Abstract. Stress resistance traits in Drosophila often show clinal variation. Although these patterns suggest selection, there is generally no attempt to test how large differences at the geographical level are relative to levels of variation within and between local populations. Here we compare these levels in D. melanogaster from temperate Tasmania versus tropical northern Queensland by focusing on adult resistance to desiccation, cold and starvation stress, as well as associated traits (size, lipid content). For starvation and desiccation resistance, levels of variation were highest among strains from the same population, whereas there was little differentiation among local populations and a low level of differentiation at the geographic level. For adult cold resistance, there was local differentiation and strain variation but no geographic variation. For size (thorax length), geographic differentiation was higher despite some overlap among strains from the tropical and temperate locations. Finally, for lipid levels there was only evidence for variation among strains. The low level of differentiation among geographic locations for stress resistance was further verified with the characterization of isofemale strains from 18 locations along a coastal transect extending from Tasmania to northern Queensland. Crosses among some of the isofemale strains showed that results were not confounded by inbreeding effects. Strains derived from a cross between a tropical and temperate strain differed for all traits, and variation among strains for body size was higher than strain variation within the geographic regions. Unlike in previous studies, lipid content and starvation resistance were not correlated in any set of strains, but there was a correlation between cold resistance and lipid content. There was also a correlation between desiccation resistance and size but only in the geographic cross strains. These findings suggest a large amount of variation in stress resistance at the population level and inconsistent correlation patterns across experimental approaches. In Drosophila, levels of adult resistance to environmental stresses can vary among populations. In particular, desiccation resistance tends to be relatively higher in populations from temperate areas compared to tropical ones, whereas the reverse pattern is evident for starvation resistance ananassae, Zaprionus indianus).Where deviations from clinal patterns occur, these have been interpreted in terms of adaptive differentiation. Stanley and Parsons (1981) and Parsons (1980) found a relatively high level of desiccation resistance in two tropical populations of D. melanogaster contrary to clinal patterns, but these populations were exposed to extremely dry conditions in winter. In the same vein, Da Lage et al. (1990) found that D. melanogaster from a Tunisian oasis exhibited a high level of desiccation resistance, contrary to expectations based on geographic location.These findings suggest that selection directly or indirectly affects resistance traits. Ne...

We investigate changes in resistance to desiccation and starvation during adaptation of Drosophila melanogaster to laboratory culture. We test the hypothesis that resistance to environmental stresses is lost under laboratory adaptation. For both traits, there was a rapid loss of resistance over a three-year period. The rapidity of the response suggested that mutation accumulation could not account for it. Rather, resistance to environmental stresses appeared to be lost as a correlated response to selection on another trait, such as early fertility, with which stress resistance is negatively genetically correlated. These results suggest that caution is needed when extrapolating from evolution of stress resistance in long-established laboratory stocks to patterns of responses and correlated responses in natural populations.

Stress resistance traits in Drosophila often show clinal variation. Although these patterns suggest selection, there is generally no attempt to test how large differences at the geographical level are relative to levels of variation within and between local populations. Here we compare these levels in D. melanogaster from temperate Tasmania versus tropical northern Queensland by focusing on adult resistance to desiccation, cold and starvation stress, as well as associated traits (size, lipid content). For starvation and desiccation resistance, levels of variation were highest among strains from the same population, whereas there was little differentiation among local populations and a low level of differentiation at the geographic level. For adult cold resistance, there was local differentiation and strain variation but no geographic variation. For size (thorax length), geographic differentiation was higher despite some overlap among strains from the tropical and temperate locations. Finally, for lipid levels there was only evidence for variation among strains. The low level of differentiation among geographic locations for stress resistance was further verified with the characterization of isofemale strains from 18 locations along a coastal transect extending from Tasmania to northern Queensland. Crosses among some of the isofemale strains showed that results were not confounded by inbreeding effects. Strains derived from a cross between a tropical and temperate strain differed for all traits, and variation among strains for body size was higher than strain variation within the geographic regions. Unlike in previous studies, lipid content and starvation resistance were not correlated in any set of strains, but there was a correlation between cold resistance and lipid content. There was also a correlation between desiccation resistance and size but only in the geographic cross strains. These findings suggest a large amount of variation in stress resistance at the population level and inconsistent correlation patterns across experimental approaches.

We investigate changes in resistance to desiccation and starvation during adaptation of Drosophila melanogaster to laboratory culture. We test the hypothesis that resistance to environmental stresses is lost under laboratory adaptation. For both traits, there was a rapid loss of resistance over a three-year period. The rapidity of the response suggested that mutation accumulation could not account for it. Rather, resistance to environmental stresses appeared to be lost as a correlated response to selection on another trait, such as early fertility, with which stress resistance is negatively genetically correlated. These results suggest that caution is needed when extrapolating from evolution of stress resistance in long-established laboratory stocks to patterns of responses and correlated responses in natural populations.

Summary 1.Measures of trait variability, in particular fluctuating asymmetry (FA), have been proposed as biological tools for monitoring environmental quality, but relevant data are often collected under artificial conditions and it can be difficult to separate genetic and environmental factors. We considered a number of trait variability measures for potential use as indicators in field grapevines exposed to salt stress. 2. Vine responses to a salt gradient were compared using two measures of developmental stability (DS). DS quantifies an organisms' ability to buffer developmental noise. The two measures of DS tested were leaf FA, representing random deviations from perfect bilateral symmetry, and translational asymmetry (TA), representing deviations in allometric relationships, in this case the relationship between internode distance and node order. Leaf size (measured as centroid size), leaf shape (calculated using the Procrustes method) and maximum internode length were also tested for sensitivity to salinity. 3. We found that both measures of DS, FA and TA, failed to identify salinity stress in grapevines. Other measures, such as maximum internode length, leaf shape and leaf size, were sensitive to salt stress. 4. Synthesis and applications. Often, salinity stress is detected only when the impact is harmful enough to cause severe biological effects. Alternative, more sensitive monitoring techniques would allow earlier intervention and management of the problem. We evaluated a number of techniques and showed that indices of bilateral and TA were not useful in detecting salt stress in grapevines. However, changes in internode length, leaf size and leaf shape proved to be sensitive and are potential tools for monitoring salinity in vineyards.