Genetic and phenotypic associations in morphological traits: a long term study of great reed warblers Acrocephalus arundinaceus


  • Mikael Åkesson,

  • Staffan Bensch,

  • Dennis Hasselquist

M. Åkesson (correspondence), S. Bensch and D. Hasselquist. Department of Animal Ecology, Ecology Building, Lund University, S-223 62 Lund, Sweden. E-mail:


We present estimates of standardized selection (directional and quadratic) differentials via reproductive success on eight morphological traits in a newly founded long-term study population of great reed warblers Acrocephalus arundinaceus in Sweden. In order to predict the evolutionary response to selection in these traits we present estimates of heritabilities (h2), phenotypic (rP) and genetic (rA) correlations among the same traits. We also examined the extent of parental effects in the expression of the phenotypic traits. Overall, the population is subject to low levels of directional selection and higher levels of stabilizing selection. This makes us predict that the population is changing very little if anything, even though h2 in many cases are considerable. Midparent-midoffspring h2 ranged from 0.14 and 0.94 (mean 0.58) and were significant for seven of eight traits. We found indications of positive maternal effects in tarsus length. Phenotypic correlations between traits ranged from 0.02 to 0.43 (mean 0.15) and showed generally much lower values than the corresponding genetic correlations that ranged between 0.08 and 1.04 (mean 0.46). Overall, the correlation between rP and rA was significant, although moderate, but they tended to differ in magnitude, possibly due to overestimation of additive covariance between traits.