Recently, heterogeneity of the environment has been suggested as an important player in the evolution of life span variation. Established ageing theories propose that life span variation is the ...result of coevolution with other traits, such as stress resistance. This study aimed to compare these alternative hypotheses by examining the relationship between four environmental variables and different types of stress resistance traits with life span in 13 Drosophila species originating from tropical, subtropical and temperate environments (ecotypes). Average life span was found to differ significantly both between species and sexes, but only male life span correlated with the environment and cold resistance. While controlling for phylogeny, the environmental variable precipitation seasonality and resistance against cold‐induced stress explained most variation in male life span. Furthermore, male life span varied between species in a manner represented by environmental variables linked to the different ecotypes, such that tropical species lived longer and were less cold resistant. The current results suggest that general mechanisms underlying stress resistance and life span are unlikely. In addition, our results point to the environment independently shaping variation in life span and cold resistance rather than genetic interactions.
1. Thermal adaptation was investigated in the fruitfly Drosophila buzzatii Patterson and Wheeler. Two natural populations originating from a high- and a low-temperature environment, respectively, ...were compared with respect to Hsp70 (heat shock protein) expression, knock-down resistance and heat shock resistance. 2. Three main hypotheses were tested: (i) The expression level of Hsp70 in flies from the high-temperature habitat should be down-regulated relative to flies from the colder habitat. (ii) Flies having higher Hsp70 expression levels should be weakened most by a hardening treatment and go faster into coma, as Hsp70 level reflects stress intensity, and therefore display reduced heat knock-down resistance. (iii) Heat shock resistance should be increased in the population with highest Hsp70 expression because the level of Hsp70 is positively associated with this trait. 3. The results generally matched the hypotheses. Hsp70 expression was reduced in the high-temperature population. Knock-down resistance was higher in the high-temperature population and survival after heat shock was lower in the high-temperature population. 4. This study showed genetic differences in thermal tolerance between populations, indicating that high temperature in nature may be an important selective factor. Moreover, knock-down resistance in this study seems to be a more relevant trait than standard heat shock resistance for identifying thermal adaptation in natural populations.
Here, we report a detailed analysis of changes in gene expression in Drosophila melanogaster selected for ecologically relevant environmental stress resistance traits. We analysed females from seven ...replicated selection regimes and one control regime using whole genome gene expression arrays. When compared with gene expression profiles of control lines, we were able to detect consistent selection responses at the transcript level in each specific selection regime and also found a group of differentially expressed genes that were changed among all selected lines. Replicated selection lines showed similar changes in gene expression (compared with controls) and thus showed that 10 generations of artificial selection give a clear signal with respect to the resulting gene expression profile. The changes in gene expression in lines selected for increased longevity, desiccation and starvation resistance, respectively, showed high similarities. Cold resistance-selected lines showed little differentiation from controls. Different methods of heat selection (heat survival, heat knock down and constant 30 °C) showed little similarity verifying that different mechanisms are involved in high temperature adaptation. For most individual selection regimes, and in the comparison of all selected lines and controls, the gene expression changes were exclusively in one direction, although the different selection regimes varied in the direction of response. The responses to selection restricted to individual selection regimes can be interpreted as stress specific, whereas the response shared among all selected lines can be considered as a general stress response. Here, we identified genes belonging to both types of responses to selection for stress resistance.
Laboratory selection in thermal regimes that differed in the amplitude and the predictability of daily fluctuations had a marked effect on stress resistance and life history traits in Drosophila ...simulans. The observed evolutionary changes are expected to be the result of both direct and correlated responses to selection. Thus, a given trait might not evolve independently from other traits because of genetic correlations among these traits. Moreover, different test environments can induce novel genetic correlations because of the activation of environmentally dependent genes. To test whether and how genetic correlations among stress resistance and life history traits constrain evolutionary adaptation, we used three populations of D. simulans selected for 20 generations in constant, predictable and unpredictable daily fluctuating thermal regimes and tested each of these selected populations in the same three thermal regimes. We explored the relationship between genetic correlations between traits and the evolutionary potential of D. simulans by comparing genetic correlation matrices in flies selected and tested in different thermal test regimes. We observed genetic correlations mainly between productivity, body size, starvation and desiccation tolerance, suggesting that adaptation to the three thermal regimes was affected by correlations between these traits. We also found that the correlations between some traits such as body size and productivity or starvation tolerance and productivity were determined by test regime rather than selection regime that is expected to limit genetic adaptation to thermal regimes in these traits. The results of this study suggest that several traits and several environments are needed to explore adaptive responses, as genetic and environmentally induced correlations between traits as results obtained in one environment cannot be used to predict the response of the same population in another environment.
The European bison (Bison bonasus) has recovered successfully after a severe bottleneck about 90 years ago but has been left with low genetic variability that may substantially hinder parentage and ...identity analysis. According to pedigree analysis, over 80% of the genes in the contemporary population descend from just two founder animals and inbreeding coefficients averaged almost 0.5, whereas microsatellite heterozygosity does not exceed 0.3. We present a comparison of the effectiveness of 17 microsatellite and 960 single nucleotide polymorphism (SNP) markers for paternity and identity analysis in the European bison. Microsatellite-based paternity and identity analysis was unsuccessful because of low marker heterozygosity and is not a practical approach in this species. Simulations using SNP markers suggest that 80-90 randomly selected loci, or just 50-60 of the most heterozygous loci, would be sufficient to ensure successful paternity and identity analysis in this species. For the purpose of standardizing future analysis, a panel of 50-60 bovine SNPs characterized by high heterozygosity and an even distribution in the genome could be selected. This panel of markers could be typed using VeraCode (Illumina) or similar SNP genotyping systems. The low cost of these SNP genotyping methods compared with a 16 locus microsatellite survey means that off-the-shelf SNP genotyping systems developed for domestic species represent powerful tools for genetic analysis in related species, and can be effective even in bottlenecked species in which heterozygosity of other markers such as microsatellites may be very low.
The behavior of ectotherm organisms is affected by both abiotic and biotic factors. However, a limited number of studies have investigated the synergistic effects on behavioral traits. This study ...examined the effect of temperature and density on locomotor activity of Musca domestica (L.). Locomotor activity was measured for both sexes and at four densities (with mixed sexes) during a full light and dark (L:D) cycle at temperatures ranging from 10 to 40°C. Locomotor activity during daytime increased with temperature at all densities until reaching 30°C and then decreased. Highdensity treatments significantly reduced the locomotor activity per fly, except at 15°C. For both sexes, daytime activity also increased with temperature until reaching 30 and 35°C for males and females, respectively, and thereafter decreased. Furthermore, males showed a significantly higher and more predictable locomotor activity than females. During nighttime, locomotor activity was considerably lower for all treatments. Altogether the results of the current study show that there is a significant interaction of temperature and density on daytime locomotor activity of M. domestica and that houseflies are likely to show significant changes in locomotor activity with change in temperature.
Laboratory experiments on Drosophila have often demonstrated increased heritability for morphological and life‐history traits under environmental stress. We used parent–offspring comparisons to ...examine the impact of humidity levels on the heritability of a physiological trait, resistance to heat, measured as knockdown time at constant temperature. Drosophila melanogaster were reared under standard nonstressful conditions and heat‐shocked as adults at extreme high or low humidity. Mean knockdown time was decreased in the stressful dry environment, but there was a significant sex‐by‐treatment interaction: at low humidity, females were more heat resistant than males, whereas at high humidity, the situation was reversed. Phenotypic variability of knockdown time was also lower in the dry environment. The magnitude of genetic correlation between the sexes at high humidity indicated genetic variation for sexual dimorphism in heat resistance. Heritability estimates based on one‐parent–offspring regressions tended to be higher under desiccation stress, and this could be explained by decreased environmental variance of heat resistance at low humidity. There was no indication that the additive genetic variance and evolvability of heat resistance differed between the environments. The pattern of heritability estimates suggests that populations of D. melanogaster may have a greater potential for evolving higher thermal tolerance under arid conditions.
Quantitative trait loci (QTL) were mapped for longevity and fecundity at two temperatures, 20 and 30 °C, in two sets of recombinant inbred lines (RIL) highly differing in thermotolerance. Early ...fecundity (EF) and longevity showed a negative association between temperatures. For instance, longevity was higher and fecundity was lower in the RIL panel showing higher life span at 30 °C. One X-linked QTL (7B3-12E) co-localized for longevity and EF at 20 °C, with one QTL allele showing a positive additive effect on longevity and a negative effect on EF. The across-RIL genetic correlation between longevity and EF was not significant within each temperature, and most QTL that affect life span have no effect on EF at each temperature. EF and longevity can mostly be genetically uncoupled in the thermotolerance-divergent RIL within each temperature as opposed to between temperatures. QTL were mostly temperature specific, although some trait-specific QTL showed possible antagonistic effects between temperatures.
Patterns of clinal genetic variation in Drosophila are often characterized after rearing at constant temperatures. However, clinal patterns might change after acclimation if populations differ in ...their plastic response to fluctuating environments. We studied longevity, starvation and heat knock-down resistance after development at either constant or fluctuating temperatures in nine Drosophila buzzatii populations collected along an altitudinal gradient in Tenerife, Spain. Flies that developed at fluctuating temperatures had higher stress resistance despite experiencing a slightly lower average temperature than those at constant temperatures. Genetic variation along the gradient was found in both stress-resistance traits. Because QST values greatly exceeded FST values, genetic drift could not explain this diversification. In general, differences among populations were larger after rearing at fluctuating temperatures, especially in heat knock-down, for which clinal patterns disappeared when flies were reared at constant temperatures. This result emphasizes the importance of determining whether populations originating from different environments differ in their plastic responses to stress.
Multiple stress resistance traits were investigated in the cactophilic fly Drosophila buzzatii. Adults from seven populations derived from North‐Western Argentina were compared with respect to traits ...relevant for thermal stress resistance and for resistance to other forms of environmental stress. The populations were collected along an altitudinal gradient spanning more than 2000 m in height, showing large climatic differences. The results suggest that knock‐down resistance to heat stress, desiccation resistance and Hsp70 expression at a relatively severe stressful temperature best reflect thermal adaptation in this species. Furthermore, cold resistance seemed to be of less importance than heat resistance, at least for the adult life stage, in these populations. Clinal variation in thermal resistance traits over short geographical distances suggests relatively strong adaptive differentiation of the populations. This study provides the first evidence for altitudinal differentiation in stress‐related traits, and suggests that Hsp70 expression level can be related to altitudinal clines of heat‐stress resistance.
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