Figure 1.
Differential life expectancies in ant colonies.
Members of a “normal” ant colony have widely varying life expectancies. Reproductive animals (males and queens) differ substantially in their lifespan compared to non-reproductive individuals. The non-reproductive animals, corresponding to members of different worker castes, have lower life expectancies (top) than the queen. In the ancestral ponerine ant Harpegnathos saltator, fully developed workers have the ability to transform into reproductive individuals, called gamergates, which increases their life expectancy several fold (bottom).
Figure 2.
Survival rates of treated ants.
Survival curves for workers (solid circles) and gamergates (solid squares) injected with live Erwinia carotovora (A, C) or with paraquat (B, D). The percentage of survivors is plotted against the time following injection (± S.E.M.). The control animals (triangles) were injected with the same volume of sterile LB-medium instead of bacterial suspension. Statistical analysis was performed with Cox regression analysis; p values are given in the figure. Survival curves for gamergates (solid squares - blue) and workers (solid circles - black) that were injected with the Erwinia carotovora (A) or the ROS generating compound paraquat (B). Workers isolated for 24 h prior to the experimental injections (solid circles - red), showed a statistically significant increased survival following injection of pathogens (matching controls; solid circles - green) (C) and paraquat (D). The number of animals per experimental group was n = 30. Mean values are given ± S.E.M., p-values are listed in the figures.
Figure 3.
Enzyme activities in different groups of ants.
Four naturally occurring groups of adult Harpegnathos were subjected to a detailed analysis regarding their antioxidant enzyme activities. Individual workers were used for analysis and the corresponding enzyme activities as well as the protein concentrations were measured and the enzyme activities per mg of protein plotted. Usually, 10 independent measurements were made for every category. The groups under investigation were workers (wo), gamergates (ga), callows (cal), and males (male). Workers and gamergates were identified by means of an in depth analysis of their social behaviour. Statistically significant differences are marked by asterisks (* p<0.05, ** p<0.01, *** p<0.001). Catalase (A) statistical analysis with Dunnett-T-test after ln-transformation, SOD (B), glutathione-S-transferase activity (GST) (C), and glutathione peroxidase activities (GPx) were measured (D). Statistical analysis for SOD, GST and GPx was performed with the Games-Howell-test.
Figure 4.
Glutathione metabolism in different groups of ants.
Different parameters of the glutathione metabolism were quantified. The experimental setup was exactly as described in figure 3. The glutathione level (A), the levels of oxidised glutathione (GSSG) (B), those of reduced glutathione (GSH)(C), as well as the ratios of reduced and oxidised glutathione (D) were measured. Statistically significant differences are marked by asterisks (* p<0.05, ** p<0.01, *** p<0.001). Number of independent samples for workers and gamergates were n = 10, for callows n = 7 and for males n = 4. Analyses in A and C were performed with the Games-Howell-test, in B using the Dunnett-T-test after ln-transformation, in D using the Mann-Whitney-U-test.
Figure 5.
Effect of oxidative stress and pre-isolation on catalase and SOD activities.
Catalase (A, C) and SOD (B, D) activities of experimentally manipulated animals were measured. The experimental setup was exactly as described in figure 3. Workers (wo) and gamergates (ga) were subjected to oxidative stress (wo-ox and ga-ox) or workers were pre-isolated 24 h before measurement (pi-wo). Effect of paraquat injection on catalase activities (A) and SOD activities (B), as well as pre-isolation on catalase activities (C) and SOD activities (D) were determined. Statistically significant differences are marked by asterisks (* p<0.05, ** p<0.01, *** p<0.001). Analyses in A and C were performed with the Dunnett-T-test after ln-transformation, in B and D using the Games-Howell-test.
Table 1.
Experimental groups of ants – characteristics and treatment