Amphioxus against a black background

Reconstructing ancestors: insights from the ocean

Giacomo Gattoni, PhD Student, writes:

When we look at the natural world we are often in awe at the richness and diversity of life forms that we can observe. As an undergraduate student, I became fascinated by evolution, the process through which this diversity originated during the history of life. I am particularly interested in reconstructing ancestors of modern animals, organisms that lived in the past and from which we descended.

One of the consequences of evolution is that each one of us, and every organism alive today, is the result of an unbroken line of ancestors that stretches back to the origin of life. This implies that reconstructing what our ancestors looked like means retracing our history and how we have obtained our peculiar traits and abilities.

When we find structures in different animals that are similar in the way they look and develop, we can often say that they derive from a common ancestor that also possessed them. Using this approach we can study modern animals to piece together the identikit (an image created by piecing together features) of animals that lived tens or hundreds of millions of years ago.

As life evolved and diversified in the sea through most of its history, it is perhaps not surprising that my interest led me to focus on marine animals.

Silhouettes of a human and a starfish showing their lines of symmetry using coloured bands

During my Master’s Degree at the University of Milan I studied the development of feather stars. These delicate and colorful animals are part of a group of marine invertebrates called echinoderms, which also includes starfish and sea urchins. Echinoderms are unique in having their body arranged in five symmetrical rays around a central axis, with most organs repeated in each ray.

It is still a mystery how this strange group of animals evolved its shape, but we know that their ancestors had a left and a right side of the body just like us. We can still see this organization in the larvae of today’s echinoderms: only when they become adults they take the five-rays form.

Comparing the development of feather stars with that of starfish and sea urchins can help us understand the origin of one of the most enigmatic groups of animals alive today.

As I moved to the Department of Zoology for a PhD funded by the Whitten Studentship, I also moved the focus of my research closer to us. One of the questions that have always intrigued me the most is the origin of our brain, which has often been described as the most complex object in the universe. The brain is the source of many of the abilities that make us humans, like thinking, talking and imagining.

How did this prodigiously complex structure evolve from our distant ancestors? When we look at other vertebrates (animals with a backbone) we can see that they too have a similar brain, although usually smaller. But where did that come from?

To answer this question I am studying a little marine animal called amphioxus, in the lab of Dr Elia Benito-Gutiérrez. Amphioxus looks like a fish with no fins and a sharp, iridescent body. The name literally means “pointed at both ends”.

Freshly collected amphioxus ready to be sorted into their new home in the specialized facility at the Department of Zoology.

It lives buried in the sand and is one of the invertebrates most closely related to us. As such, it is in a unique position to help us understand our origins.

Amphioxus with half of its body out of the sand. Showing mouth parts

The European amphioxus Branchiostoma lanceolatum spends most of its time buried in the sand, sticking out its head to filter food from the seawater. Just like a fish it can also swim in the water and even through the sand.

By studying how the tiny brain of amphioxus develop, and comparing it with our own brain, we can reconstruct one of the earliest steps that, from an ancestor that lived more than 550 million years ago, ultimately led to brains that are capable of asking all of these questions and understand their own history.

You can learn more about amphioxus and the research in our lab on our website Amphispace and our lab twitter page @eBGLab, and you can find me on twitter as @gattoni_giacomo

Header image: Adult of the European amphioxus Branchiostoma lanceolatum

Discover more about amphioxus from Dr Elia Benito-Gutiérrez in her research story “Not a fish but the making of a fish”

Hear Giacomo Gattoni talk about echinoderms in his Portals to the World interview.

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