To Metamorphose or Overwinter? The Case of an Endangered Anuran Endemic

Phenotypic plasticity in time to and size at metamorphosis are representative examples of the responses of larval amphibians to variable wetland environments. Larval growth rate is pivotal in determining the time to and size at metamorphosis. However, it is important to note that much of our understanding of life-history plasticity comes from studies conducted on species that complete their larval period in the natal year. Here, I investigated how larval growth rate influences whether individuals metamorphose in their natal year or overwinter as larvae using the Sado wrinkled frog (Glandirana susurra), an endangered anuran species endemic to Sado Island, Japan. In the laboratory experiment, larvae were kept separately, and their food levels were controlled to create variation in growth rate. It is believed that most Sado wrinkled frog larvae overwinter; however, approximately 90% of the larvae metamorphosed by the onset of the first winter. The more they grew during the early larval period, the earlier they metamorphosed with larger size and higher body condition. A high food level during the entire larval period increased size and body condition at metamorphosis. The positive relationship between the early growth rate and larval development rate suggests that the growth environment during the early larval period is key for maintaining variation in the metamorphosis timing of the endangered endemic anuran.