Fungus culturing, nutrient mining and geophagy: A geochemical investigation of Macrotermes and Trinervitermes mounds in southern Africa
Termite mounds are commonly enriched in clay and nutrients relative to surrounding topsoils. We hypothesized that: (1) nutrient enrichment of mounds differs between fungus-culturing (FC) and non-FC termites; (2) FC termites preferentially acquire materials rich in scarce nutrients which promote growth of their fungus cultures; and (3) micro-nutrient enrichment in mounds of FC termites is beneficial for wildlife. In a preliminary investigation of these hypotheses, we sampled mounds (and adjacent topsoil) of Macrotermes (FC) and Trinervitermes (non-FC) termites in Namibia and South Africa, respectively. Analyses included: 27 elements by ICPMS after a nitric acid-hydrogen peroxide digest, organic carbon, a seven fraction particle size analysis, and pH and EC (1:5 soil:water extracts). Macrotermes mounds showed significant (1.6-3.7-fold) enrichment of 23 of the 27 elements analysed relative to topsoil. By contrast, Trinervitermes mounds showed no enrichment. Clay enrichment of Macrotermes mounds (4.7-6.5-fold) was strongly correlated with element enrichment (r 2 range: 0.76-0.77), suggesting that amendment of soil texture is a main factor in enrichment. Marked enrichment of only certain nutrients in mounds - namely Mn, Co, Cu and Se - was evident at certain nutrient-poor sites, suggesting that specific materials such as Mn oxides (which adsorb Co, Cu and Se) may be gathered by termites in disproportionate amounts relative to their abundance in soils. These nutrients are likely to enhance the productivity of the fungus culture and hence the termite colony. Parts of certain mounds were enriched in Se (1.3-3.6 mg Se kg-1) to a degree likely to attract geophagy. It is suggested that in some landscapes Macrotermes mounds provide a critical supply of micro-nutrients to wildlife. © 2009 The Zoological Society of London.