Testing Mechanisms of Bergmann's Rule: Phenotypic Decline but No Genetic Change in Body Size in Three Passerine Bird Populations
2011 (English)In: American Naturalist, ISSN 0003-0147, E-ISSN 1537-5323, Vol. 178, no 2, 202-213 p.Article in journal (Refereed) Published
Bergmann's rule predicts a decrease in body size with increasing temperature and has much empirical support. Surprisingly, we know very little about whether "Bergmann size clines" are due to a genetic response or are a consequence of phenotypic plasticity. Here, we use data on body size (mass and tarsus length) from three long-term (1979-2008) study populations of great tits (Parus major) that experienced a temperature increase to examine mechanisms behind Bergmann's rule. We show that adult body mass decreased over the study period in all populations and that tarsus length increased in one population. Both body mass and tarsus length were heritable and under weak positive directional selection, predicting an increase, rather than a decrease, in body mass. There was no support for microevolutionary change, and thus the observed declines in body mass were likely a result of phenotypic plasticity. Interestingly, this plasticity was not in direct response to temperature changes but seemed to be due to changes in prey dynamics. Our results caution against interpreting recent phenotypic body size declines as adaptive evolutionary responses to temperature changes and highlight the importance of considering alternative environmental factors when testing size clines.
Place, publisher, year, edition, pages
2011. Vol. 178, no 2, 202-213 p.
animal model, climate change, heritability, Parus major, microevolution, selection
IdentifiersURN: urn:nbn:se:uu:diva-156939DOI: 10.1086/660834ISI: 000292917900008OAI: oai:DiVA.org:uu-156939DiVA: diva2:435856