes in mean ambient temperature or humidity. However, geckos exposed to decreasing temperatures huddled more closely with each other within shelters, and huddled geckos heated and cooled more slowly than did similar-sized solitary animals. We suggest that aggregative behaviour in Nephrurus milii has evolved to provide facultative control over rates of thermal exchange, an advantage because Nephrurus are large, live in cool variable climates, and occupy retreat-sites (rock crevices with high exposure to solar radiation) that experience highly variable thermal regimes. These attributes are shared by another group of lizards, the scincid genus Egernia, that exhibit the most complex sociality yet described among squamate reptiles. The initial stimulus for group formation in both geckos and skinks may have been thermal control, preadapting the scincids to further elaboration of social behaviour.

Abstract: Although reptiles of many species are often found in aggregations within retreat- sites, there is little quantitative information on the size and composition of such aggregations. Such data may clarify the processes that stimulate aggregation, and that determine patterns of co-occur- rence of individuals with respect to sex and body size. We gathered data on diurnal aggregations (under rocks) of two species of nocturnally-active gekkonid lizards (the gekkonine Christinus mar- inoratus and the diplodactyline Nephrurus tnilii) from two widely-separated localities in southern Australia (central Victoria and an island off the southern coast of Western Australia). Both species occurred at these localities, but geographic variation was evident in mean adult body sizes and in sexual size dimorphism. Both species actively aggregated, and the composition of groups differed significantly from that expected under a model of random assortment. For example, adult felnales of N. milii were rarely found with juvenile conspecifics, whereas pairs of juveniles were common. Most groups of C. marmoratus contained only a single adult male. In N. milii, members of an aggregation tended to resemble each other in body size. These significantly non-random patterns within aggregations of gekkonid lizards are suggestive of the kinds of processes that determine group size and composition, but experimental studies are needed to verify the causal factors involved.