Reference: Bid. BUN. 185: 168- 173. (October, 1993) Distinct Reproductive Types of Male Spider Crabs Libinia emarginata Differ in Circulating and Synthesizing Methyl Farnesoate AMIR SAGI’, ELLEN HOMOLA2, AND HANS LAUFER3 Department of Molecular and Cell Biology, University of Connecticut, Stows, Connecticut 06260 and Marine Biological Laboratory, Woods Hole, Massachusetts 02543 Abstract. Levels of methyl farnesoate in the blood and in vitro rates of methyl farnesoate synthesis by the man- dibular organ were investigated to determine whether this compound is related to the differences in morphology and reproductive states of distinct types of male spider crabs described by Homola et al. (1992) in winter populations. Three male types, selected from a summer population, were investigated in detail: ( 1) males with relatively large propoduses (claws) and worn exoskeletons (abraded), (2) males with relatively large propoduses and exoskeletons covered with epicuticle (unabraded), and (3) males with small propoduses and unabraded exoskeletons (small). All males examined had sperm, but abraded males, identical in propodus and body size to unabraded males, had a reproductive system that weighed twice as much. Large-clawed unabraded males had relatively small re- productive systems. Small-clawed males possessed a small reproductive system. Abraded males possessed larger mandibular organs, containing almost twice the total protein, and their man- dibular organs synthesized significantly more methyl far- nesoate in vitro than did the other types of males. Cir- culating levels of methyl farnesoate, in the hemolymph of the abraded males, were more then twice as high as the levels detected in any other type of male. Received 12 August 1991; accepted 16 July 1993. ’ Present address:Department of Life Sciences,Ben-Gurion University, P.O. Box 653, Beer-Sheva, 84105, Israel. * Present address: Bodega Marine Laboratory, University of California, P.O. Box 247, Bodega Bay, CA 94923. 3 To whom all correspondence should be addressed. Abbreviations: A, abraded; U, unabraded; S, small; MF, methyl far- nesoate. The strong relationship between methyl farnesoate lev- els, male morphology, and reproductive system devel- opment calls for further studies on the role of methyl farnesoate in the regulation of reproduction and mor- phogenesis in male crustaceans. Introduction The crustacean mandibular organ was first described by Le Roux (1968). Two decades later, Laufer et al. (1987) identified a secretory product of this gland, methyl far- nesoate, which is found both in the mandibular organ and the hemolymph of the spider crab L. emarginata. Methyl farnesoate is the unepoxidated form of the insect juvenile hormone III. In insects, juvenile hormones play several regulatory roles both as gonadotropins (Herman and Bennett, 1975) and morphogens (Wigglesworth, 1970). Different male types were described in adult spider crab populations using a propodus (claw) to carapace ratio (Tessier, 1960; Hartnoll, 1963; Aldrich, 1974). Recently, different adult male types were described in L. emarginata that were collected in the winter (Homola et al., 1992). Those types differ from each other in the appearance of the exoskeleton as well as in relative claw size. Abraded males had larger reproductive systems and higher methyl farnesoate titers compared to the unabraded males (Homola et al., 1992). The present study examines the size of the mandibular organ, its relative rate of methyl farnesoate synthesis, and level of methyl farnesoate in the circulatory system of L. emarginata males collected in the summer. We report the results of a comparative study of methyl farnesoate pro- duction and circulation in three male morphs distinctive 168