29 research outputs found
Association networks reveal social organisation in the sleepy lizard
No full textWe investigated the social organization of the Australian sleepy lizard, Tiliqua rugosa, by describing the social network of a local population. We attached activity meters and GPS recorders to 21 neighbouring lizards in a semiarid site in South Australia, and monitored their location every 10 min over 3 months (September–December 2007). From over 5000 sets of synchronized location records we calculated distances between all possible dyads of active lizards, and constructed binary social networks based on close associations between individuals. We compared empirical networks with a null model network for spatially structured populations that assumed random movement within lizard home ranges. We showed significantly lower network degree (i.e. fewer cases of individuals associating) in the observed network than in the null model, and deduced avoidance between some individuals. We found the predominant form of social organization was pair living, and, contrary to previous reports, we found pair associations persisted after mating had finished. Thus, the network analysis revealed a cryptic social organization, which cannot be explained by either biparental care or mate guarding, but may instead relate to refuge site distributions, enhanced vigilance or efficient location of mates in subsequent seasons
Transmission network predicts ectoparasite load in a lizard
No full textLiving in social groups facilitates cross-infection by parasites. However, empirical studies on indirect transmission within wildlife populations are scarce. We investigated whether asynchronous overnight refuge sharing among neighboring sleepy lizards, Tiliqua rugosa, facilitates indirect transmission of its ectoparasitic tick, Amblyomma limbatum. We fitted 18 neighboring lizards with GPS recorders, observed their overnight refuge use each night over 3 months, and counted their ticks every fortnight. We constructed a transmission network to estimate the cross-infection risk based on asynchronous refuge sharing frequencies among all lizards and the life history traits of the tick. Although self-infection was possible, the network provided a powerful predictor of measured tick loads. Highly connected lizards that frequently used their neighbors' refuges were characterized by higher tick loads. Thus, indirect contact had a major influence on transmission pathways and parasite loads. Furthermore, lizards that used many different refuges had lower cross- and self-infection risks and lower tick loads than individuals that used relatively fewer refuges. Increasing the number of refuges used by a lizard may be an important defense mechanism against ectoparasite transmission in this species. Our study provides important empirical data to further understand how indirectly transmitted parasites move through host populations and influence individual parasite loads
Artificial Water Point for Livestock Influences Spatial Ecology of a Native Lizard Species
No full textThis is an open access
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credited.Pastoralism is a major agricultural activity in drier environments, and can directly and indirectly impact native species in those areas. We investigated how the supply of an artificial watering point to support grazing livestock affected movement and activity patterns of the Australian sleepy lizard (Tiliqua rugosa) during a drought year. We observed 23 adult lizards; six had access to a dam, whereas 17 lizards did not. Lizards with access to the dam had larger home ranges, were substantially active on more days (days with >100 steps), and moved more steps per day compared to lizards that did not have access to the dam, both during the early and late period of our observation. Furthermore, while the two groups of lizards had similar body condition early in the season, they differed later in the season. Lizards with dam access retained, whereas lizards without access lost body condition. Local heterogeneity in access to an artificial water resource resulted in spatially dependent behavioural variation among sleepy lizard individuals. This suggests that sleepy lizards have flexible responses to changing climatic conditions, depending on the availability of water. Furthermore, while reducing activity appears a suitable short term strategy, if harsh conditions persist, then access to dams could be of substantial benefit and could support sustained lizard activity and movement and allow maintenance of body condition. Hence, artificial watering points, such as the dams constructed by pastoralists, may provide local higher quality refugia for sleepy lizards and other species during drought conditions
Author Correction: Combined inhibition of BET family proteins and histone deacetylases as a potential epigenetics-based therapy for pancreatic ductal adenocarcinoma
No full textMate Familiarity Affects Pairing Behaviour in a Long-Term Monogamous Lizard: Evidence from Detailed Bio-Logging and a 31-Year Field Study
No full textThis is the peer reviewed version of the following article: [Leu ST, Burzacott D, Whiting MJ, Bull CM (2015) Mate familiarity drives long-term monogamy in a lizard: evidence from detailed biologging and a thirty one year field study. Ethology 121(8) pp. 760-768], which has been published in final form at DOI:10.1111/eth.12390. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving (http://olabout.wiley.com/WileyCDA/Section/id-820227.html#terms). This article is under embargo for a period of 12 months from the date of publicationLong-term monogamy is most prevalent in birds but is also found in lizards. We combined a 31-year field study of the long-lived, monogamous Australian sleepy lizard, Tiliqua rugosa, with continuous behavioural observations through GPS data logging, in one year, to investigate the duration of pair bonds, rates of partner change and whether either the reproductive performance hypothesis or the mate familiarity hypothesis could explain this remarkable long-term monogamy. The reproductive performance hypothesis predicts higher reproductive success in more experienced parents, whereas the mate familiarity hypothesis suggests that effects of partner familiarity select for partner retention and long-term monogamy. Divorce ratios were below 34% over a five year period and most sleepy lizards formed long-term pair bonds: 31 partnerships lasted for more than 15 years, 110 for more than 10 years, and the recorded maximum was 27 years (ongoing). In the year when we conducted detailed observations, familiar pairs mated significantly earlier than unfamiliar pairs. Previous pairing experience (total number of years paired with previous partners) had no significant effect. Early mating often equates to higher reproductive success, and we infer that is the case in sleepy lizards. Early mating of familiar pairs was not due to better body condition. We propose two suggestions about the proximate mechanisms that may allow familiar pair partners to mate earlier than unfamiliar partners. First, they may have improved coordination of their reproductive sexual cycles to reach receptivity earlier and thereby maximise fertilisation success. Second, they may forage more efficiently, benefiting from effective information transfer and/or cooperative predator detection. Those ideas need empirical testing in the future. Regardless of the mechanism, our observations of sleepy lizard pairing behaviour support the mate familiarity hypothesis, but not the reproductive performance hypothesis, as an explanation for its long-term monogamous mating syste
When the going gets tough: behavioural type-dependent space use in the sleepy lizard changes as the season dries
No full textAuthor version made available here in accordance with publisher's policy.Understanding space use remains a major challenge for animal ecology, with implications for species interactions, disease spread, and conservation. Behavioural type (BT) may shape the space use of individuals within animal populations. Bolder or more aggressive individuals tend to be more exploratory and disperse further. Yet, to date we have limited knowledge on how space use other than dispersal depends on BT. To address this question we studied BT-dependent space-use patterns of sleepy lizards (Tiliqua rugosa) in southern Australia. We combined high-resolution global positioning system (GPS) tracking of 72 free-ranging lizards with repeated behavioural assays, and with a survey of the spatial distributions of their food and refuge resources. Bayesian generalized linear mixed models (GLMM) showed that lizards responded to the spatial distribution of resources at the neighbourhood scale and to the intensity of space use by other conspecifics (showing apparent conspecific avoidance). BT (especially aggressiveness) affected space use by lizards and their response to ecological and social factors, in a seasonally dependent manner. Many of these effects and interactions were stronger later in the season when food became scarce and environmental conditions got tougher. For example, refuge and food availability became more important later in the season and unaggressive lizards were more responsive to these predictors. These findings highlight a commonly overlooked source of heterogeneity in animal space use and improve our mechanistic understanding of processes leading to behaviourally driven disease dynamics and social structure.Our research was funded by the Australian Research Council, the Holsworth Wildlife Research Endowment and NSF grant no. DEB-1456730
Molecular biology of hearing
No full textThe inner ear is our most sensitive sensory organ and can be subdivided into three functional units: organ of Corti, stria vascularis and spiral ganglion. The appropriate stimulus for the organ of hearing is sound, which travels through the external auditory canal to the middle ear where it is transmitted to the inner ear. The inner ear houses the hair cells, the sensory cells of hearing. The inner hair cells are capable of mechanotransduction, the transformation of mechanical force into an electrical signal, which is the basic principle of hearing. The stria vascularis generates the endocochlear potential and maintains the ionic homeostasis of the endolymph. The dendrites of the spiral ganglion form synaptic contacts with the hair cells. The spiral ganglion is composed of neurons that transmit the electrical signals from the cochlea to the central nervous system. In recent years there has been significant progress in research on the molecular basis of hearing. An increasing number of genes and proteins related to hearing are being identified and characterized. The growing knowledge of these genes contributes not only to greater appreciation of the mechanism of hearing but also to a deeper understanding of the molecular basis of hereditary hearing loss. This basic research is a prerequisite for the development of molecular diagnostics and novel therapies for hearing loss
Explaining Output Volatility: The Case of Taxation
No full textThis paper presents empirical evidence against the popular perception that macro volatility is exogenous. We obtain tax effects on macro aggregates in the stochastic neoclassical model. Taxes are shown to affect the second moment of output growth rates without affecting the first moment. Exploiting heterogeneity patterns in a panel of OECD countries, we estimate tax effects on macro volatility, explicitly modeling the unobserved variance process. We find a strong empirical link between taxes and output volatility. Accounting for non-stationarity of taxes and output volatility, we find empirical evidence of a cointegrating relationship.macroeconomic volatility, tax effects, continuous-time DSGE models
International Energy Technology Transfersfor Climate Change Mitigation - What, who, how, why, when, where, how much … and the Implications for International Institutional Architecture
No full textThe goal of the paper is to expand and refine the international technology transfer negotiating and analytic agendas and to reframe the issues. The paper presents concepts, indicators, illustrations and data that identify and measure international transfers of energy technologies that can be used to mitigate climate change. Among the questions on that agenda are how much technology transfer there has been to date, and how much will be needed in the future, especially to assist non-Annex I developing countries in their efforts to mitigate climate change. Before the how much questions can be answered, however, there are several prior questions, and hence the many other elements of the subtitle of the paper: what, who, how, why, when, where. These aspects of international technology transfer vary significantly among three existing institutional settings and among the associated analytic paradigms: North-South Official Development Assistance, Global Private International Investment and Trade, and International Public-Private Cooperation Agreements. The principal sections of the paper focus on features of international technology transfers in these institutional settings and on illustrations drawn from the biodiesel industry, especially the use of jatropha tree as the source of the feedstock. The conclusions are summarized as follows: (i) Technologies include intangible know-how and services, as well as tangible goods in the form of production process equipment and finished products. (ii) International transfers of some types of technology are much easier to measure than others. (iii) International technology transfers are highly industry-specific. (iv) Even for individual industries, it is necessary to use multiple indicators of technology transfers. (v) Patterns in the types of technology and methods of transfer vary across the three institutional settings examined in the paper. (vi) All three of the institutional arrangements are probably under-performing and inadequa
Testing the robustness of transmission network models to predict ectoparasite loads. One lizard, two ticks and four years
No full textOpen access under CC BY-NC-SA licenseAbstract
We investigated transmission pathways for two tick species, Bothriocroton hydrosauri and Amblyomma limbatum, among their sleepy lizard (Tiliqua rugosa) hosts in a natural population in South Australia. Our aim was to determine whether a transmission network model continued to predict parasite load patterns effectively under varying ecological conditions. Using GPS loggers we identified the refuge sites used by each lizard on each day. We estimated infectious time windows for ticks that detached from a lizard in a refuge. Time windows were from the time when a detached tick molted and become infective, until the time it died from desiccation while waiting for a new host. Previous research has shown that A. limbatum molts earlier and survives longer than B. hydrosauri. We developed two transmission network models based on these differences in infective time windows for the two tick species. Directed edges were generated in the network if one lizard used a refuge that had previously been used by another lizard within the infectious time window. We used those models to generate values of network node in-strength for each lizard, a measure of how strongly connected an individual is to other lizards in the transmission network, and a prediction of infection risk for each host. The consistent correlations over time between B. hydrosauri infection intensity and network derived infection risk suggest that network models can be robust to environmental variation among years. However, the contrasting lack of consistent correlation in A. limbatum suggests that the utility of the same network models may depend on the specific biology of a parasite species
