Variation of life-history and morphometrical traits in Drosophila buzzatii and Drosophila simulans collected along an altitudinal gradient from a Canary island

Variation in three life-history traits (developmental time, preadult viability and daily female productivity) and five morphometrical traits (thorax length, wing length, wing width, wing/thorax ratio and wing-aspect ratio) was studied at three developmental temperatures (20, 25 and 30 degreesC) in Drosophila buzzatii and Drosophila simulans collected on the island of La Gomera (Canary Archipelago). The flies originated from five closely situated localities, representing different altitudes (from 20 to 886 m above sea level) and a range of climatic conditions. We found statistically significant population effects for all traits in D. buzzatii and for most of the traits in D. simulans. Although no correlations of trait values with altitude were detected, geographical patterns for three life-history traits and body size in D. buzzatii indicated that short-range geographical variation in this species could be maintained by local climatic selection. Five of eight traits showed population-by-temperature interactions either in D. buzzatii or in D. simulans, but in all cases except wing width in D. buzzatii this could not be interpreted as adaptive responses to thermal conditions in the localities. The range of plastic changes across temperatures for particular traits differed between species, indicating a possibility for different levels of environmental stress experienced by the natural populations. The reaction norm curves and the response of within-population variability to thermal treatments suggested better adaptations to higher and lower temperatures for D. buzzatii and D. simulans, respectively. The levels of among-population differentiation depended on developmental temperature, implying environmental effects on the expression of the genetic variance. At 20 and 25 degreesC, interpopulation variability in D. buzzatii was higher than in D. simulans, while at 30 degreesC the opposite trend was observed. (C) 2005 The Linnean Society of London.