How to uncoil your partner—“mating songs” in giant pill-millipedes (Diplopoda: Sphaerotheriida)

Abstract

The stridulation of the giant pill-millipede genus Sphaerotherium from South Africa, one of only three groups of millipedes that produce sounds, was studied. One hundred one stridulation series of a total of nine different species (Sphaerotherium dorsaloide, Sphaerotherium hanstroemi, Sphaerotherium mahaium, Sphaerotherium similare, Sphaerotherium punctulatum, Sphaerotherium convexitarsum, Sphaerotherium dorsale, Sphaerotherium rotundatum, and Sphaerotherium perbrincki) were analyzed. Stridulation sounds are produced only with a special field of ribs on the posterior surface of the posterior telopod, which is actively moved over a field of sclerotized nubs on the inner margin of the anal shield. The Sphaerotherium male usually stridulates only when in contact with a female to initiate mating. This seems to prevent the female from volvating into a ball or stimulate the female to uncoil when already rolled in. The sound analyzes revealed a broad frequency spectrum in all stridulation sounds produced, without obvious differences in frequency distribution among species. However, the temporal pattern of the stridulation varies greatly between species and seems to be species-specific, arguing for a species recognition function of the stridulation during courtship behavior. A single species (S. punctulatum) was found to stridulate during mating while three species also show postcopulatory stridulation. Apparently, pill-millipedes are not capable of acoustic perception, as no hearing organs are known, indicating that the communication is mainly based on perception of temporal vibration patterns, and not of the acoustic signal itself. The need to overcome the rolling-in reflex of the female is developed as a hypothesis why stridulation exists only in millipedes able to coil into a ball, and apparently evolved four times independently in the superorder Oniscomorpha.

The use of bioacoustics in anuran taxonomy: theory, terminology, methods and recommendations for best practice

“…Complex vocalizations of birds are often named songs (Baker 2001;Catchpole & Slater 2008), whereas the term 'calls' is usually used to refer to sounds of lower complexity emitted by birds in a non-reproductive context. Sounds produced by orthopterans and cicadas (e.g., Robinson & Hall 2002), and even by flies (e.g., Kyriacou & Hall 1986;von Philipsborn et al 2011) and diplopods (Wesener et al 2011) are often named songs as well, even if these are much more stereotyped and less complex than songbird vocalizations. In mammals, human speech apart, vocalizations are more commonly referred to as calls, while the complex vocalizations of gibbons and bats are named songs by some authors (e.g., Cowlishaw 1992; Clarke et al 2006;Smotherman et al 2016).…”

Integrative description of two new species of Malagasy chirping giant pill-millipedes, genus Sphaeromimus (Diplopoda: Sphaerotheriida: Arthrosphaeridae)

“…Sixteen extant orders of Diplopoda are known (Blanke & Wesener 2014), of which eight occur naturally on Madagascar (Shelley & Golovatch 2011), with two of them, Polyzoniida (Wesener 2014a) and Siphonophorida (Wesener 2014b), being only recently recorded from the island. Madagascar is host to some of the most spectacular millipedes: different genera of large-bodied pitchblack/bloodred so called "Fire-Millipedes" of the order Spirobolida (Wesener et al 2009a(Wesener et al , 2009b(Wesener et al , 2011, as well as the world's largest giant pill-millipedes, order Sphaerotheriida (see Wesener & Wägele 2008;Wesener 2009), showing island gigantism. All giant pill-millipedes of Madagascar belong to the family Arthrosphaeridae, otherwise only found in India (Wesener & VandenSpiegel 2009;Wesener et al 2010) and are an example of the interesting biogeographical history of the Malagasy fauna.…”

“…Species of Sphaeromimus and Zoosphaerium usually occur in sympatry . The number of ribs might have an impact on the sound production, but only for South African species information about the produced sounds is available (Wesener et al 2011).…”

Sexual dimorphism in pill millipedes (Diplopoda)

“…One factor was measured from Sphaerotherium species: (1) body width (mm), extracted from trusted published data [26] and intersexual comparisons performed using Wilcoxon matched pairs tests. Size was perceived as body volume and calculated based on a geometric morphometric approach using the formula for a sphere (4/3.…”