Date:

Mammals share mechanisms controlling the heart with a 400 million-year-old fish

Primitive air-breathing fish, whose direct ancestors first appeared around 400 million years ago, show mechanisms controlling the heart which were previously considered to be found only in mammals – according to a new study.

Mammals show an increase in heart rate when breathing in and a decrease during expiration – a cardiorespiratory process known as respiratory sinus arrhythmia (RSA). This process and its underlying control mechanisms have been considered by many scientists to be solely mammalian but the present study questions this assumption.

Scientists in Britain and Brazil studied the South American lungfish, Lepidosiren paradoxa, and discovered that systems enabling this primitive vertebrate to control blood flow during bouts of air-breathing have close similarities to those identified in mammals.

Lungfish are members of an ancient group of lobe-finned fishes (Class Dipnoi), having a continuous fossil record originating in the Devonian period around 400 million years ago. This was a time when the first vertebrates crawled on to land to give rise to amphibians and over succeeding millennia reptiles, birds and mammals.

- Advertisement -

With their proto-lungs and proto-limbs, lungfish represent the earliest stage in the evolution of air-breathing vertebrates. They inhabit tropical, freshwater pools and slow-flowing rivers, which often contain very low levels of dissolved oxygen and can disappear during the dry season.

The lungfish shares a periodic breathing pattern with the terrestrial vertebrates, rising to the water’s surface at regular intervals to ventilate its lung-like air-breathing organ and depending exclusively on these lungs for oxygen uptake during drought.

Led by experts at the University of Birmingham and the Federal University of São Carlos (UFSCar), in São Paulo, the international team published its findings in Science Advances.

Professor Ted Taylor, from the University of Birmingham, said: “When lungfish gulp air at the water’s surface, their heart rate instantly increases – signalling a diversion of blood to the creature’s lungs.

“This is possible because the animal has an undivided heart, enabling the proportion of blood diverted to the lungs to be varied; unlike mammals, as we have a completely divided heart with equal volumes of blood pumped separately to lungs and body with each heartbeat.

“Our study established a clear function in lungfish for these increases in heart rate in maximising oxygen uptake during each air breath that has not been definitively demonstrated for RSA in mammals. This suggests that it may be a relic of their link to ancient amphibious ancestors.”

Professor Taylor added that “The lungfish has a relatively complex control system which generates these respiration-related changes in heart rate, with properties that anticipate those described for mammals.

“We found that these include multiple locations for nerve cells in the brainstem that innervate the heart with insulated fibres that conduct rapid impulses, causing an instantaneous cardiac response to each air-breath.”

This illustration in a fish with a proven ancient lineage of a highly evolved system controlling variations in heart rate suggests that its evolution was necessarily linked to the advent of air breathing over primitive vertebrate lungs rather than the much later appearance of mammals.

This understanding questions assumptions over the primacy of mammals made by some biomedical physiologists and many psychobiologists, demonstrating that “primitive” mechanisms though early are not necessarily simple.

UNIVERSITY OF BIRMINGHAM

Header Image : This is a South American lungfish, Lepidosiren paradoxa. CREDIT Gustavo M. Oda

- Advertisement -

Mobile Application

spot_img

Related Articles

Ring discovery suggests a previously unknown princely family in Southwest Jutland

A ring discovered in Southwest Jutland, Denmark, suggests a previously unknown princely family who had strong connections with the rulers of France.

Submerged evidence of rice cultivation and slavery found in North Carolina

Researchers from the University of North Carolina Wilmington (UNCW) are using side-scan sonar and positioning systems to find evidence of rice cultivation and slavery beneath the depths of North Carolina’s lower Cape Fear and Brunswick rivers.

Study reveals oldest and longest example of Vasconic script

A new study of the 2100-year-old Hand of Irulegi has revealed the oldest and longest example of Vasconic script.

Archaeologists excavate the marginalised community of Vaakunakylä

Archaeologists have excavated the marginalised community of Vaakunakylä, a former Nazi barracks occupied by homeless Finns following the end of WW2.

Archaeologists find 4,000-year-old cobra-shaped ceramic handle

A team of archaeologists from National Tsing Hua University in Taiwan have uncovered a 4,000-year-old cobra-shaped ceramic handle in the Guanyin District of Taoyuan City.

Traces of Khan al-Tujjar caravanserais found at foot of Mount Tabor

During excavations near Beit Keshet in Lower Galilee, Israel, archaeologists from the Israel Antiquities Authority (IAA) have uncovered traces of a market within the historic Khan al-Tujjar caravanserais.

Traces of marketplace from Viking Age found on Klosterøy

Archaeologists from the University of Stavanger have announced the possible discovery of a Viking Age marketplace on the island of Klosterøy in southwestern Norway.

Fragments of Qin and Han Dynasty bamboo slips found in ancient well

Archaeologists have uncovered over 200 fragments of bamboo slips from the Qin and Han Dynasty during excavations in Changsha, China.