One leg at a time: The morphology of millipedes

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2014 FMNH REU Wilson Guillory

2014 FMNH REU: WILSON GUILLORY (freshman, University of Arkansas)

Advisor: Dr. Petra Sierwald (Curator, Arachnida and Myriapoda, S&E)

Symposium Presentation Title: A Thousand-legged Mystery: The Evolution of Millipedes

Symposium Presentation Abstract: Millipedes (Arthropoda: Diplopoda) are an exceptionally diverse group of arthropods with over 13,000 known species and an estimated 80,000 total, and are important nutrient cyclers in forest ecosystems worldwide. However, relatively little is known about their anatomy, ecology, and evolution, making the analysis of millipede phylogeny, morphology, and behavior very challenging. The present study generated image data for the creation of a comprehensive millipede morphological atlas. Atlas images will form the base for detailed morphological descriptions; the morphological data, when combined with molecular data, will be employed as characters for phylogenetic analyses of the interrelationships between millipede families. Selected morphological images will be integrated in a world-wide, illustrated family identification tree. Millipede specimens of four species from the orders Spirobolida, Polydesmida, and Stemmiulida were dissected and cleaned using an ultrasonic cleaner and enzymatic treatment with pancreatin. The specimens were then photographed with a light microscopic imaging system to generate detailed color images with high depth of focus. The specimens were subsequently dried and mounted for scanning electron microscopy, where they were separately imaged to allow for the examination of surface structures and features difficult to see with a light microscope due to transparency or small size. Males and females of the same species were both imaged in cases of sexual dimorphism. Several apomorphic and synapomorphic characters were noted, with especial attention paid to the mandibles and gnathochilaria. Apomorphic characters in Spirobolida included the presence of a small anterior tooth and the lack of an anterior fringe on the molar plate, while differences between families were also found. Mouthparts of Polydesmida and Stemmiulida were morphologically similar to each other, supporting a closer relationship between those two groups than to Spirobolida.


Original Project Title: One leg at a time: The morphology of millipedes

Original Project Description: Millipedes are the main nutrient recycler in forest ecosystems; they chew down the leaf litter for further decomposition. Despite their ecological importance for soil health, their biodiversity, morphology and general biology are severely underexplored.  The millipede research program at the Field Museum of Natural History will produce a morphological atlas of various millipede groups to develop a comprehensive identification key to millipede families. Such tools promote further research into the group, such as local species richness,  biogeography, and phylogeny. The 2014 REU project will investigate the morphology of the millipede orders Polydesmida, Julida and Stemmiulida in detail, using the scanning electron microscope and various light microscopes. High quality images will be generated for the comparative analysis of complex structures in various millipede groups, such as sense organs, mouth parts, eyes and copulatory organs.

Research methods and techniques: The intern will be trained in millipede morphology, identification, and dissections. S/He will acquire skills to operate light and scanning electron microscopes, to produce and to manipulate images using sophisticated software. The newly generated morphological data will be added to the existing data pool, allowing comparative analyses and phylogenetic inference using these data.