Social networks and the spread of Salmonella in a sleepy lizard population.

Although theoretical models consider social networks as pathways for disease transmission, strong empirical support, particularly for indirectly transmitted parasites, is lacking for many wildlife populations. We found multiple genetic strains of the enteric bacterium Salmonella enterica within a population of Australian sleepy lizards (Tiliqua rugosa), and we found that pairs of lizards that shared bacterial genotypes were more strongly connected in the social network than were pairs of lizards that did not. In contrast, there was no significant association between spatial proximity of lizard pairs and shared bacterial genotypes. These results provide strong correlative evidence that these bacteria are transmitted from host to host around the social network, rather than that adjacent lizards are picking up the same bacterial genotype from some common source.

Managed relocation as an adaptation strategy for mitigating climate change threats to the persistence of an endangered lizard.

The distributional ranges of many species are contracting with habitat conversion and climate change. For vertebrates, informed strategies for translocations are an essential option for decisions about their conservation management. The pygmy bluetongue lizard, Tiliqua adelaidensis, is an endangered reptile with a highly restricted distribution, known from only a small number of natural grassland fragments in South Australia. Land-use changes over the last century have converted perennial native grasslands into croplands, pastures and urban areas, causing substantial contraction of the species' range due to loss of essential habitat. Indeed, the species was thought to be extinct until its rediscovery in 1992. We develop coupled-models that link habitat suitability with stochastic demographic processes to estimate extinction risk and to explore the efficacy of potential climate adaptation options. These coupled-models offer improvements over simple bioclimatic envelope models for estimating the impacts of climate change on persistence probability. Applying this coupled-model approach to T. adelaidensis, we show that: (i) climate-driven changes will adversely impact the expected minimum abundance of populations and could cause extinction without management intervention, (ii) adding artificial burrows might enhance local population density, however, without targeted translocations this measure has a limited effect on extinction risk, (iii) managed relocations are critical for safeguarding lizard population persistence, as a sole or joint action and (iv) where to source and where to relocate animals in a program of translocations depends on the velocity, extent and nonlinearities in rates of climate-induced habitat change. These results underscore the need to consider managed relocations as part of any multifaceted plan to compensate the effects of habitat loss or shifting environmental conditions on species with low dispersal capacity. More broadly, we provide the first step towards a more comprehensive framework for integrating extinction risk, managed relocations and climate change information into range-wide conservation management.

Unique biological rhythm in the reproductive behaviour of female ticks of reptiles.

We report the discovery of a biological rhythm in the reproductive behaviour of the tick Bothriocroton hydrosauri that was absent in Amblyomma limbatum, a species that occurs on the same species of reptile host. Female B. hydrosauri mated in autumn or winter delayed oviposition until the following spring, while there was no diapause in conspecific females mated in spring or early summer. Initiation of ovipositional diapause in ticks is usually related to photoperiodic stimuli, but this was not the case for B. hydrosauri. The sinusoidal pattern in pre-oviposition times of B. hydrosauri females mated in different months in the laboratory suggests an internal seasonal time-keeping mechanism. We hypothesize that hormones imbibed by females during their bloodmeal may provide environmental cues associated with the induction of diapause. Irrespective of the mechanism underlying the rhythm, diapause by B. hydrosauri females mated during autumn or winter is of adaptive advantage because it synchronizes oviposition with favourable environmental conditions for egg hatching and increases the chance of larvae finding a host. The lack of a similar biological rhythm in A. limbatum may be a reflection of the different environmental conditions this species experiences throughout most of its range as compared with B. hydrosauri.

Evaluation of offspring size-number invariants in 12 species of lizard.

The optimal division of resources into offspring size vs. number is one of the classic problems in life-history evolution. Importantly, models that take into account the discrete nature of resource division at low clutch sizes suggest that the variance in offspring size should decline with increasing clutch size according to an invariant relationship. We tested this prediction in 12 species of lizard with small clutch sizes. Contrary to expectations, not all species showed a negative relationship between variance in offspring size and clutch size, and the pattern significantly deviated from quantitative predictions in five of the 12 species. We suggest that the main limitation of current size-number models for small clutch sizes is that they rely on assumptions of hierarchical allocation strategies with independence between allocation decisions. Indeed, selection may favour alternative mechanisms of reproductive allocation that avoid suboptimal allocation imposed by the indivisible fraction at low clutch sizes.

Seasonal and spatial dynamics of ectoparasite infestation of a threatened reptile, the tuatara (Sphenodon punctatus).

The conservation of threatened vertebrate species and their threatened parasites requires an understanding of the factors influencing their distribution and dynamics. This is particularly important for species maintained in conservation reserves at high densities, where increased contact among hosts could lead to increased rates of parasitism. The tuatara (Sphenodon punctatus) (Reptilia: Sphenodontia) is a threatened reptile that persists at high densities in forests (approximately 2700 tuatara/ha) and lower densities in pastures and shrubland (< 200 tuatara/ha) on Stephens Island, New Zealand. We investigated the lifecycles and seasonal dynamics of infestation of two ectoparasites (the tuatara tick, Amblyomma sphenodonti, and trombiculid mites, Neotrombicula sp.) in a mark-recapture study in three forest study plots from November 2004 to March 2007, and compared infestation levels among habitat types in March 2006. Tick loads were lowest over summer and peaked from late autumn (May) until early spring (September). Mating and engorgement of female ticks was highest over spring, and larval tick loads subsequently increased in early autumn (March). Nymphal tick loads increased in September, and adult tick loads increased in May. Our findings suggest the tuatara tick has a 2- or 3-year lifecycle. Mite loads were highest over summer and autumn, and peaked in March. Prevalences (proportion of hosts infected) and densities (estimated number of parasites per hectare) of ticks were similar among habitats, but tick loads (parasites per host) were higher in pastures than in forests and shrub. The prevalence and density of mites was higher in forests than in pasture or shrub, but mite loads were similar among habitats. We suggest that a higher density of tuatara in forests may reduce the ectoparasite loads of individuals through a dilution effect. Understanding host-parasite dynamics will help in the conservation management of both the host and its parasites.

Optimized blood cell profiling method for genomic biomarker discovery using high-density microarray.

High-quality biomarkers for disease progression, drug efficacy and toxicity liability are essential for improving the efficiency of drug discovery and development. The identification of drug-activity biomarkers is often limited by access to and the quantity of target tissue. Peripheral blood has increasingly become an attractive alternative to tissue samples from organs as source for biomarker discovery, especially during early clinical studies. However, given the heterogeneous blood cell population, possible artifacts from ex vivo activations, and technical difficulties associated with overall performance of the assay, it is challenging to profile peripheral blood cells directly for biomarker discovery. In the present study, Applied BioSystems' blood collection system was evaluated for its ability to isolate RNA suitable for use on the Affymetrix microarray platform. Blood was collected in a TEMPUS tube and RNA extracted using an ABI-6100 semi-automated workstation. Using human and rat whole blood samples, it was demonstrated that the RNA isolated using this approach was stable, of high quality and was suitable for Affymetrix microarray applications. The microarray data were statistically analysed and compared with other blood protocols. Minimal haemoglobin interference with RNA labelling efficiency and chip hybridization was found using the TEMPUS tube and extraction method. The RNA quality, stability and ease of handling requirement make the TEMPUS tube protocol an attractive approach for expression profiling of whole blood to support target and biomarker discovery.

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.

High levels of genetic monogamy in the group-living Australian lizard Egernia stokesii.

The Australian lizard Egernia stokesii lives in spatially and temporally stable groups of up to 17 individuals. We have recently shown that these groups are comprised of breeding partners, their offspring and, in some cases, highly related adults, providing the first genetic evidence of a family structure in any lizard species. Here we investigated the mating system of E. stokesii using data from up to eight polymorphic microsatellite loci and tested the hypothesis that breeding partners are monogamous both within and between mating seasons. Among 16 laboratory-born litters from field collected gravid females from two sites in South Australia, 75% had a single male parent and no male contributed to more than one litter, indicating a high level of genetic monogamy within a season. Additional analyses of field caught individuals, captured between 1994 and 1998, enabled assignment of parentage for 70 juveniles and subadults. These data showed that most young (88.6%) had both parents from within the same group and that high proportions of males (88.9%) and females (63.6%) have multiple cohorts of offspring only with the same partner. Our results suggest that monogamy both within and between seasons is a common mating strategy of E. stokesii and that breeding partners maintain stable associations together and with multiple cohorts of their offspring over periods of up to at least 5 years.

Infection dynamics of Hemolivia mariae in the sleepy lizard Tiliqua rugosa.

The blood parasite Hemolivia mariae was experimentally transmitted to lizards under laboratory and field conditions. Weekly blood samples from experimentally infected lizards were used to demonstrate the changes in composition of the different developmental stages of the parasite as infection progressed. The prepatent period and time to peak infection was longer for field-infected lizards compared to those held under laboratory conditions. Infections in naturally infected field lizards had longer pre-patent periods and lower mean-peak parasitaemia than those in lizards that were uninfected at the time of experimental infection. The results are discussed in relation to the natural field-transmission dynamics of H. mariae in its lizard and tick hosts.

Temporal and spatial dynamics of a parapatric boundary between two Australian reptile ticks.

Two tick species Aponomma hydrosauri and Amblyomma limbatum that infest large reptiles have an abrupt parapatric boundary near Mt Mary in South Australia. A previous model has suggested that the boundary is maintained at population density troughs resulting from habitat heterogeneity along a gradual environmental gradient. This paper describes the dynamics of the boundary on three transects over 17 years, 1982-98. Over the last seven years of that period there has been a significant increase in rainfall. At the same time, the boundary position has moved 1-2 km on the transects, with the more mesic adapted Ap. hydrosauri advancing into the distribution of the more xeric adapted Amb. limbatum. Also over the same time the density of ticks on lizards in regions flanking the boundary zone has increased for Ap. hydrosauri and decreased for Amb. limbatum. These results suggest that the environmental gradient has been altered, perhaps by increased rainfall, to favour Ap. hydrosauri, which has been able to colonize more successfully across the density troughs and extend its distribution.

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.

Prevalence of infection by the protozoan Hemolivia mariae in ticks.

This paper considers the prevalence of natural infections of the protozoan Hemolivia mariae, in its hosts the Australian sleepy lizard, Tiliqua rugosa, and the ixodid tick species, Amblyomma limbatum. We investigate whether the protozoan may be influencing the tick population in the field, by comparing the observed prevalence of infection in ticks with the prevalence expected from known transmission dynamics. The prevalence of infection in nymphs was similar to the expected prevalence, but the observed prevalence in adults was higher than expected. These results provide no evidence for infection-induced mortality in ticks. We also found that tick loads on infected and uninfected lizards were not significantly different and, overall, infected lizards were as likely to be tick-infested as uninfected lizards. However, infected lizards were less likely to be found carrying female ticks. On balance, the evidence did not strongly support the hypothesis that ticks avoid feeding on infected lizards. We use known parameters of H. mariae transmission to estimate the rate of tick ingestion that may be required to sustain the observed prevalences in the field.

Influence of temperature and relative humidity on the moulting success of Amblyomma limbatum and Aponomma hydrosauri (Acari: Ixodidae) larvae and nymphs.

This study compared the duration of the moulting periods of engorged larvae and nymphs of the ixodid ticks, Amblyomma limbatum and Aponomma hydrosauri, at different temperature/relative humidity regimes, and examined the relationships between the engorged weight of ticks and their weights after moulting. The results showed that for each species, there was a significant relationship between the weights of unfed nymphs and engorged larvae, and the weights of unfed adults and engorged nymphs. The weight of engorged nymphs was also a good indicator of their sex, with female ticks having heavier weights as engorged nymphs. Temperature and relative humidity had a marked effect on the moulting success of engorged ticks of both species. Aponomma hydrosauri larvae and nymphs were able to moult at lower temperatures than Amb. limbatum but most ticks, except Ap. hydrosauri larvae, failed to moult at 13 degrees C. Additionally, there was a marked decrease in the pre-moult times of ticks at higher temperatures, with larvae taking less time to moult than nymphs. At temperatures greater than 21 degrees C, Amb. limbatum took less time to moult than Ap. hydrosauri but this interspecific difference was less marked for nymphs. The interspecific differences in the responses of engorged larvae and nymphs to different temperatures and relative humidities correlated with interspecific differences in off-host behaviour and with the different climates the two species experience throughout most of their distributional range.

Prevalence and intensity of the blood parasite Hemolivia mariae in a field population of the skink Tiliqua rugosa.

The impacts of virulent parasites on humans or domestic animals are well documented. Less is known of the impact of parasites in natural host-parasite associations. A population of the Australian sleepy lizard Tiliqua rugosa is infected with the blood microparasite Hemolivia mariae, which is transmitted by the ectoparasitic tick Amblyomma limbatum. In most infected lizards a very small proportion, usually < 1%, of red blood cells are infected. A study of the prevalence of the microparasite in the field population found no difference either over 5 years of study or among times within a lizard activity season. Juvenile and sub-adult lizards and larger adults were less frequently infected with H. mariae than were other adults. In sub-adults this was related to a lower level of tick infestation. In adults, male and female lizards were equally frequently infected with H. mariae, but the presence or absence of ticks was not predictive of infection. The lizards' body condition was measured as the residual of the regression of log snout-vent length against log body mass. In female lizards the body condition was not affected by infection. In males the body condition declined over the sampling period each year, probably as a result of mate attendance. The body condition was poorer in male lizards with H. mariae infection than in uninfected males. Possible explanations for the associations of microparasites and host lizards are discussed.

The impact of tick parasites on the behaviour of the lizard Tiliqua rugosa.

Populations of the Australian sleepy lizard, Tiliqua rugosa, near Mt. Mary, South Australia carry natural infestations of two tick species Aponomma hydrosauri and Amblyomma limbatum. In field experiments at two sites, 18 km apart, lizards with experimentally increased tick loads had smaller home ranges, moved shorter distances in a day, and were found basking more but moving less often than lizards from which ticks were experimentally removed. The results were consistent for adult lizards in two years, and for sub-adults in a third year. Laboratory trials showed that juvenile lizards that had tick infestations had lower sprint speeds than uninfested siblings, and that adults with tick infestations had less endurance than those that were uninfested. The results contrast with those of a previous survey that showed that lizards with high tick loads had greater body size and remained longer at a site, but indicate that there may be a balance, for lizards, between the fitness advantages in occupying habitats with high-quality resources, and the costs from parasites that also prefer those habitats.

Transmission of the blood parasite Hemolivia mariae between its lizard and tick hosts.

The haemogregarine Hemolivia mariae is found in the erythrocytes of a natural population of the lizard Tiliqua rugosa. It infects two tick species, Amblyomma limbatum and Aponomma hydrosauri, which parasitise lizards. In laboratory experiments, engorged Amb. limbatum nymphs from infected lizards transmitted the haemogregarine to uninfected lizards significantly more often than engorged Ap. hydrosauri nymphs. Dissections of larvae and nymphs of both species fed on the same infected hosts showed that Amb. limbatum ticks were significantly more likely to become infected than Ap. hydrosauri ticks. In Amb. limbatum, oval cysts containing parasite stages thought to be infective to the lizard host had developed within 15 days of engorged nymphs detaching from an infected host. The chance of Ap. hydrosauri becoming infected and the intensity of infection in Amb. limbatum increased when ticks were fed on infected hosts as larvae and as nymphs compared with those fed on an infected host only as a nymph. This suggests that infections can accumulate over the tick life stages. Since the two tick species have broadly parapatric distributions, the boundary between the tick species may have implications for the distribution of H. mariae.

Host-seeking behaviour by Australian ticks (Acari: Ixodidae) with differing host specificities.

Ticks generally detach from their hosts into sites where they are later exposed to host species which may or may not be suitable for infestation. The question of how four species of ixodid ticks, with differing specificities, behave towards such potential host species was examined. Observations of the generalists, Aponomma hydrosauri and Amblyomma limbatum and the specialists, Aponomma fimbriatum and Aponomma concolor, showed that the generalists were attracted to a wider range of potential host species than the specialists and that the larval stages of all tick species, regardless of specificity, contacted more potential host species than the adults. The interspecific differences may be attributed to reliance on different sets of host cues, while the intraspecific differences may reflect the developmental state of the sensory system.

Reproductive interactions between two Australian reptile tick species.

In South Australia the two tick species Amblyomma limbatum and Aponomma hydrosauri share the same common reptile host species, but have allopatric distributions which abut along a narrow parapatric boundary. Reproductive interference is a mechanism that has previously been suggested could contribute to maintaining the boundary. Populations of each species were established in pens within the range of Aponomma hydrosauri. Pens held either each species alone, or the two species together. The performance of females in those pens was monitored over 28 months. There was no indication that the proportion of attached females which mated and engorged was reduced by the presence of heterospecifics. There was no indication that the time taken to mate, engorge and detach was any longer in the presence of heterospecifics. The experiment did not support the hypothesis that reproductive interference contributes to maintaining the parapatric boundary. However, Amblyomma limbatum in the pens had a shorter season of reproductive activity, and achieved much smaller numbers of reproductive females. This may inhibit successful colonization of cooler habitats to the south of its distribution.

Influence of environmental factors on oviposition and egg development in Amblyomma limbatum and Aponomma hydrosauri (Acari: Ixodidae).

This study examined the influence of temperature and light on the length of the pre-oviposition period of engorged females of two Australian ixodid ticks, Amblyomma limbatum and Aponomma hydrosauri. The hatching success and development time of eggs of both species were also compared at different temperatures and relative humidities. Darkness was found to have no effect on the duration of the pre-oviposition time or reproductive output of females of either species. In contrast, the preoviposition period of females of both species decreased with increasing temperature. Amb. limbatum females had shorter pre-oviposition periods than Ap. hydrosauri at all temperatures examined. Temperature and relative humidity had a marked effect on the hatching success of eggs. Eggs of both species had reduced hatching success at low relative humidities. Eggs failed to hatch at temperatures below 21 degrees C. Ap. hydrosauri eggs also failed to hatch at 34 degrees C while Amb. limbatum eggs failed to hatch at 36 degrees C. Within the range of temperatures suitable for egg development, the hatching times of eggs of both species decreased with increasing temperature. Amb. limbatum eggs developed faster than Ap. hydrosauri eggs at temperatures greater than 25 degrees C, but slower at cooler temperatures. These differences in the duration of their preoviposition period, and the responses of females and their eggs to different temperatures and relative humidities correlate with the different climates the two species experience throughout most of their distributional range.