Effects of different photoperiods on body weight, fat deposition, molt, and male gonadal growth in the slate-colored junco

199 Pages·04.861 MB·English

by  Winn, Hudson Sumner

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NORTHWESTERN UNIVERSITY LIBRARY
Manuscript Theses
Unpublished theses submitted for the Master’s and Doctor’s degrees
and deposited in the Northwesterh University Library are open for inspection,
but are to be used only with due regard to the rights of the authors. Biblio­
graphical references may be noted, but passages may be copied only with the
permission of the authors, and proper credit must be given in subsequent
written or published work. Extensive copying or publication of the thesis
in whole or in part requires also the consent of the Dean of the Graduate
School of Northwestern University.
Theses may be reproduced on microfilm for use in place of the
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and the rights of the author arv. in no way jeopardized.
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NAME AND ADDRESS DATE
NORTHWESTERN UNIVERSITY
EFFECTS OF DIFFERENT PHOTOPERIODS ON BODY WEIGHT, FAT
DEPOSITION, MOLT, AND MALE GONADAL GROWTH
IN THE SLATE-COLORED JUNCO.
A DISSERTATION
SUBMITTED TO THE GRADUATE SCHOOL
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
for the degree
DOCTOR OF PHILOSOPHY
FIELD OF ZOOLOGY
By
Hudson Sumner Winn
EVANSTON, ILLINOIS
June, 1950
TABLE OF CONTENTS
Acknowledgment
INTRODUCTION
Review of Literature ...... ......... 1
Development of Experimental Plan........ 15
MATERIALS AND METHODS
The Experimental Subject........................... 20
Trapping............................................22
Banding ...... 23
Maintenance Prior to Start of Experiments..........24
Segregation at Start of Experiments. ..... 26
Procedures:
1. Maintenance ...... 30
2* Periodic Observations .......... ..30
3. Sampling........................... 31
4. Measurements of Testes......... 32
5. Histologic Technique .................32
RESULTS
Body Weight and Fat Deposition.....................34
Molt................................................37
Testis Development........... 39
DISCUSSION AND CONCLUSIONS
Body Weight and Fat Deposition..................... 43
Molt .............. 48
Testis Development................................. 52
SUMMARY......... 57
LITERATURE CITED
VITA
TABLE OF CONTENTS (Continued)
LOCATIONS OF TABLES AND FIGURES IN TEST Following page
Table 0, Photometer Readings in Foot-candles.........29
Table 1, Body Weights Prior to Experiments...........34
Figures 1-12, Body Mean Weights and Fat Classes......34
Table 1A, Chronology of Weight-Fat Response..........36
Figure 13, Times of Fat Deposition by Majorities
of Responding Birds.................... ...36
Figure 14, Sequence of Fat Deposition, Fat Loss,
and Molt .......................... 39
Tables 2-7, Testis Data,......... 39
Figures 15-20, Testis Weights and Stages of Develop--
ment................................... 40
APPENDIX
Tables 8-19, Body Weights and Fat Classes
Table 20, Dates Equivalent to Days After Start of
Experiment
Plates 1-6, Experimental Rooms and Equipment
ACKNOWLEDGMENT
I wish to express my sincere appreciation to Dr.
Albert Wolfson, who suggested this problem and under whose
guidance the research was conducted. His generous assist­
ance and enthusiastic counsel during the course of the
research and the preparation of the manuscript are grate­
fully acknowledged.
1
INTRODUCTION
Review of the Literature
Man has teen curious about migrations undertaken by
many species of birds ever since he first noticed their
seasonal appearances and disappearances. Because migratory
activity was observationally associated with certain seasons
of the year, man has attempted to correlate such activity
with recognizable factors of the external environment. But
observational data have led to conflicting conclusions.
Though numerous clues have been revealed, making certain
environmental factors suspect, the inherently limited poten­
tialities of observational data alone, have prevented an
elucidation as to how those factors might operate.
The use of an experimental approach to this problem was
initiated by Rowan (in 1924 e_t sea. Y. He demonstrated that
it was possible to cause precocious gametogenesis in juncos
by subjecting them to photoperiods of gradually increasing
durations at the time of year when the gonads have reached
their annual minimum in size and activity. Rowan extended
the short, natural, fall and winter photoperiods with periods
of artificial illumination. Various modifications of this
technique have been employed by subsequent investigators to
manipulate the gonadal cycles of a wide variety of birds and
other vertebrates, providing indisputable evidence that light
affects the gonads.
Among the other factors of the external environment which
have been considered is temperature. The potentially impor­
tant role that temperature might play as a causative influence
2
in seasonal reproduction among birds is considerably diminish­
ed by the fact that Rowan fs (1989) initial experiments were
conducted during the Canadian winter at subzero temperatures*
The lowest temperature he recorded was -52° F. Riddle (1925)
reported that reproduction in pigeons is depressed by cold,
but Bissonnette and Csech (1937) hatched pheasant chicks on
Christmas Day, following a period of light experimentation.
Kendeigh (1941) reported no significant differences in re­
productive response between English sparrows kept at 36° F.
and at 72° F. Burger (1948) stated that the testes of star­
lings maintained between 90°F. and 100° F. were much larger
than the testes of starlings kept at lower, varying tempera­
tures, when both groups were exposed to photoperiods of long
duration. The higher temperatures, however, did not induce
continued spermatogenesis when the duration of the photo­
period was reduced. Burger concluded that external tempera­
tures approximating the body temperature of the Starling
neither suppress spermatogenesis nor cause regression of the
testis.
These and similar additional records in the literature
show that external temperature exerts no prohibitive effect
on the gonadal development of most of the birds studied.
Once the breeding condition is attained, however, temperature
has been shown to be correlated, at least in some birds, with
egg size and number (Kendeigh, 1941; Lee, Robinson, Yeates,
and Scott, 1945). There is no evidence, on the other hand,
to indicate that temperature is responsible for the initiation
5
or the maintenance of progressive gonadal development, such
as that resulting from light experiments.
As far as is known, food, adequate in content and amount,
plays no important role in the sexual development of season­
ally reproducing birds. Food that is deficient in known es­
sentials might be expected to produce metabolic abnormali­
ties among birds, but in such instances, food is acting only
as a limiting factor in the matter of gonadal development.
Bissonnette (1932b) maintained starlings on a low protein
diet and found no sexual response even though the birds were
exposed to photoperiods of long duration. Kendeigh (1941)
compared testicular responses in English sparrows, some of
which were permitted to feed only during restricted periods,
and others during the whole light period. The amount of food
consumed was the same in each instance, and there was no dif­
ference in testicular response. No evidence exists in the
literature to confirm the possibility that a specific ingre­
dient of food might activate birds sexually.
There can be no doubt that in the external environment
many supposed and actual factors exist which have not been
considered here. Their characters and their degrees of pos­
sible influence on gonadal rhythmicity in birds remain to be
clarified by experimental work. Yet it is clear that of the
known factors of the external environment, light alone has
been found capable of effecting complete spermatogenesis in
birds which reproduce seasonally.
If light is so firmly implicated by experimental evidence,