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

Donna G. Folk^* and Timothy J. Bradley

Department of Ecology and Evolutionary Biology, University of California, Irvine, Irvine, CA 92697, USA

View larger version (12K): [in a new window]   Fig. 1. Hemolymph volume of desiccation-resistant flies (D flies) and their controls (C flies) prior to desiccation (0 h) and at time intervals during desiccation. Values are means ± S.E.M. of five populations from either the C or D treatments. Open bars represent values from the D populations; filled bars represent values from the C populations. Significant differences within each treatment (C or D) are denoted by non-matching letters above the bars.

View larger version (13K): [in a new window]   Fig. 2. Water content of exsanguinated desiccation-resistant flies (D flies) and their controls (C flies) prior to desiccation (0 h) and at time intervals during desiccation. Values are means ± S.E.M. of five populations from either the C or D treatments. Open bars represent values from the D populations; filled bars represent values from the C populations. Significant differences within each treatment (C or D) are denoted by non-matching letters above the bars.

View larger version (11K): [in a new window]   Fig. 3. Sodium content of tissue-gut-cuticle of desiccation-resistant flies (D flies) and the controls (C flies) prior to desiccation (0 h) and at time intervals during desiccation. Values are means ± S.E.M. of five populations from either the C or D treatments. Open bars represent values from the D populations; filled bars represent values from the C populations. Significant differences within each treatment (C or D) are denoted by non-matching letters above the bars.

View larger version (14K): [in a new window]   Fig. 4. Whole-body potassium of desiccation-resistant flies (D flies) and their controls (C flies) prior to desiccation (0 h) and at time intervals during desiccation. Values are means ± S.E.M. of five populations from either the C or D treatments. Open bars represent values from the D populations; filled bars represent values from the C populations. Significant differences within each treatment (C or D) are denoted by non-matching letters above the bars.

View larger version (10K): [in a new window]   Fig. 5. Chloride content in flies prior to (0 h) and during desiccation. Both the control (r2=0.99, P=0.001, y=-0.223x+8.323) and selected (r2=0.94, P=0.023, y=-0.094x+9.875) groups showed a significant decline in chloride during desiccation. Each filled symbol represents the mean ± S.E.M. of the five C populations; each open symbol represents the mean ± S.E.M. of the five D populations.

View larger version (10K): [in a new window]   Fig. 6. A strong positive relationship was observed between chloride content and hemolymph volume in the desiccation-resistant populations prior to and during desiccation (r2=0.88, P=0.001, y=0.0163x+5.123). As desiccation proceeds, hemolymph volumes move from left to right on the graph as it is drawn. Each point represents the mean ± S.E.M. of the five D populations.

View larger version (10K): [in a new window]   Fig. 7. Changes in hemolymph Na+ and whole-body Cl- in the desiccation-resistant flies (D flies) prior to and during desiccation. Values are means ± S.E.M. of the five D populations.