Monomorphic ants undergo within-colony morphological changes along the metal-pollution gradient

Area of Science:

• Ecology
• Environmental Science
• Entomology

Background:

• Intra and inter-colony body size variation is common in ants, even in monomorphic species.
• Environmental factors are known to influence size-related parameters in ants.
• The shape of ant body size distribution is an understudied aspect of ecological research.

Purpose of the Study:

• To investigate the impact of metal pollution on the body size distribution of Lasius niger workers.
• To analyze the relationship between site pollution levels and the skewness of head width distribution.

Main Methods:

• Measurement of head widths of Lasius niger workers from 51 colonies across 19 sites in a former mining area in Poland.
• Quantification of site pollution levels using total zinc concentrations in invertebrate samples.
• Digital analysis of ant head widths to determine distribution shape parameters like skewness.

Main Results:

• A significant positive correlation was found between site metal (zinc) pollution levels and the skewness of head size distribution.
• Skewness increased from approximately -0.5 in the least polluted sites to 1.5 in the most polluted sites.
• This indicates a higher frequency of smaller workers in more polluted environments, while measures of central tendency and variation were unaffected.

Conclusions:

• Increased metal pollution levels lead to a shift in Lasius niger worker size distribution towards smaller individuals.
• Potential explanations include energy limitation, metal toxicity, or adaptive responses to environmental stress.
• Further research is needed to elucidate the mechanisms driving this observed bias in worker size.