Fluctuating asymmetry (FA), the small and random departures from perfect symmetry of an organism's bilateral traits, has been used as a measurement of developmental stability and an indicator of stress in endangered populations. We were interested in testing if the level of developmental stability is the same in different populations experiencing the same conditions, as the use of FA as an indicator of ecological stress is only meaningful if this is true. In order to do this, the effect of thermal stress on wing size FA over a range of temperatures was determined on three different lines of Drosophila melanogaster: two lines were maintained at one of two different constant temperatures (18°C or 28°C) and one under a fluctuating thermal regime (18°C and 28°C) for eight years. The differences in viability of these lines, when reared at a range of different temperatures, are associated with the temperature conditions they previously experienced. All lines showed a similar increase in FA at the two ends of the thermal range but with significantly different mean values. The two units of wing development (compartments) differed in their FA response depending on the selective history of each line. We discuss the implication of our results for the use of FA as an indicator of ecological stress.
Mating success is linked to reproductive success in males, but parameters influencing it are poorly known. The relationships between lifetime mating success (LMS), fluctuating asymmetry (FA), body size (SIZE), reproductive period (RP) and emergence date (MD) of males of Cercion lindeni were investigated. Males were marked and photographed in their pre-reproductive period, and their matings monitored. RP was assumed to be the period between the MD and the last sighting of each individual. Three different FA measures and the size of each individual were determined. The results showed that the individuals not present at the pond during the reproductive period had a higher FA (but not for meristic characters) than those present. For those individuals actually involved in reproductive activity, LMS was only positively correlated with RP, which was negatively related with MD, and this with SIZE.
We examined whether dispersal was associated with body and wing morphology and individual quality, and whether such an association was sex-specific, in the Glanville fritillary butterfly Melitaea cinxia (L.) in Paldiski on the north coast of Estonia. Body weight, size and shape of both fore- and hindwing, wing aspect ratio and wing loading were used as measures of body and wing morphology. Fluctuating asymmetry (FA) of wing shape was used as a measure of individual quality. Males and females did not differ in dispersal rates, despite large differences in overall morphology and FA. Females had a significantly higher wing loading and aspect ratio, but a lower FA than males. Females, but not males, that dispersed differed in forewing shape from those that did not disperse. The sex-specifity of the covariation between dispersal and forewing shape is most probably due to wing shape being associated with different life-history traits in both sexes, resulting in different selection pressures on wing shape in each of the sexes.