SPASOS 1.1: a program for the inference of ancestral shape ontogenies.

We recently published a method to infer ancestral landmark-based shape ontogenies that takes into account the possible existence of changes in developmental timing. Here we describe SPASOS, a software to perform that analysis. SPASOS is an open-source Windows program written in C. Input data include landmark coordinates for each specimen -with the corresponding information about developmental timing- and a phylogenetic tree showing the relationships among the species sampled. As output, the program produces image files for an easy visualization of the results and data files useful for post-processing. The program incorporates an interpolating function, based on weighting moving averages, which allows analysis of data with scarce information along the ontogenetic trajectory. An empirical evaluation of this function showed its suitability to fill in incomplete ontogenetic trajectories. Finally, we present the results of a reanalysis in SPASOS of a published dataset, where changes in developmental timing were originally inferred by considering PCA scores as shape variables. Both approaches retrieved the same four largest changes in developmental timing, but differed in the ancestral shapes inferred.

PASOS: a method for the phylogenetic analysis of shape ontogenies.

We present a novel phylogenetic approach to infer ancestral ontogenies of shape characters described as landmark configurations. The method is rooted in previously published theoretical developments to analyse landmark data in a phylogenetic context with parsimony as the optimality criterion, in this case using the minimization of differences in landmark position to define not only ancestral shapes but also the changes in developmental timing between ancestor-descendant shape ontogenies. Evolutionary changes along the tree represent changes in relative developmental timing between ontogenetic trajectories (possible heterochronic events) and changes in shape within each stage. The method requires the user to determine the shape of the specimens between two standard events, for instance birth and onset of sexual maturity. Once the ontogenetic trajectory is discretized into a series of consecutive stages, the method enables the user to identify changes in developmental timing associated with changes in the offset and/or onset of the shape ontogenetic trajectories. The method is implemented in a C language program called SPASOS. The analysis of two empirical examples (anurans and felids) using this novel method yielded results in agreement with previous hypotheses about shape evolution in these groups based on non-phylogenetic analyses.