Something for nothing? Reconstruction of ancestral character states in asterinid sea star development.

Traits from early development mapped onto phylogenetic trees can potentially offer insight into the evolutionary history of development by inferring the states of those characters among ancestors at nodes in the phylogeny. A key and often-overlooked aspect of such mapping is the underlying model of character evolution. Without a well-supported and realistic model ("nothing"), character mapping of ancestral traits onto phylogenetic trees might often return results ("something") that lack a sound basis. Here we reconsider a challenging case study in this area of evolutionary developmental biology: the inference of ancestral states for ecological and morphological characters in the reproduction and larval development of asterinid sea stars. We apply improved analytical methods to an expanded set of asterinid phylogenetic data and developmental character states. This analysis shows that the new methods might generally offer some independent insight into choice of a model of character evolution, but that in the specific case of asterinid sea stars the quantitative features of the model (especially the relative probabilities of different directions of change) have an important effect on the results. We suggest caution in applying ancestral state reconstructions in the absence of an independently corroborated model of character evolution, and highlight the need for such modeling in evolutionary developmental biology.

Complete mitochondrial genome sequences for Crown-of-thorns starfish Acanthaster planci and Acanthaster brevispinus.

BACKGROUND: The crown-of-thorns starfish, Acanthaster planci (L.), has been blamed for coral mortality in a large number of coral reef systems situated in the Indo-Pacific region. Because of its high fecundity and the long duration of the pelagic larval stage, the mechanism of outbreaks may be related to its meta-population dynamics, which should be examined by larval sampling and population genetic analysis. However, A. planci larvae have undistinguished morphological features compared with other asteroid larvae, hence it has been difficult to discriminate A. planci larvae in plankton samples without species-specific markers. Also, no tools are available to reveal the dispersal pathway of A. planci larvae. Therefore the development of highly polymorphic genetic markers has the potential to overcome these difficulties. To obtain genomic information for these purposes, the complete nucleotide sequences of the mitochondrial genome of A. planci and its putative sibling species, A. brevispinus were determined and their characteristics discussed. RESULTS: The complete mtDNA of A. planci and A. brevispinus are 16,234 bp and 16,254 bp in size, respectively. These values fall within the length variation range reported for other metazoan mitochondrial genomes. They contain 13 proteins, 2 rRNA, and 22 tRNA genes and the putative control region in the same order as the asteroid, Asterina pectinifera. The A + T contents of A. planci and A. brevispinus on their L strands that encode the majority of protein-coding genes are 56.3% and 56.4% respectively and are lower than that of A. pectinifera (61.2%). The percent similarity of nucleotide sequences between A. planci and A. brevispinus is found to be highest in the CO2 and CO3 regions (both 90.6%) and lowest in ND2 gene (84.2%) among the 13 protein-coding genes. In the deduced putative amino acid sequences, CO1 is highly conserved (99.2%), and ATP8 apparently evolves faster any of the other protein-coding gene (85.2%). CONCLUSION: The gene arrangement, base composition, codon usage and tRNA structure of A. planci are similar to those of A. brevispinus. However, there are significant variations between A. planci and A. brevispinus. Complete mtDNA sequences are useful for the study of phylogeny, larval detection and population genetics.