printed by Morphometric Analysis of Sexual Dimorphism In The Federally Endangered Dwarf Wedgemussel, Alasmidonta heterodon N. E. Baginski, K. M. O’Brion, K. L. Richardson, P. M. Larson, and B. J. Wicklow Department of Biology, Saint Anselm College, Manchester, NH, USA Small and declining populations are at risk of stochastic events that may reduce genetic diversity and effective population size leading to reduced recruitment and local extinction. Sex ratios are fundamental to understanding the potential for these populations to persist. The dwarf wedgemussel has been extirpated from or has declined to small, insular populations throughout much of its former range. Although sexual dimorphism was noted in early descriptions of the dwarf wedgemussel, there are no validated studies that define characters that can be used to differentiate sex. Length-width ratios differed significantly between male and female mussels (Figure 5), (T-test, p < 0.001). Discriminant Function Analysis predicted with 95.2% certainty the sex of each specimen based on the 4 linear measurements (Figure 6). This means that DFA correctly classified the sex of 95.2% of our specimens based on their shell morphology as compared to the actual sex as confirmed by examination swollen marsupia or gonadal fluid. Results of relative warps analyses of shell shape also showed clear sexual dimorphism in all three views (lateral, dorsal, and posterior). We took caliper measurements of length, width, height, umbo to anterior and recorded shell shape attributes. Gravid females were identified by the presence of swollen marsupia. Gonadal fluid was extracted from non-gravid individuals to discriminate between females and males (Figures 1 and 2). Our results show that A. heterodon is sexually dimorphic and that key measurements and analysis of photographs of mussel shells can be an effective, non-invasive method of determining individual sex. We plan to apply these methods to determine sex ratios in wild populations and review data from past monitoring studies to compare changes in sex ratios over time, thus providing critical information for the management of this endangered species. LOGO We collected 50 dwarf wedgemussels from the Connecticut River at Lancaster, NH. Our aim was to use geomorphic morphometric analysis to differentiate male and female mussels based on shell shape characteristics. This method could then be used as a noninvasive technique for male and female identification in the field. We hypothesized, based on preliminary results, that specific male and female measurements differed significantly. We photographed individual mussels in lateral, dorsal and posterior views then overlaid a fan with 28 digitized landmarks on each image using MakeFan 6 (Figures 7a and 8a). Landmarks were imported into Tpsdig ( We ran a relative warps analysis of the geometric morphometric data (sliding outline landmarks) in TpsRelw. Scores on the first two relative warp axes were plotted in NCSS. Finally, the four linear mesurements were anlyzed in NCSS via a discriminant functions analysis (DFA). We used a T-test to determine differences in mean length- width ratios of male and female mussels. Figure 1. A. heterodon sperm cell stained with methylene blue (see Saha and Layzer, 2008) Figure 2. Gravid female displaying. Glochidia are present just inside the exhalent aperture. Figure 3. Male relative landmark displacement computed from a consensus of 42 superimpositions. Figure 4. Female relative landmark displacement computed from a consensus of 42 superimpositions FemaleMale LW Ratio Figure 5. Box plot results for length-width ratios of male and female mussels Figure 6. NCSS plot of discriminant regression scores A B C A B C Figure 7. Male specimen in Lateral (A), Dorsal (B) and Posterior (C) views Figure 8. Female specimen in Lateral (A), Dorsal (B) and Posterior (C) views Introduction Objectives Methods Results Conclusions