Spatial variation in genomic signatures of local adaptation during the cane toad invasion of Australia.

Adaptive evolution can facilitate species' range expansions across environmentally heterogeneous landscapes. However, serial founder effects can limit the efficacy of selection, and the evolution of increased dispersal during range expansions may result in gene flow swamping local adaptation. Here, we study how genetic drift, gene flow and selection interact during the cane toad's (Rhinella marina) invasion across the heterogeneous landscape of Australia. Following its introduction in 1935, the cane toad colonised eastern Australia and established several stable range edges. The ongoing, more rapid range expansion in north-central Australia has occurred concomitant with an evolved increase in dispersal capacity. Using reduced representation genomic data of Australian cane toads from the expansion front and from two areas of their established range, we test the hypothesis that high gene flow constrains local adaptation at the expansion front relative to established areas. Genetic analyses indicate the three study areas are genetically distinct but show similar levels of allelic richness, heterozygosity and inbreeding. Markedly higher gene flow or recency of colonisation at the expansion front have likely hindered local adaptation at the time of sampling, as indicated by reduced slopes of genetic-environment associations (GEAs) estimated using a novel application of geographically weighted regression that accounts for allele surfing; GEA slopes are significantly steeper in established parts of the range. Our work bolsters evidence supporting adaptation of invasive species post-introduction and adds novel evidence for differing strengths of evolutionary forces among geographic areas with different invasion histories.

How turtles keep their cool: Seasonal and diel basking patterns in a tropical turtle.

Behavioural thermoregulation by ectotherms is an important mechanism for maintaining body temperatures to optimise physiological performance. Experimental studies suggest that nocturnal basking by Krefft's river turtles (Emydura macquarii krefftii) in the tropics may allow them to avoid high water temperatures, however, this hypothesis has yet to be tested in the field. In this study, we examined the influence of environmental temperature on seasonal and diel patterns of basking in E. m. krefftii in tropical north Queensland, Australia. Wildlife cameras were used to document turtle basking events for seven consecutive days and nights for each month over a year (April 2020-March 2021). Air and water temperatures were recorded simultaneously using temperature loggers. We used a negative binomial mixed effects model to compare mean basking durations (min) occurring among four environmental temperature categories based on population thermal preference (26 °C): 1) air temperature above and water temperature below preferred temperature; 2) air temperature below and water temperature above preferred temperature; 3) air and water temperatures both above preferred temperature; and 4) air and water temperatures both below preferred temperature. Basking behaviour was influenced significantly by the relationship between air and water temperature. During the day, turtles spent significantly less time basking when both air and water temperatures were above their preferred temperatures. Conversely, at night, turtles spent significantly more time basking when water temperatures were warm and air temperatures were cool relative to their preferred temperature. This study adds to the growing body of work indicating pronounced heat avoidance as a thermoregulatory strategy among tropical reptile populations.

The role of ecdysis in repair of an attachment system: a case study using geckos.

Skin provides functions such as protection and prevention of water loss. In some taxa, the outer surface of skin has been modified to form structures that enable attachment to various surfaces. Constant interaction with surfaces is likely to cause damage to these attachment systems and reduce function. It seems logical that when skin is shed via ecdysis, its effectiveness will increase, through repair of damage or other rejuvenating mechanisms. We address two questions using three diplodactylid geckos as model species. (1) Does repeated mechanical damage affect clinging ability in geckos to the point that they cannot support their own body weight? (2) Does use without induced damage reduce effectiveness of the attachment system, and if so, does ecdysis restore clinging ability? We found that repeated damage reduced clinging ability in all three species, although at different rates. Additionally, use reduced clinging ability over time when no apparent damage was incurred. Clinging ability increased after ecdysis in all three species, both when damage was specially induced, and when it was not. After normal use without induced damage, the increase in clinging ability after ecdysis was statistically significant in two of three species. Our findings show that use decreases clinging ability, and mechanical damage also effects geckos' capacity to exert shear forces consistently. Thus, ecdysis improves clinging ability both in scenarios where damage is induced and more generally. In addition to the physiological functions provided by skin, our study highlights an important function of ecdysis in a speciose vertebrate group.

Pathogenesis of Bohle iridovirus infection in Krefft's freshwater turtle hatchlings (Emydura macquarii krefftii).

Ranaviruses have been detected in over 12 families of reptiles including many genera of turtles, tortoises, and terrapins, but the pathogenesis of these infections is still poorly understood. Krefft's river turtle hatchlings (N = 36; Emydura macquarii krefftii) were inoculated intramuscularly with Bohle iridovirus (BIV, Ranavirus, isolate) or saline, and euthanized at 9 timepoints (3 infected and 1 control per timepoint) over a 24-day period. Samples of lung, liver, kidney, and spleen were collected for quantitative polymerase chain reaction (PCR); internal organs, skin, and oral cavity samples were fixed for histopathological examination. The earliest lesions, at 8 days postinoculation (dpi), were lymphocytic inflammation of the skin and fibrinoid necrosis of regional vessels at the site of inoculation, and mild ulcerative necrosis with lymphocytic and heterophilic inflammation in the oral, nasal, and tongue mucosae. Fibrinonecrotic foci with heterophilic inflammation were detected in spleen and gonads at 16 dpi. Multifocal hepatic necrosis, heterophilic inflammation, and occasional basophilic intracytoplasmic inclusion bodies were observed at 20 dpi, along with ulcerative lymphocytic and heterophilic tracheitis and bronchitis. Tracheitis, bronchitis, and rare bone marrow necrosis were present at 24 dpi. Of the viscera tested for ranaviral DNA by PCR, the liver and spleen had the highest viral loads throughout infection, and thus appeared to be major targets of viral replication. Testing of whole blood by qPCR was the most-effective ante-mortem method for detecting ranaviral infection compared with oral swabs. This study represents the first time-dependent pathogenesis study of a ranaviral infection in turtles.

Constant-temperature predictions underestimate growth of a fungal amphibian pathogen under individual host thermal profiles.

Ectotherm body temperatures fluctuate with environmental variability and host behavior, which may influence host-pathogen interactions. Fungal pathogens are a major threat to ectotherms and may be highly responsive to the fluctuating thermal profiles of individual hosts, especially cool-loving fungi exposed to high host temperatures. However, most studies estimate pathogen thermal performance based on averages of host or surrogate environmental temperatures, potentially missing effects of short-term host temperature shifts such as daily or hourly heat spikes. We recorded individual thermal profiles of Australian rainforest frogs using temperature-sensitive radio-transmitters. We then reproduced a subset of individual thermal profiles in growth chambers containing cultures of the near-global amphibian pathogen Batrachochytrium dendrobatidis (Bd) to investigate how realistic host temperature profiles affect Bd growth. We focused on thermal profiles that exceed the thermal optimum of Bd because the effects of realistic heat spikes on Bd growth are unresolved. Our laboratory incubation experiment revealed that Bd growth varied in response to relatively small differences in heat spike characteristics of individual frog thermal profiles, such as a single degree or a few hours, highlighting the importance of individual host behaviors in predicting population-level disease dynamics. The fungus also grew better than predicted under the most extreme and unpredictable frog temperature profile, recovering from two days of extreme (nearly 32 °C) heat spikes without negative effects on overall growth, suggesting we are underestimating the growth potential of the pathogen in nature. Combined with the previous finding that Bd reduces host heat tolerance, our study suggests that this pathogen may carry a competitive edge over hosts in the face of anthropogenic climate change.

Dancing to a different tune: changing reproductive seasonality in an introduced chital deer population.

Male and female reproductive behaviour is typically synchronised. In species such as those in the family Cervidae, reproductive timing is often cued by photoperiod, although in females, it can be dependent on body condition. When a species is introduced to a novel environment, the environment changes, or responses of the sexes to such cues differ, asynchronous reproductive behaviour between males and females may occur. We investigated the seasonality of reproductive behaviour in introduced chital deer in northern Queensland by examining male antler phase in relation to female conception rates. We then analysed the influence of different variables likely to affect the timing of male and female reproductive physiology. The lowest percentage of chital in hard antler in any 1 month in this study was 35% (Fig. 1), but the average value was closer to 50%, thus there was a seasonal peak in antler phase linked with photoperiod. Females conceived at any time of year, but were strongly influenced by the amount of rainfall 3 months prior to conception. This resulted in varying conception peaks year-to-year that often did not correspond to the male's peak in hard antler. In this system, a proportion of males and females were physiologically and behaviourally ready to mate at any time of the year. We predict that differences in the timing of the peaks between the males and females will lead to increased reproductive skew (variation in reproductive success among individual males). This pattern may select for different mating strategies or physiological mechanisms to increase reproductive success. Fig. 1 The average percentage of male chital deer in hard antler by month from 2014 to 2019 in north Queensland. Values above the bars indicate the total number of males that were sampled in each month and the error bars indicate the standard error. In the month with the lowest % males in hard antler in the entire study (November, 2017), 35% of males were in hard antler.

Geckos cling best to, and prefer to use, rough surfaces.

BACKGROUND: Fitness is strongly related to locomotor performance, which can determine success in foraging, mating, and other critical activities. Locomotor performance on different substrates is likely to require different abilities, so we expect alignment between species' locomotor performance and the habitats they use in nature. In addition, we expect behaviour to enhance performance, such that animals will use substrates on which they perform well. METHODS: We examined the associations between habitat selection and performance in three species of Oedura geckos, including two specialists, (one arboreal, and one saxicolous), and one generalist species, which used both rocks and trees. First, we described their microhabitat use in nature (tree and rock type) for these species, examined the surface roughnesses they encountered, and selected materials with comparable surface microtopographies (roughness measured as peak-to-valley heights) to use as substrates in lab experiments quantifying behavioural substrate preferences and clinging performance. RESULTS: The three Oedura species occupied different ecological niches and used different microhabitats in nature, and the two specialist species used a narrower range of surface roughnesses compared to the generalist. In the lab, Oedura geckos preferred substrates (coarse sandpaper) with roughness characteristics similar to substrates they use in nature. Further, all three species exhibited greater clinging performance on preferred (coarse sandpaper) substrates, although the generalist used fine substrates in nature and had good performance capabilities on fine substrates as well. CONCLUSION: We found a relationship between habitat use and performance, such that geckos selected microhabitats on which their performance was high. In addition, our findings highlight the extensive variation in surface roughnesses that occur in nature, both among and within microhabitats.

Infection dynamics, dispersal, and adaptation: understanding the lack of recovery in a remnant frog population following a disease outbreak.

Emerging infectious diseases can cause dramatic declines in wildlife populations. Sometimes, these declines are followed by recovery, but many populations do not recover. Studying differential recovery patterns may yield important information for managing disease-afflicted populations and facilitating population recoveries. In the late 1980s, a chytridiomycosis outbreak caused multiple frog species in Australia's Wet Tropics to decline. Populations of some species (e.g., Litoria nannotis) subsequently recovered, while others (e.g., Litoria dayi) did not. We examined the population genetics and current infection status of L. dayi, to test several hypotheses regarding the failure of its populations to recover: (1) a lack of individual dispersal abilities has prevented recolonization of previously occupied locations, (2) a loss of genetic variation has resulted in limited adaptive potential, and (3) L. dayi is currently adapting to chytridiomycosis. We found moderate-to-high levels of gene flow and diversity (Fst range: <0.01-0.15; minor allele frequency (MAF): 0.192-0.245), which were similar to previously published levels for recovered L. nannotis populations. This suggests that dispersal ability and genetic diversity do not limit the ability of L. dayi to recolonize upland sites. Further, infection intensity and prevalence increased with elevation, suggesting that chytridiomycosis is still limiting the elevational range of L. dayi. Outlier tests comparing infected and uninfected individuals consistently identified 18 markers as putatively under selection, and several of those markers matched genes that were previously implicated in infection. This suggests that L. dayi has genetic variation for genes that affect infection dynamics and may be undergoing adaptation.

Dose-dependent morbidity of freshwater turtle hatchlings, Emydura macquarii krefftii, inoculated with Ranavirus isolate (Bohle iridovirus, Iridoviridae).

Ranaviral infections cause mass die-offs in wild and captive turtle populations. Two experimental studies were performed to first determine the susceptibility of an Australian turtle species (Emydura macquarii krefftii) to different routes of infection and second examine the effect of viral titre on the morbidity in hatchlings. All inoculation routes (intracoelomic, intramuscular and oral) produced disease, but the clinical signs, histopathology and time to onset of disease varied with the route. The median infectious and lethal doses for intramuscularly inoculated hatchlings were 102.52 (1.98-2.93) and 104.43 (3.81-5.19) TCID50 ml-1, respectively. Clinical signs began 14 to 29 days post-inoculation and the median survival time was 22 days (16-25) across all dose groups. For every 10-fold increase in dose, the odds of developing any clinical signs or severe clinical signs increased by 3.39 [P<0.01, 95 % confidence interval (CI): 1.81-6.36] and 3.71 (P<0.01, 95 % CI: 1.76-7.80), respectively. Skin lesions, previously only reported in ranaviral infection in lizards, were observed in the majority of intramuscularly inoculated hatchlings that developed ranaviral disease. The histological changes were consistent with those in previous reports for reptiles and consisted of necrosis at or near the site of injection, in the spleen, liver and oral cavity. Systemic inflammation was also observed, predominantly affecting necrotic organs. The estimates reported here can be used to model ranaviral disease and quantify and manage at-risk populations.

The return of the frogs: The importance of habitat refugia in maintaining diversity during a disease outbreak.

Recent decades have seen the emergence and spread of numerous infectious diseases, often with severe negative consequences for wildlife populations. Nevertheless, many populations survive the initial outbreaks, and even undergo recoveries. Unfortunately, the long-term effects of these outbreaks on host population genetics are poorly understood; to increase this understanding, we examined the population genetics of two species of rainforest frogs (Litoria nannotis and Litoria serrata) that have largely recovered from a chytridiomycosis outbreak at two national parks in the Wet Tropics of northern Australia. At the wetter, northern park there was little evidence of decreased genetic diversity in either species, and all of the sampled sites had high minor allele frequencies (mean MAF = 0.230-0.235), high heterozygosity (0.318-0.325), and few monomorphic markers (1.4%-4.0%); however, some recovered L. nannotis populations had low Ne values (59.3-683.8) compared to populations that did not decline during the outbreak (1,537.4-1,756.5). At the drier, southern park, both species exhibited lower diversity (mean MAF = 0.084-0.180; heterozygosity = 0.126-0.257; monomorphic markers = 3.7%-43.5%; Ne  = 18.4-676.1). The diversity patterns in this park matched habitat patterns, with both species having higher diversity levels and fewer closely related individuals at sites with higher quality habitat. These patterns were more pronounced for L. nannotis, which has lower dispersal rates than L. serrata. These results suggest that refugia with high quality habitat are important for retaining genetic diversity during disease outbreaks, and that gene flow following disease outbreaks is important for re-establishing diversity in populations where it was reduced.

Ecological associations among epidermal microstructure and scale characteristics of Australian geckos (Squamata: Carphodactylidae and Diplodactylidae).

A first step in examining factors influencing trait evolution is demonstrating associations between traits and environmental factors. Scale microstructure is a well-studied feature of squamate reptiles (Squamata), including geckos, but few studies examine ecology the of microstructures, and those focus mainly on toe pads. In this study, the ecomorphology of cutaneous microstructures on the dorsum was described for eight Australian species of carphodactylid (Squamata: Carphodactylidae) and 19 diplodactylid (Squamata: Diplodactylidae) geckos. We examined scale dimensions, spinule and cutaneous sensilla (CS) morphology, using scanning electron microscopy, and described associations of these traits with microhabitat selection (arboreal, saxicoline or terrestrial) and relative humidity of each species' habitat (xeric, mesic or humid). We used a phylogenetic flexible discriminant analysis (pFDA) to describe relationships among all traits and then a modeling approach to examine each trait individually. Our analysis showed that terrestrial species tended to have long spinules and CS with more bristles, saxicoline species larger diameter CS and arboreal species tended to have large granule scales and small intergranule scales. There was high overlap in cutaneous microstructural morphology among species from xeric and mesic environments, whereas species from humid environments had large diameter CS and few bristles. Significant associations between epidermal morphology and environmental humidity and habitat suggest that epidermal microstructures have evolved in response to environmental variables. In summary, long spinules, which aid self-cleaning in terrestrial geckos, are consistent with greater exposure to dirt and debris in this habitat. Long spinules were not clearly correlated to environmental humidity. Finally, more complex CS (larger diameter with more bristles) may facilitate better perception of environmental variation in geckos living in drier habitats.

Heat seekers: A tropical nocturnal lizard uses behavioral thermoregulation to exploit rare microclimates at night.

Environmental temperatures play a vital role in the physiological and behavioral activity of ectotherms. Behavioral thermoregulation allows animals to modify their body temperature to optimize functions critical to fitness, including digestion, growth, reproduction, and locomotor performance. Diurnal reptiles are a classic model system to answer questions related to thermal ecology, whereas behavioral thermoregulation in nocturnal species is thought to be strongly constrained by low environmental thermal heterogeneity at night. The few studies describing the thermal ecology of nocturnal reptiles indicate a majority of thermoregulatory behavior (if any) occurs during the day within diurnal retreats, but few examined this behavior throughout the night. In tropical systems, thermal heterogeneity may remain high, even at night, allowing nocturnal ectotherms to thermoregulate through conduction on surfaces that retain heat after sunset. We investigated the thermoregulatory behavior of a tropical nocturnal gecko (Australian house gecko, Gehyra dubia) by measuring its preferred temperature in a thermal gradient, and selected body temperatures using radio telemetry, in relation to available operative environmental temperatures obtained using thermal models. Preferred body temperatures of geckos ranged from 31.4 ±â€¯0.59-34.5 ±â€¯0.55 °C in a laboratory thermal gradient. In the field, during winter, geckos were more effective thermoregulators than in the summer. In low thermal quality habitats, geckos sought rare, warm microclimates at night to maintain body temperatures warmer than most available environmental temperatures, and were highly effective thermoregulators. For ectotherms, appropriate environmental temperatures are a vital resource for survival, similar to food or shelter. The ability to exploit rare microclimates is especially important for nocturnal species, as heterogeneity of environmental temperatures is reduced at night compared to the day. In a warming world, it is vital to understand the thermal ecology of nocturnal ectotherms, as other species may shift to become more nocturnal to avoid lethal diurnal temperatures.

Disentangling causes of seasonal infection prevalence patterns: tropical tadpoles and chytridiomycosis as a model system.

Identifying the factors that affect pathogen prevalence is critical to understanding the effects of wildlife diseases. We aimed to examine drivers of seasonal changes in the prevalence of infection by the amphibian chytrid fungus Batrachochytrium dendrobatidis in tadpoles. Because tadpoles may be important reservoirs for this disease, examining them will aid in understanding how chytridiomycosis affects entire amphibian populations. We hypothesized that temperature is a strong driver of prevalence of Bd in tadpoles, and the accumulation of infection as tadpoles become larger and older also drives prevalence in this system. We studied Litoria rheocola, a tropical rainforest stream frog with seasonal recruitment of annual tadpoles, and surveyed 6 streams in northeastern Queensland, Australia. Comparisons among models relating infection status to stream type, season, their interaction, tadpole age, and water temperature showed that age explained a large portion of the variance in infection status. Across sites and seasons, larger, older tadpoles had increased mean probabilities of infection, indicating that a large component of the variation among individuals was related to age, and thus to cumulative infection risk. Our results indicate that in systems with annual tadpoles, seasonal changes in infection prevalence may be strongly affected by seasonal patterns of tadpole growth and development in addition to stream type, season, and water temperature. These effects may then influence prevalence of infection in terrestrial individuals in species that have relatively frequent contact with water. This reinforces the need to integrate studies of the drivers of pathogen prevalence across all host life history stages.

A Random Walk in the Park: An Individual-Based Null Model for Behavioral Thermoregulation.

Behavioral thermoregulators leverage environmental temperature to control their body temperature. Habitat thermal quality therefore dictates the difficulty and necessity of precise thermoregulation, and the quality of behavioral thermoregulation in turn impacts organism fitness via the thermal dependence of performance. Comparing the body temperature of a thermoregulator with a null (non-thermoregulating) model allows us to estimate habitat thermal quality and the effect of behavioral thermoregulation on body temperature. We define a null model for behavioral thermoregulation that is a random walk in a temporally and spatially explicit thermal landscape. Predicted body temperature is also integrated through time, so recent body temperature history, environmental temperature, and movement influence current body temperature; there is no particular reliance on an organism's equilibrium temperature. We develop a metric called thermal benefit that equates body temperature to thermally dependent performance as a proxy for fitness. We measure thermal quality of two distinct tropical habitats as a temporally dynamic distribution that is an ergodic property of many random walks, and we compare it with the thermal benefit of real lizards in both habitats. Our simple model focuses on transient body temperature; as such, using it we observe such subtleties as shifts in the thermoregulatory effort and investment of lizards throughout the day, from thermoregulators to thermoconformers.

Mixed population genomics support for the central marginal hypothesis across the invasive range of the cane toad (Rhinella marina) in Australia.

Understanding factors that cause species' geographic range limits is a major focus in ecology and evolution. The central marginal hypothesis (CMH) predicts that species cannot adapt to conditions beyond current geographic range edges because genetic diversity decreases from core to edge due to smaller, more isolated edge populations. We employed a population genomics framework using 24 235-33 112 SNP loci to test major predictions of the CMH in the ongoing invasion of the cane toad (Rhinella marina) in Australia. Cane toad tissue samples were collected along broad-scale, core-to-edge transects across their invasive range. Geographic and ecological core areas were identified using GIS and habitat suitability indices from ecological niche modelling. Bayesian clustering analyses revealed three genetic clusters, in the northwest invasion-front region, northeast precipitation-limited region and southeast cold temperature-limited region. Core-to-edge patterns of genetic diversity and differentiation were consistent with the CMH in the southeast, but were not supported in the northeast and showed mixed support in the northwest. Results suggest cold temperatures are a likely contributor to southeastern range limits, consistent with CMH predictions. In the northeast and northwest, ecological processes consisting of a steep physiological barrier and ongoing invasion dynamics, respectively, are more likely explanations for population genomic patterns than the CMH.

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.

Condition-dependent reproductive effort in frogs infected by a widespread pathogen.

To minimize the negative effects of an infection on fitness, hosts can respond adaptively by altering their reproductive effort or by adjusting their timing of reproduction. We studied effects of the pathogenic fungus Batrachochytrium dendrobatidis on the probability of calling in a stream-breeding rainforest frog (Litoria rheocola). In uninfected frogs, calling probability was relatively constant across seasons and body conditions, but in infected frogs, calling probability differed among seasons (lowest in winter, highest in summer) and was strongly and positively related to body condition. Infected frogs in poor condition were up to 40% less likely to call than uninfected frogs, whereas infected frogs in good condition were up to 30% more likely to call than uninfected frogs. Our results suggest that frogs employed a pre-existing, plastic, life-history strategy in response to infection, which may have complex evolutionary implications. If infected males in good condition reproduce at rates equal to or greater than those of uninfected males, selection on factors affecting disease susceptibility may be minimal. However, because reproductive effort in infected males is positively related to body condition, there may be selection on mechanisms that limit the negative effects of infections on hosts.

Infection dynamics in frog populations with different histories of decline caused by a deadly disease.

Pathogens can drive host population dynamics. Chytridiomycosis is a fungal disease of amphibians that is caused by the fungus Batrachochytrium dendrobatidis (Bd). This pathogen has caused declines and extinctions in some host species whereas other host species coexist with Bd without suffering declines. In the early 1990s, Bd extirpated populations of the endangered common mistfrog, Litoria rheocola, at high-elevation sites, while populations of the species persisted at low-elevation sites. Today, populations have reappeared at many high-elevation sites where they presently co-exist with the fungus. We conducted a capture-mark-recapture (CMR) study of six populations of L. rheocola over 1 year, at high and low elevations. We used multistate CMR models to determine which factors (Bd infection status, site type, and season) influenced rates of frog survival, recapture, infection, and recovery from infection. We observed Bd-induced mortality of individual frogs, but did not find any significant effect of Bd infection on the survival rate of L. rheocola at the population level. Survival and recapture rates depended on site type and season. Infection rate was highest in winter when temperatures were favourable for pathogen growth, and differed among site types. The recovery rate was high (75.7-85.8%) across seasons, and did not differ among site types. The coexistence of L. rheocola with Bd suggests that (1) frog populations are becoming resistant to the fungus, (2) Bd may have evolved lower virulence, or (3) current environmental conditions may be inhibiting outbreaks of the fatal disease.

Mechanisms causing variation in sexual size dimorphism in three sympatric, congeneric lizards.

Sexual differences in adult body size (sexual size dimorphism, or SSD) ultimately can be favored by selection because larger males are more likely to be successful competitors for females, because larger females bear larger clutches, or because intersexual size differences reduce resource competition. Natural selection during juvenile development can influence sexual dimorphism of adults, and selection on adults and juveniles may differ. Studies that address the relative contributions of adult body shape dimorphism and sexually dimorphic patterns of growth and maturity are particularly useful in understanding the evolution of size dimorphism, yet they are rare. We investigated three sympatric, congeneric lizard species with different degrees and directions of adult sexual dimorphism and compared their growth patterns, survival probabilities, and intersexual trophic niche differences. Different mechanisms, even within these closely related, sympatric species, acted on juvenile lizards to produce species differences in adult SSD. Both degree and direction of dimorphism resulted from differences between the sexes in either the duration of growth or the rate of growth, but not from differences in rates of survival or selection on juvenile growth rate. Species- and sex-specific trade-offs in the allocation of energy to growth and reproduction, as well as differential timing of maturation, thus caused the growth patterns of the sexes to diverge, producing SSD. The differences that we observed in the direction of SSD among these species is consistent with their different social systems, suggesting that differential selection on adult body size has been responsible for the observed species-specific differences in juvenile growth rates and maturational timing.

No Ranaviral DNA Found in Australian Freshwater Turtles, 2014-19, Despite Previous Serologic Evidence.

Ranaviruses are pathogens of ectothermic vertebrates (fish, amphibians, and reptiles). Turtles are the most common group of reptiles reported with ranaviral infections. However, there have been no surveys for wild ranaviral infection in any turtles from the suborder Pleurodira, despite ranaviral distributions and experimentally susceptible pleurodiran turtle populations overlapping in several areas, including Australia. We assayed 397 pooled blood samples from six Australian freshwater turtle species collected from five different sites in northern Australia between 2014 and 2019. Historical serologic surveys in the area had found antiranaviral antibodies; however, we did not detect any ranaviral DNA in our samples. Discrepancies between historical serologic and our molecular results may be explained by low viral prevalence during the years that these samples were collected, survivorship bias, or possibly an age class bias in sampling.