Ardea
Official journal of the Netherlands Ornithologists' Union

login


[close window] [previous abstract] [next abstract]

van Noordwijk A.J., van Balen J.H. & Scharloo W. (1980) Heritability of ecologically important traits in the Great Tit. ARDEA 68 (1-4): 193-203
A central theme of evolutionary ecology is that presently observed traits can be understood as the result of natural selection. Clutch size and data of laying are thought to be such that maximum productivity is ensured. Attributing this role to natural selection implies the availability of genetic variation for these traits. It appears that about 40 per cent of all variation in the size of first clutches is genetic. About 30 per cent of the variation in date of laying can be attributed to genetic causes, and for several egg characteristics the relative contribution of genetic variation is 50-70 per cent, while about 60 per cent of average body weight variation is genetic. It is shown that both for clutch size and for relative date of laying the optimal value of these characters is not constant. In some years small clutches are optimal, in other years large clutches contribute more to the next generation. These differences arise mostly after fledging. A similar pattern is found for date of laying. The existence of varying optima can contribute to the preservation of genetic variation. The potential rate of evolutionary change is high. Further, no single optimum value exists for clutch size or date of laying. The variation probably mirrors the range of values that are at some moment, or at some place more productive than others.


[close window] [previous abstract] [next abstract]