High mortality in Bufo gargarizans eggs associated with an undescribed Saprolegnia ferax strain in the Republic of Korea

Pathogenic water molds have a significant impact on many species, especially amphibians. The genus Saprolegnia is a pathogenic oomycete restricted to aquatic and moist habitats, and its presence is strongly linked to the abundance of amphibians and fishes. We investigated the influence of Saprolegnia presence on egg mortality and egg occurrence under varying environmental conditions in the Asiatic toad Bufo gargarizans at 27 breeding sites in the Republic of Korea. We then assessed the impact of Saprolegnia on the presence of B. gargarizans at the 27 sites surveyed weekly during the B. gargarizans breeding season for 3 consecutive years. We used molecular tools to identify the water molds as belonging to an undescribed S. ferax strain. We demonstrated that the presence of S. ferax was positively associated with higher water conductivity and ponds. In addition, while S. ferax prevalence was associated with a reduction in B. gargarizans breeding activity and breeding success, we could not determine its impact on the subsequent breeding seasons. Our study highlights the potential negative effects of Saprolegnia on amphibian reproduction, although additional research is necessary to determine the relationship between Saprolegnia, its hosts and the impacts of habitat loss on amphibians.

Transcriptome analysis of larval immune defence in the lamprey Lethenteron japonicum

The lamprey is a primitive jawless vertebrate that occupies a critical phylogenetic position, and its larval stage represents the major portion of its life cycle [1]. Lamprey larvae have been proven to be an important model organism for studying numerous biological problems, such as the immune system, due to their unique biological features [2]. In addition, early-stage larvae have never been obtained from the wild [3]; therefore, it is necessary to establish artificial breeding of lampreys in the laboratory. However, during early development, the larvae exhibit susceptibility to saprolegniasis, and the immune responses of lamprey larvae to this infection remain poorly understood. Here, we established a model of fungal infection in lamprey larvae and then used RNA sequencing to investigate the transcript profiles of lamprey larvae and their immune responses to Saprolegnia ferax. Among the profiled molecules, genes involved in pathogen recognition, inflammation, phagocytosis, lysosomal degradation, soluble humoral effectors, and lymphocyte development were significantly upregulated. The results were validated by analysis of several genes by quantitative real-time PCR and whole-mount in situ hybridization. Finally, we performed a Western blot for VLRs in infected and uninfected lampreys. This work not only provides an animal model for studying fungal infection but also suggests a molecular basis for developing defensive strategies to manage Saprolegnia ferax infection.