31 Chytridiomycosis reduces sperm production in young southern corroboree frogs
P. Frías-Álvareza A B , R. Webb A , L. Brannelly A , K. R. Woodley A C , L. F. Skerratt A , L. Berger A and D. B. B. P. Paris B DA One Health Research Group, Faculty of Veterinary & Agricultural Sciences, University of Melbourne, Werribee, Victoria, Australia
B Gamete and Embryology Laboratory, College of Public Health, Medical & Veterinary Sciences, James Cook University, Townsville, Queensland, Australia
C Gettysburg College, Gettysburg, Pennsylvania, USA
D Centre for Tropical Environmental & Sustainability Science, James Cook University, Townsville, Queensland, Australia
Reproduction, Fertility and Development 35(2) 141-141 https://doi.org/10.1071/RDv35n2Ab31
Published: 5 December 2022
© 2023 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of the IETS
Chytrid fungus, Batrachochytrium dendrobatidis (Bd), has caused the global decline or extinction of ∼500 amphibian species over the past 50 years. Infectious disease often reduces reproductive effort and fecundity in animals, but in some cases, can upregulate reproduction according to the “terminal investment hypothesis.” Evidence of testicular enlargement and increased spermatogenesis and mate calling has been reported in Bd-infected male amphibians. However, their reproductive fitness and gamete quality is unknown. This study aimed to measure functional sperm quality parameters and spermatogenesis in the testis of Bd-infected (n = 12) and unexposed (n = 8) three-year-old southern corroboree frogs (Pseudophryne corroboree). Males were examined four weeks after a two-day inoculation consisting of 6.4 × 105 and 6.9 × 105 zoospores, respectively. Sperm concentration (hemocytometer), motility (0–4 scale), viability (Hoechst 33342 [ThermoFisher]/propidium iodide), DNA damage (TUNEL) and morphology (SpermBlue [Microptic]) of ≥200 sperm per male were examined in the macerated left testis. Testis area, number and area of seminiferous tubules, germinal epithelium height, and number of spermatic cysts and their stage of spermatogenesis were examined in hemotoxylin-eosin stained histology sections of the right testis. Data were analysed using linear mixed effects or generalised linear mixed effects models by lme4 Software (Bates et al. 2015 J. Stat. Softw. 67, 1–48) followed by Tukey’s post hoc test using RStudio Software (rstudio.com). Among all testicular metrics analysed, Bd-infected males had 21.3% smaller seminiferous tubules (P < 0.001) with 14.7% fewer sperm bundles (P = 0.035), suggesting a decline in spermatogenesis. Sperm from Bd-infected males were shorter in total length (54.7 ± 0.1 vs 55.8 ± 0.1 μm; P = 0.048) and driven by shorter sperm heads (23.2 ± 0.05 vs 24.1 ± 0.07 μm; P = 0.001) but had 13.2% fewer sperm with malformations (P = 0.026) than controls. There was no effect of Bd infection on concentration, motility, viability, and DNA integrity of sperm. Our study on recently matured individuals indicates that sperm production is reduced during infection, possibly due to stress and debilitation or an adaptation to prioritise immunity and self-maintenance instead.
The authors thank A. Marc, S. Pena, R. Baker, P. Bauer, T. Kosch, S. Claytor, W. Wirth, A. Robert, M. McFadden, and AJ. Silla for laboratory help and/or advice on methods and husbandry. Melbourne Zoo donated eggs, and we thank D. Tegtmeier, L. Bertola, M. Stewart, N. Harney, B. Cwiklinski, C. Wei, K. McMullin, U. Roebeck, and T. Knavel for husbandry assistance. P. F-A was supported by a postdoctoral research fellowship from the Mexican Research Council (Consejo Nacional de Ciencia y Tecnología, CONACyT, 171465).
