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Fatal amphibian chytridiomycosis has typically been associated with the direct costs of infection. However the relationship between exposure to the pathogen, infection and mortality may not be so straightforward. Using results from both field work and experiments we report how exposure of common toads to Batrachochytrium dendrobatidis influences development and survival and how developmental stage influences host responses. Our results show that costs are accrued in a dose dependent manner during the larval stage and are expressed at or soon after metamorphosis. Exposure to B. dendrobatidis always incurs a growth cost for tadpoles and can lead to larval mortality before or soon after metamorphosis even when individuals do not exhibit infection at time of death. In contrast, exposure after metamorphosis almost always results in infection, but body size dictates survival to a greater extent than does dose. These data show that amphibian survival in the face of challenge by an infectious agent is dependent on host condition as well as life history stage. Under current models of climate change, many species of amphibia are predicted to increasingly occur outside their environmental optima. In this case, condition-dependent traits such as we have demonstrated may weigh heavily on species survival.

1. Recent evidence of the important role of emerging diseases in amphibian population declines makes it increasingly important to understand how environmental changes affect amphibian immune systems. 2. Temperature-dependent immunity may be particularly important to amphibian disease dynamics, especially in temperate regions. Changes in temperature are expected to cause deviations away from optimal levels of immunity until the immune system can respond. 3. To test whether temperature changes cause deviations from optimal immunity under natural conditions, we conducted a seasonal survey of adult Red-Spotted Newts and measured basal levels of several immunological variables. 4. We then examined these findings in relation to: (1) the lag hypothesis, which predicts that changes in temperature-dependent immune parameters lag behind short-term temperature changes, and (2) the seasonal acclimation hypothesis, which predicts that immune cell production declines during long-term temperature decreases until amphibians can fully acclimate to winter conditions. 5. Our results supported both hypotheses, showing a spring lag effect on lymphocyte levels and an even stronger seasonal acclimation effect on lymphocytes, neutrophils and eosinophils in the autumn. Our findings suggest that temperature variability causes increased susceptibility of amphibians to infection, and they have implications for the emergence of disease and the potential for climate change to exacerbate amphibian decline.

Sex determined by climate In vertebrates, sex can be determined either genetically or by the temperature experienced by the embryo, but the evolutionary causes of this variation remain poorly understood. Pen et al . show that a live-bearing lizard at different climatic extremes of its range uses different sex-determining mechanisms — temperature in the lowlands and genotype at higher altitudes. Divergent natural selection on sex determination by altitude is caused by climatic effects on lizard life history and variation in the magnitude of between-year temperature fluctuations. The results establish an adaptive explanation for intra-specific divergence in sex-determining systems. In vertebrates, sex can be determined either genetically or by temperature, but the evolutionary causes of this variation remain unknown. These authors show how live-bearing lizards at different climatic extremes of their range differ in their sex-determining mechanisms, with temperature-dependent sex determination in the lowlands and genotypic sex determination at higher altitudes. Their results establish an adaptive explanation for intra-specific divergence in sex-determining systems driven by phenotypic plasticity and ecological selection. Sex determination is a fundamental biological process, yet its mechanisms are remarkably diverse 1 , 2 . In vertebrates, sex can be determined by inherited genetic factors or by the temperature experienced during embryonic development 2 , 3 . However, the evolutionary causes of this diversity remain unknown. Here we show that live-bearing lizards at different climatic extremes of the species’ distribution differ in their sex-determining mechanisms, with temperature-dependent sex determination in lowlands and genotypic sex determination in highlands. A theoretical model parameterized with field data accurately predicts this divergence in sex-determining systems and the consequence thereof for variation in cohort sex ratios among years. Furthermore, we show that divergent natural selection on sex determination across altitudes is caused by climatic effects on lizard life history and variation in the magnitude of between-year temperature fluctuations. Our results establish an adaptive explanation for intra-specific divergence in sex-determining systems driven by phenotypic plasticity and ecological selection, thereby providing a unifying framework for integrating the developmental, ecological and evolutionary basis for variation in vertebrate sex determination.

Mating with another species (hybridization) is often maladaptive. Consequently, females typically avoid heterospecifics as mates. Contrary to these expectations, female spadefoot toads were more likely to choose heterospecific males when exposed to environmental conditions that favor hybridization. Indeed, those females with phenotypic characteristics for which hybridization is most favorable were most likely to switch from choosing conspecifics to heterospecifics. Moreover, environmentally dependent mate choice has evolved only in populations and species that risk engaging in, and can potentially benefit from, hybridization. Thus, when the benefits of mate choice vary, females may radically alter their mate selection in response to their own phenotype and their environment, even to the point of choosing males of other species.

Natural disturbances are key processes in the vast majority of ecosystems and a range of ecological theories have been developed in an attempt to predict biotic responses to them. However, empirical support for these theories has been inconsistent and considerable additional work remains to be done to better understand the response of biodiversity to natural disturbance. We tested predictions from the intermediate disturbance hypothesis and the habitat accommodation model of succession for reptile responses to fire history and a single major fire event. We focused our work on a broad range of vegetation types spanning sedgeland to temperate rainforest located within a national park in south‐eastern Australia. We found no significant relationships between reptile species richness and the number of fires over the past 35 years, the time since the last fire, or the severity of a major fire in 2003. Thus, we found no strong evidence to support the intermediate disturbance hypothesis. A correspondence analysis of reptile assemblages revealed a gradient in species responses to fire history. However, we found limited evidence for an ordered succession of reptiles. Nor could the responses of individual species be readily predicted from life history attributes. Thus, our findings were generally not consistent with predictions from the habitat accommodation model of succession. A possible explanation for the absence of a predictable sequence of recovery following disturbance might be the rapidity of post‐fire recovery of many components of native vegetation cover that were found to be important for reptiles (e.g. the extent of grass cover). This would have limited the time for early successional conditions to prevail and limited opportunities for species associated with such conditions. We found that most reptile species responses were much more strongly linked to vegetation type than fire variables, emphasizing a need to understand relationships with vegetation before being able to understand possible fire effects (if and where they exist). We found the disturbance concepts we examined were limited in their ability to accurately predict reptile responses to past fire history or the impacts of a single major fire in 2003. Practical management might be best guided not by disturbance theory, but by carefully setting objectives to meet conservation goals for particular individual species of reptiles.

Satellite telemetry and stable isotope analysis were used to confirm that oceanic areas (where water depths are >200 m) are alternative feeding habitats for adult female green sea turtles (Chelonia mydas), which have been thought to be obligate herbivores in neritic areas (where depths are <200 m). Four females were tagged with satellite transmitters and tracked during post-nesting periods from Ogasawara Islands, Japan. Three females migrated to neritic habitats, while transmissions from another female ceased in an oceanic habitat. The overall mean nighttime dive depths during oceanic swimming periods in two females were <20 m, implying that the main function of their nighttime dives were resting with neutral buoyancy, whereas the means in two other females were >20 m, implying that they not only rested, but also foraged on macroplankton that exhibit diel vertical migration. Comparisons of stable carbon and nitrogen isotope ratios between 89 females and the prey items in a three-source mixing model estimated that 69% of the females nesting on Ogasawara Islands mainly used neritic habitats and 31% mainly used oceanic habitats. Out of four females tracked by satellite, two females were inferred from isotope ratios to be neritic herbivores and the two others oceanic planktivores. Although post-nesting movements for four females were not completely consistent with the inferences from isotope ratios, possibly due to short tracking periods (28-42 days), their diving behaviors were consistent with the inferences. There were no relationships between body size and the two isotope ratios, indicating a lack of size-related differences in feeding habitat use by adult female green turtles, which was in contrast with loggerhead sea turtles (Caretta caretta). These results and previous findings suggest that ontogenetic habitat shifts by sea turtles are facultative, and consequently, their life histories are polymorphic.

Previous studies have suggested that most small Australian elapid snakes are nocturnal and rarely bask in the open because of the risk of predation by diurnal predatory birds. Because the physiology and behaviour of reptiles is temperature dependent, staying in refuges by day can entail high thermoregulatory costs, particularly for juveniles that must grow rapidly to maximise their chances of survival. We investigated whether the risk of predation deters juveniles of the endangered broad-headed snake (Hoplocephalus bungaroides) from basking, and if so, whether there are thermal costs associated with refuge use. To estimate avian attack rates on snakes, we placed 900 plasticine snake replicas in sunny locations and underneath small stones on three sandstone plateaus for 72 h. At the same time we quantified the thermal benefits of basking vs refuge use. On sunny days, juveniles could maintain preferred body temperatures for 4.7 h by basking but only for 2.0 h if they remained inside refuges. Our predation experiment showed that basking has high costs for juvenile snakes. Predators attacked a significantly higher proportion of exposed models (13.3%) than models under rocks (1.6%). Birds were the major predators of exposed models (75% of attacks), and avian predation did not vary across the landscape. By trading heat for safety, juvenile H. bungaroides decreased the potential time period that they could maintain preferred body temperatures by 57%. Thermal costs of refuge use may therefore contribute to the slow growth and late maturation of this endangered species. Our results support the hypothesis that nocturnal activity in elapid snakes has evolved to minimise the risk of avian predation.

Raising The Tone Some bats, dolphins and rodents are notable among vertebrates in being able to produce and detect ultrasonic frequencies. Now for the first time an amphibian can be added to that select list. The spectacular bird-like sounds made by a type of Chinese torrent frog were known to edge into the ultrasonic range: now these frogs are shown to use ultrasonics as a form of communication. The males do at least, during competition for territory. Frogs are a long way, evolutionarily speaking, from the other known users of ultrasonics so this ability seems to have evolved independently several times. It is possible, too, that many other species are chatting away in the ultrasonic waveband, but that nobody has looked for them. Among vertebrates, only microchiropteran bats, cetaceans and some rodents are known to produce and detect ultrasounds (frequencies greater than 20 kHz) for the purpose of communication and/or echolocation, suggesting that this capacity might be restricted to mammals 1 , 2 . Amphibians, reptiles and most birds generally have limited hearing capacity, with the ability to detect and produce sounds below ∼12 kHz. Here we report evidence of ultrasonic communication in an amphibian, the concave-eared torrent frog ( Amolops tormotus ) from Huangshan Hot Springs, China. Males of A. tormotus produce diverse bird-like melodic calls with pronounced frequency modulations that often contain spectral energy in the ultrasonic range 3 , 4 . To determine whether A. tormotus communicates using ultrasound to avoid masking by the wideband background noise of local fast-flowing streams, or whether the ultrasound is simply a by-product of the sound-production mechanism, we conducted acoustic playback experiments in the frogs' natural habitat. We found that the audible as well as the ultrasonic components of an A. tormotus call can evoke male vocal responses. Electrophysiological recordings from the auditory midbrain confirmed the ultrasonic hearing capacity of these frogs and that of a sympatric species facing similar environmental constraints. This extraordinary upward extension into the ultrasonic range of both the harmonic content of the advertisement calls and the frog's hearing sensitivity is likely to have co-evolved in response to the intense, predominantly low-frequency ambient noise from local streams. Because amphibians are a distinct evolutionary lineage from microchiropterans and cetaceans (which have evolved ultrasonic hearing to minimize congestion in the frequency bands used for sound communication 5 and to increase hunting efficacy in darkness 2 ), ultrasonic perception in these animals represents a new example of independent evolution.

1. There is significant concern over the impacts of plant invasions on habitat quality for native fauna. Recent research suggests that non-native Purple Loosestrife (Lythrum salicaria) invasions may negatively affect the performance of larval American Toad tadpoles (Bufo americanus), and that compounds leached from L. salicaria leaves play a direct or indirect role in this effect. 2. We raised individual B. americanus and Gray Treefrog (Hyla versicolor) tadpoles on high-quality diets in aqueous extracts of senescent leaves from L. salicaria, native Broad-Leaf Cattail (Typha latifolia), and control water to determine whether loosestrife extracts directly affect anuran tadpole performance. 3. Even at high artificial food levels, B. americanus survival was significantly lower in L. salicaria extracts compared with T. latifolia extracts and a water control. Food level strongly affected B. americanus development, but tadpoles raised in L. salicaria extract were less developed compared with conspecifics raised in cattail extract or water. Unlike B. americanus, Hyla performance was not affected by exposure to any plant extract compared with the water control. 4. Our study implicates secondary plant compounds as a mechanism underlying the impact of an invasive plant on some but not all native fauna. We hypothesize that high tannin concentrations of L. salicaria leaves have the potential to create environments that are directly toxic to B. americanus tadpoles. We hypothesize that obligate gill breathers such as B. americanus tadpoles are highly sensitive to gill damage caused by high concentrations of phenolics. Other anuran species such as H. versicolor that develop well-functioning lungs early may be less affected by high tannin concentrations.

Environmental conditions experienced early in the ontogeny can have a strong impact on individual fitness and performance later in life. Organisms may counteract the negative effects of poor developmental conditions by developing compensatory responses in growth and development. However, previous studies on compensatory responses have largely ignored the effects that poor embryonic conditions could have during the later life stages. In this study, we examined the effects of artificially delayed development in early life over two later life history transitions by investigating the compensatory growth of larval moor frogs Rana arvalis in response to temperature variation during embryonic development, and the associated costs during the larval ′and postmetamorphic stages. Low temperature during embryonic stage lead to delayed hatching at smaller size. The groups with delayed embryonic development showed strong compensatory growth during the larval stage, and reached similar metamorphic size than the controls in a shorter time. However, the most strongly delayed group was not able to fully catch up the total development time. These compensatory responses were found in the absence of photoperiod cues indicating that the delay in embryonic development was sufficient to initiate the compensatory response in larval growth and development. No apparent costs of compensatory growth were detected in terms of morphology or locomotor performance at the juvenile stage. We found that compensatory responses can be activated as early as at the embryonic stage and extend over several consecutive life history transitions, mitigating the effects of poor conditions experienced early in development. Potential short-term costs in natural environments and the occurrence of long-term costs, which prevent the generalisation of a faster larval life style, are discussed.