Phylogenetic Systematics of the Millipede Family Xystodesmidae

Abstract

The millipede family Xystodesmidae includes 486 species distributed primarily in temperate deciduous forests in North America and East Asia. Species diversity of the family is greatest in the Appalachian Mountains of the eastern United States, with 188 species. Although the group includes notable taxa such as those that are bioluminescent and others that display Müllerian mimicry, producing up to 600 mg of cyanide, basic alpha-taxonomy of the group is woefully incomplete and more than 50 species remain undescribed in the Appalachian Mountains alone. In order to establish a robust phylogenetic foundation for addressing compelling evolutionary questions and describing species diversity, we assembled the largest species phylogeny (in terms of species sampling) to date in the Diplopoda. We sampled 49 genera (out of 57) and 247 of the species in the family Xystodesmidae, recollecting fresh material from historical type localities and discovering new species in unexplored regions. Here, we present a phylogeny of the family using six genes (four mitochondrial and two nuclear) and include pivotal taxa omitted from previous studies including Nannaria, Erdelyia, taxa from East Asia, and 10 new species. We show that 6 of the 11 tribes are monophyletic, and that the family is paraphyletic with respect to the Euryuridae and Eurymerodesmidae. Prior supraspecific classification is in part inconsistent with the phylogeny and convergent evolution has caused artificial genera to be proposed. Subspecific classification is likewise incongruent with phylogeny and subspecies are consistently not sister to conspecifics. The phylogeny is used as a basis to update the classification of the family, diagnose monophyletic groups, and to inform species hypotheses.

A revision of the minor species group in the millipede genus Nannaria Chamberlin, 1918 (Diplopoda, Polydesmida, Xystodesmidae)

“…The tribe Nannariini has received little attention since being proposed in 1964 by R. L. Hoffman, and as such does not have the same nomenclatural peregrinations of some animal taxa (Hoffman 1964). The species within the Nannariini have been placed in five different genera over the years (Mimuloria Chamberlin, 1928, Fontaria Gray, 1832, Castanaria Causey, 1950, Nannaria, and Polydesmus Latreille, 1802, with the most recent change by Means et al (2021) synonymizing Mimuloria with Nannaria for the current count of two genera within the Nannariini. The oldest of these two, Nannaria, was first proposed by Chamberlin (1918), and he included within it the previously described Fontaria tennesseensis Bollman, 1888, as well as three new species, Nannaria media Chamberlin, 1918, N. infesta Chamberlin, 1918and N. minor Chamberlin, 1918.…”

“…The oldest of these two, Nannaria, was first proposed by Chamberlin (1918), and he included within it the previously described Fontaria tennesseensis Bollman, 1888, as well as three new species, Nannaria media Chamberlin, 1918, N. infesta Chamberlin, 1918and N. minor Chamberlin, 1918. Two of these species, N. infesta and N. media, have recently been shown to belong to separate genera (Means et al 2021), now Howellaria infesta (Chamberlin, 1918) and Boraria stricta (Brölemann, 1896), respectively. Chamberlin's (1918) description of Nannaria was brief, and while he stated that he would define the genus in greater detail later, Chamberlin did not revisit the task.…”

“…Hoffman (1964) also synonymized the genus Mimuloria under Nannaria, a change which would later be reversed by Hennen and Shelley (2015), and again synonymized by Hoffman, 1964. Means et al (2021). Hoffman (1964) provided a diagnosis of the tribe, which included characters such as the spatulate pregonopodal claws, the subcoxal sternal spines and the conical coxal projections on the fourth leg pair.…”

“…This was the major character that both Mimuloria and Castanaria were based upon when they were described by Chamberlin (1928) and Causey (1950a), and Hoffman (1964: 33) stated that "I find this character to be a mutable one, and more suitable for the distinction of a species-group than a separate genus." Mimuloria was thereafter synonymized under Nannaria by Means et al (2021), after their six-gene (16S, 12S, tRNAval, COI, EF1a, and 28S) molecular phylogeny found that species of Mimuloria were in multiple locations within Nannaria. Shelley and Smith (2018) moved the family Eurymerodesmidae into the Xystodesmidae, based on a hypothesized sister group relationship with the Nannariini.…”

“…Despite this extensive range, the group as a whole is poorly known, and only two studies in the last 40 years have specifically addressed taxonomic changes to Nannaria (Hennen and Shelley 2015;Shelley and Smith 2018). Furthermore, genetic techniques are still rarely applied in modern diplopod systematics, and Nannaria has been included only twice in a molecular phylogeny (Marek and Bond 2006;Means et al 2021). While these works shed light on the placement of Nannaria within the Xystodesmidae, their analyses relied on limited taxon sampling of the tribe.…”