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Cogradient pattern of growth in montane and lowland larvae of Rana remporaria (L.) at two levels of temperature

Jasieński M.

Polish Journal of Ecology

2009

Vol. 57, nr 2

353-361

Direct environmental impact and microevolutionary pressure may both shape the phenotype by acting synergistically (cogradient) or antagonistically (countergradient). An experimental approach is therefore needed to determine which environmental challenges are responsible for the observed inter-population variation in a phenotypic trait and if such variation is adaptive. Rana temporaria L. larvae were reared in a factorial experiment, with two temperature regimes (differential of 6[degrees]C) and larvae originating from two source populations in Poland: a montane pond in the Babia Gora National Park (elevation 1025 m) and a lowland swamp near Warszawa (elevation 100 m). Populations did not differ in early larval growth rates or in the length of the larval period. In both populations, the early rates of development were higher and the larval period was expectably and substantially shorter at higher temperature. The montane larvae were heavier at metamorphosis than the lowland larvae, but significantly so only at the low temperature treatment. The observed patterns of responses partially conform to the cogradient model of phenotypic variation, in which both environmental and selective effects are mutually enhancing the differentiation of populations.