Abstract
Metamorphosis is often characterized by profound changes in morphology and physiology that can affect the dynamics of species interactions. For example, the interaction between a pathogen and its host may differ depending on the life stage of the host or pathogen. One pathogen that infects hosts with complex life cycles is the emerging fungal pathogen of amphibians, Batrachochytrium dendrobatidis (Bd). We sought to determine how conditions at the larval stage can affect variation in development and patterns of Bd infection across amphibian life stages. We used outdoor experimental mesocosms to simulate natural pond habitats and manipulated the presence of Bd, the larval density, and the number of host species in larvae of two co-occurring amphibian species (Rana cascadae and Pseudacris regilla). We found that infection differed between species throughout development; P. regilla consistently had higher infection severity compared to R. cascadae. Additionally, while up to 100% of larvae were infected, only 18.2% of R. cascadae and 81.5% of P. regilla were infected after metamorphosis. This indicates that amphibians have the ability to recover from Bd infection as they undergo metamorphosis. Higher larval densities in P. regilla led to a shorter larval period, and individuals with a shorter larval period had lower infection severity. This led to a trend where P. regilla larvae reared at high densities tended to have lower infection prevalence after metamorphosis. We also found that exposure to Bd increased larval mortality and prolonged the larval period in P. regilla, indicating that P. regilla are susceptible to the negative effects of Bd as larvae. This study demonstrates that host density, species composition, and pathogen exposure may all interact to influence development and infection in hosts with complex life cycles.
Highlights
Host-pathogen interactions can be influenced by both the genotype and phenotype of the host
Since oral swabs are unable to detect low levels of Batrachochytrium dendrobatidis (Bd) infection [56], it is possible that a greater percentage of the larvae at time point 2 were infected with Bd
After metamorphosis only 18.18% (8 of 44) of Bd-exposed R. cascadae were positive for infection, while 81.49% (33 of 41) of P. regilla, exposed to Bd tested positive for Bd
Summary
Host-pathogen interactions can be influenced by both the genotype and phenotype of the host. Genetic resistance to pathogens commonly varies within a host population, with some host genotypes more resistant to a pathogen than others [1,2,3]. The physiological and morphological condition of a host can vary with developmental stage, size, and age, and affect disease risk [4,5]. Dramatic changes to host physiology and morphology occur in species with complex life cycles, such as those that undergo metamorphosis (e.g. amphibians, holometabolous insects, parasites, marine invertebrates and some fishes). The life stage of an organism can affect disease risk, transmission and susceptibility [6,7]
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