Introduction to Animal Physiology and Physiological Genetics

491 Pages·1967·20.059 MB·English

by  E. M. Pantelouris and G. A. Kerkut (Auth.)

Introduction to
Animal Physiology and
Physiological Genetics
BY
E. M. PANTELOURIS
Department of Zoology
The Queen's University of Belfast
PERGAMON PRESS
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Copyright © 1967
Pergamon Press Ltd.
First edition 1967
Library of Congress Catalog Card No. 66-13821
2709/67
PREFACE
THE very wide fields of animal physiology and, to a lesser extent,
biochemical genetics are nowadays admirably served by thorough
textbooks and works of reference. Specialized, often collective,
series and monographs devoted to a particular physiological func­
tion or animal group are appearing in quick succession. The need
for books smaller in size but wider in scope, however, remains ; it is
with this need in mind that the present Introduction to Animal Physio
logy and Physiological Genetics was written.
Every effort was made in the preparation of this book to balance
the claims of vertebrate and invertebrate groups; and to illustrate
the relevance of experimental zoology to agriculture and medicine.
The view taken of the subject is a dynamic one, hence particular
stress is laid on two aspects: firstly, the changes of physiological
patterns in the course of development; secondly, the wide variation
found, as a rule, within a species.
These aspects lead to an organic fusion of comparative physio­
logy, embryology and genetics. A special section at the end of the
book is devoted to a consideration of the most important concepts
of physiological genetics. It would be difficult and rather futile to
seek a precise ,definition of "physiological genetics", to dis­
tinguish it from "developmental" and "biochemical" genetics.
These are not different subjects but different approaches, all merging
in molecular biology. To maintain, however, the unity of the book,
the topics selected for detailed treatment are such as to display the
steps from physiological measurement and comparisons to an analysis
of the role of genotype.
There is a very brief "Summary" at the end of each chapter.
The purpose is not to provide an abbreviated repetition of the
information covered in the text, but only to indicate the topics dis­
cussed in the chapter and the main lines of argument connecting them.
There is also a "Questions" section. It was felt that summaries
of this type and questions would provide sufficient stimulation to
the interested student to revise and assimilate information as well as
vii
Vili PREFACE
to discuss problems. Suggestions for further reading are also pre­
sented at the end of the book.
The author wishes to thank a number of colleagues who have, in
connection with this book as well as on previous occasions, helped
with suggestions and criticism. In particular, he wishes to thank
Dr. Gerald Kerkut for thorough, constructive and far-sighted com­
ment.
The helpfulness of the following publishers, who generously gave
permission for the use of illustrations from their journals and books,
is here gratefully acknowledged: Academic Press Inc.; Addison-
Wesley Publishing Company ; American Association for the Advance­
ment of Science; American Physiological Society; American Society
of Clinical Investigation ; Biochemical Journal; Birkhaeuser Verlag ;
Blackwell Scientific Publications ; British Medical Bulletin ; Butterworth ;
Cambridge University Press; Company of Biologists Ltd.; Condor;
Elsevier Publishing Company; Endeavour-, Federation of American
Societies for Experimental Biology; Grune and Stratton Inc.; Her
Majesty's Stationery Office; Hilger; Dr. H. E. Huxley; Journal of
Physiology, Limnology and Oceanography, Linnean Society of London;
Long Island Biological Association ; Masson et Cie ; National Academy
of Sciences, Washington; Nature-, New York Academy of Science;
Paul Parey; Pergamon Press; Royal Society; Royal Society of Edin­
burgh; Uni versi tets Forlaget; Veterinary Record; Wiley and Sons;
Williams and Wilkins Company; Wistar Institute of Anatomy and
Biology; Yale Journal of Biology and Medicine. Complete references to
author and journal are given in the legends to the illustrations.
E. M. P.
CHAPTER 1
SIMPLE TYPES OF RESPONSE
Kinesis and Taxis
Changes in environmental conditions often elicit from living
organisms activities described as responses or reactions. The environ­
mental changes are described as stimuli and must be more or less
sudden in order to elicit responses. Stimuli utilized in experiments
for the study of response include: light, electric current, mechanical
forces, osmotic pressure, temperature, chemicals, etc.
It should be noted that it is difficult to arrive at a concise definition
of stimulus. Gravity, for instance, elicits responses from animals (and
plants), but it is not, normally, a sudden or changing influence. It
would not be more accurate to describe stimulus as a factor eliciting
a response, since similar difficulties apply to defining response.
There are, of course, many types of responses ; one of the easiest to
record is movement.
Kinesis consists in an increase of the rate of locomotory activity,
whether this is movement in one direction or involves changes of
direction (turns). In a Paramecium culture, increased activity can be
induced by dim light or moderate rise of temperature; decrease of
activity results from bright light or extreme temperatures. If the dim
light is applied at one corner of the container only, the number of
individuals that find themselves there rises; this is not the result of
many individuals "proceeding" towards that corner but the sta­
tistical result of the fact that individuals respond to light by increased
activity.
Taxis consists in maintaining the line of movement at a certain
angle to the direction of a stimulus. The photo taxis of Euglena is an
example. This flagellate has at the anterior tip a granule of red
pigment, the stigma; this shades the base of the flagellum, and the
cytoplasm surrounding it may be presumed to be hypersensitive to
light. Euglena constantly rotates round its longitudinal axis. If it
la* J
4 RESPONSE MECHANISMS
moved in a direction at an angle other than 0° to the direction of the
light, the stimulation of the eyespot would be interrupted at the
moments when the stigma is opposite the light. By orientating itself
as it moves, so as to avoid interruption of the light stimulus, the
flagellate effectively follows the line towards the source of light.
In a similar way, insects turn in relation to light so as to keep both
eyes equally illuminated. This involves, normally, movement to­
wards the light. Covering the one eye is found to lead to circular
movement on a plane, or to spiral movement when climbing; the
uncovered eye is constantly stimulated by light in excess of the other,
and the insect constantly turns as if to bring the covered eye also
into the light.
Maze 1
FIG. l. Factors influencing phototropic responses in Drosophila melano-
gaster.
A, selection for phototropic response (N. M. Hadler, Bio/. Bull. 126, 264,
1964). The author designed a maze along which flies have, at 15 points, a
"choice" between a lighted and a darkened passage. The flies are released
at the entry to this "photomaze" and are collected in food vials at 16 dif­
ferent exits. The number of the exit where a fly emerges indicates the
number of light-positive responses it has made (photo-score). After testing
hundreds of individuals the investigator separated two small extreme
groups : the most light-positive and the most light-negative flies, and bred
from these separately. Repeating the same selection procedure for 15 gene­
rations he obtained the results shown above. Each point is the average
score of males (closed circles) or females (open circles) in each generation.
It will be seen that at the end of the experiment the two selected stocks
differ widely: one makes about 13 light-positive choices out of 16 possible,
the other makes only 4 light-positive choices. The data cover 20,000 flies.
SIMPLE TYPES OF RESPONSE 5
Especially with higher animals, however, responses are not uni­
form for all individuals or for one individual on different occasions.
Experiments on the phototactic response of the fruitfly, Drosophila
melanogaster, showed that fourteen different factors influence the
response: temperature, time of day, time since anaesthetic, rearing
conditions, mechanical stimulation, time since feeding, energy and
wavelength of light, state of dark adaptation, number of trials per
individuals, age, sex. In addition, the genetic constitution of the
stock has to be taken into account; it is possible to increase the photo-
tactic performance of a population by selection (Fig. 1 A). In other
experiments, the phototactic responses of stocks differing in eye
colour were compared. Normally the eye of this insect contains a
mixture of red and brown pigment, producing the normal "red"
eye. Many single gene mutations are known, however, that result
50« ' 1 « 1 " 1 1 1
350 WO 450 500 550 600 650 700
Wavelength mji
B
B, effect of the wavelength of light on the phototropic response (M. Fin-
german,/. exp. Zool. 120,131, 1952). Upper curve: brown-eyed mutant flies.
Maximum response at 366 ιημ, gradually decreasing, then rising to 89*9%
at 560 πιμ. Lower curve: white-eyed mutant flies. The maximum response
is again at 366 ιημ, but the level is always lower than for the brown-eyed
mutant. 366 ιημ (near UV) is the maximum for all groups, and there is
also another maximum at wavelengths over 400 πιμ (monochromatic).
It will be seen that the three curves differ not only in level of response
strength but also in form. The response of w is interpreted as basic for
the species. It becomes modified by the eye pigment depending on the
wavelengths thus absorbed. Red pigment has an absorption maximum be­
tween 480-490 πιμ, and brown at about 436 πιμ.
6 RESPONSE MECHANISMS
in other eye colours. There arc striking differences in the photo tactic
response to light of different wavelengths between the white-eye,
brown-eye and red-eye ("wild type") mutant stocks (Fig. 1B).
Arenicola larvae are negatively geotactic and swim upwards even
in the dark. They swim downwards, however, if the water in which
they are placed contains an excess of calcium or magnesium ions.
Many patterns of behaviour can be analysed into component taxes.
Young turtles move instinctively from their nests towards the sea
and it was found that this is the result of positive taxes to the follow­
ing stimuli: (a) gravity—moving down slopes, (b) optic stimuli—
moving towards the uninterrupted horizon and (c) colour—moving
towards the blue colour of the sea.
However, the simple types of response cannot account, even in
Protozoa, for the whole repertory of reactions. The sequence of
responses of the ciliate, Stentor^ for instance, cannot be analysed in
terms of the above types: when this protozoan is first stimulated by
touch, its stalk bends towards the opposite side ; if stimulation is per­
sistent, it repeats the same response several times up to a point
beyond which it may also reverse its ciliary beat; if stimulation is
continued still further, it contracts and, finally, it may break off its
stalk altogether.
Mechanisms of Protozoan Locomotion
Amoeboid Movement
Pantin investigated this on Amoeba Umax. Due to the simple shape
of this amoeba, each individual may be considered as a single broad
pseudopodium of a constant shape. There is clearly a streaming of the
cytoplasm at the centre in the direction of movement. On reaching
the anterior end, the endoplasm diverges out to the periphery on all
sides and becomes part of the peripheral cytoplasmic gel. Streaming
is kept up by the reconversion of the ectoplasmic gel into endoplasm
at the posterior end of the amoeba. Gelation is combined with con­
traction, and this contraction of the sleeve of gel pushes the endo­
plasm passively to swell the advancing pseudopodium.
Deprivation of oxygen causes suspension of movement (after
6 hr) and, finally, death. Decrease of the osmotic pressure of the
medium causes water-loading and a speedier conversion of ecto­
plasm to endoplasm with consequent swelling. Increase of osmotic
pressure has the opposite effect, the amoeba shrinking and assuming
SIMPLE TYPES OF RESPONSE 7
a star-like shape. In both cases the movement stops. The uptake of
water from the endoplasm by the advancing pseudopodium and its
swelling has been attributed to a more acidic local reaction, detectable
by the use as an indicator of the vital stain, neutral red.
Contraction of the ectoplasmic gel and streaming of the endoplasm
are recognized as parts of the mechanism of amoeboid movement
quite generally. However, it is the primary metabolic changes giving
rise to these phenomena that are being sought. Working on A. pro-
feus, Bell and Yeon describe the movement as outlined in Fig. 2.
? 5 ? ? ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ 5 5 ^ ^ ^ ^ ^ ^^
y////////////^^^^
FIG. 2. Tracings of Amoeba proteus from photographs. The amoebae were
starved, and washed, and were observed in Chalkley's solution, uncovered
by coverslip (L. G. E. Bell and K. W. Jeon, Nature 198, 675, 1963).
A, an exploring pseudopod is being formed free of the substratum, and
cytoplasm streams into it. Later, small adhesive pseudopodia form on the
under surface of the main pseudopod and adhere to the bottom, providing
support. Eventually the pseudopods free themselves at the posterior end
from the glass, not by means of any movement of their own but by the
forward streaming of cytoplasm.
B, method used by A. proteus for "standing up".
Cytoplasmic streaming could be induced without it being accom­
panied by any change of shape of the amoeba and this was taken to
imply that is is not streaming that brings about the changes in shape,
but rather some process in the membrane itself. And again, the
8 RESPONSE MECHANISMS
streaming is not due simply to compression by the gel but rather to
some metabolic change in the cytoplasm itself, as postulated also by
Hyman. (The way in which streaming was obtained without shape
changes was to induce the amoeba to form two "pseudopodia"
connected by a narrow bridge. Endoplasm from this bridge is seen
to flow towards both pseudopodia simultaneously; when this is
exhausted it flows from the one pseudopodium to the other, alter­
natively.)
Goldacre and Lorch find that if amoebae are placed briefly in
neutral red, the dye accumulates in the tail of those amoebae in
which there is cytoplasmic streaming at the time; in contrast, in
amoebae without streaming the dye stains uniformly the whole peri­
phery. This is in agreement with the theory that cytoplasmic stream­
ing is due to a reversible change of the protein molecules from an
unfolded to a globular form: in the ectoplasm (gel) the protein mole­
cules are unfolded, elongated and interlocking. Where the ectoplasm
contracts (posterior end of the A. Umax cell) they are partly folded
and still interlocked. Completion of folding so that molecules are
no longer interlocked underlies the change of the gel to endoplasm,
which is squeezed forth by the contracting ectoplasm.
In the folded state, the protein would not be expected to bind the
dye, as it would do in the unfolded condition. As the unfolded mole­
cules of the gel change into the folded state, they would release the
dye, hence the endoplasm does not stain.
Adenosine triphosphate (ATP) was found to speed up streaming
if injected into the tail of the amoeba, to reverse it if injected into
the pseudopodium, and to cause "rigor" if injected into the centre.
Control injections of water do not have these effects; and heparin
injected results in liquefaction of the cortical gel giving the amoeba
(A. discoïdes) 2. spherical shape. The above-mentioned investigators
draw a parallel between the effect of ATP in the tail of the amoeba
and the effect of ATP on a gel of actomyosin—a protein involved in
the contraction of muscle. This gel is liquified by ATP and the acto­
myosin fibres contract. It is then postulated that there is an enzyme
acting as ATP, and possibly ATP itself responsible for the change
from gel to endoplasm.
The reconversion of endoplasm to ectoplasm is assumed to be
caused by the nucleus acting on the endoplasm as it streams by. The
tail organizer would be produced by the nucleus at mitosis (one for
each daughter cell) and cytoplasmic movement would stop when the