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

Our plain-English summary of Serpentine soils affect heavy metal tolerance but not genetic diversity in a common Mediterranean ant, by F. Frizzi, A. Masoni, M. Çelikkol, et al (Chemosphere, 2017).

The study

• Authors: F. Frizzi, A. Masoni, M. Çelikkol, E. Palchetti, C. Ciofi, G. Chelazzi, G. Santini
• Journal: Chemosphere
• Published: 2017;180:326-334
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Natural habitats with serpentine soils are rich in heavy metal ions, which may significantly affect ecological communities. Exposure to metal pollutants results, for instance, in a reduction of population genetic diversity and a diffused higher tolerance towards heavy metals. In this study, we investigated whether chronic exposure to metals in serpentine soils affect accumulation patterns, tolerance towards metal pollutants, and genetic diversity in ants. In particular, we studied colonies of the common Mediterranean ant, Crematogaster scutellaris, along a contamination gradient consisting of two differently contaminated forests and a reference soil with no geogenic contamination. We first evaluated the metal content in both soil and ants' body. Then, we tested for tolerance towards metal pollutants by evaluating the mortality of ants fed with nickel (Ni) solutions of increasing concentrations. Finally, differences in genetic diversity among ants from different areas were assessed using eight microsatellite loci. Interestingly, a higher tolerance to nickel solutions was found in ants sampled in sites with intermediate levels of heavy metals. This may occur, because ants inhabiting strongly contaminated areas tend to accumulate higher amounts of contaminants. Additional ingestion of toxicants beyond the saturation threshold would lead to death. There was no difference in the genetic diversity among ant colonies sampled in different sites. This was probably the result of queen mediated gene flow during nuptial flights across uncontaminated and contaminated areas of limited geographical extent.

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In plain English

This study did not examine asbestos. It looked at heavy metals in naturally metal-rich serpentine (ophiolitic) soils and their effects on a common Mediterranean ant, Crematogaster scutellaris. Between May 2013 and September 2014 the authors sampled ants and soil at three sites in Tuscany, Italy: a reference forest at Casaglia, a forest at the edge of the Monterufoli outcrop near Pomarance (intermediate contamination), and a pine forest on the Monteferrato outcrop (most contaminated). Soil and ant levels of cadmium, cobalt, chromium and nickel rose along this gradient. Ant levels of these four metals were significantly related to soil levels. In a laboratory test, ants were fed sugar solutions containing nickel at 2, 4 and 10 mM. Ants from Casaglia were always the first to die. Ants from Pomarance survived best and differed significantly from Casaglia at all three nickel levels. Genetic tests at eight DNA markers found no differences in genetic diversity among the sites. The authors suggested that Monteferrato ants may already carry metal loads near a tolerable limit. They also suggested that queens flying between areas probably explain the genetic result.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Field sampling of ants and soil along a natural contamination gradient, combined with a laboratory nickel-feeding survival experiment and a microsatellite genetic analysis (animal study)
• Who was studied: Colonies of the ant Crematogaster scutellaris at three sites in Tuscany, Italy (Casaglia reference forest, Pomarance at the margin of the Monterufoli outcrop, Monteferrato outcrop), sampled May 2013 to September 2014; 18 ant and 18 soil samples for metal analysis, 180 ants genotyped, eight colonies per site analysed for genetic diversity
• Exposure: Naturally occurring (geogenic) heavy metals in serpentine soils (cadmium, cobalt, chromium, copper, nickel, zinc measured); in the laboratory, nickel in 10% sucrose solution at 0 (control), 2, 4 and 10 mM
• Main results:
  • Soil concentrations of Cd, Co, Cr and Ni were lowest at Casaglia, intermediate at Pomarance and highest at Monteferrato (soil Ni means 57.3, 447.0 and 1849.3 in Table 1)
  • In ants, concentrations of Cd, Co, Cr and Ni were significantly related to soil concentrations
  • No significant relationship between ant and soil levels was found for Cu and Zn
  • The biota-to-soil accumulation factor was below 1 for all metals except zinc, which ranged from 1.714 at Casaglia to 3.586 at Pomarance
  • Ants fed unpolluted sucrose solution showed no significant survival differences between sites
  • Under all nickel concentrations, ants from Casaglia (reference) died first and ants from Pomarance (intermediate site) were most resistant; Pomarance differed significantly from Casaglia at 2, 4 and 10 mM (Table 4); Monteferrato ants did not show the highest resistance
  • Allelic diversity was 4.6, 4.9 and 5.7 for Casaglia, Pomarance and Monteferrato; no differences among sites in allelic diversity, gene diversity or relatedness were found
• The authors' conclusion: The authors concluded that body levels of several metals increased with soil levels, and that ants from the intermediate site were the most tolerant to acute nickel exposure. They suggested that Monteferrato ants may already be near a physiological threshold. They attributed the lack of genetic differences probably to long-range dispersal flights of queens between contaminated and uncontaminated areas.
• Limitations the authors state:
  • Metals were measured only in soil and ants, not in the ants' main food sources, so the authors could not tell whether metal exclusion is due to the ants or to lower levels of the food chain
  • Genetic effects may exist that the analysis did not detect; the authors suggest further study, possibly with genome-wide methods
  • The outcrops were small and probably not independent of the surrounding environment

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Serpentine Group.

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• Risk assessment and source analysis of heavy metals in soil around an asbestos mine in an arid plateau region, China — X. Li, D. Ding, et al. (2024)
• Genetic analyses of nickel tolerance in a North American serpentine endemic plant, Caulanthus amplexicaulis var. barbarae (Brassicaceae) — A.M. Burrell, A.K. Hawkins, et al. (2012)
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