|Size-specific reproductive effort in Chlamys islandica: reproductive senility or stabilizing selection?|
Vahl, O. (1985). Size-specific reproductive effort in Chlamys islandica: reproductive senility or stabilizing selection?, in: Gibbs, P.E. (Ed.) Proceedings of the 19th European Marine Biology Symposium, Plymouth, Devon, UK, 16-21 September 1984. pp. 521-527
In: Gibbs, P.E. (Ed.) (1985). Proceedings of the 19th European Marine Biology Symposium, Plymouth, Devon, UK, 16-21 September 1984. Cambridge University Press: Cambridge. ISBN 0-521-30294-3. 541 pp., more
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VLIZ: Proceedings 
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An analysis of data from a population of the Iceland scallop (Chlamys islandica) involving data from 1410 mature specimens of 25-100 mm shell height showed: (1) the residual variance of the regression of ln (gonad weight) on ln (shell height) was higher in smaller scallops; (2) relative to smaller specimens, the rate of increase of both soma and gonad weights decreased with increasing size, and (3) maximum gonad output occurred in scallops of ahout 80 mm shell height. The evidence of ( 1) suggests a stabilizing selection of gonad size; of (2) suggests that with increasing size, relatively less matter and energy are available to the scallop, and of (3) suggests that with increasing average scallop size, resources hecome increasingly more limited and are diverted from reproductive to somatic processes. In Chlamys islandica the recruitment to a given habitat patch may, however, either he a moderate annual recruitment to established populations, or a massive colonization of empty space made available by predators. The moderate recruitment favours a long reproductive life and a moderate reproductive effort, whereas the massive colonization favours a high reproductive effort and consequently a shorter reproductive life-span. The observed reduction in gonad output does therefore not necessarily represent a reduction in the individuals' reproductive effort (i.e. quantitative reproductive senility), but rather a lower effort in scallops surviving to reach a large size, and the reduction in the variance of gonad weight in large scallops is not necessarily a result of stabilizing selection favouring the survival of a particular phenotype in a particular habitat. Both phenomena are rather results of the unpredictable success of the individual spawning event which permit genotypes with both high and low reproductive effort to coexist.