Podotreme reproduction: occurrence of sperm plaque in sponge crabs (Decapoda: Brachyura: Dromiidae)

Abstract Sperm plaque is found around the spermathecal apertures of some podotreme crabs. The investigation examined whether plaque is a post-copulatory or a post-fertilization artefact and whether the first pleopod found in dromiids and some other podotreme females could be used to remove plaque. Data were gathered from 53 species from 27 genera of dromiids. Plaque was also found in Acanthodromia erinacea A. Milne-Edwards, 1880 (Dynomenidae) for the first time. Dromiid females were divided into those with plaque, those with eggs, and those with both plaque and eggs. Relative numbers of females in these groups was used to analyse the brood cycle. The stage of development of accompanying eggs was recorded to measure plaque decay. Plaque was found only in mature females except for Cryptodromia hilgendorfi Man, 1888, where prepubertal females were found with plaque, indicating that precocial mating had occurred. More than 30% of females carried plaque and the majority of these had plaque alone, indicating that it is an artefact of copulation rather than fertilization. Calibrating the dataset for all species using C. hilgendorfi suggests that the half-life of plaque for all species is 10.4 d, except for LauridromiaMcLay, 1993, where the half-life is at least 23.9 days. These data suggest that there is a range of male mating strategies using plaque of different decay characteristics. The first female pleopod does not have a role in plaque removal in dromiids because it is too short. The main role of this pleopod in podotremes having this structure is likely facilitation of external fertilization by mixing sperm and eggs. Reproduction of the Podotremata and Eubrachyura are also compared.