Scientists Uncover the Evolutionary Secret Behind the Different Life Cycles of Animals

The worm that the researchers studied and whose genome they sequenced. It is a segmented worm that is abundant on the coasts of the UK and Europe. It lives inside a tube that it secretes buried in the sand. Credit: Chema Martin.

For more than 100 years, biologists have wondered why animals exhibit different types of life cycles. Some species, such as humans and most vertebrates, develop directly into a fully formed but smaller version of an adult. In contrast, many other animals give rise to wonderfully diverse intermediate forms which we call larvae, which then metamorphose into adults.

Yet the researchers’ understanding of why the larvae exist and where they came from was limited. More importantly, large-scale comparative studies addressing this question had not previously used modern techniques based on sequencing an animal’s genetic information – the genome – to find out how the organism uses this information during his growth. So far.

In a study by a team from Queen Mary University of London (QMUL), published in the journal Natureresearchers discover for the first time the mechanism that probably explains how embryos form either a larva or a miniature version of the adult.

In their paper, they prove that the timing of activation of key genes involved in embryogenesis – the transformation of a fertilized egg into an organism – correlates with the presence or absence of a larval stage and with the fact that the larva feeds on its environment or relies on food that the mother has deposited in the egg.

Francisco M. Martín-Zamora, Ph.D. candidate at QMUL and co-first author of the study, said, “It’s impressive how evolution has shaped the way animal embryos” tell time. ” to activate important groups of genes earlier or later in development. Suppose that a larval stage is no longer essential for your survival. In this case, it could be evolutionarily advantageous, for example example, to activate the genes to form the trunk earlier and develop directly into an adult instead.

This new study used cutting-edge approaches to decode the genetic information, activity, and regulation of three species of marine invertebrate worms called annelids. They combined them with public datasets of other species in a large-scale study involving more than 600 datasets of more than 60 species separated by more than 500 million years of evolution.

“It is only by combining laboratory-generated experimental datasets and systematic computational analyzes that we have been able to unravel this new undiscovered biology,” said Dr. Ferdinand Marlétaz, one of the main collaborators of the study at University College London.

“While the techniques have been around for a few years, no team has used them for this purpose. The datasets we have generated and the methodologies we have developed will be extremely powerful resources for other researchers,” he said. Dr. Yan Liang, postdoctoral researcher of QMUL. and co-first author of the book.

Dr. Chema Martín-Durán, the lead author of this research, said “Developmental biology largely focuses on mice, flies, and other well-established species that we know of as model organisms. Our study demonstrates that the fascinating biology of not-often-overlooked organisms—the model species—is essential to understanding how animal development works and how it evolved.”

The genes involved in the formation of the trunk – the region of the body that follows the head and extends to the tail – are paramount. Some species will form virtually trunkless larvae, called “head larvae”, and may have been present as far back as the ancestor of all headed and tailed animals. Direct development and the formation of a small adult directly from embryogenesis would have evolved later in many groups of animals, such as us and most vertebrates, because the genes to form the trunk are activated earlier in life. embryogenesis and larval traits are gradually lost.

“We hope that other researchers in the field will continue to study the exciting subject of the evolution of animal life cycles and provide further evidence for the hypothesis we have put forward,” said Dr Andreas Hejnol, professor at the Friedrich-Schiller University of Jena. , Germany, and collaborator of the team.

More information:
José Martín-Durán, the functional genomics of annelids reveals the origins of bilateral life cycles, Nature (2023). DOI: 10.1038/s41586-022-05636-7.

Provided by Queen Mary, University of London

Quote: Scientists Discover Evolutionary Secret Behind Different Animal Life Cycles (2023, Jan 25) Retrieved Jan 25, 2023 from

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