INVESTIGADORES
CATALANO Santiago Andres
congresos y reuniones científicas
Título:
New methods for the analysis of morpho-geometric data in phylogenetics.
Autor/es:
CATALANO, SA; GOLOBOFF, PA
Lugar:
Quilmes
Reunión:
Congreso; Congreso Argentino de Bioinformática y Biología Computacional; 2010
Institución organizadora:
Asociación Argentina de Bioinformática y Biología Computacional
Resumen:
Most current methods to quantitatively analyze biological shapes are based on the representation of shape as a group of landmarks (i.e. discrete anatomical loci that can be recognized as ‘‘the same’’ in all specimens under study). A change in the position of one or more landmarks between two configurations is interpreted as a change in shape. Previous attempts to use landmark data in a phylogenetic framework failed because those just tried to accommodate the morpho-geometric data to existing phylogenetic algorithms. Here we describe a new approach to assign landmark configurations to internal nodes of a phylogenetic tree, using as optimality criterion the minimization of the sum of landmark displacements along the tree. For a tree with only three leaves, the optimal position in the inner node for a given landmark is coincident with the Fermat point and can be exactly calculated. However, there is no exact solution for trees with four or more leaves. Consequently, we developed a heuristic approach with a first approximation where only a subset of the possible positions (arranged as a grid) is considered, followed by successive refinements where the space of possible solutions is restricted to the area surrounding the optimal state found in the previous cycle. Finally, the tree is traversed and the assignment for each internal node is improved by calculating the Fermat point based on the current positions of the ancestor and the descendants. A related problem is how to superimpose (match) a group of shapes in order to infer the changes that occurred between them. Here we present a method to produce multiple alignments of landmark configurations using a tree as guide and the minimization of the landmark displacements as optimality criterion. The approach can be considered an extension of the method described above for those cases where terminals are allowed to rotate and translate.