The Sexual Behavior of Two Sympatric Species of Poeciliid Fishes and Their Laboratory-Induced Hybrids, With an Analysis of the Factors Involved In the Isolating Mechanism

139 Pages·04.877 MB·English

by  Clark Eugenie

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Xerox University Microfilms
300 North Zeeb Road
Ann Arbor, Michigan 48106
' ' -, %
“3907 13 2138
*07^ Clark, Eugenie, 1922-
1950
The sexual behavior of two sympatrri c
eC5
species of Poeciliid fishes and their
laboratory induced hybrids, with an
analysis of the factors involved in
the isolating mechanism. New York,
1914.9.
lllj. typewritten leaves. 21 plates
(incl.diagrs.) tables. 29cm.
Thesis (Ph.D.) - New York Univer­
sity, Graduate School, 1950.
Bibliography: p.l03“lllf-»
C50655 O -
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Xerox University Microfilms, Ann Arbor, Michigan 48106
THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED.
LIBRARY Of
M W TORE UNIVERSITY
OBIVERSITI HEIGHTS
THE SEXUAL BEHAVIOR OF TWO SYMPATPIC SPECIES OF
POECTLIID FISHES AND THEIR LABORATORY INDUCED HYBRIDS,
WITH AN ANALYSIS OF THE FACTORS INVOLVED
B: THE ISOLATING MECHANISM.
by
Eugenie Clark
A dissertation in the Department of Biology submitted to the
faculty of the Graduate School of Arts and Science of New York
University in partial fulfillment of the requirements for the
degree of Doctor of Philosophy.
CONTENTS
Page
INTRODUCTION AND ACKNOWLEDGEMENTS................................ 1
REVIEW OF THE LITERATURE..........................................5
MATERIAL AND METHODS............................................ 18
RESULTS..........................................................24
Resume of the normal mating pattern . . . 24
The relation of jabbing and copulation to insemination. . . . . 32
^he reliability and limits of the sperm smear technique. ..;.. 32
Role of the tip of the gonopodium during copulation. . . . . . 36
Analyses of sexual behavior................................... 43
Sexual behavior of P. maculatus............................2,3
Sexual behavior of X. hellerii..............................54
Sexual behavior of Fj hybrids.................. 62
Sexual behavior of backcross hybrid males ................ 68
Sexual behavior of F^ hybrid males. . . . . . . . ......... 72
Observations on interspecific matings......................... 77
Analysis of interspecific behavior of paired fish...........77
The behavior of males with an inter- or intraspecific
choice of females .................. 79
Experiments on sexual isolation................. ............85
The isolation index. ................. 85
Mating selection in large groups...........................91
DISCUSSION....................................................... 94
SUMMARY AND CONCLUSIONS......................................... 102
BIBLIOGRAPHY................................................ . 103
%(o
X 0 \ O
INTRODUCTION
That the platyfish, Platypoecilus maculatus. and the related
swordtail, Xinhophorus hellerii, hybridize in captivity, and that some
viable and fertile offspring are produced, has been known to aquarists
since 1910^. These fishes and their hybrid^ have provided material for
extensive investigations in fish genetics, particularly the factors
involved in atypical pigment cell growth (Bellamy, 1928; Kosswig, 1939;
Breider, 194-2; Gordon, 194-8). Most of the colorful varieties of
aquarium bred (domesticated) platies and swordtails offered on the
market to pet-fish hobbyists are probably hybrid combinations of the
two (Gordon, 194-6).
In their natural environment the territories of these two
species overlap. Gordon (1939 and 194-7) has reported that, in the rivers
of Mexico, although there is a tendency for the platyfish to live in
slower, lowland waters and the swordtails in faster headwaters, they
have been found living side by side in twenty-five per cent of the field
stations and he has occasionally obtained both species in a single seine
haul. It is of interest to the evolutionist then to find that among the
thousands of specimens collected, a hybrid has never been collected in
nature. On numerous occasions, biologists concerned with the study of
animal populations have met with situations similar to this. Where
geographical and ecological isolations are not involved, where seasonal
or temporal factors (differences in reproductive periods), mechanical
factors (incompatibility of genital parts), failure of sperm to reach or
penetrate egg, inviability or weakness of the zygote, and hybrid sterility
are not critically involved in the isolation of two species, investigators
1
Popular accounts are reported in the "Wochenschrift fttr Aquarien-
und Terrarienkunde" and the "Blatter fUr Aquarien und Terrarienkunde."
2
See figures 1 through 9.
have advanced the hypothesis that psychological phenomena form the
crucial barrier. Therefore the isolating mechanism operating is
called "psychological," "sexual" (Dobzhansky, 1941) or'fethological"
(Mayr, 1942).
In recent years, the problem of psychological isolating
mechanisms has been investigated extensively in Drosophila^ and to
some extent in other animals, P. maculatus and X. hellerii. present
the following unique combination of factors of advantage in the study
of psychological isolating mechanisms, namely that (1) they occur
sympatrically, that is, in some places they occupy the same ecological
niche in nature, (2) hybrids have not been found in nature, and (3)
fertile hybrids can be obtained easily in the laboratory. Preliminary
contributions to the study of psychological isolating mechanisms in
these fish have been made by Clark, Aronson, and Gordon (1948) and
Schlosberg, Duncan, and Daitch (1949).
The combination of the platy genes controlling the production
of macromelanophores with certain modifying genes from the swordtail,
produces a genic imbalance in the hybrid leading to the development of
melanotic tumors, the inheritance of which has been worked out in these
hybrids (Gordon, 1948). In nature an isolating mechanism prevents
hybridization between the platyfish and swordtail.
This present study is an attempt to understand this isolating
mechanism through the observation of the sexual behavior of the platyfish
and swordtail and by studying qualitative and quantitative differences in
the behavioral patterns of homo- and hetero-species matings,,
i
See references in historical review, section on psychological
isolating mechanisms.
3
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A smear technique for the detection of sperm in the female
genital tract has been developed. Along with experimental work on
the function of the gonopodium and an analysis of the sexual behavior
of the two species and their hybrids, this smear technique has
facilitated a study of the copulatory act and other aspects of repro­
ductive behavior and physiology in these viviparous fishes. Moreover,
the availability of the various hybrid combinations made possible a
supplementary study of the inheritance of their sexual behavior patterns.
ACKNOWLEDGMENTS
For their sponsorship and encouragement, I am indebted to
Dr. Ntyron Gordon of the New York Zoological Society and New York
University and Dr. Lester R. Aronson of The American Museum of Natural
History, both of whom offered valuable suggestions and constructive
criticisms. I am grateful to Miss Rosetta Natoli and Mrs. Marie
Holz-Tucker for their collaboration in some of the experimental work
and histological preparations, and to Mrs. Hedwig Englert for the typing
of the manuscript. The kind assistance of Mr. John Polo in the care and
maintenance of the large stocks of fishes used in this problem is greatly
appreciated.
Dr. Lester R. Aronson has generously permitted me to use
working space and the facilities of the laboratories and greenhouse in
the Department of Animal Behavior of The American Museum of Natural
History. The animals used in this report were obtained from the Genetics
Laboratory of the New York Zoological Society at The American Museum of
Natural History. They were made available through the courtesy of
Dr. ^^5r^on Gordon.
This study has been supported by grants to the Department
of Animal Behavior of The American Museum of Natural History from the
Committee for Research in Problems of Sex, National Research Council,
and from the Research Fund of the Council of the Scientific Staff of
The American Museum of Natural History; to the New York Zoological
Society from the National Cancer Institute of the United States Public
Health Service.
Miss Olga Aranowitz, working on the pituitary of these fish,
Dr. Margaret Tavolga, working with hormones, Dr. William Tavolga,
studying the embryology, and Mr, Donn E. Rosen, studying the external
genitalia have in many instances shared the same experimental animals
as were used in these studies of their behavior. Their data have in
some cases been correlated with our own and have given helpful back­
ground material in the final analysis.
The photographs in figures 1 through 9 were taken by
Mr. Sam C. Dunton of the New York Zoological Society. The sketches
were prepared with the help of Mr. Ross Montanari.
5
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REVIEW OF THE LITERATURE
Part I: Sexual behavior.
The viviparous poeciliids have been the subject of a number
of investigations of their reproductive morphology and physiology
(Turner, 1947) but comparatively little was known of their sexual
behavior. Numerous sketchy descriptions of poeciliid courtship activi­
ties have appeared in popular articles in aquarium journals and a
number of casual observations have been reported in the scientific
literature. The only detailed studies on poeciliid sexual behavior are
those of Breder and Coates (1935)* Noble and Curtis (1935.) on the
common guppy Lebistes, Clark, Aronson, and Gordon (194&; 1949 in press),
Schlosberg, Duncan, and Daitch (1949) on Platypoecilus maculatus and
Xiphophorus hellerii.
The copulatory organ or gonopodium of the male, a mechanism
for internal fertilization, is one of the most characteristic features
of the poeciliid fish. The gonopodium is used as a diagnostic character
for taxonomic differences in the Poeciliidae (Regan, 1913; Hubbs, 1924»
1926, etc.) and its highly modified structure has stimulated numerous
detailed studies on its morphology and development (Langer, 1913;
Dulzetto, 1931; Grobstein, 1940; Turner, 1941; Cummings, 1943; Rosen and
Gordon, in ms.; etc.).
The action of the gonopodium during courtship and copulation
is one of the most striking features in the sexual behavior of these
fishes. FitzGerald (1872) gave one of the first accounts of the action
of the gonopodium and courtship in viviparous fishes. He described how
in Poecilia sp. the gonopodium "is furnished with a hinge joint and is
capable of being thrown forward at an acute angle, being also susceptible
6
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of a alight lateral movement. The act of copulation takes place by
the male rising perpendicularly under and a little to one side of
the female and making a dart at her with the spine (of the gonopodium)
which is brought laterally forward at the instant of connection. The
act is almost momentary and is hardly noticeable without the closest
attention." Other brief reports of copulatory behavior are given for
a number of poeciliids. Agassiz (1853) witnessed copulation in
Mollienisia but gave no details of the behavior. Ryder (1885) published
a report of copulation in Gambusia during which the head of the male
was said to be turned in the direction of the tail of the female but
other investigators (Henn, 1916; Collier, 1936) relying on the more
detailed description given by Seal (1911) consider Ryder's report to
be incorrect. According to Seal (1911) the mating activity of Gambusia
holbrooki and Heterandria formosa are exactly alike. His rather
anthropomorphic account states that "The male follows incessantly and
warily after the female,, .... watching for a moment when her attention
will be distracted, when he will make a sudden dash, sometimes succeeding
in inserting the intromittent organ into the genital pore, but oftener
apparently missing, because of a quick turn of the female from which he
flees in apparent terror. The contact is so sudden and brief that it
required many observations to verify it. In these movements the male
organ is thrust forward and to the right toward the female." Zolotnisky
(1901) noted the versatile movements of the gonopodium during courtship
Giradinus and Collier (1936) studied the structure and function of
the gonopodium and associated parts in Gambusia« correlating peculiarities
of these systems with the method of insemination believed to be employed
and studying especially the mechanism for the reversal of the gonopodium.