Dirk Brandis

Morphology of the Female Reproductive System of European Pea Crabs (Crustacea, Decapoda, Brachyura, Pinnotheridae)

Commensal pea crabs inhabiting bivalves have a high reproductive output due to the extension andfecundity of the ovary. We studied the underlying morphology of the female reproductive system in the Pinnotheridae Pinnotheres pisum, Pinnotheres pectunculi and Nepinnotheres pinnotheres using light microscopy and transmission electron microscopy (TEM). Eubrachyura have internal fertilization: the paired vaginas enlarge into storage structures, the spermathecae, which are connected to the ovaries by oviducts. Sperm is stored inside the spermathecae until the oocytes are mature. The oocytes are transported by oviducts into the spermathecae where fertilization takes place. In the investigated pinnotherids, the vagina is of the “concave pattern” (sensu Hartnoll 1968 ): musculature is attached alongside flexible parts of the vagina wall that controls the dimension of its lumen. The genital opening is closed by a muscular mobile operculum. The spermatheca can be divided into two distinct regions by function and morphology. The ventral part includes the connection with vagina and oviduct and is regarded as the zone where fertilization takes place. It is lined with cuticle except where the oviduct enters the spermatheca by the “holocrine transfer tissue.” At ovulation, the oocytes have to pass through this multilayered glandular epithelium performing holocrine secretion. The dorsal part of the spermatheca is considered as the main sperm storage area. It is lined by a highly secretory apocrine glandular epithelium. Thus, two different forms of secretion occur in the spermathecae of pinnotherids. The definite role of secretion in sperm storage and fertilization is not yet resolved, but it is notable that structure and function of spermathecal secretion are more complex in pinnotherids, and probably more efficient, than in other brachyuran crabs. J. Morphol., 2011.

Morphology and function of the copulatory system in freshwater crabs of the genus Potamon

To understand the reproductive processes of freshwater crabs of the genus Potamon, we examined the first and second gonopod and the gonoducts of the female by histological methods. The gonopods are highly modified compared to those of other brachyuran crabs. In particular, the second gonopod is unusually long and has a special morphology, ending in a long sclerotized tube. Suggestions for the function of both gonopods and their different parts are presented. Tubulation of the first and second gonopod is observed. Rosette glands, which are abundant in the subterminal joint of the first gonopod, are connected to the sperm channel by cuticular pores. In females, the chitinous parts of the inner vulva may prove to have a more constant morphology than the external flexible structures. J. Morphol. 239:157–166, 1999.

Morphology and function of the reproductive system of representatives of the genus Uca.

The morphology of the reproductive organs of three species of fiddler crabs, Uca ecuadoriensis, Uca c.f. forcipata, and Uca tangeri were investigated to subsequently produce a model of their mode of operation. Vulva, vagina, and spermatheca in females, and the first and second gonopods in males were examined by applying histological techniques and electron microscopy. In all three species, vulva and vagina conform to the concave type, and the spermatheca complies with the ventral type. The tissue of the oviduct orifice is enlarged and bulges into the lumen of the spermatheca. Differences between the three species are apparent in the organization of the spermatheca, especially in the distribution and structure of glandular epithelium: In U. ecuadoriensis and U. c.f. forcipata the largest proportion of the spermathecal wall is lined with cuticle and only a small area consists of glandular epithelium, while in U. tangeri almost all of the lining is glandular. Furthermore, the glandular epithelia of the species differ in their histology and ultrastructure: In U. ecuadoriensis it is tubular and multilayered, while in U. c.f. forcipata it is mono‐layered. U. tangeri finally has both forms of this tissue. In the males, the terminal segments of the first gonopod exhibit a tight fit to female organs and narrow, tightly sealed sperm channels. These features suggest a tendency towards minimizing loss of fluids, which can be interpreted as an adaptation to mating on land. The tight fit of male gonopod and female opening seem to be protection from interbreeding, which points toward a strong sexual selection. In the terrestrial environment, these originally aquatic organisms experience serious competition for resources; therefore there is pressure on successful reproduction. According to the current results a model of the process of fertilization and egg‐laying involving the investigated organs was generated. J. Morphol., 2010.

Ultrastructure of spermatozoa and spermatophores of old world freshwater crabs (Brachyura: Potamoidea: Gecarcinucidae, Potamidae, and Potamonautidae).

We investigated the ultrastructure of spermatozoa and spermatophores of 19 palaeotropical freshwater crab species [12 species of the Gecarcinucidae, 6 of the Potamidae (Potamiscinae), and 1 species of the Potamonautidae (Deckeniinae: Hydrothelphusini)]. The investigated Potamiscinae have densely packed coenospermic spermatophores with the exception of Thaiphusa sirikit and Johora singaporensis that exhibit cleistospermia. In contrast, in the Gecarcinucidae the spermatozoa are loosely embedded in a mucous matrix. The gecarcinucid and potamiscine sperm differ, furthermore, in acrosomal structure and size. The acrosome in the Gecarcinucidae is much smaller and spherical, while the larger acrosome in the Potamiscinae has the tendency to be depressed. In the Potamiscinae, an additional middle acrosomal zone evolved between the acrosome ray zone and the outer acrosomal zone. Within the Gecarcinucidae, a differentiation into two groups (Gecarcinucinae and Parathelphusinae) is not supported by the present spermatological data. The sperm morphology of Hydrothelphusa aff. madagascariensis (Potamonautidae: Deckeniinae) differs from Potamonautes sidneyi (Potamonautidae: Potamonautinae) in acrosomal size and shape, and in the absence of a periopercular rim. A closer relationship of Deckeniinae and Gecarcinucidae cannot be confirmed by spermatology. J. Morphol., 2009.

Functional morphology of the copulatory system of box crabs with long second gonopods (Calappidae, Eubrachyura, Decapoda, Crustacea)

Male True Crabs use two pairs of gonopods to deliver mating products during copulation. Commonly, the second pair is shorter than the first pair, and most research to date has focused on species with short second gonopods. We investigated male and female copulatory organs in Calappula saussurei and Calappa pelii, two species of box crabs (Calappidae) with second gonopods which are longer than the first pair. Scanning electron microscopy and histological cross sectioning show that the female copulatory system is unique in several aspects: the genital duct is part concave and part simple type. The seminal receptacle is divided into two chambers, a ventral chamber of ectodermal and mesodermal origin, and a dorsal chamber of ectodermal origin. This dorsal chamber is the location of spermatophore reception during copulation. A sperm plug closes the dorsal chamber off. We propose that long second gonopods deliver male mating products directly into the dorsal chamber. To date, spermatophore reception has been associated with the mesodermal tissue of the seminal receptacle. The copulatory system of box crabs with long second gonopods shows novel deviations from this general pattern. J. Morphol. 276:77–89, 2015.

On the taxonomic status and biogeography of the Isolapotamidae Bott, 1970 (Decapoda, Brachyura)

Recent investigations of Asian freshwater crabs of the superfamily Potamoidea Ortmann, 1896 use the Potamidae Ortmann, 1896 as the only valid family, although three families have been described from South-East Asia: the Potamidae Ortmann, 1896, the Isolapotamidae Bott, 1970 and the Sinopotamidae Bott, 1970. Crabs formerly included in the Isolapotamidae are re-examined based on a new understanding of the morphology and function of the male gonopods. In particular, the morphology of the sperm transfer tube of the second gonopod is studied in detail. At least four types of sperm transfer are recognized representing four different modes of sperm transfer. Each type is morphologically constant for a number of genera. On the basis of these results the taxonomic status of the family Isolapotamidae is reconsidered. A new genus Takpotamon is erected for Potamon maesotense Naiyanetr, 1992 from Thailand, the genera Dromotelphusa Naiyanetr, 1992 and Flabellamon Ng, 1996 are re-characterized and the genus Thaiphusa Ng and Naiyanetr, 1993 is synonymized with Demanietta Bott, 1966. All the morphological results show biogeographical relevance and the resulting distribution patterns reflect the palaeogeographic and palaeoclimatic situation of Sundaland during the Tertiary and Quaternary.

The male copulatory system of european pea crabs (crustacea, brachyura, pinnotheridae)

The male copulatory system of the European pinnotherid species Pinnotheres pisum, Pinnotheres pectunculi, and Nepinnotheres pinnotheres was investigated by gross morphology, scanning electron microscopy, histological methods, and confocal laser scanning microscopy. The brachyuran copulatory system is consistently formed by paired penes and two pairs of abdominal appendages, the gonopods, functioning in sperm transfer. In pinnotherids, the long first gonopods transfer the sperm mass into the female ducts. The first gonopod has the ejaculatory canal inside that opens both basally and distally. The second gonopod is solid, short, and conical. During copulation, the penis and the second gonopod are inserted into the basal lumen of the first gonopod. While the penis injects the sperm mass, the second gonopod functions in the transport of spermatozoa inside the ejaculatory canal toward its distal opening. The second gonopod is adapted for the sealing of the tubular system in the first gonopod by its specific shape and the ability to swell. Longitudinal cuticle foldings of the second gonopod hook into structures inside the first gonopod. The second gonopod can interact with the penis during copulation by a flexible flap separating the lumina in which the second gonopod and the penis are inserted. J. Morphol., 2012.

Morphology and Function of the Female Reproductive System of Ebalia tumefacta (Decapoda, Brachyura, Leucosiidae)

In this article, the morphology and function of the female reproductive organs of Ebalia tumefacta were investigated using histological methods. While the vagina conforms to the concave type, the study reveals a new orientation of seminal receptacle compartments. The seminal receptacle consists of two chambers, which are oriented in anterior‐posterior direction. This is in contrast to the dorso‐ventral orientation of seminal receptacle chambers in all other known brachyuran crabs. The anterior chamber is lined by cuticle, whereas the posterior chamber is covered with a holocrine glandular epithelium. The oviduct connection is located ventrally, close to the opening of the vagina. The oviduct orifice is characterized by a transition of the epithelium lining of the oviduct to the seminal receptacle holocrine glandular epithelium. Special features are muscle fibers, which are attached to the oviduct orifice and to the sternal cuticle as well. The muscle fibers can be found exactly at that point where the oviduct opens into the seminal receptacle and are secondly attached to the sternum beneath. This musculature is newly described for Eubrachyuran crabs. This musculature can be interpreted as an important feature in the fertilization and egg‐laying process in relation to supporting and controling the inflow of eggs into the seminal receptacle lumen. These new discoveries were compared to the known pattern of an Eubrachyuran seminal receptacle. J. Morphol. 276:517–525, 2015.

Ever more complex: a new type of organization of reproductive organs in female Dorippe sinica Chen, 1980 (Decapoda: Brachyura: Dorippidae)

In this study a new organization of the female reproductive organs of Eubrachyura is presented after using both histology and MRI and μCT analyses to investigate the morphology and function of the female reproductive organs of Dorippe sinica Chen, 1980. The reproductive organ is composed of two parts: an ectodermal sperm site and a mesodermal ovary. The ectodermal sperm storage site incorporates a concave vagina and a seminal receptacle, which is completely lined by cuticle and is not connected to the ovary. Additionally, a cavernous body is attached to the seminal receptacle. This cavernous body can be interpreted as an important feature in the fertilization process in relation to transporting the spermatozoa out of the lumen of the seminal receptacle. Independently of the seminal receptacle, the ovary is connected to the oviduct via a single opening. The oviduct is lined by an apocrine glandular epithelium. The oviduct and the vagina open directly into the vulva. These new discoveries are compared to the known pattern of eubrachyuran female reproductive systems.

Evolution of male copulatory organs in box crabs (Decapoda: Eubrachyura: Calappidae De Haan, 1833)

Male genitalia are extraordinarily diverse, and this diversity makes them valuable taxonomic and phylogenetic markers. Genitalia of true crabs (Brachyura) consist of two pairs of modified appendages, or gonopods. The first pair is tubular, and holds the second pair during copulation. Whether the second pair is shorter or longer than the first pair has important implications for copulation. Its length is often similar in closely related species, e.g. within genera and families, but is highly variable in the Brachyura at large. The genus Calappa Weber, 1795 contains species with long, short, and intermediate-length second gonopods, representing an unusually variable pattern. We investigated the evolution of the second gonopods in Calappa and other members of Calappidae. We assembled a molecular multi-locus phylogeny (mitochondrial marker: COI and 16S, nuclear marker: Enolase, H3 and 28S). Based on this phylogeny, long second gonopods are the ancestral state for Calappa as well as Calappidae in general. Short second gonopods evolved once, while intermediate-length second gonopods evolved independently at least four times. Scanning electron microscopic images of second gonopods of 22 species of Calappidae reveal that shortening of the second gonopod is always achieved by a shortening of the terminal segment. Congruently, taxon-specific structures at the tip of the terminal segment of the second gonopod, such as spines and pistil-like protrusions, are limited to long second gonopods. Based on current knowledge, a shortening of the second gonopod should be accompanied by extensive changes in the copulatory mechanism of males and females, including changes to the copulatory mechanism, mechanism of species recognition, targets of sexual selection, and the potential for sperm removal. Calappa therefore provides a vital example for the study of changes in copulatory mechanisms.