Serpentine soils affect heavy metal tolerance but not genetic diversity in a common Mediterranean ant

Transfer of elements into boreal forest ants at a former uranium mining site

Ants can influence ecological processes, such as the transfer of elements or radionuclides, in several ways. For example, they redistribute materials while foraging and maintaining their nests and have an important role in terrestrial food webs. Quantitative data of the transfer of elements into ants is needed, e.g., for developing improved radioecological models. In this study, samples of red wood ants (genus Formica), nest material, litter and soil were collected from a former uranium mining site in Eastern Finland. Concentrations of 33 elements were analyzed by Inductively Coupled Plasma-Mass Spectroscopy/Optical Emission Spectroscopy. Estimated element concentrations in spruce needles were used as a proxy for studying the transfer of elements into ants via aphids because spruces host the most important aphid farms in boreal forests. Empirically determined organism/medium concentration ratios (CRs) are commonly used in radioecological models. Ant/soil CRs were calculated and the validity of the fundamental assumption behind the of use of CRs (linear transfer) was evaluated. Elements that accumulated in ants in comparison to other compartments were cadmium, potassium, phosphorus, sulfur, and zinc. Ant uranium concentrations were low in comparison to soil, litter, or nest material but slightly elevated in comparison to spruce needles. Ant element concentrations were quite constant regardless of the soil concentrations. Non-linear transfer models could therefore describe the soil-to-ant transfer better than conventional CRs.

Assessment of legacy mine metal contamination using ants as indicators of contamination

Most legacy mines contributed to contamination of the environment before and after cessation of mining. Contamination from waste rock, slag and tailings can introduce large concentrations of metals and metalloids to the surface soil and downstream sediments. Since ants are able to accumulate metals in their bodies, we investigated the possibility of using the elemental compositions of ants as indicators of metals at legacy mines developed on ores rich in copper (Cu), zinc (Zn), arsenic (As), silver (Ag) and lead (Pb). Our results showed the concentrations of manganese (Mn) and Cu in ants were not significantly different between mine and reference samples and only Zn was significantly different between contaminated and reference areas. Crematogaster spp. and Notoncus spp. from reference areas accumulated larger concentrations of metals in their bodies compared to ants from the mine. Ants accumulated metals in different parts of their bodies. The abdomen was the main site for accumulation of Mn, iron (Fe) and Zn. Mandibles were only associated with accumulation of Zn. Copper and Pb showed no area of preferential accumulation and traces were detected in the whole body of the ants. Ants from five genera had similar regions for metal accumulation. The exoskeleton did not contribute to accumulation of metals; instead all metals were stored in internal organs. Not all genera were suitable for use as indicators; only Iridomyrmex spp. and Ochetellus spp. accumulated larger amount of metals in mine samples compared to reference samples.

Body size variation of the ant Lasius niger along a metal pollution gradient

The phenotypic diversity of ant workers plays a fundamental role in their biology. In this study, we asked if the body size variation of monomorphic workers of the ant Lasius niger (Formicidae) responds adaptively to metal pollution in a post-mining metal-polluted area. Nest samples of workers were collected along a pollution gradient to calculate the within-colony variance in body size (expressed as maximum head width, HW). The results showed that the body size variation of L. niger was unrelated to the pollution index but demonstrated considerable variation between colonies even within the same study site. We suggest that the differences in morphological diversity between the colonies of L. niger could be shaped by colony personality traits, i.e., by colony-specific foraging and/or the feeding efficiency of nursing workers. The study supports previous findings, showing that morphological traits in Lasius ants are weakly related to environmental metal pollution.

Ants and their nests as indicators for industrial heavy metal contamination

Ants accumulate heavy metals and respond to pollution with modification in species composition, community structure, altered behaviour and immunity. However, the levels of heavy metals in ants' nests and explicit individual-level responses towards heavy metals have not been revealed. We found that red wood ants Formica lugubris accumulate high and correlated values of such heavy metals as Al, Cd, Co, Cu, Fe, Ni, Pb and Zn both in ants and nest material near cobalt smelter in Finland. Relative differences in metal concentrations were higher in nests than in ants. The highest values were obtained for elements such as Co (36.6), Zn (14.9), Cd (9.7), Pb (8.5), Cu (7.4), Ni (6.4), As (4.7), Cr (2.9) and Fe (2.4) in nest material, and Co (32.7), Cd (6.3), Pb (6), Fe (2.8), Ni (2.9) and Zn (2.1) in ants. In industrial and reference areas, ants have no differences in size, but differed in dry and residual body mass. In polluted areas, F. lugubris had less melanised heads, but not thoraxes. The sensitivity of cuticular colouration in red wood ants subjected to heavy metal pollution might be related to metal-binding properties of melanins. The overall results are useful for the improvement of biomonitoring techniques using ants as indicators of industrial contamination and for further discovery of novel ecotoxicological biomarkers.