Natural Variation of Model Mutant Phenotypes in Ciona intestinalis

BACKGROUND: The study of ascidians (Chordata, Tunicata) has made a considerable contribution to our understanding of the origin and evolution of basal chordates. To provide further information to support forward genetics in Ciona intestinalis, we used a combination of natural variation and neutral population genetics as an approach for the systematic identification of new mutations. In addition to the significance of developmental variation for phenotype-driven studies, this approach can encompass important implications in evolutionary and population biology. METHODOLOGY/PRINCIPAL FINDINGS: Here, we report a preliminary survey for naturally occurring mutations in three geographically interconnected populations of C. intestinalis. The influence of historical, geographical and environmental factors on the distribution of abnormal phenotypes was assessed by means of 12 microsatellites. We identified 37 possible mutant loci with stereotyped defects in embryonic development that segregate in a way typical of recessive alleles. Local populations were found to differ in genetic organization and frequency distribution of phenotypic classes. CONCLUSIONS/SIGNIFICANCE: Natural genetic polymorphism of C. intestinalis constitutes a valuable source of phenotypes for studying embryonic development in ascidians. Correlating genetic structure and the occurrence of abnormal phenotypes is a crucial focus for understanding the selective forces that shape natural finite populations, and may provide insights of great importance into the evolutionary mechanisms that generate animal diversity

The genome of the sea urchin Strongylocentrotus purpuratus

We report the sequence and analysis of the 814-megabase genome of the sea urchin Strongylocentrotus purpuratus, a model for developmental and systems biology. The sequencing strategy combined whole-genome shotgun and bacterial artificial chromosome (BAC) sequences. This use of BAC clones, aided by a pooling strategy, overcame difficulties associated with high heterozygosity of the genome. The genome encodes about 23,300 genes, including many previously thought to be vertebrate innovations or known only outside the deuterostomes. This echinoderm genome provides an evolutionary outgroup for the chordates and yields insights into the evolution of deuterostomes

THE LARGEST EARTHQUAKES OF THE APENNINES, SOUTHERN ITALY

Contouring the intensity data for the largest earthquakes recorded in Southern Italy yields areas delineated by the M.C.S. X, IX, VIII isoseisms that are markedly elongated along the axial direction of the Apennine Chain. To evaluate the attenuation of intensity with distance, four regression curves have been calculated using empirical relations of the form: I (R) -Io = a + bR + clogR in accordance with Chandra's procedure [9]. The results are compared with the attenuation relation used for the « shake ability » map of Italy. New mag¬nitudes for historical earthquakes have been calculated and an earthquake fault map is proposed. In addition, a comparison has been made between recent and historical earthquakes in some areas, including those of different magnitude, in an attempt to quantify the energies associated with the histo¬rical events