What Makes Platypus Diving Special?



Image courtesy of 
http://www.healthsci.utas.edu.au/physiol/mono/Mainpage.html

Diving mammals cannot breathe underwater.  This presents a problem, as muscular activity and oxidation of glucose require oxygen.  Most mammals solve this problem in several ways:
  • Reduce heart rate (bradycardia) and shunt blood to only the most critical organs (tissue hypoperfusion).  This conserves Oby depriving noncritical tissues.
  • Myoglobin has high oxygen affinity and can store Oin muscles during dives.  This means hemoglobin is not the only source of O2 for the muscles, somewhat counterbalancing the O2 deprivation during tissue hypoperfusion.
  • During dives, muscles use anaerobic respiration.

A consequence of these strategies is that the muscles build up an oxygen debt in the form of stored lactate.  After the dive, the animal must resume full circulation and metabolize the lactate (Schmidt-Neilson, 1997).

Although it is also a diving mammal, the platypus does not share some of these usual traits.  We already know that the platypus does not have long surface intervals between dives (dive:surface ratios range from 1:2 to 1:20) but that it does experience bradycardia and tissue hypoperfusion.  This suggests that it has found some means of avoiding anaerobic metabolism (Evans et al., 1994).

Let's look at some physiological data:
 
 

 
O2 stores in total body myoglobin (mL O2/kg)
Pyruvate inhibition ratio*
pH buffering capacity#
Platypus
5.6
1.1
35.4
Diving Eutherians
8-18
0.7-1.3
61-84
source: Evans et al., 1994

*A lower pyruvate inhibition ratio indicates more anaerobic respiration.
#A higher number indicates better capacity to buffer lactic acid produced in anaerobiosis.

Image courtesy of Healesville Sanctuary (http://www.zoo.org.au/)

What do these data tell us?
 




So, how do platypus dive with low myoglobin oxygen stores and without anaerobic respiration?
 
 
 
 
 

The whole picture of platypus diving is still unclear, but these animals are certainly doing something different from most diving eutherians.


Main page
Introduction to
Monotremes
Thermal Biology
Evolutionary Implications
of Thermal Biology
Diving
Special Aspects
of Diving
Literature 
Cited

This page is a class assignment for Animal Physiology at Davidson College.  For questions or comments, please email Will White.