Figure 1.
The distribution of methane-positive species among millipede orders.
The red row of columns (OFP) is based on all tested species classified as either obligatory or facultative producers, and the yellow row (OFAP) includes obligatory, facultative, and accidental producers.
Figure 2.
Summary of the recent information concerning methane production by millipedes.
Methane production detected by gas chromatography (Table S1) relative to millipede phylogeny. Species belonging to framed groups have been tested to date. Red lines mark the lineages containing some positive species. The phylogenetic tree was used according to Regier et al. [38].
Figure 3.
The relationship between individual methane production and the mean body mass.
Mean methane production (M) in methane-positive species of millipedes (accidental, obligatory, and facultative producers) plotted against mean body mass of species (W). Species abbreviations are indicated in Table S1. Methane production by the cockroach Blaptica dubia (Bdu) is included for comparison. Red lines = regression of M on W with 95% confidence intervals.
Figure 4.
Methane production from millipede faecal pellets relative to millipede phylogeny.
Methane production from anaerobically incubated faecal pellets was detected by gas chromatography (Table S1). Species belonging to framed groups were tested in this study. Red lines mark the lineages containing some positive species. The phylogenetic tree was used according to Regier et al. [38].
Figure 5.
Change in the rate of methane production per mass of millipede faecal pellets over time.
The pellets were anaerobically incubated at 20°C. Abbreviations of species are indicated in Table S1.
Figure 6.
Detection of the archaeal mcrA gene in millipedes relative to millipede phylogeny.
mcrA, the marker gene of methanogenic Archaea, was detected by PCR amplification (Table S1) in gut and faecal pellets of millipedes. Species belonging to framed groups were tested in this study. Red lines mark the lineages containing some positive species. Only faecal pellets were positive in Glomerida. The phylogenetic tree was used according to Regier et al. [38].
Figure 7.
Detection of the archaeal 16S rRNA gene in millipedes relative to millipede phylogeny.
The 16S rRNA gene, an indicator of methanogenic Archaea, was detected by PCR amplification (Table S1). Species belonging to framed groups were tested in this study. Red lines mark the lineages containing some positive species. In Polydesmida, only faecal pellets were tested. The phylogenetic tree was used according to Regier et al. [38].
Figure 8.
Cluster analysis of methanogenic communities in millipedes.
DGGE patterns were obtained after PCR amplification of the 16S rRNA gene of the methanogenic communities in the gut contents (Δ) or faecal pellets (•) of individual millipedes from the indicated species. Pearson correlation and UPGMA analysis were used. Abbreviations in brackets indicate the origin of animal samples (see Table S1). mgut = midgut and hgut = hindgut samples. Species belonging to different pre-defined groups of methane producers are marked with different colours: NP – black, AP – green, FP – blue, and OP – red. Asterisks indicate that the samples were from individuals or faecal pellets in which methane production was detected using gas chromatography. Blue line = similarity cutoff 70%.