Ultrastructure of spermatophores and spermatozoa of intertidal crabs Pachygrapsus transversus, Pachygrapsus gracilis and Geograpsus lividus (Decapoda: Grapsidae)

Abstract

Pachygrapsus transversus, P. gracilis, and Geograpsus lividus are intertidal crabs, whose ultrastructure of spermatophores and spermatozoa are unknown. In this work, we characterized the ultrastructure of the spermatophores and spermatozoa of these three species comparing them to the results of previous research on molecular phylogeny of Grapsidae. Fragments of the posterior vas deferens were processed for routine in transmission electron microscopy. Pachygrapsus transversus and G. lividus exhibit coenospermic spermatophores, while Pachygrapsus gracilis presents cleistospermic spermatophores. The spermatozoa of all three species present the typical pattern seen in Thoracotremata. The acrosome is wider than long, with an acrosome length to width ratio of 0.82 ± 0.022 in P. transversus, 0.75 ± 0.008 in P. gracilis, and 0.82 ± 0.024 in G. lividus. The main specific sperm differences were observed in the perforatorial chamber, the operculum and the concentric acrosomal layers. Pachygrapsus transversus has a flask-shaped perforatorial chamber with a prominent narrowing under the apex, while Pachygrapsus gracilis exhibits a flask-shaped perforatorial chamber with a slight narrowing under the apex, thus wider than that of P. transversus. Geograpsus lividus presents a club-shaped perforatorial chamber with a conical apex. The acrosome of P. transversus has a narrow inner layer while the outer layer presents peripheral concentric lamellae near the opercular pole. In P. gracilis, the inner acrosomal layer of the acrosome is shifted toward the apical portion of the spermatozoon and the outer layer exhibits peripheral concentric lamellae throughout its extension. Geograpsus lividus shows a narrow and electron-dense inner layer shifted toward the opercular pole and curved operculum, unlike the pattern found for the Pachygrapsus species. The differences in the morphology of spermatophores suggest different strategies of transfer and/or storage of spermatozoa between the studied species. The spermatozoal ultrastructure supports the phylogenetic proximity of Pachygrapsus species and also demonstrate that spermiotaxonomy is a useful tool to be associated to molecular data.