Frog (IMAGE) U.S. National Science Foundation Caption Ectotherms, or organisms without internal heat sources, such as frogs, are a 2015 OPUS topic. Credit NSF/Nicole Rager-Fuller Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.