Plasticity in age and size at metamorphosis in Rana temporaria - comparison of high and low latitude populations

Effects of different combinations of stressors (viz. temperature, food level) on growth, developmental and survival rates of Rana temporaria tadpoles from two geographically widely (approximate to 1500 km) separated populations were studied in a common garden experiment. In both populations, low temperature and low food level lead to lowered growth rates and delayed metamorphosis, whereas high temperature and high food level had the opposite effect. Tadpoles from north metamorphosed earlier and exhibited higher growth rates than tadpoles from south, suggesting local adaptation to shorter growth period and cooler ambient temperature in north. Size at metamorphosis did not differ between the two populations, but when the differences in metamorphic age were accounted for, then the tadpoles from north were larger than those from south. These results suggest considerable adaptive genetic differentiation in growth rates, size and timing of metamorphosis between northern and southern R. temporaria populations. In both populations, high food levels tended to reduce tadpole survival rates and there was a negative correlation between growth and survival rates across different treatments in both populations. In general, tadpoles from north experienced high mortality rates in high food level - low temperature treatments, whereas southern tadpoles experienced high mortality in high food level-high temperature treatments. This suggest that there may be genetic differences among different populations as how they would be influenced by high nutrient loads, such as brought along for example by fertilization of forest or agricultural soils.