Coevolution of Developmental Plasticity and Large Egg Size in Crinia georgiana Tadpoles
Developmental plasticity and large egg size are traits that can benefit offspring early in life, but their coevolution has rarely been examined. I experimentally manipulated water depth and food availability of larvae of the frog Crinia georgiana, a species with a large egg size that breeds in shallow seeps that often dry before tadpoles have metamorphosed. Tadpoles that were never fed completed metamorphosis at about the same time as tadpoles under constant conditions, although at much smaller body sizes and with higher mortality. Except for the earliest stage tested (Gosner stage 28), tadpoles that experienced a decrease in water depth accelerated development and completed metamorphosis earlier than tadpoles kept in constant conditions. Acceleration was not possible when food was withheld, except when water levels were also lowered and only during later developmental stages. Because acceleration of development was initiated at earlier larval stages than in small-egged species that breed in ephemeral water bodies, these data suggest that phenotypic plasticity and maternal provisioning strategies can coevolve to help larvae cope with unpredictable aquatic environments.Abstract
Summary of the patterns of age and size at metamorphosis of Crinia georgiana tadpoles exposed to various treatments. Lines represent stage means for each of three deteriorating aquatic conditions implemented at different Gosner (1960) developmental stages. For all three treatment lines, earlier stages are in the lower right (beginning with stage 28) and later stages are toward the upper left (ending with stage 36). Constant condition treatments that were fed are towards the top of the figure, and the group that was never fed toward the bottom right. Error bars have been omitted for clarity