Lampreys look like something from a scary movie something out of a horror movie, with their suction mouths filled with teeth, eel-like bodies, and parasitic behaviors parasitic behaviors. These “water vampires” show a split in the path of evolution between vertebrates and invertebrates, and the debate among scientists about how closely we are related to these meat-eating fish has shifted again.
Scientists have found some proof that lampreys have a basic sympathetic nervous system–which is thought to control the fight-or-flight response in vertebrates. The findings are detailed in a study released on April 17 in the journal Nature and could lead to a rethinking of the origins of the sympathetic nervous system.
Lampreys are the closest living organisms scientists have to studying the fish ancestors that vertebrates evolved from some 550 million years ago. They belong to an ancient vertebrate lineage called Agnatha–or jawless fish. Some scientists think that they represent the earliest group of vertebrates that is still living and can provide us with an evolutionary view into all vertebrate ancestors. Other scientists question the theories due to a lack of lamprey evidence in the fossil record.
Giant prehistoric lampreys probably sucked blood—and ate flesh.]
Scientists previously thought that lampreys did not have sympathetic neurons. These neurons are part of the sympathetic nervous system, a system of nerves that target the internal organs throughout the body including the gut, pancreas, and heart. The system works together to respond to dangerous or stressful situations. It also helps an organism’s body maintain homeostasis, ensuring that the heart keeps pumping, the digestive system keeps moving, and more.
In this new study, a team used lampreys to see how changes during growth may have led to the evolution of vertebrate traits like fight-or-flight. They found evidence of the types of stem cells that eventually form sympathetic neurons. The presence of these cells in lampreys could change the timeline of when the sympathetic nervous system began to evolve.
“Over a hundred years of literature has suggested that lamprey lack a sympathetic nervous system,” study co-author and California Institute of Technology biologist Marianne Bronner said in a statement. “Surprisingly, we found that sympathetic neurons do, in fact, exist in lamprey but arise at a much later time in lamprey development than expected.”
Bronner and her team studied neural crest cells. These are a kind of stem cells that are specific to vertebrates and give rise to the multiple cell types found throughout the body. Scientists previously believed that lampreys lacked the neural crest-derived precursors, or progenitors, that ultimately build the sympathetic nervous system.
According to Bronner, researchers previously looked for evidence of a sympathetic nervous system too early in lamprey development compared to other animals. For example, the sympathetic nervous system forms in the first two to three days of development in birds.
You may have a lot in common with the sea lamprey and not even realize it..]
Study co-author and Cal Tech evolutionary biologist Brittany Edens studied the precursor cells in lampreys that come from the neural crest and eventually become sympathetic neurons. She discovered that in lampreys, these precursor cells appear much later than in other animals, sometimes as long as one month after fertilization. These cells also don't become fully developed into neurons until about four months into the fish's larval stage.
It is still not known Whether the sympathetic nervous system of lampreys controls fight-or-flight-like behaviors similar to other vertebrates is still uncertain. According to the team, these discoveries suggest that the program guiding the creation of sympathetic neurons is consistent across all vertebrates, from lampreys to mammals.
