The seals are excellent divers. They can remain underwater up to 30 minutes, enough time to find food and avoid predators. During those long dives, they support very high levels of carbon dioxide (CO2) (hypercapnia) and very low oxygen (hypoxia), which can lead to drowning.
Until now, it was believed that the seals knew when it is necessary to emerge to the surface by receiving high levels of CO2 in their body. However, a group of researchers from the University of St Andrews (Scotland) believes that these animals can directly perceive their own levels of circulating oxygen in blood, a capacity that most mammals lack. In this way, they can emerge to the surface when necessary, regardless of the amount of present.
Marine mammals that breathe air, such as seals or marine elephants, have developed various physiological adaptations to survive in aquatic environments, including thermoregulation to support the pressures of the depths. However, one of its most critical evolutionary challenges is to avoid drowning. Despite adaptations for greater oxygen storage and low oxygen levels tolerance, these animals still run the risk of drowning if they cannot perceive when oxygen is exhausted.
In general, it is believed that blood -circulating oxygen is cognitively imperceptible to mammals. Instead, most have developed the ability to perceive high levels of carbon dioxide (CO₂) as a low oxygen signal, which triggers aversive feelings such as “lack of air.” According to The authors write In the ‘Science’ magazine, although the cognitive perception of CO2 serves as a crucial survival mechanism, trusting it as an indicator of lack of oxygen during the diving in Apnea, where CO2 accumulates and retains in the body, it may not be adequate to protect marine mammals from drowning for prolonged immersions.
Cognitive capacity
Chris McKnight and his colleagues carried out a study in gray seals captured in nature ( Halichoerus grypus ) to examine how controlled variations in inhaled oxygen and carbon dioxide levels influenced their diving behavior. The researchers discovered that the duration of the immersion was strongly correlated with blood oxygen levels, but it was not affected by CO2 levels or the pH of the blood.
According to the findings, even when exposed to CO2 concentrations 200 times higher in the ambient air, the duration of the dives of the seals remained unchanged. However, altering oxygen levels (either doubleing or reducing the environmental concentration by half) significantly affected the time that the seals remained submerged.
Researchers believe that gray seals have the cognitive ability to perceive oxygen levels, which allows them to regulate the duration of their dives accordingly. And, given the generalized convergent evolution of adaptations related to diving between marine mammals, there is likely that there are similar mechanisms of perception of oxygen in other species.
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