| Sumario: | Main hypothesis: Longevity and early fecundity are negatively correlated both within and between sympatric but ecologically divergent sibling species that differ in life span, as predicted by evolutionary theories of ageing. Organism: Drosophila koepferae, which mainly breeds on the patchily distributed Trychocereus cacti, and D. buzzatii, which mainly occurs on the more abundant and uniformly distributed Opuntia cacti. Methods: Flies were reared under standardized conditions from three sympatric populations. Longevity and mortality rate were studied both at 25°C and 29.5°C. Age-specific fecundity was estimated at 25°C. Other plausibly associated traits were also studied, including heat-shock resistance, Hsp70 expression and body size. Conclusions: Senescence rate was much faster in D. koepferae than in D. buzzatii in all populations at 25°C but not at 29.5°C. The interspecific difference in longevity at 25°C shifted in sign in one of the populations at 29.5°C. Neither the resistance to a heat shock nor the heat-induced Hsp70 expression showed significant interspecific variation. Body size was larger in D. koepferae than in D. buzzatii. Drosophila koepferae showed a massive reproductive output at early ages compared with D. buzzatii. Longevity and early fecundity at the non-stressful temperature (25°C) were negatively correlated both within and between species. Genotype x temperature interactions can in turn affect interspecific variation in evolutionary trajectories of both mean longevity and demographic rate of senescence. © 2005 Fabian M. Norry.
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