Field studies on a social lizard: Home range and social organization in an Australian skink,Egernia major

Abstract Although most reptiles have polygynous mating systems without long‐term pair bonds, one lineage of large scincid lizards in Australia is exceptional in this respect. Reports of complex sociality in the genus Egernia led us to conduct the first radiotelemetric field study of a species within this group. Land mullets (Egernia major) are large (60 cm total length), viviparous lizards from rainforest habitats in south‐eastern Australia. To document the spatial ecology and social organization of this species, we captured 12 adult lizards in the Barrington Tops area of eastern New South Wales and implanted them with miniature radiotransmitters. The lizards were released at their sites of capture and located daily for the next 6 weeks. All of the radiotracked lizards had discrete home ranges of approximately 10 000 m², based around well‐defined core areas (approximately 2000–3000 m²). Females tended to move further, and to range over wider areas, than did males. All of the radiotracked lizards lived in social groups consisting of one or more adult males and females plus juveniles of all age classes. Subgroups were apparent within one group of five radio‐tagged lizards: individual animals consistently shared their shelter sites and home ranges with one or more specific individuals. Male/female pairings were more frequent than expected under the null hypothesis of random association among individuals. The data in the present study support anecdotal reports of pair bonds in E. major and support suggestions that the social systems of species in this genus are more complex than those of previously studied reptiles.     

Fine‐scale genetic structuring in a group‐living lizard,the gidgee skink (Egernia stokesii)

By constraining gene flow, group living and natal philopatry can result in fine‐scale genetic structure. Although the genetic structure of some group‐living lizards has been characterised, studies are few compared with those for group‐living bird and mammal species. The Egerniinae group of lizards exhibits a high diversity of social structures, making it a useful group for comparative studies of genetic structure across a broader range of social taxa. A well‐studied member of Egerniinae is Egernia stokesii, a lizard that forms long‐term pair bonds and stable social groups and exhibits natal philopatry and limited dispersal. Evidence exists for consistent E. stokesii social structure across seven close but disconnected rocky outcrops within a 40 × 10 km area. We used summary statistics, analysis of molecular variance, Bayesian clustering, and discriminant analysis of principal components to assess if E. stokesii exhibit a consistent pattern of fine‐scale genetic structure across the same seven outcrops. Due to E. stokesii social structure and constrained dispersal, we predicted significant genetic structuring – based on microsatellite markers – among outcrops. We found significant fine‐scale genetic structuring and evidence for two genetic clusters. We discuss features of E. stokesii biology and ecology that may explain our findings. Some rocky outcrops, and some social groups, contained lizards from both genetic clusters. An examination of the composition of mixed cluster social groups did not detect any notable patterns. Therefore, further work is necessary to identify how the observed patterns may have arisen. Future investigations in E. stokesii and other group‐living lizard species are likely to contribute greatly to our understanding of the genetic consequences of group living.     

Genetic evidence for a family structure in stable social aggregations of the Australian lizard Egernia stokesii

In this study we used data from six unlinked microsatellite loci to examine stable aggregations of Egernia stokesii, from a population in the southern Flinders Ranges of South Australia. We show that these aggregations are comprised of breeding partners, their offspring from two or more cohorts, and related adults, providing the first genetic evidence of a family structure in any lizard species. Despite this high level of relatedness within aggregations, most breeding pairs were unrelated and partners were less closely related to each other than they were to other potential within-group partners. Where individuals dispersed, both sexes usually moved to social groups close to their natal group. Although both sexes showed natal philopatry, there was some evidence that females in groups were more related than males in groups. These data suggest that an active choice of unrelated partners and male-biased dispersal may be the mechanisms used by E. stokesii to avoid inbreeding within groups.     

The social elite: Habitat heterogeneity,complexity and quality in granite inselbergs influence patterns of aggregation in Egernia striolata (Lygosominae: Scincidae)

Habitat heterogeneity, structural complexity and habitat quality are key features of the environment that drive species' distribution and patterns of biological organization. Traditionally, pattern‐based studies have focused on faunal responses to biological systems. However, the influence of non‐biological environments such as insular rock outcrops on patterns of vertebrate distribution is conceivably as important, but has received less attention. Granite inselbergs are a naturally heterogeneous and spatially‐limited habitat. As such, they provide an opportunity for investigating whether environmental attributes influence social behaviour in animals that use these kinds of habitat, particularly lizards that are well adapted to saxicoline environments. We applied ecological theory to investigate the influence of habitat heterogeneity, structural complexity and habitat quality on patterns of home‐site occupancy in the crevice skink Egernia striolata (Lygosominea: Scincidae) from insular granite outcrops located within fragmented agricultural landscapes. We compared home‐site occupancy among solitary juveniles, solitary adults and lizard aggregations. We found significant differences in home‐site occupancy between aggregations and solitary lizard outcrop attributes measured at multiple spatial scales. The probability of a home‐site being occupied by an aggregation increased where large rock masses were present, on northern aspects near the core of the outcrop and in structurally variegated landscapes. Significantly more aggregations occupied home‐sites surrounded by high boulder cover and crevice microhabitat. We provide evidence that geophysical attributes of granite inselbergs and landscape context can influence patterns of lizard aggregation. Thus, we clearly document the environmental correlations of variability in sociality among subpopulations of Egernia striolata.     

Complex mating system and dispersal patterns in a social lizard, Egernia whitii

In contrast to the polygynous mating systems typically displayed by most reptilian taxa, long-term genetic monogamy appears to be widespread within a lineage of group-living Australian scincid lizards, the Egernia group. We have recently shown that White's skink, Egernia whitii, lives in small but temporally stable social aggregations. Here, we examine the mating system, spatial organization, and dispersal patterns of E. whitii using behavioural field studies and data from four microsatellite loci. Parentage analysis of E. whitii litters revealed that its mating system is characterized by both polygyny and monogamy. Polygyny was the predominant mating system but within-season social and genetic monogamy was common (36-45% of breeding pairs). The incidence of between-season monogamy in E. whitii was rare compared to that reported for its congeners. Low levels of multiple paternity (12% of litters) and extra-group paternity (16%) were detected. Social groups are generally comprised of closely related individuals, but breeding pairs were not more closely related compared to other potential mates. Spatial autocorrelation analyses revealed significant positive local genetic structure over 50 m, which was consistent for all age-sex classes. There was no clear and consistent evidence for sex-biased dispersal, with assignment tests (mean assignment index) and relatedness analyses suggesting female-biased dispersal, but spatial autocorrelation analyses indicating a trend for male-biased dispersal. We discuss the implication of our results in regard to the factors promoting the evolution of monogamy within the Egernia group.     

Lizards in 'nuclear families': a novel reptilian social system in Egernia saxatilis (Scincidae)

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.     

The evolution of social behaviour in Blaberid cockroaches with diverse habitats and social systems: phylogenetic analysis of behavioural sequences

The adequacy and utility of behavioural characters in phylogenetics is widely acknowledged, especially for stereotyped behaviours. However, the most common behaviours are not stereotyped, and these are usually seen as inappropriate or more difficult to analyze in a phylogenetic context. A few methods have been proposed to deal with such data, although they have never been tested on samples larger than six species, which limits their evolutionary interest. In the present study, we perform behavioural observations on 13 cockroach species and derive behavioural phylogenetic characters with the successive event‐pairing method. We combine these characters with morphological and molecular data (approximately 6800 bp) in a phylogenetic study of 41 species. We then reconstruct ancestral states of the behavioural data to study evolution of social behaviour in these insects with regard to their social systems (i.e. solitary, gregarious, and subsocial) and diversity of habitat choice. We report for the first time that nonstereotyped behavioural data are adequate for phylogenetic analyses: they are no more homoplastic than traditional data, and support several phylogenetic relationships that we discuss. From an evolutionary perspective, we show that the solitary species Thanatophyllum akinetum does not display original behavioural interactions, suggesting phylogenetic inertia of interactive behaviours despite a radical change in social structure. Conversely, the subsocial species Parasphaeria boleiriana shows original behavioural interactions, which could result from its peculiar social system or habitat. We conclude that phylogenetic approaches in studies of behaviour are useful for deciphering evolution of behaviour and discriminating between its different modalities, even for nonstereotyped characters. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 58–77.     

Implications of the behavioural immune system for social behaviour and human health in the modern world

The ‘behavioural immune system’ is composed of mechanisms that evolved as a means of facilitating behaviours that minimized infection risk and enhanced fitness. Recent empirical research on human populations suggests that these mechanisms have unique consequences for many aspects of human sociality—including sexual attitudes, gregariousness, xenophobia, conformity to majority opinion and conservative sociopolitical attitudes. Throughout much of human evolutionary history, these consequences may have had beneficial health implications; but health implications in modern human societies remain unclear. This article summarizes pertinent ways in which modern human societies are similar to and different from the ecologies within which the behavioural immune system evolved. By attending to these similarities and differences, we identify a set of plausible implications—both positive and negative—that the behavioural immune system may have on health outcomes in contemporary human contexts. We discuss both individual-level infection risk and population-level epidemiological outcomes. We also discuss a variety of additional implications, including compliance with public health policies, the adoption of novel therapeutic interventions and actual immunological functioning. Research on the behavioural immune system, and its implications in contemporary human societies, can provide unique insights into relationships between fitness, sociality and health.     

Intraspecific variation in behaviour: effects of evolutionary history, ontogenetic experience and sex

Geographical variation in behaviour within species is common. However, how behavioural plasticity varies between and within locally adapted populations is less studied. Here, we studied behavioural plasticity induced by perceived predation risk and food availability in pond (low predation - high competition) vs. coastal marine (high predation - low competition) nine-spined sticklebacks (Pungitius pungitius) reared in a common garden experiment. Pond sticklebacks were more active feeders, more risk-taking, aggressive and explorative than marine sticklebacks. Perceived predation risk decreased aggression and risk-taking of all fish. Food restriction increased feeding activity and risk-taking. Pond sticklebacks became more risk-taking than marine sticklebacks under food shortage, whereas well-fed fish behaved similarly. Among poorly fed fish, males showed higher drive to feed, whereas among well-fed fish, females did. Apart from showing how evolutionary history, ontogenetic experience and sex influence behaviour, the results provide evidence for habitat-dependent expression of adaptive phenotypic plasticity.     

Selected body temperatures in the lizard Lacerta vivipara: Variation within and between populations

1. 1.|Selected body temperatures (SBT) of adult male, female and subadult Lacerta vivipara from a Belgian population, were measured monthly in a laboratory thermogradient.

2. 2.|Monthly mean SBTs varied between 29.9 and 34.0°C and differed significantly among months in all three lizard groups, and among lizard groups in 4 out of 6 months.

3. 3.|Evidence for a positive relationship between monthly SBT and air temperature was found in the subadults, but not in the adult lizards.

4. 4.|Monthly mean SBTs measured in this study were consistently higher (mean difference = 2.0°C) than those obtained by Patterson and Davies (1978) in a similar study on Lacerta vivipara from southern England.

Within‐population variation in social strategies characterize the social and mating system of an Australian lizard,Egernia whitii

The lizard genus Egernia has been suggested as an excellent model system for examining the evolution of sociality as it exhibits considerable diversity in social organization both between and within species. To date the majority of work examining the factors responsible for the evolution of sociality within Egernia has advocated a broad scale approach; identifying the social structure of specific species or populations and comparing the degree of sociality between them. However, we argue that significant advancements could also be gained by examining variation in social strategies within populations. Here we integrate a detailed, 3‐year, field‐based examination of social spacing and juvenile dispersal with molecular analyses of paternity to determine the social and mating system of a Tasmanian population of White's skink (Egernia whitii). We show that E. whitii live in small stable family groups consisting of an adult male, his female partner(s), as well as juvenile or sub‐adults individuals. In addition, while the mating system is characterized by considerable genetic monogamy, extra‐pair fertilizations are relatively common, with 34% of litters containing offspring sired by males from outside the social group. We also show that traits related to social organization (social group composition, group size, stability and the level of extra‐pair paternity) vary both between and within individuals. We suggest that ecological factors, such as habitat saturation, quality and availability, play a key role in maintaining between individual variation in social strategies, and that examining these individual level processes will allow us to more clearly understand variation in sociality among species.     

Herding,social influence and economic decision-making: socio-psychological and neuroscientific analyses

Typically, modern economics has steered away from the analysis of sociological and psychological factors and has focused on narrow behavioural assumptions in which expectations are formed on the basis of mathematical algorithms. Blending together ideas from the social and behavioural sciences, this paper argues that the behavioural approach adopted in most economic analysis, in its neglect of sociological and psychological forces and its simplistically dichotomous categorization of behaviour as either rational or not rational, is too narrow and stark. Behaviour may reflect an interaction of cognitive and emotional factors and this can be captured more effectively using an approach that focuses on the interplay of different decision-making systems. In understanding the mechanisms affecting economic and financial decision-making, an interdisciplinary approach is needed which incorporates ideas from a range of disciplines including sociology, economic psychology, evolutionary biology and neuroeconomics.     

Correlated geographic variation in predation risk and antipredator behaviour within a wide‐ranging snake species (Notechis scutatus,Elapidae)

Geographic variation in antipredator behaviour within wide‐ranging species may be driven by both genetic and environmental influences. We quantified antipredator responses in neonatal (laboratory born, n = 555) and adult (field caught, n = 346) tiger snakes (Notechis scutatus) from 11 mainland and island sites in southern Australia. We used these data to test predictions from Bonnet et al.'s hypothesis that the vigour of antipredator responses in this species reflects behavioural plasticity (in turn, driven by an individual snake's exposure to predators during its lifetime) rather than by genetic variation in this trait. We used the number of predator taxa in each area as an index of predator risk. As predicted, adult snakes from predator‐rich areas had more vigorous defensive responses when handled, whereas neonatal behaviour (although also variable among populations) was unrelated to predator species richness. Adult males bit more readily than adult females (as expected from the greater predation exposure of males during mate searching) but no such sex difference was evident in neonates. Although alternative models remain possible, our data are most consistent with the hypothesis that geographic divergence in antipredator tactics within this species primarily reflects developmentally plastic responses to local predation risk.