J. Merila et al., Plasticity in age and size at metamorphosis in Rana temporaria - comparison of high and low latitude populations, ECOGRAPHY, 23(4), 2000, pp. 457-465
Effects of different combinations of stressors (viz. temperature, food leve
l) on growth, developmental and survival rates of Rana temporaria tadpoles
from two geographically widely (approximate to 1500 km) separated populatio
ns were studied in a common garden experiment. In both populations, low tem
perature and low food level lead to lowered growth rates and delayed metamo
rphosis, whereas high temperature and high food level had the opposite effe
ct. Tadpoles from north metamorphosed earlier and exhibited higher growth r
ates than tadpoles from south, suggesting local adaptation to shorter growt
h period and cooler ambient temperature in north. Size at metamorphosis did
not differ between the two populations, but when the differences in metamo
rphic age were accounted for, then the tadpoles from north were larger than
those from south. These results suggest considerable adaptive genetic diff
erentiation in growth rates, size and timing of metamorphosis between north
ern and southern R. temporaria populations. In both populations, high food
levels tended to reduce tadpole survival rates and there was a negative cor
relation between growth and survival rates across different treatments in b
oth populations. In general, tadpoles from north experienced high mortality
rates in high food level - low temperature treatments, whereas southern ta
dpoles experienced high mortality in high food level-high temperature treat
ments. This suggest that there may be genetic differences among different p
opulations as how they would be influenced by high nutrient loads, such as
brought along for example by fertilization of forest or agricultural soils.