Genetic diversity of Ascidians

polymorphism graph

Ascidians are highly polymorphic at the DNA level. Through the sequenced genomes of Ciona intestinalis and Ciona savignyi we see that the amount of genetic polymorphism within a single individual (1.2% in C. intestinalis and 4.6% in C. savignyi) can be larger than the amount of genetic variation between genera in vertebrate species. Nate Silva has been asking how widespread this elevated level of polymorphism is in Ascidians by examining polymorphism in different Ascidian species. To this end, abundance and genetics surveys are underway on local ascidian populations to quantify this level of genetic polymorphism and compare these levels between species. Since the majority of ascidian species have not been sequenced yet, a method which does not require prior sequence information (AFLP) is being used to generate molecular markers and compare these markers between individuals within a species. This gives one an idea of the polymorphism in that species. The figure shows the portion of markers which are shared by less than half of the individuals samples (blue), and the portion of markers which present in more than half the individuals. Species to the right of the graph, then, have more of the markers shared among the individuals and are therefore less polymorphic than the species on the left.