Release of greenhouse gases from millipedes as related to food, body size, and other factors

The release of greenhouse gases from millipede digestive tracts warrants study because of its potential effect on climate change and also as an indicator of microbial processes that transform organic matter during passage through the gut of these animals. Gas chromatography was used to quantify the release of methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) from living millipedes in laboratory conditions. The effect of four food types (leaf litter of alder, oak, and maple, and rotten wood) on the release of CH4, CO2, and N2O by 12 species was also assessed. In addition, two julid species were fed pure cellulose to test the ability of these millipedes to obtain energy from cellulose and to determine the effect of this diet on gas production. All of the tested millipede species produced CO2 and some produced CH4. Stable and substantial CH4 emission was restricted to the large millipedes in the tropical orders Spimbolida and Spirostreptida. This asymmetrical phylogenetic distribution of CH4 production may be related to body size and the presence of gut commensals, but these factors may influence each other and depend upon geographic distribution of species. The quality of the food and feeding regime can also affect CH4 production in that CH4 release was significantly higher when millipedes were fed alder leaf litter rather than oak or maple leaf litter. CO2 production from millipedes mainly reflected the metabolic response of the animals. Traces of N2O were only occasionally emitted by millipedes; this release evidently depends on the N content in the food and seems to be restricted to members of the Glomeridae family. Based on gas production, the tested species of millipedes were unable to obtain their energy needs from a diet of pure cellulose.