Researchers from the Consolidated Evolution and Development Research Group (evo-devo) of the Genetics Section of the Faculty of Biology of the University of Barcelona (UB) deciphered one of the enigmas about the transition between free and sedentary lifestyles in ancestors of our coast: the corded.
The deconstruction of the heart’s gene network facilitated the transition to a free pelagic lifestyle, that is, in the water column and not subject to the substrate
Work, which is on the cover of the magazine Nature, proposes a new evolutionary scenario that helps to better understand the evolution of our frontier and discover what the ancestor of the tunicated, the sister group of vertebrates.
Specifically, he reveals that the massive losses of genes that deconstructed the gene network of the heart they facilitated the transition to a free pelagic lifestyle – that is, in the water column and not subject to the substrate – in a sedentary ancestral way.
Impact of gene loss on evolution
For many years, in the area of evolutionary biology Not much attention was paid to the gene’s disappearance, and most studies focused on how gene duplication could lead to new biological functions.
“However, we are increasingly identifying more loss of genes that may be adaptive in nature,” he explains. Cristian Cañestro, Responsible Researcher of the Evo-Devo Group at UB. “In other words, losing certain genes can also have evolutionary advantages that may be related to the acquisition of biological innovations in organisms.”
We are increasingly identifying gene losses that may be adaptive in nature.
Cristian Cañestro
the edge of the corded It is formed by the group of vertebrates, tunicates and cephalochordates. The basal position of the cephalochords and the fact that they are free-living organisms such as vertebrates indicate that the predecessor of all chordates was also free-living.
However, in the case of tunicates, there are sessile animals (sea cliffs) and free life (appendicular) Whether the common ancestor of tunicates was a passive feeder filter fixed to the seabed or an active swimmer has been the main focus of debate to understand what the ancestor from which vertebrates also originated has been.
The research group is a world pioneer in the use of the species Dioic ikopleura —A marine zooplankton organism of the appendicular group— as an animal model to study the impact of gene loss as an evolutionary force.
The results of the article reveal the existence of massive disappearances of genes in the appendiculares that millions of years ago affected the cardiopharyngeal gene network.
“Our work shows that the heart of Dioic ikopleura is homologous to the rest of the chordates and, therefore, comes from a heart that already existed in the common ancestor between humans and Dioic ikopleura”, comments the expert. “However, it has been surprising to see that, despite having a homologous heart, many of the genes essential to making a heart in humans and other chordates were lost in Dioic ikopleura during a process of of construction —Elemental examination— which affected his cardiopharyngeal gene network”.
Many of the genes essential to making a heart in humans and the rest of the chordates were lost in Oikopleura dioica during a process of deconstruction.
Cristian Cañestro
Nature magazine cover. / UB
The evolutionary challenge of adapting to a free life
“Considering that vertebrates, cephalochords and appendiculars are free-living animals, it was postulated that the most plausible evolutionary scenario was that the tunicated ancestor was also free,” he says. Alfonso Ferrández-Roldán, lead author of the article.
Now, the results contradict this evolving scenario. “We were able to correlate the loss of genes with the disappearance of characteristics typical of the sessile life of ascidians. This led us to infer that the common ancestor of all tunicates was an organism of sessile life, and not free-living, as was thought until now”, continues the researcher.
The article points out that the massive disappearance of genes may be linked to three evolutionary innovations that facilitated the transition from a predecessor with characteristics similar to those of sea squirts – with mobile larvae and sessile adults – to a lifestyle completely free from appendiculation.
A first adaptation was the acceleration of the heart’s development process (cardiogenesis) This allowed the appendiculares to have this organ fully operational at the start of their free lifestyle.
The common ancestor of all tunicates was a sessile-living organism, not a free-living organism, as was previously thought.
The second is linked to the redesign of a new structure of the heart that could improve the circulation of the heart. hemolymph –The ‘blood’ of invertebrates–.
Finally, the disappearance of the pharyngeal musculature in the trunk of Dioic ikopleura it would be a third evolutionary innovation on the path to active swimming. The function that this musculature plays in sessile ascents – it regulates the siphon through which the water enters – would be totally unnecessary in the appendicular.
This basic research work outlines a new evolutionary scenario to resolve unknowns about the origin and evolution of appendiculariae, their phylogenetic relationship with other tunicates and the common ancestor of vertebrates.
“Our work reveals what the tunicate ancestor was like and opens up new questions: for example, how sessile life evolved in the ancestral tunicates of a free-living ancestor possibly similar to that observed in vertebrates,” says Cañestro.
Reference:
Ferrández-Roldán, A.; et al. “Cardiopharyngeal deconstruction and ancestral sessility of the tunicate”. Nature, November 2021. doi: 10.1038 / s41586-021-04041-w
Rights: Creative Commons.
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