Variation in Pond Hydroperiod Affects Larval Growth in Southern Leopard Frogs, Lithobates sphenocephalus

Size at metamorphosis is an important correlate of amphibian fitness. Several, often interrelated factors, such as hydroperiod, competition, and food availability, determine metamorph size. Hydroperiod is a defining characteristic of ponds, but pond drying is not always a deterministic process, and refilling can occur prior to complete drying. We conducted an experiment to test if a recurring four-week partial drying/filling cycle affected amphibian growth and size using a population of overwintering larval Lithobates sphenocephalus (Southern Leopard Frogs). Effects of the drying/filling cycle varied over time on larval mass, but this cycle had no overall effect on other measures of larval or metamorph size. Metamorph size covaried with both survival and larval period length: individuals were larger at metamorphosis when survival was lower and among individuals with longer larval periods. We observed the first reported instance of prolonged larval periods across multiple winters in L. sphenocephalus, wherein some of our larvae exposed to the drying/filling cycle required 18 months to reach metamorphosis. Individuals that overwintered as larvae for a second winter were larger at metamorphosis than those that metamorphosed at the end of the previous summer. Lithobates sphenocephalus maximize metamorphic size rather than optimize metamorphic timing, and metamorph size can also be affected by larval survival.