Life is full of compromises, which can limit change. For animals with multiple stages in their life cycle, each stage may present major compromises to adaptation. Research conducted in the Department of Biological Science at The University of Tulsa by Associate Professor Ron Bonett and former graduate student Andrea Blair (MS ’13) shows that salamanders with two-part (aquatic-to-terrestrial) life cycles have experienced limited body form and vertebral column evolution over more than 160 million years. By comparison, over a shorter duration, salamanders that have switched to one-part (aquatic-only or terrestrial-only) life cycles have undergone a higher degree of change in these characteristics. In some cases, the switch to a more-simple life cycle has had a dramatic effect on salamander anatomy. For example, some types of aquatic salamanders have quadrupled the number of vertebrae in their trunk skeleton.
“This study provides an example of how long-term shifts in life cycle complexity can alter rates of evolution. Many organisms have multistage life cycles, so changes in life cycle complexity have probably played a major role in shaping life,” Bonett said.
Their paper on “Evidence for complex life cycle constraints on salamander body form diversification” was published this week in the Proceedings of the National Academy of Sciences.