Evolution of OTP-independent larval skeleton patterning in the direct-developing sea urchin, Heliocidaris erythrogramma.

Heliocidaris erythrogramma is a direct-developing sea urchin that has evolved a modified ontogeny, a reduced larval skeleton, and accelerated development of the adult skeleton. The Orthopedia gene (Otp) encodes a homeodomain transcription factor crucial in patterning the larval skeleton of indirect-developing sea urchins. We compare the role of Otp in larvae of the indirect-developing sea urchin Heliocidaris tuberculata and its direct-developing congener H.

Regulatory punctuated equilibrium and convergence in the evolution of developmental pathways in direct-developing sea urchins.

We made hybrid crosses between closely and distantly related sea urchin species to test two hypotheses about the evolution of gene regulatory systems in the evolution of ontogenetic pathways and larval form. The first hypothesis is that gene regulatory systems governing development evolve in a punctuational manner during periods of rapid morphological evolution but are relatively stable over long periods of slow morphological evolution. We compared hybrids between direct and indirect developers from closely and distantly related families.