Climate warming is increasing the hybridization of trout-interbreeding between native and non-native species-in Western North America, according to a study published online this week in Nature Climate Change. These interactions are being enhanced under climate change and pose a serious threat to biodiversity.

Clint Muhlfeld and colleagues investigated the extent of hybridization between native westslope cutthroat trout (Oncorhynchus clarkii lewisi) and non-native rainbow trout (Oncorhynchus mykiss), which have been introduced into the Flathead River system in Montana, USA, over the past century. They found that hybridization was historically prevalent in only one source population but that during a recent 30-year period of accelerated warming, hybridization spread rapidly upstream through the river system. Decreases in spring precipitation and increases in summer stream temperature were identified as the major drivers of change.