Red frog reproductive phenology
Study area: reproductive phenology of the red frog (Rana temporaria) was studied at 5 sites that include 29 ponds located at different altitudes between 500 and 2310 meters. Dates of spawning and the appearance of the different developmental stages of the tadpoles were recorded with a weekly sampling frequency.
Protocol: observations were done in 3 ponds at the same altitude counting the number of eggs laid and then, when the tadpoles appear, scooping them in a net at different points of the pond and recording the day of the appearance of the first tadpole for each stage and in each pond. The most visible phases were considered: (0) eggs, (3) tadpoles with external gills and threadlike tail, (4) tadpoles with back legs formed, (5) tadpoles with forelegs formed and the presence of the tail (see phases pictures)
Effect of altitude: the date of the spawning is delayed with increasing altitude, but elevation lapse rate varies in different years. As an example, in 2011, spawning was earlier, especially at high altitudes.
Effect of snowmelt: in mountain areas, the main determinant of the spawning date seems to be the date of snowmelt, which ensures access to the water essential for the reproduction of the frogs. Mountain populations of red frogs are therefore closely dependent on temperature and snowfalls for reproduction.
Effect of altitude: delay at higher altitude decreases with tadpoles development: at higher elevation early phases are more delayed than later ones. The development of tadpoles is therefore more rapid at high altitudes than low altitudes.
The phenology of reproduction of red frogs seems therefore a very effective indicator of climate change effects in the mountains because it is directly influenced by temperature and snowmelt. The simplicity of the protocol devised enables anyone, even non-specialists, to undertake this monitoring and makes easy comparisons between sites.