Seasonal variation of Batrachochytrium dendrobatidis in a threatened anuran species from Uruguay

Chytridiomycosis, an emergent infectious disease caused by the fungus Batrachochytrium dendrobatidis (Bd), is considered one of the drivers of the current amphibian biodiversity loss. To inform endangered species conservation efforts, it is essential to improve our knowledge about the abiotic and biotic factors that influence Bd infection dynamics in the wild. Here, we analyzed variation of Bd infection in the redbelly toad Melanophryniscus montevidensis, a threatened bufonid from Uruguay. We tested the influence of temperature, precipitation, season, and host population size on Bd prevalence and intensity. Additionally, considering the sub-lethal effects of Bd, we tested if these variables, potentially through their effect on Bd, also explain the variation in host body condition. We determined a high Bd prevalence of 41% (100/241), and that population size influenced both Bd prevalence and infection intensity. We identified an effect of precipitation and season on Bd infection intensity and an effect of season on toad body condition. In addition, we found a negative effect of infection intensity on body condition; moreover, while some toads cleared the infection, their body condition did not improve, suggesting a long-term cost. This is the first report on host population size as an important factor in Bd infection dynamics in a threatened anuran species, and seasonal demographic changes appear to play an important role in the dynamics. Finally, we highlight the need for monitoring Bd in this and other endangered amphibian populations, especially those within the genus Melanophryniscus, which includes several Endangered and Data Deficient species in South America.

Seasonal demography of the threatened Montevideo Redbelly Toad (Melanophryniscus montevidensis) in a protected area of Uruguay

Estimates of demographic parameters are scarce for Neotropical amphibians, a concerning fact because this region has the highest proportion of threatened amphibians in the world. We conducted a 3-year study where we applied a robust capture–mark–recapture design to assess the importance of breeding and non-breeding activity patterns over the survival rates, detection probabilities, and abundances of the Montevideo Redbelly Toad (Melanophryniscus montevidensis (Philippi, 1902)), a threatened anuran from Uruguay. The best models grouped seasons into hot and cold periods cyclically, were state-dependent in transition probabilities, and were time-dependent in detection probabilities for adults, but had constant detection probabilities for juveniles. Averaged estimates suggest a high survivorship rate during cold seasons (above 80%), but lower probabilities (below 60%) during hot seasons, especially for males. Analogously, the non-breeding activity had a seasonal pattern, with higher activity during spring and higher sheltering rates during autumn. These activity rates negatively influenced the averaged survivorship rates of adult males and females. Long-term (matrix) projections of seasonal survivorships, along with assessments of the causes of these patterns, should be carried out to determine extinction probabilities and possible threats for the conservation of the genus Melanophryniscus.

Examining the viability of dorsal fin pigmentation for individual identification of poorly-marked delphinids

Dolphin photo-identification has traditionally relied only on distinctive markings on the dorsal fin—this is problematic for delphinids whose populations exhibit a low mark ratio. We used common dolphins (genus Delphinus) as a model species to assess the viability of using pigmentation for photo-identification. Using a photo-identification catalogue of 169 adult individuals collected between 2002 and 2013, we extracted features that quantified pigmentation in a manner that was robust to lighting artefacts and dorsal fin orientation. We determined the proportion of individuals which exhibited pigmentation and examined temporal stability by (i) visually examining individuals and (ii) testing for seriation. We found 88–91% of images could be manually matched to the correct individual in the catalogue based on pigmentation patterns alone. A linear discriminant analysis classifier correctly identified the correct individual 77% of the time. We found 95% common dolphins exhibited distinctive pigmentation—all of which were temporarily stable. Our work challenges the current thinking that pigmentation is an unreliable feature for delphinid photo-identification and suggests that this feature could be applied to common dolphins and other poorly-marked delphinids.