Animal evolution cannot be explained solely by the modification of preexisting forms. Many novel structures have been acquired since our ancestors became multicellular organisms. This structural diversity can be easily demonstrated by comparing human morphology with that of sponges or placozoans.

Evolution is defined as a change in the ratio of a heritable property within a group of organisms over the course of generations. Thus, novel features of organisms emerge in individuals through changes in the genetic code; subsequently, the property will (or will not) spread among populations. 

In our research group, we are trying to answer several evolutionary questions. How did the shell plate emerge in mollusc ancestors? What type of genetic evolution drove the process of splitting the shell plate into two plates in bivalve ancestors? 

Perhaps these evolutionary processes required the modification of more than one gene. If the modification of several genes was required, then how did organisms overcome intermediate evolutionary stages? To answer these questions, we are focusing on a phenomenon called developmental system drift. There may be several pathways by which organisms can develop a specific morphology; if this is true, then developmental processes can change without changing the final morphology.

Project 1: Evolution of shell morphology in mollusks

We are studying how mollusk shells were acquired through genetic rewriting, and how bivalves acquired two shells through genetic rewriting. Bivalves also newly acquired adductor muscles (muscles that close the shells). While the division of the shell into two parts and the acquisition of adductor muscles are functionally closely related (neither would be beneficial without the other), were there any points of connection in terms of developmental modifications or genetic rewriting?

Mollusks have hard tissues not only in the form of shells but also in the form of spines in some species. Among them, the chitons has both a shell and spines, and there is debate as to whether the first hard tissue acquired by mollusks was a shell or a spine. We are approaching this issue through research on the development of the hard tissues of chitons.

Project 2: Evolution of the unique body plan of cephalopods

Most mollusks undergo spiral cleavage and develop into trochophore larvae, but cephalopods have significantly altered their early development to acquire a unique body plan. By comparing the mechanisms of spiral cleavage development revealed in our research with those of cephalopods, we aim to clarify how the unique body plan of cephalopods evolved.

Project 3: Research on developmental system drift in animals with spiral cleavage

We are conducting research on developmental system drift using the early development of Spiralians. Animals with spiral cleavage include mollusks, annelids, and flatworms. One of their characteristics is that the developmental fate of each cleavage ball during the cleavage stage is well preserved across animal phyla. It is natural to assume that the mechanisms governing the developmental fate of blastomeres are also conserved. However, it has become clear that even in corresponding blastomeres, the genes active in the earliest stages are not necessarily the same. How can similar developmental fates be determined despite differences in the genes active upstream in the developmental cascade? We are seeking to elucidate the mechanisms underlying developmental system drift and its role in the evolution of development.

Project 4: Evolutionary developmental biology of the pentaradial symmetry characteristic of echinoderms

Echinoderms have acquired a unique five-fold radial symmetry. We are attempting to clarify the mechanism by which “five” is created during the developmental process, using starfish.

Project 5: Research on developmental system drift observed in echinoderms

Developmental system drift is also observed in the early developmental process of echinoderms. When examining the differentiation of mesoderm cells in sea urchins and starfish, it is known that completely different interactions of transcription factors are observed. If we can understand how the mechanisms for forming the same mesoderm have changed, we may be able to understand the changes in the developmental process that are linked to morphological evolution.

Additionally, we have discovered that there are individual differences in the mutual control relationships of developmental genes in sea urchins collected in the wild. In the wild, development must proceed under various environmental conditions, such as seawater temperature and food availability. We speculate that the observed individual differences in development may reflect the flexibility in adapting developmental processes to advance morphogenesis, and that this flexibility may also be involved in morphological evolution.

Looking back, before Darwin, individual differences in organisms were considered mere noise. Darwin argued that individual differences are the driving force of evolution. We believe that individual differences of development are also not mere noise.

Project 6: Phylogeny, taxonomy, biogeography, and conservation of reptiles

We conduct phylogenetic studies on Japanese and foreign reptiles, including descriptive taxonomy, based on morphological and molecular data. We also conduct field research on their biogeography and conservation.

Project 7: "Species" in science textbooks

In Japanese elementary and high school science textbooks, some different taxonomic statuses have been treated in the same manner, or only the names of species that do not correspond to each region have been included. We are conducting bibliometric studies focusing on textbooks to solve these problems.

For inquiries regarding our research, please contact us at the following address.(Please remove one “@” from the email addresses below before sending.)

Hiroshi Wada: ant09champ@@icloud.com

Yoshiaki Morino: morino.yoshiaki.ge@@u.tsukuba.ac.jp

Projects 6, 7:

Masanao Honda (honda.masanao.ge@@u.tsukuba.ac.jp)