Bojan Kenig

Population specific fitness response of Drosophila subobscura to lead pollution

Abstract  Differences in heavy metal tolerance among separate populations of the same species have often been interpreted as local adaptation. Persistence of differences after removing the stressor indicates that mechanisms responsible for the increased tolerance were genetically determined. Drosophila subobscura Collin (Diptera: Drosophilidae) populations were sampled from two localities with different history of heavy metal pollution, and reared for eight generations in the laboratory on a standard medium and on media with different concentrations of lead (Pb). To determine whether flies from different natural populations exposed to the Pb‐contaminated media in the laboratory show population specific variability in fitness components over generations, experimental groups with different concentrations of lead were assayed in three generations (F2, F5, and F8) for fecundity, developmental time, and egg‐to‐adult viability. On the contaminated medium, fecundity was reduced in later generations and viability was increased, irrespective of the environmental origin of populations. For both populations, developmental time showed a tendency of slowing down on media with lead. Faster development was observed in later generations. Preadaptation to contamination, meaning higher fecundity, higher viability, and faster egg to adult development in all studied generations, was found in D. subobscura originating from the locality with a higher level of heavy metal pollution.

Sex-specific effects of sympatric mitonuclear variation on fitness in Drosophila subobscura

BackgroundA number of recent studies have shown that the pattern of mitochondrial DNA variation and evolution is at odds with a neutral equilibrium model. Theory has suggested that selection on mitonuclear genotypes can act to maintain stable mitonuclear polymorphism within populations. However, this effect largely relies upon selection being either sex-specific or frequency dependent. Here, we use mitonuclear introgression lines to assess differences in a series of key life-history traits (egg-to-adult developmental time, viability, offspring sex-ratio, adult longevity and resistance to desiccation) in Drosophila subobscura fruit flies carrying one of three different sympatric mtDNA haplotypes.ResultsWe found functional differences between these sympatric mtDNA haplotypes, but these effects were contingent upon the nuclear genome with which they were co-expressed. Further, we demonstrate a significant mitonuclear genetic effect on adult sex ratio, as well as a sex × mtDNA × nuDNA interaction for adult longevity.ConclusionsThe observed effects suggest that sex specific mitonuclear selection contributes to the maintenance of mtDNA polymorphism and to mitonuclear linkage disequilibrium in this model system.

Adaptive Role of Inversion Polymorphism of Drosophila subobscura in Lead Stressed Environment

Local adaptation to environmental stress at different levels of genetic polymorphism in various plants and animals has been documented through evolution of heavy metal tolerance. We used samples of Drosophila subobscura populations from two differently polluted environments to analyze the change of chromosomal inversion polymorphism as genetic marker during laboratory exposure to lead. Exposure to environmental contamination can affect the genetic content within a particular inversion and produce targets for selection in populations from different environments. The aims were to discover whether the inversion polymorphism is shaped by the local natural environments, and if lead as a selection pressure would cause adaptive divergence of two populations during the multigenerational laboratory experiment. The results showed that populations retain signatures from past contamination events, and that heavy metal pollution can cause adaptive changes in population. Differences in inversion polymorphism between the two populations increased over generations under lead contamination in the laboratory. The inversion polymorphism of population originating from the more polluted natural environment was more stable during the experiment, both under conditions with and without lead. Therefore, results showed that inversion polymorphism as a genetic marker reflects a strong signature of adaptation to the local environment, and that historical demographic events and selection are important for both prediction of evolutionary potential and long-term viability of natural populations.

Drosophila subobscura flies adapted to low lead concentration carry no fitness cost.

As a response to the long-term presence of heavy metals in the environment, populations can evolve resistance. Its maintenance may have detrimental effect on populations fitness, causing a fitness cost. Lead is one of the widely distributed elements in the environment exhibiting high toxicity on organisms. By analyzing developmental stages viability and developmental time, we evaluated fitness cost in Drosophila subobscura flies adapted to low lead concentration and control flies derived from the same wild population, as well as their hybrids. Significant changes in specific developmental stages viability were detected in both lines, as well as their hybrids, suggesting complex response to low lead concentration. The results show that a long-term exposure to low lead concentration may have a significant impact on a populations survival, especially in a changing environment conditions.

Lead-Induced Variation in Wing Size and Shape in Populations of Drosophila subobscura

ABSTRACT The aim of the current study was to analyze the direction and range of changes in wing size and shape in both sexes of Drosophila subobscura (Collin, 1936) flies that originated from two natural populations with different evolutionary history (sampled from ecologically distinct habitats) maintained during seven generations in laboratory conditions on different lead (Pb) concentrations. The results showed significant wing size variability differences across seven generations of rearing on lead for both populations. Wing size is negatively correlated with lead level, in contrast with wing shape in which significant variation was observed in just one of the populations. According to our results, wing size seems to be more affected by lead pollution in both tested populations compared with wing shape. Our data suggest that presence of lead in higher concentration over extended period of time may reduce the stability of wing morphology and consequently reduce the fitness of exposed individuals. Therefore, specific stress that persists over multiple generations could increase the probabilities for extinction of populations composed of sensitive individuals.

Effect of lead pollution on fitness and its dependence on heterozygosity in Drosophila subobscura.

Lead is one of the most present contaminants in the environment, and different species respond differently to this type of pollution. If combined with genomic stress, lead may act synergistically, causing significant decrease of fitness components. We used two genetically diverse Drosophila subobscura populations (regarding both putatively adaptive inversion and microsatellite loci polymorphisms) originating from two ecologically distinct habitats. To establish different levels of genome heterozygosity, series of intraline, intrapopulation and interpopulation crosses were made. The progeny were reared on a standard medium and a medium with 200 μg/mL of lead acetate. Development time was significantly extended to all groups reared on lead. The progeny of intraline crosses showed significantly extended development time compared to all other groups. The obtained results suggest that genome heterozygosity reduces the effect of lead pollution.

Synergistic Effect Of Environmental And Genomic Stress On Wing Size Of Drosophila Subobscura

Growing anthropogenic influence on every aspect of environment arise important issues regarding the ability of populations and species to adapt to variant pressures. Lead is one of the most present contaminants in the environment with detrimental influence on organisms and populations. In combination with genomic stress, lead may act synergistically, leading to reduction in adaptive values. We sampled two Drosophila subobscura populations, from ecologically different habitats and established differences in genetic backgrounds and population histories. In order to establish different levels of genome heterozygosity, series of intra-line, intra-population and between population crosses were made. The progeny was reared on a standard Drosophila medium and a medium with 200μg/mL of lead acetate and right wing of approximately 4000 individuals was used for geometric morphometric analysis of wing size. Results showed that lead significantly reduces wing size and that magnitude of this reduction is dependent on genetic background, indicating synergistic effect of genomic and environmental stress. There is also an indication of strong female origin influence on the outcome of hybridization when source of environmental stress is lead. Our results showed that the genetic structure of populations is of great importance for population fitness in anthropogenic induced stressful conditions. Further studies of synergistic effect of genetic and environmental stress are needed, as well as studies of its outcome in natural populations. [Projekat Ministarstva nauke Republike Srbije, br. 173012]