Department of Anatomy and Physiology, Faculty of Veterinary Science, University of Pretoria, Onderstepoort 0110, South Africa

MAMMALIAN ENERGETICS

This is new research on the metabolic energy expenditure, external mechanical work, and metabolic-mechanical efficiency of wild African antelope.  Because they are prey animals, antelope provide unparalleled models of peak structural and functional performance.  This springbok is living it up in the Kalahari.

INTERSPECIFIC ANALYSES OF THE HEART

We've recently been using wild African antelope to study the structure and function of the mammalian heart as a function of body mass.  The smaller species tend to have relatively larger hearts with relatively greater anatomical aerobic power densities, possibly because they are under strong predation pressure.  Here is the morphology and cardiomyocyte ultrastructure of the heart in different sized antelope, from small duiker to large eland.

TEM antelope hearts 4.jpg

FISH ENERGETICS

I sometimes help a friend (Nick Payne, Trinity College Dublin) swim fish in flumes to measure their metabolic energy expenditure as a function of swimming speed.  Here's a schematic of a giant submersible swim tunnel that was built for sharks and performed very well.

ONTOGENETIC ANALYSES OF THE HEART

We've also been busy studying the morphology and cardiomyocyte ultrastructure of the heart as a function of body mass across development.  It seems there is often a breakpoint in the scaling relationship between heart size and body size, which coincides with birth in placental mammals, separating the fetal and postnatal life stages.  At birth, there is closure of the foramen ovale and ductus arteriosus, and there are significant changes to the flow and pressure of the heart.

Fetal heart 3.jpg

OXYGEN SUPPLY AND DEMAND

The economic design principle of symmorphosis posits that no more structure should exist in a system than necessary to satisfy the functional capacity of the system.  In other words, there is no point wasting energy and space building structures you will never need.  To test the principle, we applied this three-dimensional mathematical model for oxygen transport through the tissue of the left ventricle.  Indeed, it does look like there is just enough capillaries to deliver oxygen, and just enough mitochondria to consume that oxygen, when the myocardium is working at its maximum sustainable capacity during strenuous exercise.

INSECT ENERGETICS

Insects in flight achieve the highest mass-specific metabolic rates of all animals.  To measure their real-time metabolic rates, flight chambers are built and incorporated into flow-through respirometry systems.  Here is one of my old locusts, tethered to a vertical force transducer and coupled to a polygraph and data acquisition system, allowing measurement of lift generation during flight exercise.

Locust and polygraph.jpg

INSECT GIGANTISM

Gigantic dragonflies might seem the stuff of nightmares, but these insects ruled the air 300-million years ago.  The hypothesis is that elevated atmospheric oxygen partial pressures during the Carboniferous enabled insects to evolve to a considerably large body size.  A larger pressure differential between the atmosphere and the respiring tissues hypothetically allowed for longer diffusion distances and therefore larger body sizes.

Protodonata.jpg

SCALING

Much of my work is underpinned by scaling analysis.  Scaling shows how body mass () affects a variable (Y ) by setting that variable to the equation, Y = aM   , where 'a' is the scaling coefficient that defines the elevation of the curve above the x-axis and 'b' is the scaling exponent that describes the shape of the curve.

b

b

b

THERMAL ENERGY AND BODY TEMPERATURE

Body temperature is determined by a number of factors, physiological, behavioral and environmental.  I'm interested in how these factors interplay, giving rise to operative temperature, in different animals, both in the lab and in the field.

Thermal types 3.jpg

BRAIN BLOOD FLOW AND METABOLISM

It occurred to my former PhD advisor (Roger Seymour, University of Adelaide) that if you know the size of a vessel, then you ought to be able to calculate the rate of blood flow through that vessel, and when that vessel is transmitted snugly through a bony canal, then all you need to know is the size of the canal.  Here are the carotid foramina (arrows) that provide passage for the internal carotid arteries to the brain.  Using this principle, we have calculated blood flow rates to the brain across three-million years of human evolution.

Human skull.jpg