Path. vet. 2: 553-565 (1965)
From the Department of Pathology, University of Texas LMedical Branch,
Galveston, Texas
Testis in the Sterile Hybrid Duck
A Histologic and Histochemical Study
R. H. RIGDONand CHARLES
MOTT
The cross mating of birds is frequent. Many of the resulting
hybrids are fertile; however, some are sterile. In 1958 GRAY^^ compiled much data referable to these crosses. The Mallard (AnasplaQrbynchos) female duck and the Muscovy (Cairina moschata) male duck
frequently mate and their male hybrids show some sexual behavior but
apparently are sterile. The females usually have poorly developed
ovaries and oviducts and show no mating response. A few have been
reported to have laid very small eggs during their second year. Both
sexes are crested. The females are male-like in size and conformation.
In 1936 CREWand KOLLER’observed sterility in the hybrids obtained by crossing the Muscovy male and the Aylesbury female, one of
the species of Anas platyv-bynchos. The male hybrids had large testicles
but were infertile and the females had rudimentary ovaries and infantile
oviducts and exhibited no sex behavior. However, when the investigators crossed a Muscovy female with an Aylesbury male, the female
hybrids had normal ovaries and oviducts and laid eggs, but none were
fertile. The male hybrids were larger than the females and sterile.
Microscopically the spermatogonia in the seminiferous tubules formed
several layers of cells showing mitotic division. “Nuclear granules”
were present and contained nucleic acid as indicated by the Feulgen
reaction; it was assumed that chromosomes were present. Binucleate
spermatogonia were frequent. Multinucleated cells often were present
in the center of seminiferous tubules and these were thought to represent abnormal spermatids. No spermatozoa were present.
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RIGDONIMOTT
The explanation for hybrid sterility is varied. WHITE^^ in 1954
discussed the many problems associated with sterility. BENIRSCHKE
et al.2 in 1962 expressed the opinion that “the paucity of data on
mammalian hybrid testicular preparations and the large number of
chromosomes not yet satisfactorily enumerated, let alone structurally
characterized, make it impossible at this time to assign a definite
mechanism.. . From the few direct studies of mule’s testes, azoospermia appears to result from degeneration of spermatocytes”.
Several studies recently have been made on the sperm and spermatogenesis in birds43 113 133 143 213 22; however, as far as we have been
able to determine, no histochemical study has been reported on the
sterile hybrid duck. Our observations on the testicle of the normal
duck and of the sterile hybrids resulting from the mating of the
Muscovy male with the white Pekin and Mallard female are reported
herein.
9 9
Methods and Materials
The 88 ducks used in this study were white Pekins, Mallards,
Khaki Campbells and Cayugas (all of which are domestic forms of
Anas plat_yrh_ynchos)and crosses among themselves. The white Pekin
and the Mallard females were crossed with the male Cairina moschuta.
A majority of these ducks were raised in our laboratory. They were fed
a commercial ration and kept in outside pens with food and water
available ad libitum.
The testes were removed immediately after the ducks were killed
by severing the cervical vertebrae; the size of the testicles was recorded
in most of the birds. Sections were removed and fixed in a 4% buffered
solution of formaldehyde. Paraffin sections were prepared and stained
with hematoxylin and eosin, by the periodic acid SchiFs (PAS)
technique with and without prior diastase digestion, for desoxyribonucleic acid (DNA) by the Feulgen technique, iron by the Mallory
technique, and fat with oil red 0. Dab smears were made from the
testes of some of the ducks and dried. These were stained by thefollowing techniques: hematoxylin and eosin, PAS, diastase and then PAS,
Feulgen’s technique, Mallory’s technique for iron and oil red 0 and
Sudan black for fat. Some of the smears were treated for 30 minutes
with 95% ethyl alcohol before they were stained with PAS,
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Testis in the Sterile Hybrid Duck
555
Results
Spermatozoa were present in the testes of 44 of the 51 mature
Cayugas, Mallards, Khaki Campbells, MUSCOVYS,
white Pekins and
hybrids resulting from the mating of Cayugas, Mallards and white
Pekins. No spermatozoa were found in the testes of 24 other ducks
resulting from mating 2 Muscovy males with white Pekin and Mallard
females and only 3 of these may be considered immature. The seven
ducks in which no sperm were demonstrated were two Muscovys, age
7 and 18 months, one white Pekin, age 234 days, two hybrids, age 383
and 420 days, resulting from the mating of a white Pekin male with a
Mallard, one hybrid, age 306 days, resulting from the mating of a white
Pekin with a hybrid female, and one hybrid, age 371 days, resulting
from the mating of a Mallard male with a hybrid female. In this report
birds resulting from the mating of the Muscovy male with the white
Pekin and Mallard female are referred to as “sterile hybrids”.
The adult ducks resulting from the mating of Mallard females and
a black and white Muscovy male usually were predominantly black and
those resulting from the mating of the same male with white Pekin
females were black and white. There was little difference in the size and
appearance of the males and females in this group of sterile hybrids.
Females showed little sexual activity and none have laid within a
period of 18 months.
The size of the testis varied with the species, the age and the time
of year referable to mating. The maximum size of the testis in the adult
white Pekin was 5.0 x 3.0 x 2.5 cm, the Muscovy 3.5 x 2.0 x 1.5 cm,
the Mallard 1.9 x 1.0 x 0.8 cm, the Cayuga 6.0 x 2.5 x 1.5 cm, and the
hybrid resulting from the mating of a Muscovy male with white Pekin
females 5.5 x 2.5 x 2.0 cm, the Muscovy male with the Mallard female
3.5 x 2.0 x 1.5 cm.
Histologically the testes from the normal and sterile hybrid ducks
were similar in some respects and different in others (Figs. 1, 2). The
spermatogonia and spermatocytes were similar; however, abnormal
cells were present in the lumen of the seminiferous tubules of the
sterile hybrids that were not present in the normal ducks. The size and
shape of these abnormal cells varied; many were multinucleated (Fig.
3). The spermatogonia and primary spermatocytes appeared normal
with respect to amount of DNA as shown by Feulgen technique.
However, after this stage there seemed to be a change in the amount
and distribution of chromatin in the cells.
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556
RIGDON/MOTT
A PAS positive-staining granular material was present in the
extracellular spaces and in the cytoplasm of the cells within the
seminiferous tubules of the testes other than the spermatogonia (Fig.
4).These granules were all more or less uniform in size and were about
a micron in diameter. This PAS positive material within the tubules
was not removed by diastase digestion. Its amount varied in different
ducks; however, the average in normal birds was approximately onefourth that present in the sterile hybrids. An iron-staining substance
was present in the cytoplasm of a few cells in the seminiferous tubules
of these ducks (Fig. 5); however, it was most conspicuous in several of
the sterile hybrid birds. In this latter group of ducks there also was
some lipid material that gave a positive oil red 0 reaction in paraffin
Fig. 1. D2696. Seminiferous tubule from the testis of a hybrid, age 367 days,
resulting from the mating of a Mallard male with a hybrid female. Observe
the number of cells lining the tubules and the number of sperm. H & E,
x 170.
Fig. 2. D2703. Seminiferous tubule from testis of a sterile hybrid duck, age 353
days, resulting from the mating of a Muscovy male with a white Pekin
female. Observe the number of cells lining the tubule and the cells within
the lumen. H & E , x 170.
Fig. 3. D2816. The seminiferous tubules from testis of a sterile hybrid duck, age
355 days, resulting from the mating of a Muscovy male with a Mallard
female. Multinucleated cells are present in the lumen. No sperm are
present. Feulgen’s reaction (DNA), x 420.
Fig. 4. D2816. Granules in the cytoplasm of spermatogonia and in cells in lumen
of seminiferous tubules of a sterile hybrid duck 355 days cf age. This is the
same testis as shown in Figure 3. Periodic Acid Schiff’s reaction, x 420.
A b b . 1. D2696. Samenkanalchen aus dem Hoden einer hybriden, 367 Tage alten
Ente, die durch Paarung eines Mallard-Erpels mit einer hybriden Ente
entstand. Beachte die Anzahl der Zellen, die die Tubuli auskleiden, und
die Spermien.
A b b . 2. D 2703. Samenkanalchen aus dem Hoden einer sterilen, hybriden, 353 Tage
alten Ente, die durch Paarung eines Muscovy-Erpels mit einer weissen
Pekin-Ente entstand. Beachte die Anzahl der Zellen, die das Kanalchen
auskleiden, und die Zellen innerhalb des Lumens.
A b b . 3. D2816. Samenkanalchen aus dem Hoden einer sterilen, hybriden, 355 Tage
alten Ente, die durch Paarung eines Muscovy-Erpels mit einer MallardEnte erzeugt wurde. Multinukleare Zellen finden sich im Lumen. Spermien
fehlen. Feulgen Reaktion (DNS).
A b b . 4. D2816. Granula im Zytoplasma von Spermiogonien und in Zellen im
Lumen der Samenkanalchen einer sterilen hybriden, 355 Tage alten Ente.
Gleicher Hoden wie in Ahb. 3. Perjodsaure-Schiff-Reaktion.
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Testis in the Sterile Hybrid Duck
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558
RIGDON~MOTT
sections. Sometimes it appeared that a portion of some of the PAS
staining granules also stained positive for iron and/or fat.
Similar PAS positive-staining granules were present in the lumen
of the epididymis and adjacent to and between the epithelial cells that
lined these ducts within the epididymis (Fig. 7). A large amount of
lipid also was present in these same areas, as indicated by oil red 0
stains on formalin-fixed and paraffin-embedded sections. A strongly
positive reaction for iron was present almost routinely in the epididymis of all birds (Fig. 6). However, the quantity of this iron staining,
oil red 0 positive and PAS positive granular material always was much
greater in the epididymis of the sterile ducks than in the normal.
Dab smears from the testis were positive for granules when
stained with PAS and for lipids with both oil red 0 and Sudan black
(Fig. 8). The fat droplets varied in size and usually were much larger
than the PAS staining granules. These lipid droplets were present
extracellularly and within the cytoplasm of the spermatocytes. The
Fig. 5. D2816. The cytoplasm of the cells in lumen of seminiferous tubules and
small granules in the cytoplasm of spermatogonia stain positive for iron.
Same testis as shown in Figures 3 and 4. Mallory's iron stain, x 500.
Fig. 6. D2672. Granules in tubules of epididymis of a sterile hybrid duck, 372
days old, resulting from the mating of a Muscovy male with a white Pekin
female. Periodic Acid Schiff and Mallory's iron reaction, x 424.
Fig. 7. D 2770. Granules in lumen and in wall of epididymis of a cross between a
white Pekin male and a Mallard female. This duck, age 383 days, did not
have any sperm in the testis. Periodic Acid SchiFs reaction, x 550.
Fig. 8. D2816. Granules in cytoplasm of cells in a dab smear from the testis of a
sterile hybrid duck shown in Figures 3 and 4. (A) PAS; (B) Diastase
digested and PAS; (C) oil red 0; (D) Sudan black, x 420.
A b b . 5. D 2816. Das Zytoplasma der Zellen im Lumen der Samenkanalchen und die
kleinen Granula im Zytoplasma der Spermiogonien sind Eisen positiv.
Gleicher Hoden wie in Abb. 3 und 4. Eisenfarbung nach MALLORY.
Abb. 6. D2672. Granula in den Nebenhodentubuli einer sterilen hybriden, 372
Tage alten Ente, einer Kreuzung von Muscovy-Erpel mit einer weissen
Pekin-Ente. Perjodsaure-Schiff-Reaktion und MALLORY
Eisenreaktion.
Abb. 7. D 2770. Granula in Lumen und Wand vom Nebenhoden ekes Kreuzungsproduktes zwischen weissem Pekin-Erpel und Mallard-Ente. Diese 383
Tage alte Ente hatte keinerlei Spermien im Hoden. Perjodsaure-SchiffReaktion.
Abb. 8. D2816. Granula im Zytoplasma von Zellen im Hoden-Tupfpraparat yon
einer sterilen hybriden Ente, wie in Abb. 3 und 4. A) PAS; B) Diastase
Einwirkung und PAS; C) Sudanrot 0; D) Sudanschwarz.
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Testis in the Sterile Hybrid Duck
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RIGDON/MOTT
amount of lipid varied in different cells from the same bird, and more
was demonstrable by the oil red 0 stain than by Sudan black. The
quantity of lipid, as indicated by these two fat stains, apparently was
much greater than the PAS positive-staining material. Both the lipids
and the PAS staining granules were present in the cytoplasm of cells
when stained with PAS and then stained with Sudan black. The amount
of lipid staining material appeared to be much greater in the testes of
the sterile hybrid ducks than it was in the testes of normal ducks.
Discussion
The testes of ducks that resulted from mating the Muscovy male
with white Pekin and Mallard females were similar in size and shape to
those of normal ducks. They differed, however, in that the number of
abnormal cells within the lumen of the seminiferous tubules was much
greater in the sterile hybrids than in the normal. Furthermore, the cells
within the tubules of the sterile hybrids contained a very large amount
of lipids, PAS positive-staining granules resistant to diastase digestion
and some iron-staining particles. There were no sperm in the seminiferous tubules in the testes of these hybrids. These differences in the
testis of the sterile hybrid and the normal duck are of considerable
interest when one considers similar observations referable to hormones
made by other investigators in the adult chicken and pigeon59 6 s 16.
COOMBS
and MARSH ALL^ reported that seminiferous tubules in the
normal rooster were free of lipids and contained many sperm. The
testes following hypophysectomy regressed in size, the tubules decreased, the lumens were filled with cellular debris, and there was
massive steatogenesis6. The growth division of the germ cells apparently decreased and no sperm were present in the hypophysectomized
pigeons killed after 15 to 20 [email protected] similar metamorphosis normally
occurred in the testis of birds following the breeding season and, too,
in birds that were prevented from undergoing their normal sexual
cycle because of abnormal environmental conditionss. If lipids remained in the tubules, spermatogenesis did not occurl6. Massive
steatogenesis and inhibitions of spermatogenesis occurred in male
birds when given a single intramuscular injection of 1 mg (20-25 IU of
prolactin)l6.
There was considerable similarity in the seminiferous tubules of
birds following hypophysectomy, as described by COOMBS
and MAR-
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561
Testis in the Sterile Hybrid Duck
SHALL^, and the sterile hybrid ducks resulting from the mating of the
Muscovy male with white Pekin and Mallard females. There was an
absence of sperm and a large amount of lipidal-staining material in
both groups. The occurrence of these changes in the tubules of the
testis in all of these sterile hybrid ducks, regardless of the time when
they were killed, would suggest that a basic defect may be present that
is related in some way to the pituitary gland. Similar morphological
changes, as present in these hybrid ducks, have been produced in the
rooster by the intramuscular injection of prolactin16 and in the pigeon
by hypophysectomy5. Experiments are now in progress in our laboratory to investigate the hypothesis that the testicular lesion, as observed
in the sterile hybrid duck, may be related in some way to the pituitary
gland.
The histologic changes present in these sterile hybrid ducks are
unlike many of the observations made on the testis of the mule19 159 19.
The testes in these hybrid ducks may be the same size as those in the
normal duck. The seminiferous tubules were large and contained
many cells, apparentlyspermatocytes,many of which were degenerated
and multinucleated. There were no sperm. The seminiferous tubules
in the mule’s testis were markedly decreased in diameter and contained very few germ cellsl5~19. In the majority of the seminiferous
tubules only one or two layers of cells lined the wall. The lumens
were either empty or had a mass of degenerating debris159 19. WHITEHEAD~
found
~
no secondary spermatocytes and no spermatozoa in the
testis of the mule.
Histochemical changes similar to those observed in the seminiferous tubules and epididymis of these hybrid ducks have been observed in both man and experimental animalsl7~20. Nearly all the cells
in the seminiferous tubules of normal human testes contained demonstrable lipids. The spermatogonia and the small primary spermatocytes
were often repleted with glycogen; the fully-grown primary spermatocytes contained none. Secondary spermatocytes and spermatids
showed no glycogen, but necrotic cells and germ cells free in the
lumen often were rich in glycogenzo. LONGand E N G L E
observed
~~
that glycogen was present in discrete droplets. Therewere droplets in the
interstitial cells of a substance oxidized by periodic acid but not
removed by diastase digestion in the human testes. In this connection
it is of interest to note that the quantity of PAS diastase-positive
granules present in the spermatocytes was much greater in our sterile
hybrid ducks than in the normal.
2 9
41 Path. vet., Vol. 2, No. 6 (1965)
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562
RIGDONJMOTT
The epithelial cells of the ductuli efferentes in the testes of man
contained an abundant sudanophilic lipid, PAS positive and saliva
resistant granules20. In the pseudostratified columnar epithelial cells
that lined the tubules in the epididymis of these sterile hybrid ducks,
there was also a large amount of PAS positive, diastase resistant
granules similar to those in the seminiferous tubules. Apparently these
same granules or portions thereof stained positive for iron by Mallory’s
technique. A similar iron-staining material was also present in the
epididymis of normal ducks. MONTAGNA~~
has suggested that the
principal function of the caput epididymis and particularly the ductuli
efferentes in man is the removal of fluid, cell debris and pigment
coming from the seminiferous tubules. Furthermore, it is entirely
possible that the abundant lipid found in the lumen of the ductuli
efferentes may be in the process of being absorbed rather than secreted’s. Such a process may well explain the presence of the excessive
amount of fat, iron and PAS positive material in the epididymis of the
duck. There was, however, a marked disproportion in the amount of
iron in the seminiferous tubules and in the epididymis. Apparently,
the same granules sometimes may stain positive with periodic acid
S c M and with Mallory’s stain for iron. However, the iron reaction in
all ducks was always more extensive in the epididymis than it was in
the seminiferous tubules.
The anatomy and physiology of the testis in birds were recently
reviewed by VANT I E N H O ~ E
He
Npointed
~ ~ . out that the seminiferous
tubules may have an endocrine function in some birds. The large
number of PAS positive, diastase resistant granules, the positive ironstaining material, and the excessive amount of lipids in the hybrid duck
suggest that some endocrine function may well be present.
The morphologic findings and the absence of sperm in these
sterile hybrid ducks were similar in many ways to the testes in man
when there was spermatogenic arrest, as described by ENGLE~.
He
concluded from his study that “the essential defect appears to lie in the
inability of the primary spermatocytes to pass through this reductiondivision phase”. The relationship of spermatogenic arrest to the
mechanism of sterility in the hybrid duck and mule is of interest.
BENIRSCHKE
et al.2 in 1962 from their study of the mule’s testis expressed the opinion that “azoospermia appears to result from degeneration of spermatocytes”. Several investigators’. 1%26 have considered
that sterile hybrids resulted from abnormalities in chromosomes.
There is, however, much controversy over using the chromosome
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Testis in the Sterile Hybrid Duck
563
mechanism as an explanation for sterility in the duck. We are unable at
this time to explain the mechanism of sterility in the hybrid ducks and
to interpret satisfactorily the histochemical changes that are present.
Summary
The histologic and histochemical characteristics of the testis and epididymis
in normal and hybrid ducks are described. Granules are present in the cytoplasm of
the spermatocytes in all ducks; however, the amount is much greater in the sterile
hybrid birds. These granules stain PAS positive and are diastase resistant. Associated with, or as a part of, these PAS positive granules are foci that stain positive for
iron in some of the cells in the seminiferous tubules. This reaction, too, is more
often present in the sterile hybrid than in the normal. Lipids are present in the
spermatocytes and, likewise, in much larger amounts in the sterile hybrids than in
the normals. PAS positive and diastase resistant granules are present in the tubules
of the epididymis of all ducks. A majority of these granules also give a strongly
positive reaction for iron. The amount of iron is greater in the sterile hybrids than
in the normal ducks. Lipids are also present in the epididymis.
Zusainmcnfasstng
Die histologischen und histochemischen Eigenschaften des Hoden- und
Nebenhodengewebes normaler und hybrider Enten werden beschrieben. Granula
finden sich im Zytoplasma der Spermiozyten aller Entcn, jedoch in besonders
grosser Menge bei den sterilen Hybriden. Die Granula farben sich PAS-positiv
und sind Diastase-resistent. Vergesellschaftet damit, bzw. gleichzeitig weisen diese
PAS-positiven Granula in manchen Zellen der Samenkanalchen cine positive
Eisenreaktion auf. Diese Reaktion ist ebenfalls haufiger bei sterilen Hybriden als
bei normalen Enten vorhanden. Gleiches lasst sich fur die in den Spermiozyten
vorkommenden Lipide sagen. PAS-positive und Diastase-resistente Granula sind
in den Tubuli der Nebenhoden dler Enten vorhanden. Die Mehrzahl dieser
Granula gibt ausserdem eine stark positive Eisenreaktion. Eisen ist bci sterilen
Hybriden in grosserer Menge als bei normalen Enten nachzuweisen. Lipide finden
sich ebenfalls im Nebenhoden.
Acknowledgements
This investigation was supported by grant NB 02951-05 from the National
Institutes of Neurological Diseases and Blindness, U.S. Public Health Service, and
by a NIH-Medical Student Research Training Grant.
The technical assistance of JOHNMACKand MARIONGAYhas contributed
greatly to this study.
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564
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