Bad neighbours: amphibian chytrid fungus Batrachochytrium dendrobatidis infection dynamics in three co-occurring frog species of southern Sydney, Australia.

Wildlife disease is a major cause of global biodiversity loss. Amongst the most devastating is the disease chytridiomycosis, caused by the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd). This disease has contributed to declines and extinctions in hundreds of amphibian species, but not all species are affected equally. Some amphibian hosts are capable of carrying high levels of Bd infection without population declines, acting as reservoir species for the pathogen and driving population declines in sympatric species. In Australia, several species have been proposed as reservoir species; however, our understanding of Bd is derived from studies that are highly geographically and taxonomically biased, and our ability to extrapolate from these systems is unknown. We examined the prevalence and intensity of Bd infection in 3 frog species in a previously unstudied host-pathogen system in temperate eastern Australia: the Blue Mountains tree frog Litoria citropa, a poorly-known species predicted to be susceptible to Bd infection; and the common eastern froglet Crinia signifera and the stony creek frog L. lesueuri, which have both been identified as reservoir species in other regions. We found that L. citropa and L. lesueuri were infected with Bd at a high prevalence and often high intensity, while the reverse was true for C. signifera. All species were detected at moderate abundance and there was no evidence of morbidity and mortality. Our findings do not support C. signifera and L. lesueuri being reservoir species in this system, highlighting the importance of region-specific studies to inform conservation management.

Context dependence of transgenerational plasticity: the influence of parental temperature depends on offspring environment and sex.

Under environmental change, the relationship between phenotype and fitness can change rapidly, leaving populations vulnerable. Plasticity within and between generations could provide the fastest mitigation to environmental change. However, plasticity may depend on interactions among parental environment, offspring environment and offspring sex, and we know little of how these interactions manifest. We examine the importance of parental and offspring thermal environment in the context of a terrestrial ectotherm (the jacky lizard, Amphibolurus muricatus), where the thermal environment depends on complex thermoregulatory behaviours. By manipulating both parental and offspring thermoregulatory (basking) opportunities in a full factorial design, we found that transgenerational plasticity was highly context dependent. Overall, longer parental thermoregulatory opportunities led to increased growth in offspring, providing a clear fitness benefit to daughters but inducing a cost of increased oxidative stress in sons. Daughters, but not sons, received the greatest advantage when their thermal environment matched that of their parents. The offspring thermal environment had little independent effect on offspring phenotype. Together, the results suggest that both directional selection on offspring size (leading to growth being dependent on thermal conditions) and selection for anticipatory parental effects operate, but with a different balance in males and females. More broadly, restrictions in thermoregulatory opportunities under climatic warming will have negative consequences both within and between generations, but the exact nature will depend on the evolved functional form of plasticity.