1. Evolutionary Biology

Study suggests later evolutionary shift to blood-cell production in bones

The evolutionary shift to producing blood cells in bone marrow occurred after creatures began moving onto land – later than previously thought.
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Red-blood-cell production in bone marrow evolved after backboned creatures made the shift from living in water to land, a study published today in eLife suggests.

3D models of the inner architecture of bones from a lobe-finned fish and an early four-legged animal. Image credit: Estefa et al. (CC BY 4.0)

Fish make red blood cells in their liver and kidney, while most terrestrial creatures with backbones produce these cells in their bone marrow. The study provides new information about when these terrestrial creatures first began producing blood cells in bone marrow and may lead to new insights about why this occurred.

“The migration of blood-cell production to bone marrow was believed to have occurred before the first creatures left water to move on land more than 360 million years ago,” explains lead author Jordi Estefa, who worked on the study as a PhD student at the Department of Organismal Biology, Evolution and Development, Uppsala University, Sweden. “Some scientists speculate that the shift was necessary to protect blood-cell-producing tissue from exposure to temperature extremes or harmful ultraviolet radiation on land. But it hasn’t been possible to prove this without fossil evidence.”

Using the powerful X-rays at the European Synchrotron Radiation Facility in France, Estefa and colleagues studied the structure of limb bones from early land creatures and their lobe-finned fish relatives. This allowed them to create 3D models of the inner architecture of the bones to try and determine when bone marrow first evolved.

They found that both fish and early four-legged creatures living 380 to 360 million years ago did not develop the conditions needed to support blood production in their bone marrow. Organisms need to have an open marrow cavity that allows marrow cells to interact with both a centralised mesh of blood vessels and the inner bone surface to produce blood cells this way, but this was lacking in the bones of lobe-finned fish and early tetrapods studied by the team. In fact, the oldest creature they found with a bone marrow cavity large enough to produce blood cells existed around 300 million years ago – long after the shift to land.

“More evidence is needed to understand what happened during the 60 million years after the arrival of the first creatures on land to cause the development of open bone marrow and blood production within the bones,” says senior author Sophie Sanchez, Senior Lecturer and Associate Professor at Uppsala University. “Our study marks a crucial first step to identifying the environmental or biological factors that caused blood-cell production to migrate into the bone marrow.”

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