Variation in soil content of faecal pellets of a tropical millipede, Doratogonus uncinatus (Attems, 1914) (Diplopoda, Spirostreptida, Spirostreptidae).

Abstract

Millipedes feed on a wide range of food items (Dangerfield, 1993; Ord & Dangerfield, 2001). Besides feeding on decomposing plant material, millipedes ingest mineral soil (Kadamannaya & Sridhar, 2009; Ramanathan & Alagesan, 2012), their own faecal material (Dangerfield, 1994; Mwabvu, 1998), flowers, fruits, mammalian faeces and dead invertebrates (Dangerfield, 1993). According to Hashimoto, Kaneko, Ito, and Toyota (2004), mineral soil constitutes approximately 60% by weight of ingested food in the Japanese train millipede, Parafontaria laminata. Furthermore, Mwabvu (1996) reported that field faecal pellets of Doratogonus uncinatus (Attems, 1914) contained 52% soil by weight. Hashimoto et al. (2004), Dangerfield (1993) and Ord and Dangerfield (2001) suggested that soil in millipede diet might be critical in digesting organic material in the gut. However, David (2014) reported that ingested soil is probably important for constructing moulting chambers and protecting eggs of millipedes. Southern African millipedes emerge from the soil at the onset of the summer rainfall season between November and March. They are surface active, primarily to feed and mate (Dangerfield & Telford, 1991). Whether or not soil content in millipede diet varies within the rainfall season is worth investigating because it has implications for decomposition of organic matter. As such, given that soil availability is unlimited unlike organic material, the proportion of soil in faecal pellets of a tropical millipede, D. uncinatus, during a summer rainfall season was investigated. It was hypothesized that soil content of faecal pellets will peak at the beginning and end of the wet season. Surface-active D. uncinatus specimens were collected by hand every fortnight before 10.00 hours during the rainfall season (November 2000–March 2001). Sampling was along a 100-m transect for 10 min at each site on each sampling day at Mazowe (17°31ʹS, 30°59ʹE) and Mount Pleasant (17°30ʹS, 30°57ʹE), Zimbabwe. On average, 30 millipedes were collected on each sampling day at each site and taken to the laboratory. When fewer than 10 millipedes were encountered after 10 min of searching, the millipedes were not taken to the laboratory because not enough faecal pellets would have been generated. The millipedes collected on each sampling day from each site were kept separate in plastic pots (diameter 15 cm, depth 20 cm) at 25°C without food or water for 2 hr during which faecal pellets that were produced were collected. After generating the faecal pellets, the millipedes were returned to their respective sites. The faecal pellet samples were dried at 60°C for 24 hr, weighed and then ashed at 650°C in a muffle furnace for 24 hr. After ashing, the pellets were weighed again to determine the proportion of mineral particles and organic matter.