Stabilising selection on wing length in reed warblers Acrocephalus

Sedge Warbler (Acrocephalus schoenobaenus) Science Article 5

abstract

The size of an animal is of utmost importance for its overall success and each species isthought to have its own optimal size. If this is true, size traits ought to be understabilising selection unless the animal is living in a highly unstable environment. Winglength is a standard measurement of the size of birds, but up to date there have beenfew indications of stabilising selection on wing length. In this study we analyse recoverydata for reed warblers Acrocephalus scirpaceus (n771) ringed as juveniles in Swedenfrom 1981 until 2001. The data showed a significant relationship between juvenile winglength and survival time, with median juvenile wing lengths (66/67 mm) being the mostfavourable. The estimated stabilising selection differential (C0.094) supports thatwing length of the reed warblers in our study is under stabilising selection. The reedwarbler is a long-distance migratory species and we suggest that opposing selectionpressures may act on wing length during different life history stages, and that this mightexplain the rather broad peak of favourable wing lengths found.

Hall, K. S. S., Ryttman, H., Fransson, T. and Stolt,, J. Avian Biol. 35: 7-12.

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