Recipient Organization
UNIV OF MARYLAND
(N/A)
COLLEGE PARK,MD 20742
Performing Department
Entomology
Non Technical Summary
This work is concerned with species delimitation of a common and ecologically significant group of forest arthropods in the eastern United States, the leiobunine harvestmen or daddy longlegs. It has also been implicated as pest predator on soy beans in the midwest. The systematics of the group is substantially underworked. Given the importance of species identification in ecological studies, the lack of taxonomic information currently inhibits research on the group. The work therefore touches on forest ecology, biodiversity and natural predators in agroecosystems. The work is not targeted at gathering data to use in a special competitive program ARTS at NSF, in keeping with the goal of the state competitive program.
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
This research uses an innovative combination of micro-computed tomography (mCT), evolutionary theory, and multivariate statistical analysis to delimit new species of harvestmen (Opiliones) and to test hypotheses about mating-system evolution. Discovery and identification of species is fundamental for classifying, measuring and conserving biodiversity, and reproductive morphology has been widely and successfully used for these purposes. However, persistent reliance on standard taxon-specific methods and characters limits progress, leading some to question their continuing utility for taxonomy. The proposed work will expand the range reproductive features available to taxonomy by optimizing preservation and mCT settings for internal cuticular and soft structures; obtain tomograms from multiple species and multiple populations within widespread, heterogenous species; quantify lengths, volumes, shapes, etc. of muscles, glands and other structures; and use multivariate clustering methods to delimit species. Specifically, new characters will determine whether the striped harvestman, Leiobunum vittatum, is one heterogeneous species or multiple "cryptic" species, and whether covariation among reproductive structures are consistent with sexually antagonistic coevolution, cryptic female choice or other processes. Results will serve as preliminary data for a proposal to the Advances in Revisionary Taxonomy and Systematics program at the NSF to extend this research to leiobunine harvestmen of eastern North America generally.
Project Methods
Winter 2016. We will explore optimal methods for fixation and preservation of specimens for micro-CT following (16): A. Fix specimens in 70% EtOH, dehydrate through graded series to 99% EtOH, preserve in 99% EtOH. B. Fix and dehydrate specimens as above, incubate in 1% iodine solution overnight, wash several times in 99% EtOH. C. As in B, but eliminate EtOH via critical point drying D. Fix in Bouin's solution overnight, dehydrate and preserve as in A. E. Fix and dehydrate as in C, incubate in 1% iodine solution, wash several times in 99% EtOH. F. As in E, but eliminate EtOH via critical point drying.Each step in the progression provides great resolution during micro-CT scan but also increases the potential for tissue shrinkage or distortion. We will choose the optimal permutation for subsequent use for all specimens.Micro-CT intensity and wavelengths will be optimized at GE Measurement & Control Inspection Technologies' Customer Solutions Center in Lewistown, PACollect specimens of L. vittatum relatives. (Spring and Summer 2016)The following leiobunine species, which are close relatives of Leiobunum vittatum. (State abbreviation in parentheses). Leiobunum aldrichi (MD), L. bracchiolum (MD), L. calcar (MD), L. cumberlandense (VA) L. euserratipalpe (MD), L. nigropalpi (MD), L. politum (MD), L. vittatum species-group: L. crassipalpe (MO), L. relictum (OK), L. uxorium (MD)Collect specimens of L. vittatum (Summer 2016) "Typical" form: southeastern GA (type locality), central VA, central MD, central MA, southern MI, central MS, northern MO, central OK. "Great Plains" form: central NE, central ND. "L. speciosum" form: Delmarva (MD), southeastern VA. L. crassipalpe-like form: southern AR.Features to be measured using ORS VisualSI software. (Spring 2016 to Winter 2017)Male: Accessory (nuptial gift) glands: total luminal volume, number of lobes, duct lengths and volume. Penile gift-bearing sac: volume. Ejaculatory duct: length; luminal diameter; Intrinsic penile muscle: number, length and orientation of fibers (used in calculating relative effective force). Penis: length, cuticular investment, dorsal and lateral shape parameters of "warp" scores, second moment of area (midshaft), length of glans and stylus, lever arm of shaft-glans joint, cuticular investment in fulturae. Penile protractor and retractor, penis-fultura and opercular closer muscles: relative effective forces (see penile muscle). Testis: volume. Seminal vesicle: luminal dimensions, effective force of spiral muscle. Pedipalps: relative effective force of femur-patella, patella-tibia and tibia-tarsus muscles. Endosternite: connective tissue investment, relative effective force of dorsal suspensors. Tracheae: relative tracheal inventment in glands and muscles. Female: Accessory glands: total luminal volume, number of lobes, duct lengths and volume. Seminal receptacles: volume, length, cuticular investment of sclerite, distance from vaginal opening, volume of glands. Ovipositor: length, muscular investment, number of annuli, vaginal length. Ovary: tissue volume, volume of mature eggs. Extrinsic ovipositor muscles - protractor and retractor: relative effective force. Genital operculum: relative effective force of closer and operculum-sternum muscles, cuticular investment and shape parameters of "warp" scores. Sternum: cuticular investment and shape parameters of "warp" scores. Pedipalps: relative effective force of femur-patella, patella-tibia and tibia-tarsus muscles. Endosternite: connective tissue investment, relative effective force of dorsal suspensors. Tracheae: relative tracheal inventment in glands and muscles.Data analysisData will be combined in varying classes (individuals, populations sexes, character classes) and analyzed for patterns in covariation consistent with clustering in species groups or functional relationships predicted by different models of sexual selection and mating-system evolution. This will be accomplished by analyzing data using R-based programs. Shape data will entered as warp scores (=principal component scores from landmark data). These and size-corrected measurements will be analyzed using k-means clustering and clusters will be tested for robustness using cross-validation and linear discriminant analysis. Robust and well separated clusters will indicate species.