Morphology of seminal receptacle of the harvested golden crab Chaceon chilensis and its implication in the fertilization process

The external and internal architecture of crab seminal receptacles are closely associated with mating behavior, sperm transfer, and storage patterns, and ultimately reproductive success. Therefore, describing their anatomy contributes to the development of a greater understanding of crab reproductive biology. In this study, we describe the anatomy and tissue characteristics of the seminal receptacle of the golden crab Chaceon chilensis, a harvested deep-sea species from the Juan Fern andez Archipelago (off central Chile). Females in the late mature stage were used as reference for histological description. Morphological features of the seminal receptacle included: (1) a dorsal receptacle–oviduct connection, (2) velum and septum separating the dorsal and ventral chambers, (3) extensive glandular epithelium in both chambers, (4) a ribbed chitin line, (5) a highly folded, bilobulated ventral chamber, and (6) a simple-type vagina. Some of these traits (2, 3, 4, 5) are novel for crab receptacles and could contradict the generalized idea about the pattern of sperm precedence associated with the location of the receptacle–oviduct connection. External sperm plugs were not found in mature females, but variations in the color of opercula occluding the vulva were used to assess sexual maturity. The seminal receptacle of C. chilensis has an unusual internal morphology with vast sperm storage capacity and separate storage areas for sperm ejaculates, which could allow for cryptic female choice. In cases like these, male–male competition is usually intense and males deliver large quantities of sperm in each mating event, which makes them vulnerable to sperm depletion. Additional key words: reproduction, Brachyura, fishery, sperm storage, mating The seminal receptacles of diverse brachyuran crabs have been described in order to understand their role in sperm storage dynamics, fertilization, and multiple paternity (Hartnoll 1968; Sainte-Marie et al. 2000; Becker et al. 2011; Gonz alez-Pisani et al. 2012; Pardo et al. 2013). All of these aspects can influence the reproductive success of a species. The receptacle structure that is unique to Eubrachyurans allows females to store ejaculates (sperm and seminal liquid) to produce several broods in short time periods under favorable conditions (Fischer & Thatje 2008) or produce broods without the need of a fresh sperm supply over long time periods (Hines et al. 2003). In crabs, it has been hypothesized that the seminal receptacle has a meso-ectodermal origin (McLay & L opez-Greco 2011) and a generally similar morphology among species (i.e., a sac that can be elongate, globose, or kidney-shaped). However, fine anatomical configuration and details of internal architecture of eubrachyuran seminal receptacles are species specific. Golden crabs, which belong to the family Geryonidae, are deep-sea crabs mostly distributed on continental slopes and are often intensively harvested around the world (Hastie 1995). In Chile, the golden crab Chaceon chilensis CHIRINO-G ALVEZ & MANNING 1989 has been the focus of a small artisanal fishery in the Juan Fern andez Archipelago since the early 2000s (Ernst et al. 2011). This fishery, Author for correspondence. E-mail: luispardo@uach.cl Invertebrate Biology 136(2): 199–206. © 2017, The American Microscopical Society, Inc. DOI: 10.1111/ivb.12170 operating at a depth of 300–1000 m, has shown a high prevalence of males in the catch (Guerrero & Arana 2009), which could indicate a partial spatial segregation by sex, as in other geryonids (MelvilleSmith 1987). Little information has been reported on seminal receptacle morphology of golden crabs. Seasonal variation in size and turgidity of the seminal receptacle has been described for Chaceon quinquedens (SMITH 1879), Chaceon maritae (MANNING & HOLTHUIS 1981), and Chaceon fenerii (MANNING & HOLTHUIS 1984) (Haefner 1977; Melville-Smith 1987); however, these studies did not provide a detailed description of the structure. Hinsch (1988), using lightand electron-microscopic techniques, provided the first description of sperm and spermatophores inside receptacles of C. fenerii, but the study did not include a detailed description of the internal anatomy or histological characteristics of the receptacle. This study provides a fine-scale description of the morphology of the seminal receptacle and its associated structures from mature female specimens of C. chilensis, using different histological techniques to identify different components. Anatomical studies of receptacles are an important first step toward addressing questions about sexual selection and providing information relevant to fisheries assessment (Sainte-Marie & Lovrich 1994; Hines et al. 2003; McLay & L opez-Greco 2011; Pardo et al. 2016).