Article

Phylogeny of Tunicata inferred from molecular and morphological characters.

Department of Biological Sciences, University of Arkansas, 019 West Avenue Annex, Fayetteville 72701, USA.
Molecular Phylogenetics and Evolution (Impact Factor: 4.02). 01/2003; 25(3):408-28. DOI: 10.1016/S1055-7903(02)00305-6
Source: PubMed

ABSTRACT The phylogeny of the Tunicata was reconstructed using molecular and morphological characters. Mitochondrial cytochrome oxidase I (cox1) and 18S rDNA sequences were obtained for 14 and 4 tunicate species, respectively. 18S rDNA sequences were aligned with gene sequences obtained from GenBank of 57 tunicates, a cephalochordate, and a selachian craniate. Cox1 sequences were aligned with the sequence of two ascidians and a cephalochordate obtained from GenBank. Traditional, morphological, life history, and biochemical characters of larval and adult stages were compiled from the literature and analyzed cladistically. Separate and simultaneous parsimony analyses of molecular and morphological data were carried out. Aplousobranch ascidians from three different families were included in a molecular phylogenetic analysis for the first time. Analysis of the morphological, life history, and biochemical characters results in a highly unresolved tree. Aplousobranchiata form a strongly supported monophylum in the analysis of the 18S rDNA data, the morphological data, and the combined data set. Cionidae is not included in the Aplousobranchiata but nests within the Phlebobranchiata. Appendicularia (=Larvacea) nest within the 'Ascidiacea' as the sister taxon of Aplousobranchiata in the parsimony analysis of the 18S rDNA data and the combined analysis. A potential morphological synapomorphy of Aplousobranchiata plus Appendicularia is the horizontal orientation of the larval tail. In the 18S rDNA and the combined analysis, Thaliacea is included in the 'Ascidiacea' as the sister group to Phlebobranchiata. Pyrosomatida is found to be the sister taxon to the Salpidae in analyses of 18S rDNA and combined data, whereas the analysis of the morphological data recovers a sister group relationship between Doliolidae and Salpidae. Results of cox1 analyses are incongruent with both the 18S rDNA and the morphological phylogenies. Cox1 sequences may evolve too rapidly to resolve relationships of higher tunicate taxa. However, the cox1 data may be useful at lower taxonomic levels.

0 Followers
 · 
179 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Identification of marine invertebrate larvae using morphological characters is laborious and complicated by phenotypic plas-ticity. Balanus amphitrite is a dominant barnacle, important in the context of intertidal ecology and biofouling of manmade structures. Morphological identification of barnacle larval forms in a mixed population is difficult because of their intricacy and similarity in size, shape and developmental stages. We report the development and application of a nucleic acid-based Polymerase Chain Reaction (PCR) method for the specific identification of the barnacle, B. amphitrite, from the heteroge-neous zooplankton sample. This method is reliable and accurate thereby overcoming taxonomic ambiguity. Sequence align-ment of the 18S rRNA gene region of selected species of barnacles allowed the design of B. amphitrite-specific PCR primers. Assay specificity was evaluated by screening DNA obtained from selected species of barnacles. The oligonucleotide primers used in the study flanked a 1600 bp region within the 18S rRNA gene. The primer is specific and can detect as few as 10 indi-viduals of B. amphitrite larvae spiked in a background of 186 mg of zooplankton. This technique facilitates accurate iden-tification and the primer can be used as a marker for enumeration of B. amphitrite larvae in the plankton. Larval ecology studies help in understanding the population dynamics, community patterns, ecosystem structure and bio-diversity of native and invasive species (Webb et al., 2006). Identification of marine invertebrate larvae is a tedious, labour intensive task by expert taxonomists. Traditionally, planktonic larval identification is difficult because of larval intricacy and similarity in size, shape and developmental stages (Chanley & Andrews, 1971; Branscomb & Vedder, 1982; Shanks, 1986; Nichols & Black, 1994). Due to their small size, shape and similar developmental stages, it is diffi-cult to identify these larvae morphologically, although they play a pivotal role in taxonomic identification (Levin, 1990). Sometimes larval identification becomes extremely difficult due to phenotypic plasticity (Hebert, 2002). Molecular techniques have the potential to accurately iden-tify the organism to its species level, thereby overcoming taxo-nomic ambiguity. Identification and quantification of marine invertebrate larvae is far easier using molecular techniques (Baldwin et al., 1996; Bilodeau et al., 1999; Makinster et al., 1999; Morgan & Rogers, 2001; Deagle et al., 2003; Larsen et al., 2005; Vadopalas et al., 2006; Jones et al., 2008; Chen et al., 2013). Polymerase Chain Reaction (PCR) along with sequencing has led to accurate identification of any organism to its species level. Appropriate use of specific primers can facilitate rapid, sensitive and accurate detection of any individ-ual species in a population. Some molecular techniques which assist in identification or characterization of organisms are DNA barcoding (Hebert et al., 2003a, b); Random amplified polymorphic DNA (Coffroth & Mulawka, 1995); multiplex PCR (Hare et al., 2000); Middle repetitive sequence analysis (MaKinster et al., 1999); Amplified fragment length poly-morphism (Bucklin, 2000; Rogers, 2001); Restriction fragment length polymorphism and Single strand conformation poly-morphism analysis (Hillis et al., 1996). Oligonucleotide probes used for specific detection of individual larvae in a mixed population are either concise to family level (Bell & Grassle, 1998), genus level (Frischer et al., 2000) or species level (Frischer et al., 2000; Hare et al., 2000). Molecular tools with respect to PCR-based approaches are more reliable and frequently used in larval identification (Hare et al., 2000; Wood et al., 2003; Webb et al., 2006; Chen et al., 2013). Barnacles are of major concern in biofouling studies around the world. They have drawn the attention of many investigators in marine plankton ecology owing to their easy accessibility on the rocky intertidal regions and also because some species are dominant in marine fouling (Strathmann et al., Thiyagarajan et al., 1997a, b). Barnacles possess both a plank-totrophic and a lecithotropic larval stage, which settle and metamorphose on hard substratum resulting in macrofouling. Morphological identification of barnacle larval forms in a population is difficult because of their intricacy and similarity
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Comparison of features of the cell lineages and fate maps of early embryos between related species is useful in inferring developmental mechanisms and amenable to evolutionary considerations. We present cleavage patterns, cell lineage trees, and fate maps of ascidian and appendicularian embryos side by side to facilitate comparison. This revealed a number of significant differences in cleavage patterns and cell lineage trees, whereas the fate maps were found to be conserved. This fate map similarity can be extended to vertebrates, thus representing the fate map characteristics of chordates. Cleavage patterns and cell lineages may have been modified during evolution without any drastic changes in fate maps. Selective pressures that constrain developmental mechanisms at early embryonic stages might not be so strong as long as embryos are still able to generate a chordate-type fate map. Aquatic chordates share similar fate maps and morphogenetic movements during gastrulation and neurulation, eventually developing into tadpole-shaped larvae. As swimming by tail beats, and not by cilia, is advantageous, selective pressure may maintain the basic elements of the tadpole shape. We also discuss the evolutionary origin of the vertebrate neural crest and the embryonic origin of the appendicularian heart to illustrate the usefulness of cell lineage data. From an evolutionary standpoint, cell lineages behave like other characteristics such as morphology or protein sequences. Both novel and primitive features are present in extant organisms, and it is of interest to identify the relative degree of evolutionary conservation as well as the level at which homology is inferred.
    ZOOLOGICAL SCIENCE 10/2014; 31(10):645-652. DOI:10.2108/zs140117 · 0.88 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Fifty-three algal cultures were isolated from freshwater lakes in Hainan, China. Four microalgal isolates were selected because they could be successfully cultivated at high density and demostrated a strong fluorescence after being stained with nile red. These cultures were identified as strains of Chlorella sp. C11, Chlamydomonas reinhardtii C22, Monoraphidium dybowskii C29, and Chlorella sp. HK12 through microscopic and 18S rDNA analysis. Under similar conditions, the lipid productivity of Chlorella sp. C11, Chla. reinhardtii C22, M. dybowskii C29 , and Chlorella sp. HK12 were 1.88, 2.79, 2.00, and 3.25 g L -1 , respectively. Chla. reinhardtii C22 yielded a higher lipid content (51%), with a lower biomass concentration (5.47 g dwt L -1). Chlorella sp. HK12 reached a growth rate of 0.88 day -1 at OD540nm and yielded a biomass concentration of 7.56 g dwt L -1 , with a high lipid content of 43%. Gas chromatography/ mass spectrometry analysis indicated that lipid fraction mainly comprises hydrocarbons including palmitic acid, stearic acid, oleic acid, linoleic acid, and linolenic acids. Our results suggest that Chlorella sp. HK12 is a promising species for biodiesel production, because of its high lipid productivity and a relatively high content of oleic acid.

Full-text (2 Sources)

Download
425 Downloads
Available from
Jun 5, 2014