Clinal patterns of desiccation and starvation resistance in ancestral and invading populations of Drosophila subobscura.

As invading species expand, they eventually encounter physical and biotic stressors that limit their spread. We examine latitudinal and climatic variation in physiological tolerance in one native and two invading populations of Drosophila subobscura. These flies are native to the Palearctic region, but invaded both South and North America around 1980 and spread rapidly across 15° of latitude on each continent.

Critical thermal maxima in knockdown-selected Drosophila: are thermal endpoints correlated?

To explore the correlation of traits linked to thermotolerance, we compared three thermal endpoints (knockdown temperature and two critical thermal maxima) among replicate populations of Drosophila melanogaster selected for high, or low, knockdown temperature. The high knockdown flies maintain normal posture and locomotor ability within a knockdown column at temperatures >or=40 degrees C, whereas the low knockdown flies fall out of the column at much cooler temperatures (approximately 35 degrees C, on average). The critical thermal maximum (CT(max)) for respiratory control in the selected knockdown populations was determined by analyzing CO(2) output of individuals during exposure to a temperature ramp (from 30 degrees C to >45 degrees C) and was indicated by an abrupt alteration in the pattern of CO(2) release.

Selection on knockdown performance in Drosophila melanogaster impacts thermotolerance and heat-shock response differently in females and males.

We studied adaptive thermotolerance in replicate populations of Drosophila melanogaster artificially selected for high and low knockdown temperature (T(KD)), the upper temperature at which flies can no longer remain upright or locomote effectively. Responses to selection have generated High T(KD) populations capable of maintaining locomotor function at approximately 40 degrees C, and Low T(KD) populations with T(KD) of approximately 35 degrees C. We examined inducible knockdown thermotolerance, as well as inducible thermal survivorship, following a pretreatment heat-shock (known to induce heat-shock proteins) for males and females from the T(KD) selected lines.

Adaptive evolution in the lab: unique phenotypes in fruit flies comprise a fertile field of study.

Laboratory selection for desiccation resistance, which has been imposed on five replicate populations of Drosophila melanogaster for >200 generations, has resulted in enhanced survivability during periods of extreme water stress. The ability of these populations to persistently resist the fatal effects of desiccation is correlated with evolved physiological traits, namely preferential storage of carbohydrates (associated with reduced lipid reserves) and a dramatic increase in blood volume, which has led to a significant increase in extracellular sodium and chloride content, as well as body mass. When compared to other populations of this drosophilid species, these adaptive traits are unique.

The evolution of recovery from desiccation stress in laboratory-selected populations of Drosophila melanogaster.

We examined the capacity for physiological recovery from the effects of desiccation in five replicate populations of Drosophila melanogaster that have been selected for enhanced desiccation resistance (D populations) and in five replicate control populations (C populations). The capacity to recover was signified by the ability to restore three somatic components, namely whole-body water, dry mass and sodium content, all of which are reduced during desiccation. Throughout a period of recovery following a bout of desiccation, the flies were offered one of three fluids: distilled water, saline solution, or saline+sucrose solution.

Analyses of physiological evolutionary response.

Selection studies are useful if they can provide us with insights into the patterns and processes of evolution in populations under controlled conditions. In this context it is particularly valuable to be able to analyze the limitations of and constraints on evolutionary responses to allow predictions concerning evolutionary change. The concept of a selection pathway is presented as a means of visualizing this predictive process and the constraints that help define the population's response to selection.

Evolved patterns and rates of water loss and ion regulation in laboratory-selected populations of Drosophila melanogaster.

We have investigated water loss from, and ion regulation within, the hemolymph and tissues of five replicate populations of Drosophila melanogaster that have undergone laboratory selection for enhanced desiccation resistance (i.e. the D populations).