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

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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.

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... Riley unpublished data). The Armadillo Lizard (Ouroborus cataphractus) can live in groups of up to 60 individuals in rocky outcrops (Mouton et al., 2014) and we observed O. cataphractus in groups of up to 27 juveniles and adults (J. Riley unpublished data). ...
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Hatching/birthing asynchrony, when siblings emerge at least 12 h apart, is thought to be a significant driver of phenotypic variation and group cohesion that is commonly reported in invertebrates and birds, but rarely in squamates. We examined birthing asynchrony in African cordylid lizards (Cordylidae), a clade characterized by a wide range of sociality (a hypothesized evolutionary driver of this unique phenomenon). We monitored parturition from wild-caught mothers from four species, which vary in their conspecific grouping behaviour. In two species, most litters were born asynchronously, over a maximum of 3-4 days respectively. The other two cordylids also exhibited asynchronous birth in all litters with more than one offspring, although this was not applicable for most litters because there was a prevalence of singleton litters. Our study uncovered birthing asynchrony in a novel taxonomic group, which suggests it evolved convergently in at least two social lizard clades from different continents. Furthermore, the function of birthing asyn-chrony and limiting litter size to a single offspring may be similar in social animals. We discuss the potential significance of this rare phenomenon in this disparate taxon, and compare it with other more well-studied taxa, in order to guide future research directions.
Aggregation behaviour in a rock‐dwelling gecko Chondrodactylus bibronii was investigated. In a laboratory setup, individuals were provided with an excess of shelters to determine whether limited availability of optimal shelters may be the cause of this species’ aggregation behaviour in the wild. Chondrodactylus bibronii grouped significantly more than predicted by the urn model of random occupation, hinting at mutual conspecific attraction as a possible mechanism for the observed aggregating behaviour. A slight temperature gradient in our laboratory setup, however, precludes a firmer conclusion. In addition to the laboratory study, a field‐survey was conducted to investigate the incidence, size and composition of groups. The proportion of solitary C. bibronii individuals (39%) in our sample was more than double that found in the group‐living lizard, Cordylus cataphractus where the mechanism for aggregation behaviour is known to be mutual conspecific attraction. Similar to small groups of C. cataphractus, the C. bibronii groups in our sample never contained more than one adult male. Like in C. cataphractus, solitary males were also found to be significantly smaller in body size than group‐living ones. Unlike in C. cataphractus, there was no statistical difference in the proportions of solitary males and solitary females in our sample. It thus remains unclear whether aggregation in C. bibronii is induced by limited availability of optimal shelters or whether it is the result of mutual conspecific attraction. Our data provide support for both mechanisms.
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