Phylogenetic Analysis Of Arcoidea And Genetic Diversity Of Different Populations Of Tegillarca Granosa (Linnaeus,1758) Along Chinese Coasts

The superfamily Arcoidea (Lamarck,1809) belongs to Arcoida, Pteriomorphia,Bivalvia and is supposed to encompass over300species globally, with only one freshwater taxon Scaphula (Benson,1834), which inhabits fully freshwaters in South-EastAsia. Arcoids are primarily components of tropical shallow waters and warmtemperate seas, and have their maximum species richness in the Indo-West Pacific.There are71species in total pertaining to22genera and5families off China coasts.Many arcoids are famous for their delicious flavor and regarded as tonic products.Scapharca kagoshimensis (Tokunaga,1906), Tegillarca granosa (Linnaeus,1758),Scapharca broughtonii (Schrenck,1867), Estellacar olivacea (Reeve,1844), Barbatiavirescens (Wood,1828) and Anadara antiquata (Linnaeus,1758) are typical marineproducts in Chinese aquaculture. Despite their notable importance in the economics,arcoids lack research especially on phylogeny within Arcoidea.We obtained the CO Ⅰ,12S and28S gene sequences from161samplesbelonging to34species, and constructed neighbor-joining tree (NJ), BEAST tree andBayesian tree (BI) with Pinctada fucata martensii (Dunker,1872) as outgroup. Wefound out that:(1) At the family level, only the monophyly of Noetiidae andsubfamily Anadarinae have strong support in almost all trees, while that ofGlycymerididae received supports only in some of the phylogenetic trees. As wasshown in all trees, Noetiidae, Cucullaeidae and Glycymerididae all belonged toArcoidea and arose from Arcidae. We suggest that current taxonomy of Arcoideadeserve more discussion.(2) At the genus level, the monophyly of Tegillarca andArcopsis was supported steadily. Although Bentharca showed close relationship withAcar, we couldn’t come to the conclusion that they are synonym to each other orshould be combined.(3) Scapharca india (Gmelin,1791) formed a subclade withAnadara antiquata (Linnaeus,1758) instead of the rest of Scapharca, which led to theparaphyly of Scapharca. So we claim that Scapharca india to be a member ofAnadara rather than Scapharca, and it therefore may be renamed as Anadara india (Gmelin,1791).(4) Nipponarca bistrigata (Dunker,1866) showed close relationshipwith subfamily Anadarinae in many trees. However, its morphological charactersshowed similarity to both Anadarinae and Arcinae. Take all these into account, weinsisit Nipponarca to be an independent genus rather than a subgenus in Barbatia,though whether it should be attributed to Anadarinae or Arcinae is still underdiscussion.(5) From the molecular results of Barbatia virescens (Reeve,1844) ofdifferent morphological characters, we reach the conclusion that Barbatia virescensshowed obvious morphological heterogeneity.A new species, Barbatia hainanensis sp. nov., was found during2011to2013from Li’an, Houhai and Nanyan Harbor in Hainan. This new species was defined as amember of Barbatia (Gray,1842) for these characteristics: Shell small, Inequivalve,with the left valve larger and rougher than the right one. Outer surface ornamentedwith about60fine radial ribs, which become stronger anteriorly and rougherposteriorly. These ribs run across concentric threads, forming irregular nodules. Someribs split or bear secondary ribs in the interspaces near the ventral margin. Shellgreyish white, with thin light brown periostracum. The later falls easily, with flakyremains near the ventral margin. Shells of B. cometa and B. hainanensis are similar inshape, while The L/H and L/W ratios of B. hainanensis are both smaller than those ofB. cometa, resulting in the shells of B. hainanensis showing a more inflated shapethan those of B. cometa.We obtained the COⅠ gene sequence of B.hainanensis and constructedphylogenetic trees with11other sequences from the Genbank, Cucullaea labiosagranulosa Jonas,1846being the outgroup. The phylogenetic trees constructed usingthe NJ, MP and BI methods were highly congruent, with almost identical topologies.Trisidos kiyonoi (Kuroda,1930) nested within Barbatia, which was obviouslyparaphyletic. Trisidos kiyonoi and the tribe comprising B. hainanensis, B. parva, B.virescens hap18and B.virescens hap19formed a subclade, which was a sister taxon toB. barbata and B. fusca. Morphological analysis and molecular results suggested B.hainanensis to be a transitional taxon between Barbatia and Trisidos.Total of62Tegillarca granosa samples were collected from Haikou, Hainan, Fangchenggang, Beihai, Zhanjiang, Zhangzhou, Rongcheng and Weihai along China’scoastal waters.593bp nucleotide sequences of mitochondrial COⅠ gene fragmentsof Tegillarca granosa were obtained. The results revealed103variable nucleotidepositions and26haplotypes in the seven populations. The haplotype diversity (Hd)was0.834, the nucleotide diversity (Pi)0.01665, and the average nucleotidedifference (K)9.85772. Results showed high genetic diversity and genetic distanceswithin populations, which suggested that genetic diversity and Fst within Tegillarcagranosa populations along China’s coastal waters increased from the north to thesouth generally. The NJ tree and UPGMA tree based on the sequences of the26haplotypes and the UPGMA tree based on genetic distances showed close relationshipbetween Rongcheng and Weihai, and later the two populations formed a clade withZhangzhou population, while the southern groups didn’t form an independent clade.