Comparative cytogenetic analysis of marine Palaemon species reveals a X1X1X2X2/X1X2Y sex chromosome system in Palaemon elegans

Abstract

BackgroundThe maintenance of species and the promotion of speciation are closely related to chromosomal rearrangements throughout evolution. Decapoda represents the most species-rich order among crustaceans and, despite its ecological and economic importance, little is known about decapod karyology. We aim at cytogenetically characterizing two sympatric prawn species.ResultsAnalysis of mitotic metaphases and meiotic diakinesis of the common prawn Palaemon serratus and the rockpool prawn P. elegans, revealed considerable differences between their karyotypes including chromosome numbers and sex determination systems. The cytogenetic data for P. serratus showed a diploid number of 56 and the putative absence of heteromorphic sex chromosomes. However, the diploid chromosome number in P. elegans was 90 for females and 89 for males. The karyotype of the females consisted of the three largest acrocentric pairs and 42 submetacentric and metacentric pairs, while the karyotype of the males comprised a clearly identifiable large metacentric chromosome and two acrocentric pairs as well as the smaller 42 pairs. These results highlight the presence of the X1X1X2X2/X1X2Y multiple sex chromosome system in P. elegans, which constitute the only sexual system for Decapoda reported cytogenetically using modern techniques. The origin of this sex chromosome system is discussed. We hypothesize that the chromosome evolution within the genus could involve several fusion events giving rise to a reduction on the chromosome number in P. serratus. In both species, the major ribosomal genes were located in two chromosome pairs and hybridization signals of the telomeric sequences (TTAGGG)n were visualized at the telomeres of all chromosomes. C-banding revealed that, when present, constitutive heterochromatin had a predominantly telomeric distribution and no centromeric constitutive heterochromatin was observed.ConclusionsAlthough more comparative cytogenetic analyses are needed to clarify our hypotheses, the findings of this work indicate that the prawns of the genus Palaemon represent a promising model among Decapoda representatives to investigate the karyotype evolution and the patterns of sex chromosome differentiation.

Assessment of genetic diversity and population structure of the common littoral shrimp Palaemon serratus (Pennant, 1777) by microsatellites: Towards a sustainable management

“…Similar deficits have been widely observed and regarded as quite common in shrimp species (Cannas et al, ; Li et al, ; Meng, Wang, Jang, Liu, & Kong, ; You et al, ). The causes for the deviations from HWE include: (a) the stutter‐related scoring errors, so those microsatellite loci that had a difficult‐to‐interpret pattern were removed from the study; (b) inbreeding in this case ( F IS was positive in the 85.71% of departures from HWE); (c) the Wahlund effect (heterozygote deficiency caused by subpopulation structure, which is a plausible explanation because an arbitrary admixture of individuals was found); (d) null alleles (the presence of homozygotes with null alleles could be the most likely hypothesis to explain this deviation due to the instability of the flanking sequences of microsatellites); and (e) aneuploidy, although observations of metaphases in this species have not reported the existence of aneuploid individuals (González‐Tizón, Rojo, Menini, Torrecilla, & Martínez‐Lage, ; Torrecilla, Martínez‐Lage, Perina, González‐Ortegón, & González‐Tizón, ).…”

A chromosome-level genome of Portunus trituberculatus provides insights into its evolution, salinity adaptation, and sex determination

“…In crabs, some species (Eriocheir japonicus , Hemigrapsus sanguineus ,Hemigrapsus penicillatus and Plagusia dentipes ) were believed to have an XY sex determination system based on karyotype analysis (Lecher & Noel, 1995;Niiyama, 1937Niiyama, , 1938Niiyama, , 1959; however, due to the large numbers of chromosomes and complex genomes, sex determination by karyotype analysis cannot be determined in most crustaceans (Z. Torrecilla, Martínezlage, Perina, Gonzálezortegón, & Gonzáleztizón, 2017).…”

De novo gonad transcriptome analysis of the common littoral shrimp Palaemon serratus: novel insights into sex-related genes

“…Solely one transcriptomic work is available for this species, providing data to study larval development and metamorphosis [19]. Regarding to sex determination in P. serratus, it is only known that heteromorphic sex chromosomes are absent [20]. No sex determination or sex differentiation genes or pathways have been reported for this shrimp.…”