Can fluctuating asymmetry be used to detect inbreeding and loss of genetic diversity in endangered populations?

Fluctuating asymmetry (FA), a measure of developmental stability, has been proposed as a simple technique for identifying populations suffering from inbreeding and a loss of genetic diversity. However, there is controversy regarding the relationship between FA and both allozyme heterozygosity and pedigree inbreeding coefficients (F). FA of sternopleural bristle number in Drosophila melanogaster was measured in populations maintained at effective sizes of 25 (8 replicates), 50 (6), 100 (4), 250 (3) and 500 (2) for 50 generations (inbreeding coefficients of 0.05-0.71). FA was calculated from the same data set using three different indices (FA₁, FA₅ and FA₆). There was no significant relationship of FA with pedigree inbreeding coefficients for any of the three indices. The relationship between FA and allozyme heterozygosity was non-significant for indices FA₅ and FA₆ (the more powerful indices) and only significant for FA₁. A second comparison of highly inbred (F ≈ 1) populations with their outbred base population showed significantly greater FA in the inbred populations only when analysed with FA₆. Analysis of the same data using FA₁ and FA₅ showed non-significant relationships in the opposite direction. If a relationship between FA and genetic diversity does exist, it is weak and inconsistent. Consequently, our results do not support the use of FA as a monitoring tool to detect inbreeding or loss of genetic diversity.