Integrative analysis of sperm ultrastructure and molecular genetics supports the phylogenetic positioning of the sympatric rock shrimps Sicyonia dorsalis and Sicyonia typica (Decapoda, Sicyoniidae)

We describe the sperm ultrastructure of two sympatric rock shrimps, Sicyonia dorsalis and Sicyonia typica, and compare them in a molecular context to provide new insight into the sperm morphology of the Sicyoniidae. To accomplish this, the vasa deferentia of males of both species were fixed and prepared for transmission electron microscopy and light microscopy cytochemistry. Sperm of S. typica exhibit an oval main body and a short subacrosomal complex region with convoluted membrane pouches, a crystalline lattice and a well-developed large granule anterior to the spike, as previously described for Sicyonia carinata. In contrast, the ultrastructure of S. dorsalis sperm features an elongated complex subacrosomal region above the main body and a flat nucleus, and small cytoplasmic membrane vesicles are not present. Although S. dorsalis sperm are similar to those of Sicyonia ingentis, the spike of S. dorsalis is shorter than S. ingentis. A phylogenetic tree was built by Bayesian inference based on 19 sequences of 16S rDNA of some representatives of the genus. Our findings show that sperm analysis of these shrimps reflects their phylogenetic history and that such analysis is very useful for taxonomic studies. Species with corresponding sperm ultrastructure are in the same clade of the proposed phylogeny. Moreover, it is possible to detect different groups within the genus based on the presence of at least two distinct morphological patterns of ultrastructure in the spermatozoa of Sicyonia.