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Representative Egernia lizards. Top panel: White's skink lives in stable 'nuclear' family groups. Pairs are mostly monogamous and rarely divorce. Bottom left: the sleepy lizard is long lived and forms life-long pair bonds but pairs separate outside the breeding season and there is no parental care. Bottom middle: the black rock skink (Egernia saxatilis) also lives in family groups and parent–offspring associations are thought to reduce the likelihood of infanticide. Bottom right: the gidgee skink lives in large communal groups containing multiple adults and multiple cohorts of young. (Photos: Geoff While, Dave O'Connor, Dale Burzacott.)
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While et al's quick guide to Egernia lizards, a group of social lizards from Austalasia.
Copyright © 2015 Elsevier Ltd. All rights reserved.
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... However, some organisms, such as lizards, live in stable family groups in the absence of overt parental care and their social interactions may be less pronounced. For example, species in the Australian Egernia group of skinks commonly live in nuclear families and may have several generations of offspring living together (Chapple, 2003;While et al., 2015;Whiting and While, 2017). The parental unit is monogamous and offspring gain protection, particularly from infanticide, by associating with their parents (O'Connor and Shine, 2004). ...
Social learning is widespread among family living species, particularly mammals and birds with relatively high levels of social complexity and overt social interaction. However, the occurrence of social learning has never been documented in lizards with kin-based sociality, which have less obvious social interactions. We tested for social learning in Australian tree skinks (Egernia striolata), a species that commonly lives in family groups in the wild, using a two-step foraging task. Lizards were randomly allocated to either a social learning treatment or a control group and presented first with an instrumental task requiring the displacement of a lid, followed by an association task, consisting of two dishes with different colored lids. Prior to each task, lizards in the social learning treatment observed a trained demonstrator extract a food reward while the control also viewed a conspecific, but in the absence of the foraging task. The social learning treatment and control group solved the instrumental task at similar rates, but in the association task lizards in the social learning treatment made fewer errors and reached our learning criterion sooner. To the best of our knowledge, we present the first evidence for social learning in a lizard with kin-based sociality.
... For example, yellow-bellied marmots (Marmota flaviventris) that are more affiliative are more likely to die during hibernation, potentially because hibernating in close proximity to other individuals may disrupt required thermoregulation (Yang et al. 2017). Although we did not directly quantify the fitness consequences of the altered social behavior we observed in isolation-reared tree skinks, we interpret our findings based on our knowledge of Egernia-group social systems (While et al. 2015;Whiting and While 2017 ...
An animal’s social environment can be both dynamic and complex. Thus, social species often garner fitness benefits through being plastic in their social behavior. Yet, social plasticity can be constrained by an individual’s experience. We examined the influence of early social environment on social behavior in the tree skink (Egernia striolata), a family-living lizard. In the first phase of this study, we reared juveniles in 2 different social environments for 1.5 years: either in isolation or in unrelated pairs. We quantified each lizard’s sociability at 4-month intervals using a standardized laboratory assay and found that isolated lizards were more sociable, spending the assay closer to an adult female, than socially-reared lizards. In the second phase of this study (at the end of 1.5 years), we released all lizards into a semi-natural environment, observed their associations, and used social network analysis to quantify social behavior. During the initial 6 weeks post-release, we detected no differences in social behavior between rearing treatments. However, during the following 6 months differences emerged. Isolated lizards were more homogeneous in the strength of their associations than socially-reared lizards. Also, at first, isolated lizards associated more strongly than socially-reared lizards. Over time, isolated lizard associations became weaker and involved fewer lizards. In contrast, the level and number of associations of socially-reared lizards were stable over time. Our findings suggest that early experience influences tree skink social behavior but does not constrain social plasticity: isolation rearing did not limit their ability to respond to a novel social environment.
... There is increasing evidence that reptiles exhibit diverse social systems that can be kin-based (Doody et al. 2012;Gardner et al. 2015). For example, Australian skinks in the Egernia group exist in stable social aggregations, some with kin, some exhibiting long-term monogamy, and even parental care of offspring (Chapple 2003;Gardner et al. 2015;While et al. 2015). Egernia striolata (the Australian tree skink) is known to aggregate in social groups consisting of mating adult pairs, parents with offspring, and juveniles (Bonnett 1999;Duckett et al. 2012). ...
Early developmental environment can have profound effects on individual physiology, behaviour, and learning. In birds and mammals, social isolation during development is known to negatively affect learning ability; yet in other taxa, like reptiles, the effect of social isolation during development on learning ability is unknown. We investigated how social environment affects learning ability in the family-living tree skink (Egernia striolata). We hypothesized that early social environment shapes cognitive development in skinks and predicted that skinks raised in social isolation would have reduced learning ability compared to skinks raised socially. Offspring were separated at birth into two rearing treatments: (1) raised alone or (2) in a pair. After 1 year, we quantified spatial learning ability of skinks in these rearing treatments (N = 14 solitary, 14 social). We found no effect of rearing treatment on learning ability. The number of skinks to successfully learn the task, the number of trials taken to learn the task, the latency to perform the task, and the number of errors in each trial did not differ between isolated and socially reared skinks. Our results were unexpected, yet the facultative nature of this species’ social system may result in a reduced effect of social isolation on behaviour when compared to species with obligate sociality. Overall, our findings do not provide evidence that social environment affects development of spatial learning ability in this family-living lizard.
... living (Chapple, 2003;While, et al., 2015;Gardner, et al., 2016). The Egernia group is a Melanesian-Australian radiation (Gardner, et al., 2008) consisting of seven genera (Egernia, Liopholis, Lissolepis, Bellatorias, Cyclodomorphus, Tiliqua, and Corucia), and is so called because the former Egernia genus was paraphyletic and split into four monophyletic genera. ...
... presence of parent deters potential predators, particularly conspecific adults), with social bonds and interactions between parents and offspring typically less complex than in many avian and mammalian systems (While, et al., 2014a). As such, they offer great potential as models for understanding transitions to more complex forms of social structure and for uncovering the mechanisms that triggered the initial origins as well as the maintenance of family living and sociality in animals (Chapple, 2003;Doody, et al., 2013;While, et al., 2015). To understand the evolution of kin-based sociality in lizards, it is important to first consider the nature of social interactions in lizards more generally, since social selection (sensu Lyon & Montgomerie, 2012) acts on all aspects of social interactions that might lead to pair bonding and group formation (Kavaliers & Choleris, 2013). ...
Darwin famously described special difficulties in explaining social evolution in insects. More than a century later, the evolution of sociality - defined broadly as cooperative group living - remains one of the most intriguing problems in biology. Providing a unique perspective on the study of social evolution, this volume synthesizes the features of animal social life across the principle taxonomic groups in which sociality has evolved. The chapters explore sociality in a range of species, from ants to primates, highlighting key natural and life history data and providing a comparative view across animal societies. In establishing a single framework for a common, trait-based approach towards social synthesis, this volume will enable graduate students and investigators new to the field to systematically compare taxonomic groups and reinvigorate comparative approaches to studying animal social evolution.
... The wide range of life history characteristics, mating systems and social structures (from solitary to family living) exhibited by related species in the Egernia group of lizards (Gardner, Pearson, Johnston, & Schwarz, 2015) offers comparative taxa to investigate the evolution and ecology of the MHC. For example, living in groups increases the risk of pathogen transmission, making Egernia an emerging model group for studying the influence of group living on the MHC While, Chapple, Gardner, Uller, & Whiting, 2015). Increased parasite risk predicts stronger selective pressure on the MHC class I and class II genes, to combat disease in group living compared to solitary species (Alexander, 1974;Møller, Merino, Brown, & Robertson, 2001). ...
Next-generation sequencing has revolutionised molecular ecology. Its key advantages are a more accurate representation of genetic variation made possible by the generation of large volumes of data, more quickly and at a lower price per sequence than traditional sequencing methods. Yet these benefits come with a cost. For example, next-generation sequencing is error prone and requires increased quality control compared with traditional methods. Problems associated with next-generation sequencing may be exacerbated when sequencing gene complexes such as the major histocompatibility complex (MHC). Although not eliminated, significant progress has been made in addressing some of those problems and there is an increasing literature utilising this technology for studies of the MHC. However, what is generally lacking is detailed documentation of the methods used, and clear reasoning, for each step. Here we document detailed methodology, using an Australian lizard, Egernia stokesii, as a case study, with explanations, for MHC amplification, sequencing and allele identification. This work provides molecular ecologists with a comprehensive guide to follow, particularly when first employing next-generation sequencing techniques similar to those used here. In addition, the E. stokesii MHC genotypes derived from this work provide foundation data for future investigations of the influence of social structure on the MHC.
... This enhanced kin association sets the foundation from which more complex care behaviors can emerge. The Egernia lineage show variation between populations and species in the environments they inhabit and the degree to which they associate with offspring (from no care in species, such as L. inornata, to extended family groups with multiple cohorts of offspring cared for in E. cunninghami-reviewed in Chapple, 2003;While et al., 2015). These species therefore offer opportunities to connect within species patterns between ecology and parent-offspring association with the emergence and diversification of more complex forms of parental care across species in the Egernia lineage. ...
Parental care emerges as a result of an increase in the extent of interaction between parents and their offspring. These interactions can provide the foundation for the evolution of a range of complex parental behaviors. Therefore, fundamental to understanding the evolution of parental care is an understanding of the factors that promote this initial increase in parent-offspring association. Here, we used large outdoor enclosures to test how the spatial structure of high-quality habitat affects the occurrence of parent-offspring associations in a social lizard (Liopholis whitii). We found that the extent of parent-offspring association was higher when high-quality habitat was aggregated relative to when it was dispersed. This may be the result of greater competitive exclusion of adults and offspring from high quality crevices sites in the aggregated treatment compared to the dispersed treatment. Associating with parents had significant benefits for offspring growth and body condition but there were no concomitant effects on offspring survival. We did not find costs of parent-offspring association for parents in terms of increased harassment and loss of body condition. We discuss a number of potential mechanisms underlying these results. Regardless of mechanisms, our results suggest that habitat structure may shape the extent of parent-offspring association in L. whitti, and that highly aggregated habitats may set the stage for the diversification of more complex forms of care observed across closely related species.
Most of the more than 11,000 extant species of nonavian reptiles are squamates (lizards and snakes); there are about 360 extant species of turtles, 26 crocodylians, and one rhynchocephalian. Although the diversity of reptiles is greatest in the tropics, many species occur in temperate regions and a few have geographic ranges that extend north of the Arctic Circle. Antarctica is the only continent with no extant reptiles. Oviparity is the ancestral mode of reproduction, but viviparity has evolved repeatedly among squamates. Both genetic sex determination (XX/XY and ZW/ZZ) and environmental sex determination are represented, and genetic, environmental, and non-genetic maternal factors interact in some species. Environmental sex-determination is universal in crocodylians, widespread among turtles, and present in some clades of squamates. Parental care is universal among crocodylians and is present in some species of squamates and turtles. Ectothermy, an ancestral character, is central to the biology of reptiles, and is responsible for their low metabolic rates and their high efficiency of secondary production. Lizards typically eat daily and consume many small prey items, whereas snakes eat less frequently and consume larger prey items relative to their body size. Low metabolic rates make small body sizes energetically feasible for ectotherms, and more than half of the extant species of lizards are smaller than nearly all mammals and birds. Among squamates, the mode of predation – from sit-and-wait to widely foraging – has a strong phylogenetic component and correlates with many elements of ecology, morphology, physiology, and behavior. Many species of snakes and a few lizards are venomous, and some snakes are poisonous because they sequester toxins from their prey. Although most species of reptiles have little economic value, they are important components of energy and nutrient flow in terrestrial ecosystems. Habitat loss, pollution, invasive species, disease, and global climate change affect many species. The life histories of most large species of turtles, lizards, snakes, and crocodylians depend on prolonged adult survival and reproduction, and these species are vulnerable to commercial exploitation.
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 asynchrony 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.
There is great diversity in social behavior across the animal kingdom. Understanding the factors responsible for this diversity can help inform theory about how sociality evolves and is maintained. The Australian Tree Skink (Egernia striolata) exhibits inter- and intra-population variability in sociality and is therefore a good system for informing models of social evolution. Here, we conducted a multi-year study of a Tree Skink population to describe intra-population variation in the social organization and mating system of this species. Skinks aggregated in small groups of 2–5 individuals, and these aggregations were typically associated with shared shelter sites (crevices and hollows within rocks and trees). Aggregations were typically made up of one or more adult females and, often, one male and/or juvenile(s). Social network and spatial overlap analyses showed that social associations were strongly biased toward kin. Tree skinks also exhibited high site fidelity regardless of age or sex. There were high levels of genetic monogamy observed with most females (87%) and males (68%) only breeding with a single partner. Our results indicate that Tree Skinks reside in small family groups and are monogamous, which corresponds with existing research across populations. Similar to previous work, our study area consisted of discrete habitat patches (i.e., rock outcrops, trees, or both), which likely limits offspring dispersal and promotes social tolerance between parents and their offspring. Our study clearly demonstrates that there is intra-population variability in Tree Skink social behavior, but it also provides evidence that there is a high degree of inter-population consistency in sociality across their geographic range. We also highlight promising possible avenues for future research, specifically discussing the importance of studying the nature and extent of Tree Skink parental care and quantifying the fitness outcomes of kin-based sociality in this species, which are topics that will further our understanding of the mechanisms underlying variation in vertebrate social behavior.
The ability to produce viable offspring without recently mating, either through sperm storage or parthenogenesis, can provide fitness advantages under a suite of challenging ecological scenarios. Using genetic analysis, we demonstrate that three wild-caught female Tree Skinks (Egernia striolata) reproduced in captivity with no access to males for over a year, and that this is best explained by sperm storage. To the best of our knowledge, this is the first time female sperm storage has been documented in any monogamous family-living reptile, including social Australian egerniine skinks (from the subfamily Egerniinae). Furthermore, by using paternal reconstruction of genotypes we show that captive-born offspring produced by the same females in the preceding year, presumably without sperm storage, were sired by different males. We qualitatively compared aspects of these females’ mates and offspring between years. The parents of each litter were unrelated, but paternal and offspring genotypes from litters resulting from stored sperm were more heterozygous than those inferred to be from recent matings. Family-living egerniine skinks generally have low rates of multiple paternity, yet our study suggests that female sperm storage, potentially from outside social partners, offers the real possibility of benefits. Possible benefits include increasing genetic compatibility of mates and avoiding inbreeding depression via cryptic female choice. Sperm storage in Tree Skinks, a family-living lizard with a monogamous mating system, suggests that females may bet-hedge through extra-pair copulation with more heterozygous males, reinforcing the idea that females could have more control on reproductive outcomes than previously thought.
