One-thousand legs: up close and personal

2013 REU Intern Madeleine Metz


Sophomore Biology and Classical Civilizations double major at Oxford College of Emory University

REU Mentor: Dr. Petra Sierwald (Associate Curator, Zoology/Insects)

Symposium Presentation Title: Now you setae, now you don't: Comparing millipede morphology up close and personal

Symposium Presentation Abstract: While millipedes (Arthropoda: Diplopoda) are critical for vegetative decomposition in forest nutrient cycling, they have not yet been extensively researched employing modern technologies such as scanning electron microscopy. This means their morphological structures are not well documented and the function of these structures is poorly understood, hindering the analysis of millipede ecology, evolutionary history, and basic biology. This project focused on creating a morphological atlas using scanning electron microscopy to gain insight into millipede phylogeny, biodiversity, and ecological niches. Male and female specimens from two orders and four families were dissected using a light microscope; samples were cleaned, dried, and mounted, then imaged using a scanning electron microscope. These images were compared for shared and variable morphological features with the goal to identify apomorphic characters indicating the monophyly of various taxa, e.g., for the order, family, or genus. Some of the more complex structures in millipedes are the antennae, the gnathochilarium (a lower-lip type structure), the mandibles, and the copulatory organs. These differences are caused by several evolutionary processes: the variations in copulatory organs have evolved due to sexual selection, while the mandibles, the gnathochilarium, and the antennae are altered by natural selection from different habitats and food sources. We found mandible modifications when comparing an arboreal and a terrestrial species in the same family, indicating that this change is an individual adaptation to a disparate habitat. However, we also found apomorphic differences between orders—all members of the spirobolida sampled so far possess a large separate tooth at the edge of the pectinate lamella. These are only a few of the connections we have found, but there is a clear need for greater sampling across orders and families. Without this information, it will be impossible to expand on arthropod evolution or understand millipedes’ role in different ecosystems.

Original Project Description: Millipedes play a crucial role in the nutrient cycling of forests around the globe. Despite their ecological importance for soil health, their biodiversity, morphology and general biology are severely underexplored.  The millipede research program at The Field Museum 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 2013 REU project will investigate the morphology of the order Spirostreptida 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: Interns will be trained in millipede morphology, identification, and dissections. Interns will acquire skills to operate  light and scanning electron microscopes, produce and 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.