Browsing by Author "Shear, William A."
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- Biodiversity, conservation and mimicry rings of Appalachian millipedesMeans, Jackson C. (Virginia Tech, 2019-01-18)The Appalachian Mountains contain some of the highest millipede diversity on the planet, including many endemic and range-restricted species. Millipedes have extremely low dispersal capacity, strict environmental requirements for survival and, in the case of the family Xystodesmidae, are completely blind. Coupled with the complex topology of the Appalachians, xystodesmid millipedes have speciated in the eastern United States to a greater degree than in any other region. Many of the taxonomic relationships within the Xystodesmidae remain to be tested using modern molecular techniques, and numerous species await description. The subtribe Nannariina, for example, contains 3 genera and 19 species, yet evidence suggests the tribe may actually contain over 100 species. Traditional taxonomic work has been hindered by a paucity of researchers in the field, and a necessary reliance on morphological characters for species delimitation. The external male genitalia, known as gonopods, are the structures which have most often been used to define species boundaries. However, in many groups, including the Xystodesmidae, the gonopods are extremely simple, making it difficult to discern whether similarity between gonopods is a result of shared ancestry or morphological convergence. Further complicating matters, somatic characters are often uniform between species, and some obvious phenotypes, such as color pattern and hue, are shared between genera in aposematic mimicry rings. Leading to the formation of mimicry rings between distantly related genera, their bright coloration functions to advertise a cyanide-based defense. Some species have been recorded as having six color patterns, each a member of a different mimicry rings. The factors which drive some taxa to participate in mimicry rings, while others have a myriad of hues and patterns, unmatched by other species, are unknown. Here I investigate the phylogenetic relationships between the tribes and genera of the Xystodesmidae, with the aims of (1) understanding the role of homoplasy within the Xystodesmidae, (2) delineating tribal and generic boundaries within the family, (3) describing species in the genus Nannaria for the purposes of revising the subtribe Nannariina, and (4) investigating mimicry and color variability through a detailed color atlas for North American Xystodesmidae. I found that 95% of the morphological characters traditionally used in xystodesmid taxonomy are homoplasious (HI > 0.5), delineated the Apheloriini, Appalachioria and Sigmoria, described 34 new Nannaria species, and created a color and mimicry dataset of 956 Xystodesmidae for use in future studies of color variability.
- The first true millipede—1306 legs longMarek, Paul E.; Buzatto, Bruno A.; Shear, William A.; Means, Jackson C.; Black, Dennis G.; Harvey, Mark S.; Rodriguez, Juanita (Springer, 2021-12-01)The name “millipede” translates to a thousand feet (from mille “thousand” and pes “foot”). However, no millipede has ever been described with more than 750 legs. We discovered a new record-setting species of millipede with 1,306 legs, Eumillipes persephone, from Western Australia. This diminutive animal (0.95 mm wide, 95.7 mm long) has 330 segments, a cone-shaped head with enormous antennae, and a beak for feeding. A distant relative of the previous record holder, Illacme plenipes from California, it belongs to a different order, the Polyzoniida. Discovered 60 m below ground in a drill hole created for mineral exploration, E. persephone possesses troglomorphic features; it lacks eyes and pigmentation, and it has a greatly elongated body—features that stand in stark contrast to its closest surface-dwelling relatives in Australia and all other members of its order. Using phylogenomics, we found that super-elongation (> 180 segments) evolved repeatedly in the millipede class Diplopoda. The striking morphological similarity between E. persephone and I. plenipes is a result of convergent evolution, probably for locomotion in similar soil habitats. Discovered in the resource-rich Goldfields-Esperance region and threatened by encroaching surface mining, documentation of this species and conservation of its habitat are of critical importance.
- The milliped family Striariidae Bollman, 1893. V. Stegostriaria dulcidormus, n. gen., n. sp., Kentrostriaria ohara, n. gen., n. sp., and the convergent evolution of exaggerated metazonital crests (Diplopoda, Chordeumatida, Striarioidea)Marek, Paul E.; Shear, William A. (Magnolia Press, 2022-02-04)Two new genera and species, Stegostriaria dulcidormus (Trisariinae) and Kentrostriaria ohara (Striariinae), are described from Oregon and Idaho, respectively. The new species are distinct from any other striariids, and indeed from any other chordeumatidan millipedes, in having the second dorsal crests greatly enlarged, giving them a fanciful resemblance to stegosaurid dinosaurs. In spite of this similarity, the two species are so distinct they cannot be accommodated in the same genus or the same subfamily. The exaggerated metazonital crests are therefore attributed to convergent evolution. We present a key to the genera of the family Striariidae.
- The millipede family Striariidae Bollman, 1893. IV. Amplaria oedipus, n. sp., with a secondary sexual modification of males unique among millipedes (Diplopoda, Chordeumatida, Striarioidea)Shear, William A.; Nosler, Philip; Marek, Paul E. (Magnolia Press, 2022-02-10)A new species, Amplaria oedipus, is described from Oregon, USA. Males of the new species have greatly inflated pyriform tarsi on the 5th and 6th legpairs, which is a secondary sexual modification previously not known from any other millipede.
- The millipede family Striariidae Bollman, 1893. VIII. Three new genera and four new species of minute millipedes from Oregon and Washington, USA (Diplopoda, Chordeumatida, Striarioidea)Shear, William A.; Marek, Paul E. (Magnolia Press, 2023-04-14)We describe three new genera and four new species of small, litter-dwelling millipedes from the states of Oregon and Washington, USA: Miniaria ramifera, n. gen., n. sp., Miniaria richarti, n. gen., n. sp., Tigraria oregonensis, n. gen., n. sp., and Kingaria prattensis, n. gen., n. sp. Some of the unusual characters of these species are discussed, including a new type of sensory array on the third tarsus of males and a newly observed mandibular gland.
- Natural history, taxonomy, and phylogenetics of Appalachian flat-backed millipedes (Diplopoda: Polydesmida)Hennen, Derek Alan (Virginia Tech, 2020-04-29)Millipedes (class Diplopoda) are ubiquitous in forests worldwide, with about 12,000 described species and an estimated 30,000 undescribed species. The most species-rich order is the Polydesmida, the flat-backed millipedes, which encompasses about 3,500 species. Appalachia has an abundance of Polydesmida, and is a biodiversity hotspot for millipedes in the family Xystodesmidae. These diplopods are chemically defended with hydrogen cyanide and benzaldehyde, and sometimes form mimicry rings based on shared color. The evolutionary dynamics of model and mimic are incompletely known in these rings, so I investigated a mimicry ring in the central Appalachian Mountains to determine if the species Apheloria polychroma functions as a model for the genus Brachoria. I measured the size of the chemical gland to assess toxicity in 15 species, and reconstructed the ancestral dimensions of the gland to determine the direction of volume change over evolutionary time. Using a molecular phylogeny, I traced the miniaturization of chemical glands in the mimic genus Brachoria and found that in areas without Apheloria, Brachoria and related xystodesmids have larger chemical glands. Non-aposematic millipedes of the genus Nannaria have significantly smaller glands, and ostensibly rely on camouflage to avoid predation. This genus is known as the twisted claw millipedes and occur throughout eastern North America, but have their center of diversity in the Appalachian Mountains. About 22 species are described, but many undescribed species are known. To determine the diversity of this group, field collection and examination of museum specimens took place from 2015-2020. Examination of morphology, combined with molecular phylogenetics, revealed two distinct clades in the genus. One is distributed throughout the eastern United States, while the other is found only in the Appalachian Mountains. This Appalachian clade contains six described species, and I describe an additional 18 species, quadrupling the diversity of the group. Additionally, the phylogenetics of the polydesmid genus Pseudopolydesmus is investigated in an integrative taxonomic framework using five genes. I find that the genus is monophyletic, contains 8 species, and are related to one another in a hierarchical way according to a molecular phylogeny. I provide complete distributional records and live photographs of each species.
- Phylogenetic revision of the genus Cherokia (Chamberlin, 1949) (Polydesmida: Xystodesmidae)Vasquez Valverde, Luisa Fernanda (Virginia Tech, 2021-06-02)The family Xystodesmidae (Polydesmida) includes 521 species with a center of diversity concentrated in the Appalachian Mountains. Within this family, the genus Cherokia, a monotypic taxon with the type species Cherokia georgiana, is divided into three subspecies. The last revision of this genus was made by Richard Hoffman in 1960. Here, I used morphological and molecular data sets to review the genus, and evaluate whether it is a monophyletic group. I included material from literature records and three natural history collections. Newly collected samples were obtained through a citizen science project. Morphological characters such as the shape of the paranota, body size, and coloration were evaluated. Seven gene loci were used to estimate a molecular phylogeny of the genus, and a species delimitation analysis was used to evaluate the status of the subspecies. The geographical range of Cherokia was expanded to include a newly reported state (Virginia) and ca. 160 new localities compared to the previously known range. Morphological characters such as the shape of the paranota and body size that were historically used to establish subspecies, showed a direct relation with geographical distribution and elevation (clinal variation), but not with the phylogeny. Coloration was variable and did not accord with geography or phylogeny. The phylogeny recovered a monophyletic lineage, and the species delimitation test supports a single species. The molecular and morphological evidence showed that Cherokia is a monotypic genus with the sole species Cherokia georgiana being geographically widespread and highly variable in its morphology
- Quick Guide: MyriapodaMarek, Paul E.; Shear, William A. (Elsevier, 2022-12-05)Paul Marek and William Shear introduce the arthropod sub-phylum myriapoda, which includes centipedes, millipedes and other multi-legged animals.
- Step-wise evolution of complex chemical defenses in millipedes: a phylogenomic approachRodriguez, Juanita; Jones, Tappey H.; Sierwald, Petra; Marek, Paul E.; Shear, William A.; Brewer, Michael S.; Kocot, Kevin M.; Bond, Jason E. (Springer Nature, 2018-02-16)With fossil representatives from the Silurian capable of respiring atmospheric oxygen, millipedes are among the oldest terrestrial animals, and likely the first to acquire diverse and complex chemical defenses against predators. Exploring the origin of complex adaptive traits is critical for understanding the evolution of Earth’s biological complexity, and chemical defense evolution serves as an ideal study system. The classic explanation for the evolution of complexity is by gradual increase from simple to complex, passing through intermediate “stepping stone” states. Here we present the first phylogenetic-based study of the evolution of complex chemical defenses in millipedes by generating the largest genomic-based phylogenetic dataset ever assembled for the group. Our phylogenomic results demonstrate that chemical complexity shows a clear pattern of escalation through time. New pathways are added in a stepwise pattern, leading to greater chemical complexity, independently in a number of derived lineages. This complexity gradually increased through time, leading to the advent of three distantly related chemically complex evolutionary lineages, each uniquely characteristic of each of the respective millipede groups.