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Mortality rates and division of labor in the leaf-cutting ant, Atta colombica.

Brown MJ, Bot AN, Hart AG - J. Insect Sci. (2006)

Bottom Line: Intrinsic mortality rates were similar across external task groups.Exposure to waste (a task-related environment) led to a 60% increase in the mortality rate of waste-heap workers compared to workers not exposed to waste.Given the small number of workers present in the waste-heap task group, such increases in mortality are unlikely to affect division of labor and task allocation dramatically, except perhaps under conditions of stress.

View Article: PubMed Central - PubMed

Affiliation: Ecology and Evolution, ETH-Zürich, Switzerland. mabrown@tcd.ie

ABSTRACT
Division of labor in social groups is affected by the relative costs and benefits of conducting different tasks. However, most studies have examined the dynamics of division of labor, rather than the costs and benefits that presumably underlie the evolution of such systems. In social insects, division of labor may be simplistically described as a source-sink system, with external tasks, such as foraging, acting as sinks for the work force. The implications of two distinct sinks - foraging and waste-heap working - for division of labor were examined in the leaf-cutting ant Atta colombica. Intrinsic mortality rates were similar across external task groups. Exposure to waste (a task-related environment) led to a 60% increase in the mortality rate of waste-heap workers compared to workers not exposed to waste. Given the small number of workers present in the waste-heap task group, such increases in mortality are unlikely to affect division of labor and task allocation dramatically, except perhaps under conditions of stress.

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Mortality rate varies across the three waste material treatments. The rate of mortality for control ants (Atta colombica) (without waste material; red line to the right) was slower than for the Own (green line) and Foreign (blue line) waste treatments (these two lines overlap on the graph). The x-axis shows time in hours and the y-axis shows survival curves for the three treatments. Curves represent the survival functions calculated by the Cox regression survival analysis. See text for statistical analyses.
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i1536-2442-6-18-1-f02: Mortality rate varies across the three waste material treatments. The rate of mortality for control ants (Atta colombica) (without waste material; red line to the right) was slower than for the Own (green line) and Foreign (blue line) waste treatments (these two lines overlap on the graph). The x-axis shows time in hours and the y-axis shows survival curves for the three treatments. Curves represent the survival functions calculated by the Cox regression survival analysis. See text for statistical analyses.

Mentions: Exposure to waste significantly increased the mortality rate of workers (Fig 2; DF = 2, Wald statistic = 11.6, P = 0.003). This was true both for workers with waste from their own colony (58% increase over controlled workers; DF = 1, Wald statistic = 8.4, P = 0.004) and workers with waste from foreign colonies (52% increase; DF = 1, Wald statistic = 9.3, P = 0.002). There was no difference in the mortality rate of the two waste treatments. As with experiment one, there was also a significant effect of body size, with heavier workers living longer (Fig 1b; DF = 1, Wald statistic = 30.0, P < 0.001), but no effect of colony-of-origin (DF = 2, Likelihood score = 2.8, P = 0.253).


Mortality rates and division of labor in the leaf-cutting ant, Atta colombica.

Brown MJ, Bot AN, Hart AG - J. Insect Sci. (2006)

Mortality rate varies across the three waste material treatments. The rate of mortality for control ants (Atta colombica) (without waste material; red line to the right) was slower than for the Own (green line) and Foreign (blue line) waste treatments (these two lines overlap on the graph). The x-axis shows time in hours and the y-axis shows survival curves for the three treatments. Curves represent the survival functions calculated by the Cox regression survival analysis. See text for statistical analyses.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2990307&req=5

i1536-2442-6-18-1-f02: Mortality rate varies across the three waste material treatments. The rate of mortality for control ants (Atta colombica) (without waste material; red line to the right) was slower than for the Own (green line) and Foreign (blue line) waste treatments (these two lines overlap on the graph). The x-axis shows time in hours and the y-axis shows survival curves for the three treatments. Curves represent the survival functions calculated by the Cox regression survival analysis. See text for statistical analyses.
Mentions: Exposure to waste significantly increased the mortality rate of workers (Fig 2; DF = 2, Wald statistic = 11.6, P = 0.003). This was true both for workers with waste from their own colony (58% increase over controlled workers; DF = 1, Wald statistic = 8.4, P = 0.004) and workers with waste from foreign colonies (52% increase; DF = 1, Wald statistic = 9.3, P = 0.002). There was no difference in the mortality rate of the two waste treatments. As with experiment one, there was also a significant effect of body size, with heavier workers living longer (Fig 1b; DF = 1, Wald statistic = 30.0, P < 0.001), but no effect of colony-of-origin (DF = 2, Likelihood score = 2.8, P = 0.253).

Bottom Line: Intrinsic mortality rates were similar across external task groups.Exposure to waste (a task-related environment) led to a 60% increase in the mortality rate of waste-heap workers compared to workers not exposed to waste.Given the small number of workers present in the waste-heap task group, such increases in mortality are unlikely to affect division of labor and task allocation dramatically, except perhaps under conditions of stress.

View Article: PubMed Central - PubMed

Affiliation: Ecology and Evolution, ETH-Zürich, Switzerland. mabrown@tcd.ie

ABSTRACT
Division of labor in social groups is affected by the relative costs and benefits of conducting different tasks. However, most studies have examined the dynamics of division of labor, rather than the costs and benefits that presumably underlie the evolution of such systems. In social insects, division of labor may be simplistically described as a source-sink system, with external tasks, such as foraging, acting as sinks for the work force. The implications of two distinct sinks - foraging and waste-heap working - for division of labor were examined in the leaf-cutting ant Atta colombica. Intrinsic mortality rates were similar across external task groups. Exposure to waste (a task-related environment) led to a 60% increase in the mortality rate of waste-heap workers compared to workers not exposed to waste. Given the small number of workers present in the waste-heap task group, such increases in mortality are unlikely to affect division of labor and task allocation dramatically, except perhaps under conditions of stress.

Show MeSH
Related in: MedlinePlus