Evol Ecol Res 7: 717-731 (2005)     Full PDF if your library subscribes.

Do common frogs (Rana temporaria) follow Bergmann’s rule?

Ane T. Laugen,1 Anssi Laurila,1 K. Ingemar Jönsson,2 Fredrik Söderman1 and Juha Merilä3*

1Department of Population Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden,  2Department of Theoretical Ecology, Ecology Building, Lund University, SE-223 62 Lund, Sweden and  3Ecological Genetics Research Unit, Department of Bio- and Environmental Sciences, University of Helsinki, PO Box 65, FIN-00014 Helsinki, Finland

Author to whom all correspondence should be addressed.
e-mail: juha.merila@helsinki.fi


Questions: Does intraspecific extension of Bergmann′s rule – larger size within a species in cooler areas – hold true for ectotherms in general, and for the common frog (Rana temporaria) in particular? What is the relative importance of genetic and environmental factors (i.e. direct environmental induction) in determining latitudinal patterns of body size variation in common frogs?

Methods: We tested for a positive association between mean body size and latitude in common frogs (Rana temporaria) across a 1600 km long latitudinal gradient in Scandinavia both for wild-collected adults and laboratory-reared metamorphs.

Results: In adults, the mean body size increased from south to mid-latitudes, and declined thereafter. This occurred despite the fact that the mean age of adult frogs increased with increasing latitude, and age and body size were positively correlated. The latitudinal pattern of body size variation in metamorphs reared in a common garden experiment was similar to that observed among wild-caught adults.

Conclusions: The results suggest that the concave pattern of body size variation across the latitudinal cline may be at least partly genetically determined, and that although there is considerable geographic variation in mean body size of R. temporaria, this variation does not conform with Bergmann’s rule.

Keywords: age, amphibians, body size, cline, growth, latitude, temperature.

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