David Adler Gold.com

The Origins and Evolution of Animal Multicellularity

Paleobiology: Combining Genomes and Fossils to Study Animal Origins

When did animal life first appear? What did these early animals look like? What environmental changes allowed for the evolution and radiation of animal life?

The early fossil record is full of extinct life forms that might be animals. For example, see the picture of Dickinsonia to the left. Unfortunately, scientists have had a hard time reaching consensus about what these fossils are, partially because they are so simple. In my research I study the fossil record using phylogenetic tools, meaning I build trees that represent the evolutionary relationships of between animals. These trees are made by comparing the DNA between species to determine how closely related they are to each other. A simple animal tree (phylogeny) is presented below:

Animal Phylogney

I map genetic and physical traits onto these trees to study how animals have evolved over time. This work helps clarify what types of life forms ancient fossils could or could not represent.

For some relevant publications, check out these papers in the Reprints section:

Gold D.A., Grabenstatter J., de Mendoza A., Riesgo A., Ruiz-Trillo I., and Summons R.E. (2016) Sterol and genomic analyses validate the sponge biomarker hypothesis. Proceedings of the National Academy of Sciences of the United States of America. 113(10 ): 2684–2689.

Gold D.A., Gehling J.G., Runnegar B., and Jacobs D.K. (2015) Ancestral state reconstruction of ontogeny supports a bilaterian affinity for DickinsoniaEvolution and Development. 17(6): 315-397.

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Developmental Biology: Cell Differentiation and Tissue Regeneration Across Animal Life

It is common knowledge that many animals can regenerate lost body parts. Some lizards can regrow lost tails; earthworms can be cut in two, with each piece regenerating its missing half. Surprisingly, no clear pattern seems to separate the species that can regenerate lost tissues from those that cannot. Why can some flatworms regrow a lost head when other, closely related flatworms cannot? Why can some salamanders regrow lost legs, but humans can’t?

I think that the answer is related–in part–to how cells become “committed” during development, and their potential to function as stem cells to rebuild lost body parts. I use phylogenetic tools (as described earlier) to study how cell differentiation has evolved in different groups of animals. Additionally, I study the moon jellyfish Aurelia as a model organism in this research. Although Aurelia is a simple animal, it has a complex life cycle, with some stages capable of unlimited regeneration, while other stages have much more limited capabilities. Aurelia also appears to lack stem cells (as their classically defined), which might be an ancient trait it shares with corals, sea anemones, and sea sponges. This work could help explain why some animals can regenerate tissue better than others, and has broad implications to evolutionary medicine.

For relevant publications, check out these papers in the Reprints section:

Gold D.A., Gates R.D., Jacobs D.K. (2014) The early expansion and evolutionary dynamics of POU class genes. Molecular Biology and Evolution. 31(12):3136-3147.

Gold D.A., and Jacobs D.K. (2013) Stem cell dynamics in Cnidaria: are there unifying principles? Development Genes and Evolution. 223(1-2):53-66.

Takashima S., Gold D., and Hartenstein V. (2013) Stem cells and lineages of the intestine: a developmental and evolutionary perspective. Development Genes and Evolution. 223(1-2):85-102.

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