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.     

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.     

Plasma corticosterone concentrations in males of the skink Egernia whitii during acute and chronic confinement, and over a diel period

This study examined adrenal and gonadal responses to capture and to longer term captivity in males of the scincid lizard, Egernia whitii. Animals subjected to acute capture stress in the field exhibited a rapid rise in plasma corticosterone concentrations that had not attenuated by 4 h after capture; plasma testosterone concentrations decreased significantly over this period. Animals returned to captive conditions in the laboratory showed little change in plasma corticosterone concentrations by 1 week, but concentrations were significantly lower at 4 weeks. Plasma testosterone did not vary significantly during this period. Sampling over a diel period indicated that plasma corticosterone concentrations vary little over the daylight hours; however, there was a significant decrease between the samples taken at 17:00 h and 21:00 h. These results suggest that, as in other species, the acute adrenal response to capture stress may confound assessment of other physiological parameters, although if experiments are carried out during daylight hours, time of sampling should have little influence on plasma corticosterone concentrations. The results also suggest that males of E. whitii require at least a week to adapt to captivity, although further studies investigating different captive conditions are warranted for this social species.     

Experimental evidence for parental,but not parentally biased,favouritism in relation to offspring size in Blue Tits Cyanistes caeruleus

In species with biparental care, males and females share the benefits of investing in offspring but pay the costs individually. As a result of these evolutionary conflicts of interest between the sexes, it is expected that the two parents should follow different behavioural rules when providing food to the young. Such a discrepancy may be accentuated when parents have to choose between different subsets of offspring (e.g. large and small nestlings). We manipulated the degree of hatching asynchrony in Blue Tits Cyanistes caeruleus and quantified male and female feeding behaviour when nestlings were 7 and 10 days old. First, we tested for a difference in the role of the sexes during the nestling rearing period between experimentally asynchronous and synchronous control broods. We then used experimentally asynchronous broods to assess differences between the sexes in the pattern of food distribution in terms of number of feedings and prey types, between junior and senior siblings. When nestlings in experimental nests were 7 days old, females fed young more often than did males despite facing a trade‐off between brooding the smallest nestlings and bringing food to the nest. At this age, there was also a skew in food delivery in favour of senior siblings, whereas food was more evenly distributed across the brood when nestlings were 10 days old. We found no difference in how male and female Blue Tits distributed feeding visits among junior and senior nestlings. However, females fed the smallest nestlings with more spiders in comparison with their senior siblings. This could be related to their more suitable size relative to other prey types, their high content of essential nutrients, or both, and may represent a more cryptic form of parentally biased favouritism. We compare these findings with previous work on other species and discuss why parents did not feed junior siblings more frequently.     

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.     

Histology of abortive egg sites in the uterus of a viviparous,placentotrophic lizard,the skink Chalcides chalcides

Although abortive uterine eggs are often assumed to be resorbed by females of the viviparous skink Chalcides chalcides, little microscopic evidence of resorption of such eggs is available. Oviducts from pregnant female C. chalcides in which egg resorption was inferred were examined histologically to seek a morphological basis for resorption. Uterine histology at the site of abortive eggs was very similar to that of lizards in early pregnancy. The uterine epithelium consisted of a monolayer of pseudostratifed columnar cells that showed no evidence of yolk phagocytosis. The uterine lamina propria exhibited shell glands and modest vascularity, typical of early gestation, and contained neither yolk droplets nor accumulating leukocytes. Unattenuated regions of the lamina propria contained occasional macrophages and mast cells, some of the latter of which were undergoing degranulation. The abortive eggs often were collapsed with ruptured shell membranes, and some were undergoing extrusion from the incubation chambers down the oviduct. In eggs that had begun developing, extraembryonic ectoderm and endoderm were atypical in location, and had failed to enclose yolk leaking from the eggs. Oviducts sampled from later in the reproductive season were reproductively inactive, and showed no trace of abortive eggs or egg components. We postulate that abortive eggs are extruded from the oviduct by pregnant females under conditions of physiological stress, as a means of enhancing future reproductive effort. J. Morphol. 235:97–108, 1998. © 1998 Wiley-Liss, Inc.     

Nestling aggression in broods of a siblicidal kingfisher, the laughing kookaburra

Third-hatched nestling in broods of the laughing kookaburra(Dacelo novaeguineae) are often killed by aggressive attacksfrom their older siblings within days of hatching. By installingsurveillance cameras inside nest hollows, we examined nestlingaggression over the "siblicidal" period, in particular to identifywhether parental behavior and competitive disparities betweennestlings affected aggression, and hence the likelihood ofsiblicide. Aggression decreased as nestlings aged and dominancehierarchies became established. The first-hatched nestling was the most aggressive. Fighting between the first-hatched nestlingand its closest rival (second-hatched nestling) increased whenthe hatch interval between them was short, when the size differencebetween them at hatching was small, and when the second nestlingwas female. Female nestlings are faster-growing than males,so young sisters may be an incipient threat requiring preemptiveaction by older siblings. When the second-hatched nestlingwas female, the first-hatched also attacked the third-hatched nestling more frequently. Thus the third-hatched nestling seemsto experience some of the "overflow" of aggression occurringbetween its two older siblings. Nestlings in siblicidal broodswere not fed less compared to nonsiblicidal broods; this isunsurprising because siblicide occurs when feeding rates arecomparatively low. However, siblicidal nestlings were broodedless, and in shorter bouts, which allowed them more time tofight.     

Clustering of related individuals in a population of the Australian lizard, Egernia frerei

Stable social aggregations are rarely recorded in lizards, but have now been reported from several species in the Australian scincid genus Egernia. Most of those examples come from species using rock crevice refuges that are relatively easy to observe. But for many other Egernia species that occupy different habitats and are more secretive, it is hard to gather the observational data needed to deduce their social structure. Therefore, we used genotypes at six polymorphic microsatellite DNA loci of 229 individuals of Egernia frerei, trapped in 22 sampling sites over 3500 ha of eucalypt forest on Fraser Island, Australia. Each sampling site contained 15 trap locations in a 100 x 50 m grid. We estimated relatedness among pairs of individuals and found that relatedness was higher within than between sites. Relatedness of females within sites was higher than relatedness of males, and was higher than relatedness between males and females. Within sites we found that juvenile lizards were highly related to other juveniles and to adults trapped at the same location, or at adjacent locations, but relatedness decreased with increasing trap separation. We interpreted the results as suggesting high natal philopatry among juvenile lizards and adult females. This result is consistent with stable family group structure previously reported in rock dwelling Egernia species, and suggests that social behaviour in this genus is not habitat driven.     

Leech removal is not the primary driver of basking behavior in a freshwater turtle

Leaving the water to bask (usually in the sun) is a common behavior for many freshwater turtles, with some species also engaging in “nocturnal basking.” Ectoparasite removal is an obvious hypothesis to explain nocturnal basking and has also been proposed as a key driver of diurnal basking. However, the efficacy of basking, day or night, to remove leeches has not been experimentally tested. Therefore, we examined the number of leeches that were removed from Krefft''s river turtles (Emydura macquarii krefftii) after experimentally making turtles bask at a range of times of day, durations, and temperatures. Turtles had high initial leech loads, with a mean of 32.1 leeches per turtle. Diurnal basking under a heat lamp for 3 hr at ~28°C significantly reduced numbers of leeches relative to controls. In diurnal trials, 90.9% of turtles lost leeches (mean loss of 7.1 leeches per turtle), whereas basking for 30 min under the same conditions was not effective (no turtles lost leeches, and all turtles were still visibly wet). Similarly, “nocturnal basking” at ~23°C for 3 hr was not effective at removing leeches. Only 18% of turtles lost leeches (one turtle lost one leech and another lost four leeches). Diurnal basking outdoors under direct sunlight for 20 min (mean temp = 34.5°C) resulted in a small reduction in leeches, with 50% of turtles losing leeches and an average loss of 0.7 leeches per turtle. These results indicate basking can remove leeches if temperatures are high or basking durations are long. However, it was only effective at unusually long basking durations in this system. Our data showed even the 20‐min period was longer than 70.1% of natural diurnal basking events, many of which took place at cooler temperatures. Therefore, leech removal does not appear to be the purpose of the majority of basking events.     

Identifying a surrogate metric for monitoring the population status of a secretive habitat specialist,the heath skink Liopholis multiscutata,in south‐eastern Australia

Threatened species that exist in small isolated populations are vulnerable to extinction processes, so effectively monitoring the trajectory of such populations will help determine the most appropriate management actions to combat extinction threats. In this study, we aimed to track the population status of the fossorial heath skink Liopholis multiscutata that is listed as threatened in Victoria, south‐eastern Australia, and exists there as a few small and highly disjunct populations, by using an appropriate surrogate population monitoring metric. This secretive lizard is a habitat specialist, is highly localised in Victoria and lives in warrens in semi‐arid heathland or mallee on large dunes. Survey data, which included every warren and their constituent burrows, as well as an assessment of whether each burrow was ‘active’, were collected for the four known Victorian populations in 2007 and annually during 2014–2018 inclusive. We compared five population indices per monitoring site: number of active warrens (NAW), number of active burrows (NAB), population area for 80% of active warrens (PA80), percentage of warrens that were active (PAW) and average number of active burrows per active warren. The heath skink currently occurs in small populations (8–46 active warrens) and these populations have typically declined over recent years. NAW was the most robust metric; NAB and PA80 did not reveal strong temporal trends. PAW indicated that inactive warrens and burrows persist less than a year and hence may provide information about recent (within months) population changes. It is imperative to establish a material link between the effective monitoring of small, vulnerable populations and the implementation of management actions that benefit such populations. Here, NAW could be used as a long‐term monitoring tool to provide an estimate of the minimum population size of the heath skink at a site. Its use would also ensure continuity in monitoring approaches for the Victorian populations.     

Monitoring the population status of a secretive lizard,the threatened heath skink Liopholis multiscutata,in south-eastern Australia using surrogate metrics: An update

Our recent study compared monitoring data collected using surrogate metrics during 2014–2018 inclusive with baseline data from 2007 to evaluate the trajectory of the population status of the threatened heath skink Liopholis multiscutata in Victoria. The heath skink is a secretive burrowing species that is a habitat specialist and exists in north-western Victoria as a few small and highly disjunct populations on large dunes in semi-arid heathland or mallee. We re-assessed the trajectories of the Victorian populations with additional monitoring data collected in 2021 and found continuing decline across all four Victorian heath skink populations. Urgent management intervention is required to arrest this decline, likely due to predation, reduced availability of habitat and life history and demographic traits that make this species susceptible to decline.     

Scat on the doorstep: Refuge choice in a group‐living lizard is influenced by the presence of scat piles

Group living often requires strong levels of communication between individuals. This communication is usually studied in the context of visual or auditory communication. However, chemical communication is the most widely used form of communication. We examined the role of chemical communication in mediating social decisions in a group‐living lizard, Egernia stokesii. Specifically, we examined the extent to which scat‐piling, a behaviour by which individuals deposit scat in a communal area, affected the refuge choice of individual E. stokesii. To achieve this, we examined individual refuge choice in response to scat piles or single scats and against two types of scat stimuli, one being their own scat and the other being scat belonging to an unrelated and unfamiliar conspecific. We show that lizards behave differently when presented with a scat pile compared with a single scat, and whether the scat stimulus was their own or sourced from an unfamiliar conspecific. When scats were in piles, individuals spent more time inspecting, more time in, and more often chose the treatment refuge as their final refuge choice, at a trial’s end, when the treatment was their own scat compared with when the treatment was the refuge with the unfamiliar scat. In contrast, for individual scat treatments, individuals spent more time inspecting and more often ended up in the treatment refuge with an unfamiliar scat compared with when the treatment was their own scat. These results suggest that individuals are responding to information contained within multiple components of the scats – both their volume and their source. These results have implications for understanding how social aggregations are maintained within squamates, where sociality has evolved independently from other vertebrate lineages.     

Oxidative stress is a consequence, not a cause, of aluminum toxicity in the forage legume Lotus corniculatus

? Aluminum (Al) toxicity is a major limiting factor of crop production on acid soils, but the implication of oxidative stress in this process is controversial. A multidisciplinary approach was used here to address this question in the forage legume Lotus corniculatus. ? Plants were treated with low Al concentrations in hydroponic culture, and physiological and biochemical parameters, together with semiquantitative metabolic and proteomic profiles, were determined. ? The exposure of plants to 10 μM Al inhibited root and leaf growth, but had no effect on the production of reactive oxygen species or lipid peroxides. By contrast, exposure to 20 μM Al elicited the production of superoxide radicals, peroxide and malondialdehyde. In response to Al, there was a progressive replacement of the superoxide dismutase isoforms in the cytosol, a loss of ascorbate and consistent changes in amino acids, sugars and associated enzymes. ? We conclude that oxidative stress is not a causative factor of Al toxicity. The increased contents in roots of two powerful Al chelators, malic and 2-isopropylmalic acids, together with the induction of an Al-activated malate transporter gene, strongly suggest that both organic acids are implicated in Al detoxification. The effects of Al on key proteins involved in cytoskeleton dynamics, protein turnover, transport, methylation reactions, redox control and stress responses underscore a metabolic dysfunction, which affects multiple cellular compartments, particularly in plants exposed to 20 μM Al.     

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.     

Melanin-based coloration is a nondirectionally selected sex-specific signal of offspring development in the alpine swift

Two mutually exclusive hypotheses have been put forward to explain the evolution and adaptive function of melanin-based color traits. According to sexual selection theory melanism is a directionally selected signal of individual quality, whereas theory on the maintenance of genetic polymorphism proposes that alternative melanin-based variants achieve equal fitness. Alpine swift (Apus melba) males and females have a conspicuous patch of white feathers on the breast with their rachis varying continuously from white to black, and hence the breast varies from white to striated. If this trait is a sexually selected signal of quality, its expression should be condition dependent and the degree of melanism directionally selected. If variation in melanism is a polymorphism, its expression should be genetically determined and fitness of melanin-based variants equal. We experimentally tested these predictions by exchanging eggs or hatchlings between randomly chosen nests and by estimating survival and reproduction in relation to melanism. We found that breast melanism is heritable and that the environment and body condition do not significantly influence its expression. Between 5 and 50 days of age nestlings were heavier and their wings longer when breast feathers of their biological father were blacker, and they also fledged at a younger age. This shows that aspects of offspring quality covary positively with the degree of melanism. However, this did not result in directional selection because nestling survival and recruitment in the local breeding population were not associated with father breast melanism. Furthermore, adult survival, age at first reproduction and probability of skipping reproduction did not covary with the degree of melanism. Genetic variation in breast melanism is therefore maintained either because nonmelanic males achieve fitness similar to melanic males via a different route than producing fast-growing offspring, or because the advantage of producing fast-growing offspring is not sufficiently pronounced to result in directional selection.     

aproctous,a locus that is necessary for the development of the proctodeum in Drosophila embryos,encodes a homolog of the vertebrate Brachyury gene

The proctodeum of the Drosophila embryo originates from the posterior end of the blastoderm and forms the hindgut. By enhancer-trap mutagenesis, using a P-element-lacZ vector, we identified a mutation that caused degeneration of the proctodeum during shortening of the germ band and named it aproctous (apro). Expression of the lacZ reporter gene, which was assumed to represent expression of the apro gene, began at the cellular blastoderm stage in a ring that encompassed about 10–15% of the egg's length (EL) and included the future proctodeum, anal pads, and posterior-most part of the visceral mesoderm. In later stages, strong expression of lacZ was detected in the developing hindgut and anal pads. Expression continued in the anal pads and epithelium of the hindgut of larvae; the epithelium of the hindgut of the adult fly also expressed lacZ. The spatial patterns of the expression of lacZ in various mutants suggested that the embryonic expression of apro was regulated predominantly by two gap genes, tailless (tll) and huckebein (hkb): tll is necessary for the activation of apro, while hkb suppressed the expression of apro in the region posterior to 10% EL. Cloning and sequencing of the apro cDNA revealed that apro was identical to the T-related gene (Trg) that is a Drosophila homolog of the vertebrate Brachyury gene. apro appears to play a key role in the development of tissues derived from the proctodeum.     

Molybdate toxicity in Chinese cabbage is not the direct consequence of changes in sulphur metabolism

• In polluted areas, plants may be exposed to supra‐optimal levels of the micronutrient molybdenum. The physiological basis of molybdenum phytotoxicity is poorly understood. Plants take up molybdenum as molybdate, which is a structural analogue of sulphate. Therefore, it is presumed that elevated molybdate concentrations may hamper the uptake and subsequent metabolism of sulphate, which may induce sulphur deficiency.
• In the current research, Chinese cabbage (Brassica pekinensis) seedlings were exposed to 50, 100, 150 and 200 μm Na₂MoO₄ for 9 days.
• Leaf chlorosis and a decreased plant growth occurred at concentrations ≥100 μm . Root growth was more affected than shoot growth. At ≥100 μm Na₂MoO₄, the sulphate uptake rate and capacity were increased, although only when expressed on a root fresh weight basis. When expressed on a whole plant fresh weight basis, which corrects for the impact of molybdate on the shoot‐to‐root ratio, the sulphate uptake rate and capacity remained unaffected. Molybdate concentrations ≥100 μm altered the mineral nutrient composition of plant tissues, although the levels of sulphur metabolites (sulphate, water‐soluble non‐protein thiols and total sulphur) were not altered. Moreover, the levels of nitrogen metabolites (nitrate, amino acids, proteins and total nitrogen), which are generally strongly affected by sulphate deprivation, were not affected. The root water‐soluble non‐protein thiol content was increased, and the tissue nitrate levels decreased, only at 200 μm Na₂MoO₄.
• Evidently, molybdenum toxicity in Chinese cabbage was not due to the direct interference of molybdate with the uptake and subsequent metabolism of sulphate.