Elevated extension of longevity by cyclically heat stressing a set of recombinant inbred lines of Drosophila melanogaster throughout their adult life

Heat-induced hormesis in longevity is linked to heat-stress sensitivity across laboratory populations from diverse altitude of origin in Drosophila buzzatii

Heat-induced hormesis in longevity is the increase in life span resulting from the previous exposure to a mild heat stress early in life. Here we examined heat-induced hormesis of Drosophila buzzatii in five mass-mating populations, which were derived from five wild populations along an elevation gradient from 202 to 1855 m above sea level in North-Western Argentina. Five day old flies were exposed to 37.5 °C for 90 min to induce hormesis and its possible variation across altitudinal populations. This heat treatment strongly extended longevity in lowland-derived flies from the most heat-resistant population only. Both heat-induced effects on longevity and heat-knockdown time (heat-stress sensitivity) were negatively correlated to altitude of population of origin. Hormesis was positively correlated to heat-knockdown time across populations. These results indicate that variation in heat-induced hormesis can not be considered as independent of heat-stress sensitivity (or heat-knockdown time) in populations of insects.

Mating success at elevated temperature is associated to thermal adaptation in a set of recombinant inbred lines of Drosophila melanogaster

In insects, mating ability at elevated temperature can be relevant for adaptation to heat-stressed environments and global warming. Here, we examined copulation latency (T1), copulation duration (T2), and mating frequency (T3, an index of mating success) in two related sets of recombinant inbred lines (RIL) in Drosophila melanogaster at both elevated (33 °C) and benign (25 °C) temperatures. One of these RIL sets (RIL-SH2) was shown to be consistently more resistant in both heat knockdown and heat-shock survival assays than its related set (RIL-D48) in previous studies. Negative correlations across RILs were found between T1 and T3 in this study. Flies from the heat-resistant set of RIL (RIL-SH2) were better able to mate at elevated temperature than flies from the heat-susceptible set (RIL-D48). Quantitative trait locus (QTL) mapping identified temperature-dependent QTLs for all traits (T1, T2 and T3) on all the three major chromosomes. Mating success at elevated temperature was found to be influenced by multiple QTLs. At elevated temperature, several QTLs for mating traits co-localized with QTLs that were previously associated with thermotolerance. The genetic basis for T1, T2 and T3 at the elevated temperature was found to be largely different from the genetic basis controlling the variation for mating success at benign temperature, as there was only a very low (or even null) number of QTLs overlapping across temperatures.

Negative genetic correlation between longevity and its hormetic extension by dietary restriction in Drosophila melanogaster

Longevity is a highly malleable trait which is influenced by many genetic and environmental factors including nutrition. Mild stress of dietary restriction (DR) is often beneficial by extending longevity in many organisms. Here, DR-induced effects on longevity were tested for genetic variation in a set of recombinant inbred lines (RIL) in D. melanogaster. Genetic variability was significant in the longevity response following a DR-treatment across RIL, with detrimental effects in several RIL but beneficial effects in other RIL. One quantitative trait locus (QTL) was consistently significant in the middle of chromosome 2 for DR-induced changes in longevity, including hormesis (an increase in longevity by DR). Another QTL co-localized with a previously found QTL for starvation resistance in females. Several other QTL were also significant on most chromosomal arms. Longevity in controls was negatively correlated to DR effects across RIL for longevity in females, the sex showing higher DR-induced hormesis. This negative genetic correlation highlights the importance to further investigate the effects of genetic variation in the strength of DR-induced hormesis in longevity and its sex-specificity.

Epithelial cell shape change of Drosophila as a biomonitoring model for the dose assessment of environmental radiation

Inevitable exposure to ionizing radiation from natural and human-made sources has been increasing over time. After nuclear disasters, such as the Fukushima accident, the public concerns on health risk of radiation exposure because of radioactive contamination of the environment have increased. However, it is very difficult to assess the biological effects of exposure caused by environmental radiation. A reliable and rapid bioassay to monitor the physiological effects of radiation exposure is therefore needed. Here, we quantitatively analyzed the changes in cell shape in Drosophila epidermis after irradiation as a model for biomonitoring of radiation. Interestingly, the number of irregularly shaped epithelial cells was increased by irradiation in a dose-dependent manner. A dose-response curve constructed with the obtained data suggests that the measurement of the number of irregular shaped cell in the epidermis is useful for the assessment of radiation dose. In addition, a comparison of the variation in the different samples and the data scored by different observers showed that our evaluation for cellular morphology was highly reliable and accurate and would, therefore, have immense practical application. Overall, our study suggests that detection of morphological changes in the epithelial cells is one of the efficient ways to quantify the levels of exposure to radioactive radiation from the environment.

Combining three mild stresses in Drosophila melanogaster flies does not have a more positive effect on resistance to a severe cold stress than combining two mild stresses

Among other positive effects, mild stresses can increase resistance to severe stresses. Previous studies combining two mild stresses showed that when each mild stress had positive effects their combination had more positive effects than each mild stress. The present study tested whether combining three mild stresses could still provide positive additive effects, or whether this combination has negative effects because it is no longer a mild stress but rather a strong stress with negative effects. Flies were subjected to either fasting, hypergravity for one or two weeks, or cold shocks, to combinations of two or of the three mild stresses, and survival to a severe cold stress was observed at 13 or 20 days of age. Positive effects of each mild stress and of combining two stresses could be observed, but combining the three stresses provided a similar survival or a lower survival than the combination of two stresses. Thus, combining three stresses was not more efficient than combining two stresses.