The return of marine mammals to the cradle still has to go through "seventy-two changes"

Marine mammals "return to the cradle" and need to go through "seventy-two changes"

"Return to the cradle" of marine mammals needs to go through the "seventy-two changes"

The ocean is the cradle of life
.

According to the biological evolutionary history, the emergence of mammals has gone from the origin of life on earth to the birth of ancient fishes, and then some fishes moved from the ocean to the land, and amphibians and even amniotic animals that truly escape the water environment began to appear.

The ocean is the cradle of life

Why do these mammals who have finally climbed up from the water to the land "enter the water twice"? How does it evolve and adapt from land to water? Recently, the Chinese Academy of Sciences Institute of Science and Engineering, deep sea marine mammal research team co-Northwestern Polytechnical University, Qingdao, Beijing Genomics Institute and other research institutions in the "American Academy of Sciences, the Academy of Sciences," issued a document, reveals marine mammals adapt to the marine environment and its convergent evolution Important genetic mechanism
.

Academy of Sciences

Species evolution is driven by climate and environment

Species evolution is driven by climate and environment

Marine mammals refer to mammals adapted to the aquatic environment, with 129 existing species
.

They are vertebrates with viviparous lactation, lung respiration, constant body temperature, streamlined and fin-shaped forelimbs in the ocean, including cetaceans, pinnipeds, manatees, polar bears and sea otters, and a small part of them live in fresh water, such as Baiji dolphin inhabits the middle and lower reaches of the Yangtze River in China

Marine mammals have some common characteristics that are adapted to the aquatic environment, such as streamlined bodies, finned or degenerated limbs, developed hearing, degraded sense of smell and taste, thickened body fat, hypoxic tolerance, stress tolerance, and osmotic pressure regulation capacity enhancement
.

According to Darwin's theory of evolution, only the fittest can survive
.

The evolution of species on earth is a concrete manifestation of the evolution of animals' adaptation to the environment, which is mainly driven by climate and environmental changes

"The evolutionary history of marine mammals is a typical case of survival of the fittest
.

" The corresponding author of the paper told a reporter from Science and Technology Daily

Regarding the magical evolutionary history of different branches of marine mammals, one can start from the Cretaceous
.

At the end of the Cretaceous period 65 million years ago, the fifth mass extinction event occurred in the history of the earth, and about 75% to 80% of species were extinct
.

Some researchers believe that the impact of asteroids on the earth changed the earth's environment at that time, leading to the extinction of a large number of large terrestrial animals, especially dinosaurs

Cetaceans originated from the Paleocene-Eocene extreme heat event about 55.
5 million years ago
.

According to Bergman's law, it was the active period of the earth's plate movement.

The middle and late Eocene was a period of time when the earth's temperature continued to drop, and the trend of continuous decline in global temperature was interrupted in the Oligocene
.

At the beginning of the Oligocene, the temperature dropped sharply by 8.

Dual regulation to achieve constant body temperature

Dual regulation to achieve constant body temperature

The research team conducted this study through whole-genome sequencing
.

In order to find the commonalities in each group of marine mammals to the greatest extent, they started from the divisional level of the natural classification of animals, sequenced and assembled the whole genomes of 17 marine mammal species, and reconstructed them based on the whole genome.
The most comprehensive marine mammal phylogenetic tree in data history
.

Not only that, in order to analyze the molecular adaptation mechanism of marine mammals returning to the ocean from land, the scientific research team made a lot of comparisons between the whole genomes of marine mammals and the whole genomes of their terrestrial and related species, and further progressed from genome evolution, genetic evolution, and genetic evolution.
Non-coding conservative elements and many other aspects have carried out a comprehensive analysis and exploration of the molecular adaptation mechanisms of the three main branches of marine mammals, cetaceans, pinnipeds, and manatees, from the land to the sea
.

"We found that although marine mammals of different branches have completely different ancestors and different evolutionary processes, these animals have different genes related to body temperature maintenance, body size, hypoxia tolerance, echolocation, deep diving, and vision.
Consistency changes have taken place, showing an adaptive evolution mechanism of convergent evolution
.
" said the corresponding author of the paper
.

The high thermal conductivity of sea water makes it easier for animals to lose body heat to the water, which is one of the main challenges that mammals face when they return to the sea from land
.
While marine mammals return to the ocean from land, they still maintain an amazing body temperature control ability just like on land
.
How do they do it?

Regarding this issue, the scientific research team found a clearer explanation from the molecular level
.
"Different marine mammalian branches all have thermoregulation from two aspects of heat production and heat dissipation," said the corresponding author of the paper, "both NFIA and UCP1 two genes are used to regulate the synthesis and utilization of brown fat cells.
, So as to control the change of heat production, and through the change of SMEA3E gene, make the marine mammal's vascular system adaptively change to regulate the loss of heat
.
The dual regulation finally achieves the maintenance of a constant body temperature
.
"

In fact, what researchers have discovered in the genomes of marine mammals is the potential use of these gene coding instructions, that is, the up-regulation or down-regulation of the NFIA gene affects the cell fate of mesenchymal precursors, and the integrity of the UCP1 gene affects the normal function of brown adipocytes.
The developed vascular system of marine mammals helps heat transfer to maintain a constant body temperature
.

Adaptive evolution of multiple genes

Adaptive evolution of multiple genes

According to further introduction, in order to adapt to the aquatic environment, the skeletal morphology of marine mammals has also undergone changes to varying degrees.
For example, the forelimbs become flippers and the body is streamlined or spindle-shaped
.
Studies have found that in the biosynthetic pathway of proteoglycan, which is closely related to bone development, two key genes have undergone specific changes in marine mammals.
This is very likely to affect the changes in marine mammal bone morphology
.

In addition, the study also found that genes related to hypoxia tolerance, echolocation, deep diving, and vision have undergone molecular adaptive evolution in marine mammals
.

The research results of the scientific research team have established a comprehensive marine mammal genome data set, and provided more genetic evidence for the marine mammal’s aquatic adaptation-related traits and the convergent evolution between different marine mammal branches.
Subsequent studies on the adaptation mechanisms of marine mammals to the aquatic environment have provided good data support
.
At the same time, this research is of great significance to reveal the formation and maintenance mechanism of global biodiversity, and to explore the relationship between environmental adaptability and species evolution
.

However, researchers believe that although some evidence has been found at the genetic level, to further reveal the molecular adaptation mechanisms of marine mammals to the aquatic environment, more high-quality genome-wide data of more species, as well as single-cell transcriptome data, are needed.
Proteome and metabolome data, a large number of more detailed comparative analysis and experimental verification
.

"In addition, the molecular mechanisms of marine mammals' high IQ, high socialization, and longevity are still poorly understood, and further research is expected to achieve breakthroughs in these areas,
" said the corresponding author of the paper
.