Gavin Naylor PhD

Program Director, Florida Program for Shark Research

gnaylor@flmnh.ufl.edu · 352-273-1954

Research

I am an evolutionary biologist.

I am interested in why there are so many different forms of life on earth.

Simplistic evolutionary wisdom holds that organismal diversification is the result of a random walk through phenotypic space mediated by natural selection. In its purest form, any biological form is possible so long as it is coherently viable and can reproduce.

I hold a different view.

I suspect that self-organizational principles, not just chance and contingency, constrain how organisms can be built. These alternative perspectives have profound consequences for how we view the world. They impact what we (think we) can do in medicine, in agriculture, and how we view our place in the universe.

Characterizing Constraints

If constraints exist, what do they look like? And how can we find them? Maybe we could compare organisms that appear not to have diversified much over time with those that have.

About 425 million years ago the ancestral vertebrate lineage split into two. One branch yielded about 70,000 species of bony fishes, amphibians, mammals, and birds. The other yielded 1,250 species of sharks, skates, rays, and chimaeras. That’s a ~50-fold difference in species diversity. Hmm.

We are often told sharks are “prehistoric animals.” What does this mean? It means that we can go a long way back in the fossil record and find fossils that seem similar in form to modern sharks. We can’t do the same for birds because they have changed so much that we can’t recognize the bird ancestors from the same time periods — even though their ancestors must have been there. So, sharks are not any “older” than birds; they just haven’t changed as much.

So why haven’t sharks changed much over 425 million years? Is their subdued rate of diversification tied up with their slower rate of change? And how have they survived all of the environmental changes they have been exposed to over the past 425 million years?

These are the questions we are keen to understand in our group. We suspect the answers to these questions are all inter-related. They are the consequence of mechanisms that have both constrained their evolution and diversification and allowed them to deal with environmental change. Together with collaborators, we explore these questions using comparative anatomical, genomic, developmental, and paleontological data.

A central part of our work focuses on reconstructing the evolutionary history of the group — to give us a better sense of the patterns we are trying to explain. (Chondrichthyan Tree of Life website: sharksrays.org)