Methods for the analysis of developmental sequence data.

Heterochrony, evolutionary changes in developmental timing, can be studied either by examining changes in growth or changes in the sequence of developmental events. Developmental sequence data has the potential to address many important questions in the field of developmental evolution, but methodological challenges remain due to the biological and logical dependence of events in a ranked sequence. In the past 10 years, the study of sequence heterochrony has undergone a rebirth, with the creation of several new methods for the analysis of this type of data. These methods can be divided into two broad categories: phenetic comparisons between terminal taxa that strive to uncover integrations within the developmental sequences and putative shared sequence heterochronies, and phylogeny-based methods that derive ancestor-descendent sequence heterochronies and establish statements of sequence evolution. In this review, we will discuss the strengths and weaknesses of the methodologies that have been proposed to quantitatively examine developmental sequence data, and studies that have attempted to implement them in an evolutionary context.