Article

Aggregation in Bibron's Gecko, Chondrodactylus bibronii

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Abstract

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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... These aggregations are usually temporary only, and may serve thermoregulatory (e.g., winter aggregations), antipredatory or reproductive purposes (Burghardt, 1977;Cooper and Garstka, 1987;Elfström and Zucker, 1999;Aubret and Shine, 2009). Permanent communal living is uncommon among reptiles and mainly found in squamates, including Cordylidae (Nieuwoudt et al., 2003;Schutz et al., 2007), Phrynosomatidae (Lemos-Espinal et al., 1997), and Gekkonidae (Burke, 1994;Kearney et al., 2001;Meyer and Mouton, 2007). Long-term associations between closely related individuals have been documented in three viviparous lizard lineages only. ...
... Complex sociality in gekkonids has not been reported. Communal shelter use appears particularly common, however, and a number of species including Coleonyx variegatus (Eublepharidae), Nephrurus milii, Woodworthia maculatus (Diplodactylidae), Christinus marmoratus, and Chondrodactylus bibronii (Gekkonidae) form groups in retreats in the wild (Burke, 1994;Kearney et al., 2001;Todd, 2005;Meyer and Mouton, 2007) or under laboratory conditions (Shah et al., 2003;Lancaster et al., 2006;Meyer and Mouton, 2007). Geckos might primarily aggregate for physiological rather than social benefits (Shah et al., 2003;Lancaster et al., 2006), but the combination of specific age-sex classes and evidence of size-assortative grouping in some species indicates that social factors can influence group composition (Kearney et al., 2001). ...
... Complex sociality in gekkonids has not been reported. Communal shelter use appears particularly common, however, and a number of species including Coleonyx variegatus (Eublepharidae), Nephrurus milii, Woodworthia maculatus (Diplodactylidae), Christinus marmoratus, and Chondrodactylus bibronii (Gekkonidae) form groups in retreats in the wild (Burke, 1994;Kearney et al., 2001;Todd, 2005;Meyer and Mouton, 2007) or under laboratory conditions (Shah et al., 2003;Lancaster et al., 2006;Meyer and Mouton, 2007). Geckos might primarily aggregate for physiological rather than social benefits (Shah et al., 2003;Lancaster et al., 2006), but the combination of specific age-sex classes and evidence of size-assortative grouping in some species indicates that social factors can influence group composition (Kearney et al., 2001). ...
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Little information on the behavioral ecology and social organization of New Zealand's diplodactylid geckos is available. At least two species may be gregarious and share shelters, but data on the extent and possible function of this behavior are lacking. We examined the spatial distribution patterns of Duvaucel's Geckos in diurnal retreats over the four seasons. We tested whether geckos formed aggregations more often than expected by chance, and investigated whether or not the thermal properties of used shelters, gecko body temperatures and group composition affected aggregation patterns. Duvaucel's Geckos utilized a range of natural structures as diurnal shelters and showed a tendency to aggregate throughout the year (47–71% of individuals). Mixed-sex groups of up to eight individuals, including juveniles, occurred year round. Aggregations never contained more than one adult male and typically consisted of a male–female pair. Shelter-sharing adult males were larger than solitary males. Juveniles sheltered in close association with adults of either sex throughout the study. Shelter thermal properties did not appear to influence aggregative behavior. Aggregation patterns fluctuated seasonally, but the factors affecting these distribution patterns remain unclear. The occurrence of year-round shelter aggregations and frequent male–female and adult–juvenile associations indicate that this species might possess a complex social system. Further research examining the social and genetic relationships between group members, juvenile dispersal rates, and the temporal stability of aggregations is required to confirm the degree of complexity.
... With little ecological data to draw from, it is difficult to determine how species remain discrete from one another in sympatry, or even syntopy (FitzSimons, 1938;Branch, ''2001'' 2003). Chondrodactylus bibronii have been noted to display gregarious aggregation behavior, with multiple full-grown adults of both sexes found in the same rock crevices (FitzSimons, 1943;Branch, 1998;Meyer and Mouton 2007). Though a study as to whether this aggregation is induced by limited availability of optimal shelters or whether it is the result of mutual conspecific attraction was inconclusive (Meyer and Mouton 2007), these observations suggest behavioral cues may mediate interactions, hinting at the possibility that behavioral isolation may be reinforcing species-level boundaries. ...
... Chondrodactylus bibronii have been noted to display gregarious aggregation behavior, with multiple full-grown adults of both sexes found in the same rock crevices (FitzSimons, 1943;Branch, 1998;Meyer and Mouton 2007). Though a study as to whether this aggregation is induced by limited availability of optimal shelters or whether it is the result of mutual conspecific attraction was inconclusive (Meyer and Mouton 2007), these observations suggest behavioral cues may mediate interactions, hinting at the possibility that behavioral isolation may be reinforcing species-level boundaries. These limited ecological insights highlight how much more there is to learn about Chondrodactylus and Africa's herpetofauna in general. ...
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Despite being among the largest and most conspicuous geckos across southern and eastern Africa, the toe-padded species of Chondrodactylus have remained one of the most taxonomically difficult groups of African lizards, due chiefly to their overall morphological conservativeness accompanied by high intraspecific variation. Current recognition of taxa is based on recent molecular phylogenetic analyses, but the application of the currently recognized nomina to particular populations has not yet been presented. We present a much-expanded multigene analysis of 234 representatives of the genus Chondrodactylus that supports the recognition of 6 species-level taxa, one without toepads, C. angulifer, as sister to five with pads: C. bibronii, C. turneri, C. laevigatus, C. pulitzerae, and C. fitzsimonsi. In general, the species can be recognized on the basis of the relative size of chin and gular scales, dorsal scalation, and head shape. However, the most widespread species, C. laevigatus is only very subtly distinct from C. turneri, with which it is likely parapatric in East Africa (although western populations of C. laevigatus are unambiguously diagnosable from all other congeners). Intraspecific divergences are high in some of the species. In C. fitzsimonsi there is evidence of shared nuclear haplotypes with C. pulitzerae and potential morphological evidence for hybridization or introgression with C. laevigatus. Chondrodactylus turneri exhibits a mitochondrial gene rearrangement that is unique among all geckos followed by an insertion of roughly 200 base pairs that do not correspond to known sequences. Most Chondrodactylus species are primarily distributed in arid to semiarid southwestern Africa, where as many as 4 species occur in sympatry in northern Namibia. In contrast, C. turneri is limited to the lowlands of the southeast and C. laevigatus follows the arid-corridor traversing sub-Saharan Africa southwest to northeast.
... We often found two or three geckos sharing vertical tiles, suggesting that geckos might have chosen to retreat with conspecifics within a single substrate. Aggregation in diurnal retreat sites has been observed in other lizard species, and might be attributable to mutual conspecific attraction (Meyer & Mouton, 2007), enhanced predator detection (Pulliam, 1973), mitigation of water loss (Lancaster et al., 2006) or to provide control over rates of thermal exchange (Shah et al., 2004), or some combination of these. Results from our experiment, in which temperatures were similar among microhabitats, suggest that gravid female geckos aggregated for some social or behavioural Abbreviations: H., horizontal; V., vertical. ...
Article
Microhabitat orientation and structure and the presence of conspecifics may strongly influence the choice of habitat. We studied how these variables influence retreat- and nest-site selection in gravid females of a globally successful invasive species, the Asian house gecko (Hemidactylus frenatus). When provided with various substrates (vertical and horizontal ceramic tiles, vertical and horizontal plywood tiles, horizontal bark over leaf litter, vertical bark over a log, and sand) gravid female geckos preferred to retreat to, and nest in, materials with crevices commonly found in urban habitats. When housed alone, gravid females most frequently retreated to vertical ceramic tile or wooden crevices, and 66.7% nested in vertical ceramic tiles. When housed with two other conspecifics, gravid females most frequently retreated to vertical ceramic tiles, but selected a wider range of nest sites. Overall, gravid geckos housed alone typically nested in the same substrates that they used as diurnal retreats; when housed in groups, however, females oviposited in locations different from those they selected as retreats. Thus, H. frenatus females use a wider range of substrates when conspecifics are present. Invasion success in this species might be driven, in part, by preferences for retreat and nest substrates that are common in human-dominated habitats.
... Geckos use visual displays in part for intraspecific signalling (Marcellini 1977) and in least some species are able to distinguish colours even under night-time conditions (Kelber and Roth 2006). Chondrodactylus bibronii may use signalling to aggregate (Meyer and Mouton 2007), while males are territorial and behave aggressively towards each other (Barts 2010). Potentially therefore UV fluorescence could serve a number of signalling purposes, but further work is required to confirm or refute this role. ...
... Male skinks (Mabuya heathi) experience greater frequencies of tail autotomy and, when captive, often bite at each other's tails (Vitt 1981). Chondrodactylus bibronii, a close-relative to C. turneri, provides some interesting avenues for future research-aggregations are common and are formed either by mutual conspecific attraction or by a shortage of optimal shelters, with aggregations only containing a single male (Meyer and Mouton 2007). Their aggregations might be driven by foraging that occurs away from the crevice entrance, coupled with their nocturnal, rock-dwelling lifestyle (Mouton 2011). ...
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Intraspecific variation in behavior is often associated with age or size class, with many animals experiencing ontogenetic differences in diet, predation risk, physiological function, and competition. The nature of intraspecific behavioral variation will depend on the environmental context and has been more thoroughly examined for diurnal species. We studied microhabitat use and activity relative to time of night and the lunar cycle for the nocturnal gecko Chondrodactylus turneri, in the Namib Desert. Geckos preferred larger rocks with more crevices and were clumped in their occupancy of rocks, with some rocks being occupied by as many as eight individuals. Age classes differed in their use of open areas, with juveniles being encountered more often in the open. Activity levels varied with moon phase and time, with adults and juveniles exhibiting different relationships. Our results indicate that multiple factors might be influencing intraspecific behavioral variation.
... In geckos, there are apparently no general rules for explaining aggregation patterns and their composition. For example, Meyer & Mouton (2007) showed that Bibron's gecko (Chondrodactylus bibronii) lives in groups composed by one male and up to 15 females and juveniles, although they could not distinguish whether or not aggregation was the result of limited availability of optimal shelters or of conspecific attraction. Social aggregations which allow the control of thermal exchange rates via huddling were reported for thick-tailed geckos Underwoodisaurus milii (Shah, 2002; Shine et al., 2003) and common brown geckos Woodworthia maculatus (Bauer, 1990). ...
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Near times of gestation, oviposition, and parturition, habitat features that facilitate these processes may be specialized and of paramount importance to the fitness of gravid individuals. Additionally, spatial proximity to conspecifics may enhance individual fitness through antipredator, thermoregulatory, or osmoregulatory effects. Furthermore, philopatry and the proximity of littermates, parents, and offspring at the time of parturition of hatching would enhance inclusive fitness effects of mutualistic interactions. Mutual attraction to preferred habitat features as exhibited by gravid squamates may provide a useful model of early stages in the evolution of more complex social systems. Literature concerning aggregation of gravid squamates, communal nesting and birth, and interactions among neonates and postparturient females is reviewed. -from Authors
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Varied aspects of the general ecology of little-known gekkonid lizards from the southern Kalahari semi-desert of Africa are documented. Four to seven species of geckos coexist on ten study areas. Six of the seven species are nocturnal: three species are ground-dwellers, three climb (of these, one is diurnal) and one is semiarboreal. The percentage of climbing species in various areas is positively correlated with plant height diversity. Body temperatures of nocturnal geckos are very similar and these lizards thermoregulate less carefully than diurnal Kalahari lizards. Pairs of species differ in habitat, microhabitat and/or diet. Resource utilization patterns among Kalahari geckos are compared with those of an independently-evolved, but otherwise ecologically similar, nocturnal saurofauna: the geckos of the western Australian desert. Microhabitat utilization is similar on both continents, but Australian geckos eat a greater variety of prey taxa than Kalahari geckos. Pairs of morphologically similar species on the two continents do not necessarily converge ecologically in diet and microhabitat. The frequency of pairs with high overlap in both diet and microhabitat is greater among intercontinental comparisons than it is among intracontinental ones, suggesting a limit to the similarity of potentially competing species.
Article
Sex ratio, group composition, and male spacing were studied in Cordylus macropholis, a terrestrial lizard that inhabits the succulent Euphorbia caput-medusae. Repetitive sampling of two populations revealed highly female-biased sex ratios for adult, as well as juvenile size classes. The near 1:1 ratio observed in the smallest size class, however, suggests that the sex-ratio is 1:1 at birth. Sex ratio was found to relate positively to population density. Among aggregations containing more than one adult individual, a composition consisting of a male/female pair with or without juveniles, was the most common. Few cases were recorded where an adult male shared a plant shelter with more than one adult female or with another adult male. Adult males were randomly spaced among plants, both in and outside the mating season. Data on group structure and male spacing, especially the lack of clear differences between the mating and the nonmating season, provide little indication that male territoriality may be the cause of the highly female-biased sex ratio recorded for C. macropholis in the E. caput-medusae habitat.
Article
Aggregation behaviour and movement patterns were studied in the large-scaled girdled lizard, Cordylus macropholis. The size of aggregations within Euphorbia caput-medusae plants ranged from one to 14 individuals. Aggregation was a year-round phenomenon and aggregations were generally larger during autumn/winter than during spring/summer. Most aggregations consisted of an adult pair together with a varying number of juveniles. Site fidelity was low, with females showing significantly higher site fidelity than males. Movement of individuals in and out of the marked population was high, with no sex differences. Females covered slightly greater distances than males outside the mating season, whereas males covered slightly greater distances than females within the mating season. The results suggest that aggregation behaviour and high degree of movement in C. macropholis are the result of competition for a limited plant resource. The results do not confirm differential movement patterns between the sexes.
Article
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.
Article
The major ideas of modern probability theory are presented without assuming a mathematical background necessary for a rigorous discussion. The first 6 chapters deal with: basic theory; dependence and independence; distribution and moment generating functions; and the normal, Poisson, and related probability laws. Chapters 7 and 8 deal with random variables and their expectations and may be included with the first 6 chapters as a part of a one quarter undergraduate course. Chapters 9 and 10 introduce limit theorems and characteristic functions. Over 160 worked examples, 120 exercises requiring proof, and 480 numerical problems with 1/2 of them answered in the back. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Article
The aim of the study was to determine the space use of individuals in a multi-male group of the armadillo lizard Cordylus cataphractus. Specific focus was on the adult males and females of the group, because, ultimately, the manner in which adult males and females utilize space determines the mating system. A two-dimensional (2D) grid pattern was delineated at the crevice of a free-living, multi-male group to facilitate the recording of the positions of individuals during observations. All marked individuals (n=55) that were visible were scanned through a telescope, and their respective positions were recorded at 30-min intervals over several days during the breeding season. Arcview 3.2 Geographical Information Software was used to create a computerized replicate of the 2D grid pattern at the crevice and to depict graphically the recorded positions for each individual using a minimum convex polygon procedure. From the polygons generated by this procedure, it was clear that the space use of adult males overlapped greatly with the space use of adult females, but that there was no overlap in space-use among adult males. Space use overlapped greatly among subadults and juveniles and also among these size classes and adult males and females. Adult male C. cataphractus are territorial, defending specific sites at the crevice. The territory of each male in the group incorporated at least one female. The space use of several females overlapped with the space use of two or more males. Males were observed to mate with one or more females, and one female was observed to mate with two different males on more than one occasion. Cordylus cataphractus males display typical territorial polygyny whereas females may be promiscuous.
Article
Thesis (MSc)--University of Stellenbosch, 2004. Bibliography.
Article
Recent research has revealed unsuspected complexity in social organization among squamate reptiles. In particular, large Australian scincid lizards of the genus Egernia have been reported to occur in large aggregations of closely related individuals. However, the 'nuclear family' structure found in many other 'social' organisms (especially birds) has not been reported from reptiles. Our field studies on black rock skinks (Egernia saxatilis) in southeastern Australia document exactly this pattern. We quantified group composition using behavioural observations at regular intervals over three field seasons, and took tissue samples for parentage analysis. On the focal rock outcrop 72% of lizards were typically found as part of a stable social grouping, with individuals physically associated with other group members in a third of observations. Eighty-five per cent of juveniles lived in social groups, 65% in family groups with at least one of their parents (including 39% with both parents as revealed by parentage analysis of five microsatellite loci). Broader sampling in surrounding areas revealed similar patterns of group size, composition and relatedness. Overall, of the groups that contained more than one adult, 83% contained a single adult pair. Long-term monogamy and group stability were evident from our genetic data, with up to three annual cohorts of full-sib offspring living with their biological parents. Our data expand the range of social systems known for reptiles, and reveal strong convergence towards 'nuclear family' systems in distantly related vertebrates.
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Spaceuse in a multi-male group of the group-living lizard, Cordylus cataphractus
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Group dynamics and anti-predatory advantages of group-living in the armadillo lizard
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An unusual congregation of the gekkonid lizard Tarentola annularis
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A record of the peculiarities of the lizard Zonurus cataphractus (Boie), as observed during travels in Namaqualand in
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Grouping behaviour in the armadillo girdled lizard
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VISAGIE, L. 2001. Grouping behaviour in the armadillo girdled lizard, Cordylus cataphractus from South Africa. Unpubl. M.Sc. thesis. Stellenbosch University.
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