Testing models of parental investment strategy and offspring size in ants |
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Authors: | Smadar Gilboa Peter Nonacs |
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Institution: | (1) Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA 90095, USA |
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Abstract: | Parental investment strategies can be fixed or flexible. A fixed strategy predicts making all offspring a single ‘optimal’
size. Dynamic models predict flexible strategies with more than one optimal size of offspring. Patterns in the distribution
of offspring sizes may thus reveal the investment strategy. Static strategies should produce normal distributions. Dynamic
strategies should often result in non-normal distributions. Furthermore, variance in morphological traits should be positively
correlated with the length of developmental time the traits are exposed to environmental influences. Finally, the type of
deviation from normality (i.e., skewed left or right, or platykurtic) should be correlated with the average offspring size.
To test the latter prediction, we used simulations to detect significant departures from normality and categorize distribution
types. Data from three species of ants strongly support the predicted patterns for dynamic parental investment. Offspring
size distributions are often significantly non-normal. Traits fixed earlier in development, such as head width, are less variable
than final body weight. The type of distribution observed correlates with mean female dry weight. The overall support for
a dynamic parental investment model has implications for life history theory. Predicted conflicts over parental effort, sex
investment ratios, and reproductive skew in cooperative breeders follow from assumptions of static parental investment strategies
and omnipresent resource limitations. By contrast, with flexible investment strategies such conflicts can be either absent
or maladaptive.
Electronic Supplementary Material Supplementary material is available for this article at |
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Keywords: | Dynamic parental investment Skew Kurtosis Variance Formica Pogonomyrmex |
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