Warmer Ambient Temperatures Depress Detoxification and Food Intake by Marsupial Folivores

Ambient temperature is an underappreciated determinant of foraging behaviour in wild endotherms, and the requirement to thermoregulate likely influences food intake through multiple interacting mechanisms. We investigated relationships between ambient temperature and hepatic detoxification capacity in two herbivorous marsupials, the common ringtail possum (Pseudocheirus peregrinus) and common brushtail possum (Trichosurus vulpecula) that regularly feed on diets rich in plant toxins. As an indicator of hepatic detoxification capacity, we determined the functional clearance rate of an anaesthetic agent, Alfaxalone, after possums were acclimated to 10°C [below the thermoneutral zone (TNZ)], 18°C [approximately lower critical temperature (LCT)], and 26°C [approximately upper critical temperature (UCT)] for either 7 days or less than 24 h. We then measured intake of foods with high or low plant secondary metabolite (PSM) concentrations under the same temperature regimes. After 7 days of acclimation, we found a positive correlation between the functional clearance rate of Alfaxalone and ambient temperature, and a negative relationship between ambient temperature and intake of foods with high or low PSM concentrations for both species. The effect of ambient temperature on intake of diets rich in PSMs was absent or reduced when possums were kept at temperatures for less than 24 h. Our results underscore the effects of ambient temperature in hepatic metabolism particularly with respect intake of diets containing PSMs. Given that the planet is warming, it is vital that effects of ambient temperature on metabolism, nutrition and foraging by mammalian herbivores is taken into account to predict range changes of species and their impact on ecosystems

Coordinated Activation of Candidate Proto-Oncogenes and Cancer Testes Antigens via Promoter Demethylation in Head and Neck Cancer and Lung Cancer

Background: Epigenetic alterations have been implicated in the pathogenesis of solid tumors, however, proto-oncogenes activated by promoter demethylation have been sporadically reported. We used an integrative method to analyze expression in primary head and neck squamous cell carcinoma (HNSCC) and pharmacologically demethylated cell lines to identify aberrantly demethylated and expressed candidate proto-oncogenes and cancer testes antigens in HNSCC. Methodology/Principal Findings: We noted coordinated promoter demethylation and simultaneous transcriptional upregulation of proto-oncogene candidates with promoter homology, and phylogenetic footprinting of these promoters demonstrated potential recognition sites for the transcription factor BORIS. Aberrant BORIS expression correlated with upregulation of candidate proto-oncogenes in multiple human malignancies including primary non-small cell lung cancers and HNSCC, induced coordinated proto-oncogene specific promoter demethylation and expression in non-tumorigenic cells, and transformed NIH3T3 cells. Conclusions/Significance: Coordinated, epigenetic unmasking of multiple genes with growth promoting activity occurs i

Genomic comparisons reveal biogeographic and anthropogenic impacts in the koala (Phascolarctos cinereus): a dietary-specialist species distributed across heterogeneous environments

The Australian koala is an iconic marsupial with highly specific dietary requirements distributed across heterogeneous environments, over a large geographic range. The distribution and genetic structure of koala populations has been heavily influenced by human actions, specifically habitat modification, hunting and translocation of koalas. There is currently limited information on population diversity and gene flow at a species-wide scale, or with consideration to the potential impacts of local adaptation. Using species-wide sampling across heterogeneous environments, and high-density genome-wide markers (SNPs and PAVs), we show that most koala populations display levels of diversity comparable to other outbred species, except for those populations impacted by population reductions. Genetic clustering analysis and phylogenetic reconstruction reveals a lack of support for current taxonomic classification of three koala subspecies, with only a single evolutionary significant unit supported. Furthermore, similar to 70% of genetic variance is accounted for at the individual level. The Sydney Basin region is highlighted as a unique reservoir of genetic diversity, having higher diversity levels (i.e., Blue Mountains region; AvHe(corr)-0.20, PL% = 68.6). Broad-scale population differentiation is primarily driven by an isolation by distance genetic structure model (49% of genetic variance), with clinal local adaptation corresponding to habitat bioregions. Signatures of selection were detected between bioregions, with no single region returning evidence of strong selection. The results of this study show that although the koala is widely considered to be a dietary-specialist species, this apparent specialisation has not limited the koala's ability to maintain gene flow and adapt across divergent environments as long as the required food source is available

Behavioural thermoregulation in butterflies: the interacting effects of body size and basking posture in Hypolimnas bolina (L.) (Lepidoptera: Nymphalidae)

The evolutionary significance of body size variation in male insects is often obscure. One way in which this parameter could affect reproductive success is via its relevance to thermoregulation. In this study we investigated the relevance of body size to heat exchange rates in a tropical nymphalid, the common eggfly (Hypolimnas bolina) (L.). Males of this territorial species elevate their body temperature above ambient levels via a series of basking postures coupled with strategic choice of perching microhabitat. In an experiment with dead butterfly models we found, as expected, heightened rates of heat exchange (heating and cooling rates) in smaller individuals. There was also a significant interaction between basking posture and body size, with smaller individuals exhibiting significantly greater variation in heating rate across all available basking postures. This suggests that smaller males would have greater control over their rate of basking heat gain (by having at their disposal a greater potential range of heating rates), but they would also radiate body heat at a higher rate than their larger conspecifics. Using 'grab and stab' techniques, we found no evidence that smaller individuals are closer to their putative thermal optimum under a range of ambient conditions in the field. However, a more substantive field program, incorporating a more precise characterisation of the ambient thermal environment, will be required to fully evaluate the thermal significance of body size variation in males of this territorial butterfly

Spatial Requirements of Free-Ranging Huon Tree Kangaroos, Dendrolagus matschiei (Macropodidae), in Upper Montane Forest

Tree kangaroos (Macropodidae, Dendrolagus) are some of Australasia's least known mammals. However, there is sufficient evidence of population decline and local extinctions that all New Guinea tree kangaroos are considered threatened. Understanding spatial requirements is important in conservation and management. Expectations from studies of Australian tree kangaroos and other rainforest macropodids suggest that tree kangaroos should have small discrete home ranges with the potential for high population densities, but there are no published estimates of spatial requirements of any New Guinea tree kangaroo species. Home ranges of 15 Huon tree kangaroos, Dendrolagus matschiei, were measured in upper montane forest on the Huon Peninsula, Papua New Guinea. The home range area was an average of 139.6±26.5 ha (100% MCP; n = 15) or 81.8±28.3 ha (90% harmonic mean; n = 15), and did not differ between males and females. Home ranges of D. matschiei were 40–100 times larger than those of Australian tree kangaroos or other rainforest macropods, possibly due to the impact of hunting reducing density, or low productivity of their high altitude habitat. Huon tree kangaroos had cores of activity within their range at 45% (20.9±4.1 ha) and 70% (36.6±7.5 ha) harmonic mean isopleths, with little overlap (4.8±2.9%; n = 15 pairs) between neighbouring females at the 45% isopleth, but, unlike the Australian species, extensive overlap between females (20.8±5.5%; n = 15 pairs) at the complete range (90% harmonic mean). Males overlapped each other and females to a greater extent than did pairs of females. From core areas and overlap, the density of female D. matschiei was one per 19.4 ha. Understanding the cause of this low density is crucial in gaining greater understanding of variations in density of tree kangaroos across the landscape. We consider the potential role of habitat fragmentation, productivity and hunting pressure in limiting tree kangaroo density in New Guinea rainforests

The limit to the distribution of a rainforest marsupial folivore is consistent with the thermal intolerance hypothesis

Models of impacts of climate change on species are generally based on correlations between current distributions and climatic variables, rather than a detailed understanding of the mechanisms that actually limit distribution. Many of the vertebrates endemic to rainforests of northeastern Australia are restricted to upland forests and considered to be threatened by climate change. However, for most of these species, the factors controlling their distributions are unknown. We examined the role of thermal intolerance as a possible mechanism limiting the distribution of Pseudochirops archeri (green ringtail possum), a specialist arboreal folivore restricted to rainforests above an altitude of 300 m in Australia's Wet Tropics. We measured short-term metabolic responses to a range of ambient temperatures, and found that P. archeri stores heat when ambient temperatures exceed 30°C, reducing water requirements for evaporative cooling. Due to the rate at which body temperature increases with ambient temperatures >30°C, this strategy is not effective over periods longer than 5 h. We hypothesise that the distribution of P. archeri is limited by interactions between (i) the duration and severity of extreme ambient temperatures (over 30°C), (ii) the scarcity of free water in the rainforest canopy in the dry season, and (iii) constraints on water intake from foliage imposed by plant secondary metabolites and fibre. We predict that dehydration becomes limiting for P. archeri where extreme ambient temperatures (>30°C) persist for more than 5 h per day over 4–6 days or more. Consistent with our hypothesis, the abundance of P. archeri in the field is correlated with the occurrence of extreme temperatures, declining markedly at sites where the average maximum temperature of the warmest week of the year is above 30°C. Assuming the mechanism of limitation is based on extreme temperatures, we expect impacts of climate change on P. archeri to occur in discrete, rapid events rather than as a slow contraction in range

Hydroregulation in a tropical dry-skinned ectotherm

While temperature effects on species' vulnerability to climate change are well studied, desiccation effects receive comparatively little attention. In addition, we poorly understand the capacity of ectotherms, and especially reptiles, to control water loss rates behaviourally by selecting suitable microhabitats. This study examined water loss rates and behavioural hydroregulation in the tropical rainforest skink Carlia rubrigularis to assess whether this dry-skinned ectotherm actively avoids desiccation and whether trade-offs occur between desiccation avoidance and selection of optimal temperatures, as previously shown in amphibians. Higher temperatures elicited humid refuge choice despite placing individuals in suboptimal thermal conditions, as indicated by preferred substrate temperatures. This finding emphasizes the importance of water loss even for taxa traditionally assumed to be highly desiccation resistant, and highlights this factor's potential influence on vulnerability to climate change by limiting activity times or by restricting individuals to thermally suboptimal microhabitats

Costs of venom production in the common death adder (Acanthophis antarcticus)

The utilization of venom in predatory and defensive contexts is associated with benefits regarding minimization of energetic expenditure on hunting, maximization of success in prey acquisition and avoidance of injury from dangerous prey and aggressors. Multiple characteristics suggest that venom is quite expensive to produce, thereby creating a tradeoff between advantages and disadvantages associated with its possession. The metabolic costs of venom production have rarely been studied and no information on the detailed metabolic processes during venom replenishment exists. Where costs of venom production have been studied they are often not in context with other components of the energy budget of the study organism. Using flow-through respirometry, we examined changes in metabolic rate in the Australian elapid Acanthophis antarcticus after venom expenditure and feeding as well as during preparation for shedding to establish a comparison of the magnitude of energetic expenditure during venom replenishment and other common physiological processes. We also defined the temporal pattern of metabolic processes during venom replenishment at a higher resolution than has previously been attempted in snakes. Our results suggest that total costs of venom replenishment are relatively small when compared to costs of digestion and shedding. We conclude that, in spite of the manifold factors suggesting a high cost of venom in snakes, its production is less energetically costly than often assumed. Until further research can clarify the reasons for this more caution should therefore be applied when assuming that costs of venom production exert strong selection pressures on the ecology, behavior and evolution of venomous taxa

The empirical relevance of short run efficiency

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Rapoport's Rule: do climatic variability gradients shape range extent?

The trend of increasing latitudinal range sizes of species towards higher latitudes, known as Rapoport's Rule, has been highly controversial in the literature since it was first proposed by Stevens in 1989. We contend that the question of interest is not whether general global patterns occur, nor whether they support or refute Rapoport's Rule, but whether the mechanism thought to underlie such patterns, the Climatic Variability Hypothesis, is supported. The Climatic Variability Hypothesis suggests that taxa originating from environmentally variable habitats, such as those at high latitudes and altitudes, should evolve wider environmental tolerances, and consequently establish wider distributions along climate gradients than taxa originating from relatively stable habitats. We applied a novel approach, incorporating measures of temperature variability across habitats within species' ranges into models of range size distributions, to determine whether the Climatic Variability Hypothesis applied to three clades of medium-sized ectotherms (lizards) distributed over Australia. Our results show that the Climatic Variability Hypothesis is supported, even in taxa that do not exhibit a traditional Rapoport Effect, due to complex, non-unidirectional climatic gradients in our study area. The results highlight the strong impact of climatic variability on species' physiological tolerances and their associated geographic distributions