Many of the controversies in Anthoxanthum can be explained by recurring hybridization and/or polyploidization on time scales ranging from the Miocene to the Late Pleistocene. All but one of the extant species shared most recent common ancestors in the Late Pliocene to the Late Pleistocene. The disjunct occurrences in Africa originated in the Late Pliocene via independent immigrations, whereas Macaronesia was colonized in the Late Pleistocene.

The rockpool shrimp Palaemon elegans is considered an important crustacean species within the European coastline fauna. This species is experiencing an ongoing geographical expansion beyond its native distribution range due to unintentional human introductions. A better knowledge of the genetic diversity, geographic structure and connectivity of its populations is necessary. In the present study, microsatellite loci were isolated using the Illumina MiSeq platform. The microsatellite-enriched library sequencing produced 3.9 million raw reads. Reads were processed and primer pairs were designed for microsatellite sequences amplification. Ninety-six microsatellite loci were preliminary screened in individuals from Atlantic and Mediterranean localities. From them, 21 loci exhibited reliable polymorphism and were thoroughly characterized in 30 individuals from a Cantabrian locality (Spain). No linkage disequilibrium between pairs of loci was detected. Number of alleles per locus ranged from 2 to 12. Observed and expected heterozygosities ranged from 0.033 to 0.833 and from 0.033 to 0.869 respectively. No significant departure from the Hardy-Weinberg equilibrium was detected in most of loci. This is the first time that microsatellite markers have been developed for P. elegans. This characterized microsatellite suite provides new suitable tools for further analyses, facilitating the understanding of population genetics both in natural and introduced populations.

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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.

The common littoral shrimp Palaemon serratus is an ecologically and economically important decapod crustacean. Understanding the spatial structure of its populations is crucial to implement effective management strategies. In this study, 17 polymorphic microsatellite nuclear markers were examined in 252 individuals to explore the genetic diversity and the population structure underlying the geographical distribution of this crustacean in European waters. Basic genetic descriptors, population genetic analyses based on FST, analysis of the molecular variance (AMOVA), Bayesian clustering and the Mantel test were performed. Genetic differentiation was significant among sampling sites. AMOVAs and Bayesian assignment tests showed genetic differentiation among localities from the Atlantic coast and those belonging to the area of the Strait of Gibraltar and the Mediterranean Sea. The Guadalquivir estuary was significantly different from the remaining localities. A biogeographical break was detected to the west of the Strait of Gibraltar, and evidence of isolation by distance was obtained. Localities on both sides of the English Channel showed genetic differentiation with the rest of the Atlantic sampling sites, indicating a biogeographical break in this area. These results will contribute towards the better understanding of the biology and ecology of this shrimp and management of the valuable fishery. Two priority areas were delimited: the Atlantic and the Gibraltar–Mediterranean. The Guadalquivir estuary, Anglesey and Calais should also be considered as different genetic stocks.

The Atlantic–Mediterranean transition zone between the Alborán Sea and the Gulf of Cádiz constitutes the most prominent marine geographic barrier in European waters and includes known phylogeographic breaks such as the Strait of Gibraltar and the Almería-Oran Front. A genetic shift in this area has been previously documented for the European littoral shrimp Palaemon elegans. Here we carried out a phylogeographic analysis with the congeneric and sympatric species Palaemon serratus to test for similar intraspecific genetic differentiation and geographic structure. This littoral prawn is distributed in the Northeastern Atlantic Ocean, the Mediterranean Sea and the Black Sea. We compared DNA sequences from the mitochondrial genes Cox1 and to a lesser extent from 16S rRNA of several Atlantic and Mediterranean populations. Furthermore, sequences from the nuclear gene Enolase were included for corroborating differences between Mediterranean and Atlantic individuals. A pronounced genetic differentiation was detected between the Mediterranean and Atlantic populations, amounting to 10.14% in Cox1 and 2.0% in 16S, indicating the occurrence of two independent evolutionary lineages. Interestingly, specimens from the Atlantic Gulf of Cadiz cluster together with the Mediterranean individuals, indicating that a biogeographic barrier appears to be located west of the Strait of Gibraltar.

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