Development of multicellular organisms is characterized as a series of morphological events, whose temporal sequence, called as the developmental sequence, is well conserved in each individual species. In this study, we hypothesized that evolutionary changes in the sequence can be the basis for morphological diversifications, and examined the evolutionary dynamics of the developmental sequence in teleosts. Using the information from previous reports describing the development of 30 teleost species, we extracted the developmental sequences of 19 landmark events involving the formation of phylogenetically conserved body parts. Ancestral developmental sequences were then estimated by two different parsimony based methods. The phylogenetic comparisons of these sequences revealed that (1) the frequency of sequence changes differs among the events, (2) most of the sequence changes occurred as exchanges of temporally neighboring events, and (3) these changes in developmental sequences accumulate along the evolutionary time.

Figure: the rank changeability of individual developmental events (A) and the relationship between rank changes and divergent times (B) in teleost lineage estimated by the event-pairing method.