Age structure of amphibian populations with endemic chytridiomycosis, across climatic regions with markedly different infection risk

Abstract

Threatening processes, such as disease, can drive major changes in population demographics of the host. Chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis ( Bd ), has led to the decline of at least 500 amphibian species across the globe and has been shown to truncate host age structure by lowering adult survival rates. This results in heavy reliance on annual recruitment and the inability to recover in the event of periodic recruitment failure. We used skeletochronology to determine the age structure, growth, and survival rates of populations of an endangered amphibian, Litoria raniformis , with endemic chytridiomycosis, across two climatically disparate regions in south‐eastern Australia: semi‐arid and temperate. Contrary to predictions, populations in the semi‐arid region (in which chytrid prevalence is substantially lower due to high temperatures) displayed a more truncated age structure than populations in the temperate study regions. Maximum recorded age was only two years in the semi‐arid region compared with up to four years in the temperate region. Wetland hydroperiod and average seasonal air temperature were correlated with age, and males had a slightly higher survival rate than females (0.31 for males and 0.27 for females). Despite the previously documented differences in chytrid prevalence between the two climatic regions, water availability and wetland hydroperiods appear the over‐riding determinants of the age structure and survival rates of L. raniformis . Targeted management which ensures water availability and improves survival of 1‐year‐old frogs into their second and third breeding season would reduce the impact of stochastic events on L. raniformis , and this may be true for numerous frog species susceptible to chytridiomycosis.

Modelling the sustainable harvest of wild populations for the conservation of a threatened amphibian

“…We combined these annual survival probabilities and resampled tadpole survival from the resultant beta distribution with shape parameters α = 3.4667 and β = 10.3734. Annual adult survival probability varies by wetland hydrology, and we used the annual survival probability of adults from Turner et al (2022), classifying Hogwash Bend central basin as ephemeral (mean = 0.23, standard deviation = 0.08), Nap Nap wetland as semi-permanent (mean annual adult survival probability 0.25, standard deviation 0.05), and Bendigo Water Reclamation Plant as permanent (mean = 0.28, standard deviation = 0.06) and all resampled from Normal distributions. We enforced senescence during the sixth year (Mann et al, 2010).…”

Current State of Conservation Physiology for Amphibians: Major Research Topics and Physiological Parameters

“…Population decline and extinction threaten amphibians due to habitat loss, climate change, pollution, and disease [77]. Conservation genetics focuses on genetic diversity, population structure, and gene flow in amphibians [78], while population ecology studies statistical processes regulating populations, such as birth rates, death rates, and interpopulation movement [79]. Research in these areas also involves genetic resource management, hormone induction in breeding systems, and suitable habitat models (Figure 4b).…”