Genetical Research

Comparative losses of quantitative and molecular genetic variation in finite populations of Drosophila melanogaster

a1 Key Centre for Biodiversity and Bioresources, Department of Biological Sciences, Macquarie University, Sydney, NSW 2109, Australia
a2 School of Tropical Biology, James Cook University, Townsville, Qld 4811, Australia
a3 Program for Evolutionary Dynamics and Department of Organismic Biology, Harvard University, One Brattle Square level 6, Cambridge, MA 02138, USA
a4 Australian Museum, 6 College Street, Sydney, NSW 2010, Australia

Article author query
gilligan dm   [PubMed][Google Scholar] 
briscoe da   [PubMed][Google Scholar] 
frankham r   [PubMed][Google Scholar] 


Quantitative genetic variation, the main determinant of the ability to evolve, is expected to be lost in small populations, but there are limited data on the effect, and controversy as to whether it is similar to that for near neutral molecular variation. Genetic variation for abdominal and sternopleural bristle numbers and allozyme heterozygosity were estimated in 23 populations of Drosophila melanogaster maintained at effective population sizes of 25, 50, 100, 250 or 500 for 50 generations, as well as in 19 highly inbred populations and the wild outbred base population. Highly significant negative regressions of proportion of initial genetic variation retained on inbreeding due to finite population size were observed for both quantitative characters (b=−0·67±0·14 and −0·58±0·11) and allozyme heterozygosity (b=−0·79±0·10), and the regression coefficients did not differ significantly. Thus, quantitative genetic variation is being lost at a similar rate to molecular genetic variation. However, genetic variation for all traits was lost at rates significantly slower than predicted by neutral theory, most likely due to associative overdominance. Positive, but relatively low correlations were found among the different measures of genetic variation, but their low magnitudes were attributed to large sampling errors, rather than differences in the underlying processes of loss.

(Received April 21 2004)
(Revised October 26 2004)
(Revised December 5 2004)

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p1 Current address: NSW Department of Primary Industries Science and Research Division – Aquatic Ecosystems, Narrandera Fisheries Centre, PO Box 182, Narrandera, NSW, Australia, 2700.