Aerobic margin line

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Young Weddell seal

The aerobic dive limit (ATG; English aerobic dive limit ; ADL) is a concept from animal physiology and marine biology. The aerobic diving limit corresponds to the maximum duration of a continuous dive after which no increase in the lactic acid concentration can be measured in the diving organism .

background

The diving skills of the different species of seals have been known for centuries. At the end of the first third of the 20th century, systematic research into these skills began.

The main barrier mammals face from making long dives is their inability to extract oxygen from a liquid medium. In contrast to fish , for example , mammals have to stop breathing during the diving process . With increasing duration and physical activity, this leads to an oxygen deficiency in the diving organism. A hypoxia is especially sensitive to the active cells of organs such as the brain and heart muscle . If the hypoxic condition persists, they cease to work, which can lead to permanent damage or death. A reliable marker of acute hypoxia in a tissue is an increasing or increased concentration of lactic acid . This arises when the cellular metabolism is switched from aerobic to anaerobic energy supply from pyruvate through lactate dehydrogenase activity . If the lactate in the tissue cannot be removed and broken down, it becomes the cause of additional harmful effects under hypoxia.

The earliest attempts at diving behavior and diving skills of seals were carried out in the 1930s by L. Irving and P. F. Scholander and were based on the seals being forced to submerge under artificial conditions. They ignored the fact that diving activity is an actively controlled and controlled process by the seal. G. L. Kooyman and W. B. Campbell developed the ice-hole paradigm, with which the diving activity of Weddell seals under as natural conditions as possible could be examined for the first time. For the first time, blood samples from the observed animals were taken and compared before and after the immersion process. For reasons already mentioned, special attention was paid to the lactic acid concentration before and after diving. It was found that most of the seals' diving operations are within their aerobic margin. By actively regulating the duration of the dive, seals seem to be able to avoid acute hypoxia. Periodically and by some animals, however, this diving duration is significantly exceeded without suffering permanent damage. This indicates additional, molecular mechanisms in the seals that counteract the negative effects of increased lactic acid concentrations. Nonetheless, the recovery phase after dives beyond the ATG is significantly extended.

Differentiation between ADL and cADL

In its original definition, the aerobic margin line is a key figure that has to be determined by frequent, time-consuming measurements of the lactic acid level in the blood of the test animals under realistic conditions. This is difficult to do in practice and has so far only been determined for the Weddell seal and the emperor penguin . As an alternative, a calculated aerobic dive limit is therefore usually used ( cADL).

The cADL is calculated by dividing the oxygen stores in the organism by the expected rate of oxygen consumption. The cADL therefore indicates the duration of the dive by which the organism's entire oxygen storage is used up. The use of ADL in the name of this metric is misleading, as it refers to the definition of ADL as the maximum diving duration after which no increased lactic acid concentration is observed. However, when the ADL is reached, a larger amount of oxygen is still present in the diving animal. Reaching the cADL during a dive usually takes 2-3 times as long as reaching the ADL.

Patrick J. Butler therefore suggests using the more concrete term of the diving lactate threshold (DLT) for the ADL .

Individual evidence

  1. ↑ Gerald L. Kooyman: Aerobic Dive Limit . In: Diverse Divers (=  Zoophysiology ). No. 23 . Springer, Berlin / Heidelberg 1989, ISBN 978-3-642-83604-6 , pp. 143-149 , doi : 10.1007 / 978-3-642-83602-2_12 .
  2. ↑ Randall W. Davis, A review of the multi-level adaptations for maximizing aerobic dive duration in marine mammals: from biochemistry to behavior . In: Journal of Comparative Physiology. B, Biochemical, Systemic, and Environmental Physiology . tape 184 , no. 1 , January 1, 2014, ISSN  1432-136X , p. 23-53 , doi : 10.1007 / s00360-013-0782-z , PMID 24126963 .
  3. ^ Daniel P Costa: Diving Physiology of Marine Vertebrates . In: eLS . John Wiley & Sons, 2001, ISBN 978-0-470-01590-2 , doi : 10.1002 / 9780470015902.a0004230 / abstract .
  4. ↑ GL Kooyman, EA Wahrenbrock, MA Castellini, RW Davis, EE Sinnett: Aerobic and anaerobic metabolism during voluntary diving in Weddell seals: Evidence of preferred pathways from blood chemistry and behavior . In: Journal of comparative physiology . tape 138 , no. 4 , ISSN  0340-7594 , p. 335-346 , doi : 10.1007 / BF00691568 .
  5. ↑ a b Patrick J. Butler: Aerobic dive limit. What is it and is it always used appropriately? In: Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology . tape 145 , no. 1 , September 1, 2006, p. 1-6 , doi : 10.1016 / j.cbpa.2006.06.006 .