Evolutionary responses of amphibian populations exposed to mining-impacted environments and climate stress

Abstract

Environments impacted by pollution can often be characterized by numerous compounding stressors. These pollutants, and their interactions with environmental variables, present unique challenges for wildlife, often resulting in profound evolutionary changes. However, evolutionary mechanisms such as local adaptation to multiple anthropogenic and environmental selection pressures are still poorly understood. I conducted a laboratory experiment with Northern leopard frog (Rana pipiens) tadpoles from three populations to test if they are adapted to miningimpacted environmental conditions. I also assessed the potential role of global warming on the evolutionary outcome of these different populations by using two different temperature regimes. Variability in survival was largely consistent with life-history trade-offs associated with local adaptation to environments impacted by metals. Specifically, tadpoles from the environment with high levels of toxic metals showed no difference in mortality, but had slower growth rates, when raised in environments with medium and low levels of toxic metals. By contrast, tadpoles from environments with medium and low levels of toxic metals displayed a higher risk of mortality but no changes in growth rate when raised in an environment with high levels of toxic metals. Unexpectedly, a warmer environment (25°C) led to higher survival for tadpoles from the high toxic metal environment when raised in medium and low toxic metal environments compared to tadpoles born in medium and low toxic metal environments. My study demonstrates the potential for amphibian populations to adapt to mining-impacted environments and provides evidence that such environmental conditions can influence life-history traits. This work also highlights that multiple stressors associated with pollution and climate change can produce a greater effect in isolation than in combination, which is an unlikely scenario according to current climate change research.