Relationship between growth and ageing in Drosophila

Arthropods life cycle and temperature: Beyond isomorphy hypothesis

In poikilotherms, developmental time and adult lifespan are biological traits driven by temperature although their underlying physiological mechanisms differ. The developmental theory of ageing predicts a positive correlation between these two traits without confirming a genetic or causal relationship. The developmental rate isomorphy hypothesis established that the proportionality in the duration of each pre-imaginal stage with respect to total developmental time does not vary with temperature. This may have important evolutionary implications. We conducted an analysis with arthropods of agronomic interest to study if the hypothesis could be extended to the total lifespan of poikilotherms, including adult lifespan. We showed that isomorphy could be acceptable for a global description of this relationship. However a general model of power law type is more appropriate for characterizing the relationship between developmental time and adult lifespan. In this model, the shape of the curve is a constant characteristic, but the parameters that control it depend on the functional type of the arthropod (phytophagous, predator or parasitoid). Presumably this power law could be extended to all arthropods of agricultural interest, and more generally to all arthropod.

Mode of inheritance of major genes controlling life span differences between two inbred strains of Drosophila melanogaster

Although life span is generally considered to be under polygenic control, we obtained experimental evidence of Mendelian genes exerting major effects on life span differences between two inbred strains of Drosophila melanogaster. Our data indicate two loci with major effects, one being autosomal and the other sex-linked. The alleles at the autosomal locus are designated A1 and A2, the latter producing longer life. Heterozygotes, A1A2, exhibit over-dominance. The alleles at the sex-linked locus, designated X1 and X2, produce life-extending effects. X1 revealed a dosage effect, causing homozygous females to live longer than hemizygous males; X2 showed no dosage effect. The identified genes are considered to control the period of activity of many genes maintaining life.

Consequences of artificial selection on pre-adult development for adult lifespan under benign conditions in the butterfly Bicyclus anynana

The genetic architecture underlying the regulation of lifespan is shaped by evolutionary history, thus, including selection in past environments. In particular, the developmental environment is important, because selection pressure for survival is highest during development. From this life-history point of view, the ageing phenotype is the outcome of these factors, and links between the developmental and adult life stage are expected. In this study, we specifically address whether genetic variation in pre-adult traits affects adult lifespan. We use lines artificially selected for divergence in development time, pupal mass or egg size, thus, exploiting the standing genetic variation in pre-adult traits present in natural populations of Bicyclus anynana. We then reared individuals from each line and the unselected base population in a common environment, and recorded each selected trait and adult longevity. In general, differences in adult lifespan across selection lines were small. This is not surprising given the benign conditions used here. The minor differences in adult survival were only partially the result of environmental influences, as indicated by low phenotypic correlations. However, significant genetic correlations point to possible intrinsic mechanisms involved in lifespan regulation. Genetic variation in egg mass or pupal mass did not contribute to variation in lifespan. However, we found a negative genetic correlation between developmental time and lifespan, suggesting a genetic coupling of faster development with a longer adult lifespan in this species. A follow-up study with an identical set-up that introduces stress during development should give a more detailed insight into the role of development in the regulation of lifespan.

Cytoplasmic influence on the expression of nuclear genes affecting life span in Drosophila melanogaster

In earlier studies we have found that the difference between short and long life spans of two inbred strains of Drosophila melanogaster is controlled by nuclear major genes. The present study has revealed a cytoplasmic factor that influences the expression of the nuclear longevity genes. The factor shows a typical maternal inheritance and is considered to be an extranuclear gene, such as mitochondrial DNA (chondriome). This paper marks the discovery of two basic forms of inheritance, nuclear and extra-nuclear, in the genetics of life span of D. melanogaster. These findings suggest that further studies, including genetic engineering, on longevity and aging might enable direct manipulation of these characters.

On the developmental theory of ageing. I. starvation resistance and longevity in Drosophila melanogaster in relation to pre-adult breeding conditions

The developmental theory of ageing predicts a positive correlation between developmental time and adult longevity. Experiments that vary larval density and food level have been carried out to test this prediction. The results show differences in viability, developmental time, starvation resistance and adult longevity. It is concluded that pre-adult developmental time is not a causal factor for the determination of adult longevity in Drosophila melanogaster. The observed variation in adult longevity is discussed in relation to viability selection and changed adult physiology.