Response to environmental change: genetic variation and fitness in Drosophila buzzatii following temperature stress.
Drosophila buzzatii typically may encounter high temperatures in nature, and this species is genetically variable for resistance to stress, both within and among populations. Fitness of survivors to stress, however, was reduced, and observed as a reduction in male fertility and female fecundity. With time following exposure to severe stress, reproductive capacity improved, but lifetime offspring production still was reduced significantly. This effect would greatly reduce a population's recovery from small size, which could occur following exposure to some man-made or environmental extreme. Although the results presented here were obtained for effects of heat stress, such consequences likely apply to a wide range of natural and man-made environmental stresses, including heavy metal toxicity or other pollutants. Low levels of these pollutants may not cause an observable effect on populations, even if some individuals are killed or offspring production is decreased. If genetic variation for resistance is present, higher tolerance may evolve. However, if concentrations are permitted to rise too far, some stress threshold may be reached, as observed for thermal stress, causing mass die-off or sterility and, possibly, local extinction. Understanding the effects of stress is important when preparing programs for the conservation of species. Organisms generally do not become extinct when resources are abundant and the climate benign, but unfortunately, no guarantee can be made that environmental conditions in any locality will remain stable over a long time. Consequently, a high possibility of exposure to an extreme stress in an area would greatly reduce its usefulness as a reserve. Likewise, when choosing organisms for reintroduction, stress resistance of the chosen individuals and high levels of genetic variation within a population would be valuable. The organisms placed there must be able to change. Analysis of stress resistance (at non-lethal levels) among either family groups or for different populations would be very useful when deciding which individuals to reintroduce to an area or place in a reserve. Additionally, analysis may suggest that stress resistance is very low in a population or species. If identified, particular care may be taken to monitor the occurrence of that stress in the environment, and to take action to protect the population from that stress. Preservation of species should be designed for the future, with the goal to preserve, not simply to postpone extinction.
Department of Ecology and Genetics, University of Aarhus, Denmark.
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D000704:Analysis of Variance; D000818:Animals; D003247:Conservation of Natural Resources; D004330:Drosophila / Q000235:genetics / Q000502:physiology*; D004777:Environment; D005260:Female; D008136:Longevity; D008297:Male; D012641:Selection, Genetic; D013696:Temperature