Aaron L. Fenner

Using social networks to deduce whether residents or dispersers spread parasites in a lizard population.

1. Heterogeneity of host behaviour can play an important role in the spread of parasites and pathogens around wildlife populations. Social networks have previously been suggested to represent transmission pathways within a population, but where the dynamics of host-parasite interactions are difficult to observe, networks may also be used to provide insights into transmission processes. 2. Pygmy bluetongue lizards, Tiliqua adelaidensis, occupy individual territories, live exclusively in burrows constructed by spiders in Australian native grasslands and are hosts to a tick, Bothriocroton hydrosauri, and a nematode, Pharyngodon wandillahensis. 3. On five monthly occasions, the locations of all individual lizards in three study plots were used to construct weighted, undirected networks based on proximity of adjacent burrows. 4. The networks were used to explore alternative hypotheses about the spread of each parasite through the population: that stable population members that remained in the same burrow over the study period played a major role in influencing the pattern of infection or that dispersing individuals played a more significant role. 5. For ticks, host individuals that were infected were more connected in the network than uninfected hosts and this relationship remained significant for connections to residents in the population, but not for connections to dispersers. 6. For nematodes, infected and uninfected hosts did not differ in their overall strength of connection in the network, but infected hosts were more connected to dispersers than were uninfected hosts, suggesting that lizards moving across the population are the major agents for the transmission of nematodes. 7. This study shows how network analyses can provide new insights into alternative pathways of parasite spread in wildlife populations, where it is difficult to make direct observations of transmission-related behaviours.

Consistent social structure within aggregations of the Australian lizard, Egernia stokesii across seven disconnected rocky outcrops

The Australian skink lizard Egernia stokesii lives in aggregations of up to 17 individuals. Previously, at one site, these aggregations have been shown to comprise paired unrelated individuals and several cohorts of their young. To investigate whether social structuring in this species is a response to ecological conditions or is phylogenetically constrained, we sampled social aggregations of E. stokesii from seven geographically adjacent rocky outcrops (including the site previously studied) that differ in the availability of homesite crevices. Analysis of genotypes from ten microsatellite loci indicate that social structures were similar at all sites and were comparable with that of the previous study. Over all sites highly significant positive relationships were observed between the number of crevices at a site and both the number of lizards and the number of social groups. Social structure in this species seems to be phylogenetically constrained, at least in relation to the abundance of potential homesite crevices.

Responses of the endangered pygmy bluetongue lizard to conspecific scats

Many animals use chemical signals for communication between conspecifics and for territory marking. The pygmy bluetongue lizard is normally solitary, focussing activity around the entrance of its burrow, from where it ambushes prey, and rarely contacts other individuals. In this paper we examined whether lizards in laboratory experiments alter their behaviour in the presence of scats from conspecifics. In the first experiment, when lizards were offered a choice of two vacant burrows with or without a scat close to the entrance, they tongue flicked more often at the burrow entrance when the scat was present, and more often chose to occupy the burrow with the scat. An interpretation is that lizards use scat signals to recognise burrows that may be suitable because they have previously been occupied by a conspecific, but that they approach those burrows cautiously in case a resident is still present and likely to resist a takeover. Scats from male lizards were inspected (by both sexes) for longer than scats of female lizards. In the second experiment, when resident lizards were presented with scats outside of their burrows, they inspected and tongue flicked at those scats more often if the scat came from a male than a female lizard, but there was no definitive evidence from our experiments that lizards differentiated in their response to scats from lizards that were found close to or far from the test lizard. The results were consistent with a communication system in which lizards use scats to advertise their presence, independent of any direct contact.

Injuries to lizards: conservation implications for the endangered pygmy bluetongue lizard (Tiliqua adelaidensis)

Understanding the potential threats of predation can play a crucial role in conservation management of threatened species. We investigated the frequency of sublethal injuries to live individuals of the endangered pygmy bluetongue lizard (Tiliqua adelaidensis). We found that there was no significant difference in the frequency of injury between males and females. However, there was a significant difference in injury frequency between adults and subadult animals and also between two close, but isolated, populations of pygmy bluetongue lizards. These data can be used, with caution, to understand the predation risks in natural populations of this species. They also suggest that predation would be a significant hazard that must be considered in any translocation program that is considered for this species.

Male-biased movement in pygmy bluetongue lizards: implications for conservation

Abstract Context. Translocation has become an increasingly common tool in the conservation of species. Understanding the movement patterns of some species can be important to minimise loss of individuals from the translocation release site. Aims. To describe seasonal and sex-biased movements within populations of an endangered Australian lizard. Methods. We monitored seasonal movement in the endangered pygmy bluetongue lizard (Tiliqua adelaidensis) by using pitfall trapping, with a total of 49 440 trap-nights from three sites over 2 years. Other studies have shown that individual pygmy bluetongue lizards normally remained closely associated with their spider burrow refuges, with very little movement. Thus, we interpreted any captures detected through pitfall trapping as out of burrow movements. We investigated whether there was any seasonal, age or sex bias in moving individuals. Key results. We found that male pygmy bluetongue lizards were more likely to move than were females. After adults, neonates were the second-most captured age class. Spring was the peak movement time for adults, whereas movement of neonates occurred in autumn. Key conclusions. The majority of movement can be attributed to males in the breeding season, whereas females move very little. Implications. The present study provides some baseline data that would allow more informed decisions about the most appropriate individuals in a population to choose for a translocation program and the times to conduct translocations to allow the maximum chance for establishment.

Behavioural observations and use of burrow systems by an endangered Australian arid-zone lizard, Slater's skink (Liopholis slateri)

Abstract. The endangered Slater’s skink (Liopholis slateri) is restricted to the river floodplain habitat of central Australia. It is an obligate burrower and creates complex, multientrance burrow systems in the mound of soil that builds up around the base of some shrubs and small trees. We provide detailed information about the behaviour and use of the burrow systems by Slater’s skink. The behaviour of lizards remained consistent over the four months (October–January) of the study, and lizards performed almost all of their daily activities around their burrow/mound systems. Lizards also showed signs of sociality, as pairs of lizards were observed to share occupancy of single burrow systems over extended periods, and demonstrated a high level of tolerance to conspecifics. This study emphasises the importance of the burrow systems for the daily life of this lizard and suggests that conservation measures should focus on ensuring that the lizards have a reliable supply of stable and suitable burrows in their preferred habitat.

The use of scats as social signals in a solitary, endangered scincid lizard, Tiliqua adelaidensis

Context The deliberate accumulation of faeces or scats in one location is a common behaviour used for social signalling. The endangered pygmy bluetongue lizard, Tiliqua adelaidensis, is a solitary-living species that appears to use scats as social signals. Previous studies have found that these lizards approach burrows more cautiously if there is a conspecific scat present and behave differently to scats from male and female conspecifics, indicating that these lizards can recognise scat-based conspecific cues. For endangered species, understanding how an animal uses and responds to chemical cues has the potential to become a powerful tool in conservation management. Aims To investigate whether these solitary lizards might be using scats as social signals by testing whether scats were being deposited in a non-random pattern designed to maximise their exposure to the nearest neighbour conspecifics. Method In the present study, we investigated the spatial pattern of scatting behaviour by pygmy bluetongue lizards in the field. Results Scats were consistently deposited in one direction that was significantly aligned with the nearest occupied burrow of a neighbouring lizard. The same deposition sites were used when previous scats were either destroyed by rain, or experimentally moved to a different location. Male lizards deposited scats significantly closer to their own burrows when neighbours were closer. Key conclusions The results were consistent with the lizards using scats to advertise their presence and status. The scat-deposition patterns observed in the present study suggest that scats are used as an olfactory signal associated with social organisation of pygmy bluetongue lizards. Implications Current plans for the conservation management of this endangered species include translocations. By understanding how these lizards respond to, and use chemical cues, we may be able to use this knowledge to aid in translocation programs, e.g. by pre-establishing territories for individuals before they are introduced into the population.

Mating behaviour in pygmy bluetongue lizards: do females ‘attract’ male lizards?

Abstract. Mating behaviour in lizards has been well studied, with most reports indicating that the male dominates in initiating the mating, characteristically displaying visually to attract partners. This strategy may be less successful in secretive species that remain in small areas around their refuge, infrequently encountering other conspecifics, like the endangered Australian pygmy bluetongue lizard (Tiliqua adelaidensis). Adult lizards of this species spend most of their time in or at the entrance of single-entrance vertical burrows, built by spiders, in patches of native grassland in South Australia. We filmed the behaviour of nine female lizards for 10 days in each month from October 2011 to February 2012. During filming in October, the austral spring, we observed 43 cases of females making moves away from their burrows, and back along the same path, in that month, that we did not observe among males, or among females in any other month. We observed 27 cases of males approaching female burrows, only in October and mostly along the paths previously taken by the females. Males attempted to mate, and were successful on five occasions. We describe the female movements and suggest that their function is to attract male mating partners.

Long and short term residence in refuge burrows by endangered pygmy bluetongue lizards

The pygmy bluetongue lizard ( Tiliqua adelaidensis) is an endangered species which is restricted to native grassland remnants in South Australia. Individuals live in vertical burrows with a single entrance from which they ambush invertebrate prey. We monitored marked burrows over two entire spring-summer seasons, the period when the lizards are active, and found that the population contained a mixture of dispersers that remained in a burrow briefly, and residents that occupy a burrow for the entire study period. There were more females than males among the residents and most of the burrow abandonment happened in the early spring, the time when male lizards probably move around to seek matings. Our study described burrow occupancy dynamics, and will assist the conservation management of this endangered species.

Lizard behaviour suggests a new design for artificial burrows

Abstract Context. The use of artificial refuges is a common strategy for the conservation management of endangered species. However, artificial refuges may alter an animal’s natural behaviour that in turn may be detrimental to the species. The endangered pygmy bluetongue lizard from Australia is one species that will accept artificial burrows. Aims. The aim of the present research was to determine whether the normal behaviour of the pygmy bluetongue lizards differed between artificial and natural burrows, so as to determine whether the existing artificial burrow is an optimal design for this species. Methods. In the present study, we filmed the behaviour of lizards as they entered artificial and natural burrows. We compared the number of times a lizard entered a burrow, the time that lizards spent inspecting burrows, and the behaviours that lizards used when entering artificial and natural burrows. Key results. We found that in natural burrows, lizards always entered head first, and then usually reversed direction inside, using an enlarged basal chamber, to sit with their head uppermost in the entrance. In artificial burrows, however, lizards had to enter head first, then reverse tail-first back out, and then reverse tail-first back into the burrow (so as to have their head facing upwards) We called this behaviour reversing from outside. Key conclusion. The stereotyped reversing-from-outside behaviour when entering artificial burrows, and its occasional occurrence in natural burrows, suggest that it has evolved to allow lizards to use narrow burrows as well as those with a chamber, even though it can increase lizard’s surface activity and exposure to predation. Implication. The reversing behaviour from outside the artificial burrow increases exposure to potential predators, and our observations suggest that a re-design of artificial burrows to incorporate internal space for turning around may improve their effectiveness in conservation management interventions.