Effects of temperature on metamorphosis in the Indian Rice Frog, Rana limnocharis, in Taiwan: Do spring and summer cohorts use different life-history strategies?

    The Indian rice frogs (Rana limnocharis) are widely distributed in rice fields in northern Taiwan.  Their long breeding period (March-September) is interrupted by a “mid-summer drainage”(July) between the first (spring) and second (summer) rice crops, which cut the breeding period into two.  We hypothesize that the interruption leads to temporal differentiation within populations, and the spring and summer frogs evolve different life-history strategies due to differences in rice field temperature between crops.  We used a common garden experiment to test whether developmental strategies differed between the two crops.  The Indian rice frog tadpoles were collected in May (spring cohort) and September (summer cohort) in 2006 from Taipei.  Each cohort was housed in 2 temperatures 22°C and 29°C, to simulate the air temperatures of spring and summer crops, respectively.  We recorded age and size of tadpoles weekly until metamorphosis completed. The results showed that the spring and summer cohorts did use different life-history strategies.  Under low (spring) temperature, spring tadpoles metamorphosed at bigger sizes though similar ages than summer ones.  On the other hand, under high (summer) temperature, summer tadpoles metamorphosed at older ages but similar sizes than spring ones.  It suggested that spring tadpoles perform better at spring (low) temperature by facilitating growth rates, while summer tadpoles perform better at summer (high) temperature by facilitating developmental rates.  Our study supports that the drainage interruption in rice fields leads to temporal differentiation of Indian rice frog populations.