Plastic response to pond drying in tadpoles Rana temporaria: tests of cost models

Tadpoles from two types of ponds, temporary and permanent, were raised in a common garden experiment. There was no clear effect of pond type on development rate (time for metamorphosis). From each sibship, one group was raised under a constant water regime (deep tanks) and one was subject to simulated pond drying (shallow tanks). The tadpoles exhibited a plastic response to pond drying: they metamorphosed earlier in the shallow than in the deep tanks. There was no interaction between pond type and tank type; that is, there was no indication of microevolution on plasticity per se. Sibships with a high degree of plasticity (much earlier metamorphosis in shallow than in deep tanks) had a larger size reduction from deep to shallow tanks, suggesting a trade-off between time and size. This may be considered an allocation cost sensu Tollrian and Harvell (1999). However, tadpoles from early sibships that were plastic were of a similar size to those from early sibships that were not plastic (those that were early in the deep tank as well). This suggests that there was no production cost sensu DeWitt et at (1998). Sibships with high plasticity had tadpoles that grew large in the deep tank and developed slowly (late metamorphosis) in this tank. This suggests that plastic tadpoles were those that, because of their size, most readily could afford any costs associated with plasticity and those that, because of slow development, most easily could increase development rate. The relation to size is the opposite to that predicted if the capacity for plasticity is associated with cost (plasticity cost sensu Tollrian and Harvell, 1999; maintenance cost sensu De Witt et al, 1998).