The impact of genetic parental distance on developmental stability and fitness in Drosophila buzzatii.

Measures of genetic parental distances (GPD) based on microsatellite loci (D(2) and IR), have been suggested to be better correlated with fitness than individual heterozygosity (H), as they contain information about past events of inbreeding or admixture. We investigated if GPD increased with increasing genetic divergence between parental populations in Drosophila buzzatii and if the measures indicate past events of admixture. Further we evaluated the relationship between GPD, fitness and fluctuating asymmetry (FA) of size and shape. We investigated three populations of Drosophila buzzati, from Argentina, Europe and Australia. From these populations two intraspecific hybridisation lines were made; one between the Argentinean and European populations, which have been separated 200 years and one between the populations from Argentina and Australia, which have been separated 80 years. By doing this we obtained hybrid progeny having different levels of GPD. We found that D(2) and H can be used as indicators of admixture when comparing hybrid individuals with their parentals. IR was not informative. Our results does not exclude the presence of genetic fitness correlations (GFC) over individuals with a broad fitness range from populations in equilibrium, but we doubt the presence of GFC using GPD measures in admixed populations. Shape FA could be a relevant measure for fitness, however, only when comparing populations, not at individual level.

Maternal and grandmaternal age effects on developmental instability and wing size in parthenogenetic Drosophila mercatorum.

Age is known to have a large effect upon fertility and survival. Here we study the impact of maternal and grandmaternal age on wing size and developmental instability (DI) in offspring using a parthenogenetic strain of Drosophila mercatorum. This enabled us to cancel out any genetic variance between individuals. The mean centroid size of the wings was estimated in offspring from four maternal/grandmaternal age groups. Further, DI was calculated by measuring phenotypic variability and correcting this index for the bias produced by the environmental variability. The offspring developed from eggs laid by mothers belonging to four different age groups with young (Y) or old (O) mothers and grandmothers. The age groups are: YY, YO, OY and OO, with the first letter referring to the age of the grandmother and the second letter to the age of the mother. We consider flies between three to six days of age as young and flies between 15 and 18 days of age as old. We found that environmental variability was present in this study and therefore the correction for its bias on phenotypic variability was shown to be necessary for a correct interpretation of the results. DI displayed, for most of the traits investigated, a significantly higher level in the OY and OO age groups, as compared to the YY and YO age groups. The mean centroid size of the wings were in almost all cases significantly different among the age groups with the highest mean value in the OY group for all traits. This investigation shows that offspring are affected by maternal age and that this effect can be transmitted maternally across more than one generation.