First report of overwintering tadpoles in the endemic Italian agile frog Rana latastei

Climate change is affecting organism seasonality patterns, and this can drive phenological shifts in key traits, including breeding activity. Here, we report the first record of overwintering tadpoles in the Italian agile frog (Rana latastei), a threatened endemic species of Northern Italy. This species usually breeds between late January and April, with tadpoles reaching metamorphosis by early summer. In February 2025, alongside the first freshly-laid egg-clutches of the usual breeding season, we observed several large-sized tadpoles at a reproductive site of R. latastei within Como province. A few days after hatching, six newly hatched tadpoles and six large-sized individuals at a later developmental stage were captured, photographed, and measured. Concurrently, a recently metamorphosed froglet was found at the same site. Morphological analyses revealed that individuals showed typical traits of R. latastei. Moreover, while newly hatched tadpoles were at Gosner’s development stages 25-26, large-sized individuals were visibly bigger and at a late developmental stage, which was incompatible with the classical late-winter breeding timing of this species. Our study provides the first evidence of overwintering tadpoles in R. latastei, suggesting that potential shifts in development timing (prolonged larval time) or altered breeding habits (autumnal reproduction) may be occurring. Although the mechanisms behind this unusual observation remain unclear, such a phenological shift may have been favoured by variation in climatic regime.