Artificial light at night decreases metamorphic duration and juvenile growth in a widespread amphibian

Artificial Light at Night (ALAN) affects over 20% of the earth’s surface and is estimated to increase 6% per year. Most studies of ALAN have focused on a single mechanism or life-stage. We tested for indirect and direct ALAN effects that occurred by altering American toads’ (Anaxyrus americanus) ecological interactions or by altering toad development and growth, respectively. We conducted an experiment over two life-stages using outdoor mesocosms and indoor terraria. In the first phase, the presence of ALAN reduced metamorphic duration and periphyton biomass. The effects of ALAN appeared to be mediated through direct effects on toad development, and we found no evidence for indirect effects of ALAN acting through altered ecological interactions or colonization. In the second phase, post-metamorphic toad growth was reduced by 15% in the ALAN treatment. Juvenile-stage ALAN also affected toad activity: in natural light, toads retreated into leaf litter at night whereas ALAN toads did not c...