Morphology of the female reproductive system of three dorippid crabs (Crustacea: Decapoda: Brachyura: Dorippidae) and the role of accessory cuticle structures associated with seminal receptacles

Abstract

The reproductive systems of crabs reveal characters of considerable importance for the understanding of brachyuran phylogeny and evolution. The Dorippoidea show several plesiomorphic characters within Eubrachyura and similarities to podotreme crabs. Hence, they are often considered as an early diverging lineage, sometimes even as the sister group to all remaining eubrachyurans. Due to their role as prime candidates for putative plesiomorphic characters of the reproductive system of the Eubrachyura, we compared the morphology of the vaginae, seminal receptacles, and ovaries of three dorippid species using histological methods, micro‐computed tomography, and 3‐D reconstructions. Despite the putative phylogenetic position of dorippids, the female reproductive system shows features that are regarded as derived characters in eubrachyurans, including a concave vagina and a ventral‐type seminal receptacle. In contrast to other eubrachyurans, the oviduct does not enter the seminal receptacle directly but through specific cuticular valves. The female reproductive systems of Dorippe sinica and Dorippe quadridens are remarkable in further aspects. The seminal receptacles of both species are completely cuticle‐lined and have accessory sperm storage structures, the bursae. Our findings on the morphology of the female reproductive system of dorippids with its unique combination of basal, derived, and new characters challenges the prevailing hypothesis on the evolution of sperm storage organs in Eubrachyura.

The morphology of the reproductive system in the crab Percnon gibbesi (Decapoda: Brachyura: Grapsoidea) reveals a new combination of characters in Thoracotremata

“…Interestingly, in all species investigated, the bursae were situated on the medial side of the seminal receptacle. While the bursae of M. magister (Jensen et al, ) is large in relation to the seminal receptacle, the bursae of dorippids (Vehof et al, ) and the herein studied P. gibbesi are rather small. The bursae are collapsed when they are empty and have a bulbous saclike appearance when filled with sperm.…”

“…This contrasts with all available descriptions of thoracotreme female reproductive systems. A corresponding condition has only been described in the Dorippidae MacLeay, 1838 (Hayer, Köhnk, Boretius, & Brandis, ; Vehof et al, ). Dorippids are either considered as an early diverging lineage within the Heterotremata (Guinot et al, ; Tsang et al, ) or as a sister group of the remaining Eubrachyura (Jamieson, Guinot, & Richer de Forges, ; Ahyong, Lai, Sharkey, Colgan, & Ng, ).…”

“…Dorippids are either considered as an early diverging lineage within the Heterotremata (Guinot et al, ; Tsang et al, ) or as a sister group of the remaining Eubrachyura (Jamieson, Guinot, & Richer de Forges, ; Ahyong, Lai, Sharkey, Colgan, & Ng, ). Whether a spatial separation of the seminal receptacle and the oviduct is the ancestral character state of the sperm storage system in Eubrachyura remains a controversial issue (see Hayer et al, ; Vehof et al, ). The different phylogenetic positions of Dorippidae and Percnidae render the situation even more problematic.…”

“…Another noteworthy character in the female reproductive system of P. gibbesi is the presence of an accessory sperm storage structure, the bursa, at the junction of seminal receptacle, cuticular duct and vagina. Bursae have only been described in very few heterotreme species, for example, Metacarcinus magister (Dana 1852): Jensen et al (); Limnopilos naiyanetri Chuang & Ng 1991: Klaus et al (); Dorippe sinica Chen 1980, Dorippe quadridens (Fabricius 1793): Vehof et al ().…”

“…The bursae are collapsed when they are empty and have a bulbous saclike appearance when filled with sperm. Only in dorippids, are bursae so strongly cuticularised that they keep their shape even when they are not filled with sperm (Vehof et al, ). Bursae were discussed with regard to sperm competition (Jensen et al, ; Jensen & Bentzen, ) and cryptic female choice (Klaus et al, ).…”