A preliminary study of 16S rRNA sequence variation in Australia Macrobrachium shrimps (Palaemonidae: Decapoda) reveals inconsistencies in their current classification

The systematic relationships among Australian palaemonid shrimps have been the subject of speculation for some time. A preliminary phylogenetic study was undertaken to clarify the relationships of five species, Macrobrachium intermedium (Stimpson), M. australiense (Holthuis), M. atactum (Riek), M. rosenbergii (de Man) and Palaemon serenus (Heller), using 16S rRNA mitochondrial gene sequences. Phylogenetic analyses indicated inconsistencies with the current classification in two respects. First, M. intermedium formed a very well-supported clade with P. serenus distinct from M. australiense, M. atactum and M. rosenbergii. Second, the two species from inland Australia, M. australiense and M. atactum, showed a high level of genetic similarity over a substantial geographic range, suggesting that they may represent conspecific populations. The taxonomic and biogeographic implications of these findings for Macrobrachium in Australia are discussed.

Phylogeography of the widespread Australian freshwater prawn, Macrobrachium australiense (Decapoda, Palaemonidae)

Aim: To investigate the phylogeographic structure of the widespread freshwater prawn, Macrobrachium australiense, within and between major Australian drainage basins using mitochondrial sequence data. This will enable the investigation of historical connections between major drainages and examination of hypotheses of biogeographic associations among Australian freshwater basins.

Location: Inland, eastern and northern Australia.

Methods: Sequencing 16S rRNA and ATPase 6 protein coding mitochondrial DNA genes from M. australiense from 19 locations from inland, eastern and northern Australia.

Results: Within drainage basins, haplotype trees are monophyletic, with the exception of the Finke River from the Lake Eyre Basin. Macrobrachium australiense from the two main inland drainages, the Murray–Darling and Lake Eyre Basin are divergent from each other and do not form a monophyletic group, instead the Murray–Darling Basin haplotypes clade with eastern coastal haplotypes. Haplotypes from neighbouring eastern coastal drainages were found to be quite divergent from each other.

Main conclusions: The phylogeographic relationships among M. australiense suggest that the two major inland drainages, the Murray–Darling Basin and the Lake Eyre Basin, are not biogeographically closely associated to each other. Instead the Murray–Darling Basin is more closely allied with the eastern coastal drainages across the Great Dividing Range. Despite their proximity the neighbouring southeast Queensland coastal Mary and Brisbane Rivers are also biogeographically divergent from each other. The results also indicate that the Finke River appears to have been isolated from the remainder of the Lake Eyre Basin catchment for a significant period of time.

Multiple origins of the endemic Australian Macrobrachium (Descapoda: Palaemonidae) based on 16S rRNA mitochondrial sequences

The evolutionary relationships of the freshwater prawn genus Macrobrachium are obscure. Members of this genus are widely distributed across tropical and subtropical regions. The phylogenetic relationships among the seven endemic and six non-endemic Australian Macrobrachium, along with five non-Australian species, were inferred from the mitochondrial 16S rRNA gene sequences. Methods of analysis yielded phylogenetic trees of differing topologies; however, none supported a monophyletic origin for endemic Australian Macrobrachium. Enforced monophyly of a single origin of endemic Macrobrachium was statistically tested and rejected. These results support the view that the endemic Australian Macrobrachium arose from multiple origins. Previous biogeographical hypotheses related to the radiation of Macrobrachium into Australia are re-examined in the context of these results.

Re-examination of the taxonomy of the macrobrachium australiense holthuis (Decapoda: Palaemonidae) species-complex: molecular evidence for a single species

The freshwater shrimp Macrobrachium australiense is distributed throughout the majority of inland, north-west, north-east and eastern drainages. Owing to the large amount of morphological divergence, both between and within catchments, this species has proven to be taxonomically difficult and, until recently, consisted of three separate species, each with subsequent subspecies. This study uses nucleotide sequences from the 16S rRNA mitochondrial gene region to investigate the genetic relationships between populations and confirm the taxonomic status of M. australiense. The results from sequencing an approximately 450-bp fragment from this gene region from M. australiense sampled from 12 locations across inland, eastern and northern Australia identified very little variation. The variation found between 16S M. australiense haplotypes is much less than that found between Macrobrachium species, indicating that it is in fact a single species. The results are concordant with a recent morphological revision of Australian species in which nominal taxa of the M. australiense complex were synonymised.

Complete mitochondrial DNA sequences of the decapod crustaceans pseudocarcinus gigas (Menippidae) and macrobrachium rosenbergii (Palaemonidae)

The complete mitochondrial DNA sequence was determined for the Australian giant crab Pseudocarcinns gigas (Crustacea: Decapoda: Menippidae) and the giant freshwater shrimp Macrobrachium rosenbergii (Crustacea: Decapoda: Palaemonidae). The Pse gigas and Mrosenbergii mitochondrial genomes are circular molecules, 15,515 and 15,772 bp in length, respectively, and have the same gene composition as found in other metazoans. The gene arrangement of M. rosenbergii corresponds with that of the presumed ancestral arthropod gene order, represented by Limulus polyphemus, except for the position of the tRNA^Leu(UUR) gene. The Pse. gigas gene arrangement corresponds exactly with that reported for another brachyuran, Portunus trituberculatus, and differs from the M. rosenbergii gene order by only the position of the tRNA^His gene. Given the relative positions of intergenic nonoding nucleotides, the “duplication/random loss” model appears to be the most plausible mechanism for the translocation of this gene. These data represent the first caridean and only the second brachyuran complete mtDNA sequences, and a source of information that will facilitate surveys of intraspecific variation within these commercially important decapod species.

Phylogenetic relationships of the globally distributed freshwater prawn genus Macrobrachium (Crustacea: Decapoda: Palaemonidae): biogeography, taxonomy, and the convergent evolution of abbreviated larval development

There has hitherto been little research into evolutionary and taxonomic relationships amongst species of the freshwater prawn genus Macrobrachium Bate across its global distribution. Previous work by the authors demonstrated that the endemic Australian species did not evolve from a single ancestral lineage. To examine whether other regional Macrobrachium faunas also reflect this pattern of multiple origins, the phylogeny of 30 Macrobrachium species from Asia, Central/South America and Australia was inferred from mitochondrial 16S rRNA sequences. Phylogenetic relationships demonstrate that, despite some evidence for regional diversification, Australia, Asia and South America clearly contain Macrobrachium species that do not share a common ancestry, suggesting that large-scale dispersal has been a major feature of the evolutionary history of the genus. The evolution of abbreviated larval development (ALD), associated with the transition from an estuarine into a purely freshwater lifecycle, was also mapped onto the phylogeny and was shown to be a relatively homoplasious trait and not taxonomically informative. Other taxonomic issues, as well as the evolutionary origins of Macrobrachium, are also discussed.

Molecular systematic studies of freshwater prawns of the genus Macrobrachium

Freshwater prawns in the genus Macrobrachium are found throughout the tropical and subtropical regions of the world, however, evolutionary relationships are poorly understood. Using molecular techniques taxonomic uncertainty is resolved and the evolution and distribution of this enigmatic genus across a range of taxonomic and geographic levels is examined.

Expression of the male reproduction-related gene (Mar-Mrr) in the spermatic duct of the giant freshwater prawn, Macrobrachium rosenbergii

Phosphorylated sperm proteins are crucial for sperm maturation and capacitation as a priori to their fertilization with eggs. In the freshwater prawn, Macrobrachium rosenbergii, a male reproduction-related protein (Mar-Mrr) was known to be expressed only in the spermatic ducts as a protein with putative phosphorylation and may be involved in sperm capacitation in this species. We investigated further the temporal and spatial expression of the Mar-Mrr gene using RT-PCR and in situ hybridization and the characteristics and fate of the protein using immunblotting and immunocytochemistry. The Mar-Mrr gene was first expressed in 4-week-old post larvae and the protein was produced in epithelial cells lining the spermatic ducts, at the highest level in the proximal region and decreased in the middle and distal parts. The native protein had a MW of 17 kDa and a high degree of serine/threonine phosphorylation. It was transferred from the epithelial cells to become a major protein at the anterior region of the sperm. We suggest that it is involved in sperm capacitation and fertilization in this open thelycal species and this is being investigated.