T.-Y. Chan

Phylogeny of Decapoda using two nuclear protein-coding genes: Origin and evolution of the Reptantia

The phylogeny of Decapoda is contentious and many hypotheses have been proposed based on morphological cladistic analyses. Recent molecular studies, however, yielded contrasting results despite their use of similar data (nuclear and mitochondrial rDNA). Here we present the first application of two nuclear protein-coding genes, phosphoenolpyruvate carboxykinase and sodium-potassium ATPase alpha-subunit, to reconstruct the phylogeny of major infraorders within Decapoda. A total of 64 species representing all infraorders of Pleocyemata were analyzed with five species from Dendrobranchiata as outgroups. Maximum likelihood and Bayesian inference reveal that the Reptantia and all but one infraorder are monophyletic. Thalassinidea, however, is polyphyletic. The nodal support for most of the infraordinal and inter-familial relationships is high. Stenopodidea and Caridea form a clade sister to Reptantia, which comprises two major clades. The first clade, consisting of Astacidea, Achelata, Polychelida and three thalassinidean families (Axiidae, Calocarididae and Eiconaxiidae), corresponds essentially to the old taxon suborder Macrura Reptantia. Polychelida nests within Macrura Reptantia instead of being the most basal reptant as suggested in previous studies. The high level of morphological and genetic divergence of Polychelida from Achelata and Astacidea justifies its infraorder status. The second major reptant clade consists of Anomura, Brachyura and two thalassindean families (Thalassinidae and Upogebiidae). Anomura and Brachyura form Meiura, with moderate support. Notably thalassinidean families are sister to both major reptant clades, suggesting that the stem lineage reptants were thalassinidean-like. Moreover, some families (e.g. Nephropidae, Diogenidae, Paguridae) are paraphyletic, warranting further studies to evaluate their status. The present study ably demonstrates the utility of nuclear protein-coding genes in phylogenetic inference in decapods. The topologies obtained are robust and the two molecular markers are informative across a wide range of taxonomic levels. We propose that nuclear protein-coding genes should constitute core markers for future phylogenetic studies of decapods, especially for higher systematics.

Phylogeny of penaeoid shrimps (Decapoda: Penaeoidea) inferred from nuclear protein-coding genes

Penaeoidea is a diverse group of economically important marine shrimps. Attention to the evolutionary history of the penaeoids has been raised since studies using mitochondrial DNA markers and sperm ultrastructure contradict classification of the penaeoid families based on morphology and hence challenge the long standing taxonomy of this superfamily. In this study, DNA sequences of two nuclear protein-coding genes, phosphoenolpyruvate carboxykinase and sodium-potassium ATPase alpha-subunit, were determined from 37 penaeoid genera to reconstruct the evolutionary relationships and to estimate divergence ages of the penaeoid shrimps. Phylogenetic analyses using maximum likelihood and Bayesian approaches strongly support the monophyly of Solenoceridae, Aristeidae and Benthesicymidae, but find Sicyoniidae nested within Penaeidae, making this family paraphyletic. Penaeoidea comprises two lineages: the former three families in one while the latter two in another. The diversification of these lineages may be related to bathymetry. The penaeid-like lineage diversified in the Triassic, earlier than the aristeid-like lineage with an origin in the Jurassic. Taxonomic revisions within Penaeoidea are also proposed for further investigation. Due to the paraphyly of Penaeidae and the high genetic divergence among the three penaeid tribes of Burkenroad [Burkenroad, M.D., 1983. Natural classification of Dendrobranchiata, with a key to recent genera. In: Schram, F.R. (Ed.), Crustacean Issues I. Crustacean Phylogeny. A.A. Balkema, Rotterdam, pp. 279-290], these tribes should be treated as having the same taxonomic rank as Sicyoniidae, while the family ranking of Benthesicymidae has to be re-considered owing to the low genetic divergence between the benthesicymids and the aristeids.

MOLECULAR PHYLOGENETICS OF THE MITTEN CRAB SPECIES IN ERIOCHEIR, SENSU LATO (BRACHYURA: GRAPSIDAE)

Abstract Taxonomy of mitten crabs has been problematic and confusing. Eriocheir was considered to comprise four species (E. japonica, E. sinensis, E. recta, and E. leptognathus). However, recent taxonomic revision has recognized five species and three genera, Eriocheir being restricted to E. sinensis, E. japonica, and E. hepuensis, and the establishment of two genera for Neoeriocheir leptognathus and Platyeriocheir formosa. The present study analyzed the phylogeny of the species of Eriocheir, sensu lato, based on DNA sequence analysis of mitochondrial 16S rRNA, cytochrome c oxidase I, and the first internal transcribed spacer of nuclear rRNA. The results show that the three Eriocheir, sensu stricto, species are genetically similar, indicating that they have recently radiated. Eriocheir formosa is the sister taxon of these three species, with E. leptognathus the most distantly related taxon within the group. These results support the affinities of the mitten crabs, but the genetic divergence among the crabs provides no support for separating Eriocheir, s. l., to three different genera. We suggest to retain the apparently monophyletic mitten crabs in a single genus until more evidence is available.

Systematic status of the caridean families Gnathophyllidae Dana and Hymenoceridae Ortmann (Crustacea : Decapoda): a preliminary examination based on nuclear rDNA sequences

The systematic positions of the caridean families Gnathophyllidae and Hymenoceridae are inferred based on analyses of nuclear 18S rRNA and 28S rRNA genes. The phylogenetic trees based on 18S rRNA and 28S rRNA from selected species of one genus of the family Gnathophyllidae, two genera of the family Hymenoceridae, one genus of the family Anchistioididae, eight genera of the subfamily Pontoniinae and five genera of the subfamily Palaemoninae show a close relationship between Hymenoceridae, Gnathophyllidae and Pontoniinae, with the last group constituting a paraphyletic assemblage. This result concurs with the morphology of maxilla in the first zoea, but not the shape of the third maxilliped in adults, based on which Gnathophyllidae and Hymenoceridae are treated as families. Molecular analysis supports the similarities in larval morphology between Hymenoceridae, Gnathophyllidae and Pontoniinae and therefore draws into question the familial status of the former two groups.

The ‘giant phyllosoma’ are larval stages of Parribacus antarcticus (Decapoda : Scyllaridae)

Abstract. Early reports on larval distributions are frustratingly obscure due to ambiguous identification of plankton samples. A particularly striking case is posed by the so-called ‘giant phyllosoma’ which attain 80 mm in total length and are among the largest larvae known in marine invertebrates. Based on the supposition that these giant larvae are produced by local species, Philip Robertson (1968) assigned them to Parribacus. In the present study, 12 phyllosoma larvae collected in the Coral Sea and corresponding to intermediate stages VI to IX are described in detail. The identity of these freshly caught specimens was confirmed as belonging to Parribacus antarcticus (Lund, 1793) by using DNA barcoding methods. This new collection further allowed us to complete the larval series for the genus. The intermediate stage VI, which was missing in previous accounts, is described here for the first time. Besides the Coral Sea larvae, another five phyllosoma specimens previously deposited in UK and German museum collections are also described. Given that no useful DNA could be obtained from the old collection specimens, these larvae were identified as Parribacus sp. based on morphology only. Furthermore, a complete morphometric analysis of Parribacus larvae was undertaken including information from literature dating back to 1830. The first detailed description of all dactyli from a complete phyllosoma of the genus Parribacus is presented, with further comparison with those from other genera of Scyllaridae.

Verification of the cryptic species Penaeus pulchricaudatus in the commercially important kuruma shrimp P. japonicus (Decapoda : Penaeidae) using molecular taxonomy

Abstract. The kuruma shrimp Penaeus japonicus Bate, 1888 (Decapoda : Penaeidae) is economically important in the global shrimp market. It was regarded as the only species in the subgenus Marsupenaeus. However, our previous molecular analyses revealed two cryptic species (Forms I and II) in this species complex. In this study, we confirm the phylogenetic relatedness between the two cryptic species; revise their taxonomic status; and review their range distribution. The name Penaeus pulchricaudatus Stebbing, 1914 (with type-locality off the eastern coast of South Africa), previously considered as a junior synonym of P. japonicus, is fixed for Form II through a neotype selection. P. japonicus (Form I) is only confined to the East China Sea (including Japan, its type-locality) and the northern South China Sea. P. pulchricaudatus is widely distributed in the South China Sea, Australia, the Red Sea, the Mediterranean, and the western Indian Ocean. Phylogenetic analysis shows that P. japonicus is genetically homogeneous yet P. pulchricaudatus exhibits a strong phylogeographical structure. The Mediterranean stock of P. pulchricaudatus originated from the Red Sea population, supporting the Lessepsian migration hypothesis. The presence of two closely related cryptic species in the P. japonicus species complex provides important insights into fishery management and aquaculture development.

Feeding hermit crabs to shrimp broodstock increases their risk of WSSV infection.

White spot syndrome virus (WSSV) is a serious shrimp pathogen that has spread globally to all major shrimp farming areas, causing enormous economic losses. Here we investigate the role of hermit crabs in transmitting WSSV to Penaeus monodon brooders used in hatcheries in Vietnam. WSSV-free brooders became PCR-positive for WSSV within 2 to 14 d, and the source of infection was traced to hermit crabs being used as live feed. Challenging hermit crabs with WSSV confirmed their susceptibility to infection, but they remained tolerant to disease even at virus loads equivalent to those causing acute disease in shrimp. As PCR screening also suggests that WSSV infection occurs commonly in hermit crab populations in both Vietnam and Taiwan, their use as live feed for shrimp brooders is not recommended.