Our study was conducted in the municipality of Toro, Zamora. In this area, the old cattle troughs that have survived among the vineyards maintain large populations of the Common Midwife Toad. While in the summer this area is hot and dry, the winters are quite cold. During one year, automatic thermometers placed at 6 of these streams recorded water temperature every 10 minutes, and once a month, we collected samples of infected larvae of the Common Midwife Toad.
The water temperature in summer (always less than 24°C) proved ideal for the growth of the fungus. However the proportion of infected larvae and their burden of zoospores, exhibited their lowest values during this time of year. On the other hand, the low temperatures reached during the winter, although not suitable for the growth of the fungus, did not represent a problem for its survival. Finally, in any case the temperature of the water was insufficient to kill the fungus (estimated at 35°C according to our study).
Interestingly, the minimum water temperature, and not the maximum was found to be the best predictor of larval fungal burden. Furthermore, the minimum temperature, only two days prior to sampling, was found to be a more determinant factor of infection intensity than impacts of longer-term spans of temperature. Probably the low temperatures during the coldest months weaken the immune system of the larvae, making them more vulnerable to fungus attack, although these temperatures are not the most favourable for disease development.
You can download the study here.