Cytogenetic of brachyura (Decapoda): Testing technical aspects for obtaining metaphase chromosomes in six mangrove crab species

Brachyura is one of the most specious infra-order belonging to Decapoda and it plays a central role from an ecological and economic point of view. Despite its importance, cytogenetic studies on Brachyura (Decapoda) are extremely limited due to the difficulties in obtaining chromosome preparations of good quality. Molecular cytogenetic have proven to provide basic knowledge on the genome organization of species and in methods for manipulating genomes. It is also very useful to support aquaculture. In this study we focused on six semi-terrestrial mangrove crab species to test several variations of technical steps to produce chromosome preparations in Brachyura. The best results were obtained using cells from early stage embryos incu-bated with 0.0005% nocodazole or 0.05% colchicine and hypotonized with 0.075 M KCl solution. The best method to analyze the chromosomes was the use of confocal microscope after DAPI staining. We recorded a high chromosome number for the six study species. Similar chromosome morphology was recorded for allied species likely due to phylogenetic relationship. Variable results with cytogenetic treatments in different species suggest that there may be a species-specific response to the techniques we tested. Chromosome number ranges reported in this study will be useful in future genome sequencing studies, i.e. to assess the quality of sequencing assemblies.