Table Of Content<JvLemoirs of the
Conneäicut Academy of Arts & Sciences
November Volume XIII 1957
The Systematics
of North American Daphnia
BY
JOHN LANGDON BROOKS
Published by the Academy
TO BE OBTAINED ALSO FROM
Yale University Press
PRICE $ 8.00
BIANCO LUNO'S PRINTING - COPENHAGEN
DENMARK
7.
ALEXANDER PETRUNKEVITCH
teacher, friend and wise counsellor
on the occasion of his eightieth birthday,
22 December W5
PREFACE
Early in the course of the author's experimental and observational studies into the ecology of
Daphnia, the inaccuracies and omissions in the existing systems of nomenclature for this genus
were readily apparent. Isolated probings into the taxonomy of the few species immediately
concerned sufficed for the interpretation and presentation of these early studies. However, with
the widening scope of the ecological investigations it became evident that a thorough knowledge
of the systematics of the genus was essential. It was with considerable reluctance that the study
to provide this knowledge was undertaken, because it is quite clear that a systematic study is
of limited utility unless its geographical limits coincide with significant boundaries for the
organisms involved. This study, then, must consider the representatives of the genus Daphnia
that occur on the North American continent. The primary aims of this investigation were to
determine: (1) the species found on this continent; (2) the broad aspects of the geographical
and ecological distribution of each; (3) the appropriate name for each.
The procedure followed was first to examine as many populations from as many parts of the
continent as possible. Most of the material was, of necessity, collected by other investigators
so that the areas sampled were determined in large part by the sites of previous collections.
Nevertheless, all parts of the continent except the Labrador Peninsula are reasonably well
represented. Scattered collections from other parts of the world were made available to the
author and these were of considerable value in determining the status of the North American
populations of species with intercontinental distributions. The results of this portion of the study
achieved the first two aims, and provided the material for a meaningful pursuit of the third.
Search of the ample taxonomic literature disclosed that a pertinent name was available for
each of the fifteen species revealed in the first part of the investigation.
This monograph presents the major results of this inquiry into the systematics of North
American Daphnia. It is divided into the following four chapters:
Chapter I is a general discussion of the systematic and Zoogeographie findings. The classifica
tion revealed by this investigation is compared with previous classifications. It is also considered
as a contribution toward the worldwide systematics of the genus. An attempt is made to compre
hend the Zoogeographie history of each species that has representatives in North America, through
an integrated study of morphological, ecological, and distributional data.
Chapter II is concerned with the identification of species. The key is accompanied by illustra
tions which depict the alternative diagnostic characters. It is preceded by remarks on the pre
paration of material for identification.
Chapter III contains the descriptions of the fifteen species. The 317 camera lucida drawings
(grouped into 29 plates) which record the form and variation of each species constitute a major
part of the descriptions. There is also given for each species a synonymy, notes on the taxonomic
history (see below), a differential diagnosis to supplement the key, and pertinent ecological and
distributional data (including maps indicating the distribution of each species on the North
American continent).
6 THE SYSTEMATICS OF NORTH AMERICAN DAPHNIA
Chapter IV is entitled "Regional Aspects of Daphnia Systematics." Herein are indicated the
ten regions into which the North American continent can be divided on the basis of the as
semblages of Daphnia species. This will, it is hoped, indicate some of the possible interspecific
interactions which have undoubtedly played important roles in the evolution of the species
concerned. A series of plates show the assemblages characteristic of each region, and also serve
to emphasize the regional aspects of the variation of each species. These plates serve as an adjunct
to the key in the identification of specimens by illustrating the most probable appearance of
each species found in any collecting area.
A list of the North American localities (except for those in New England, which will be detailed
elsewhere) from which populations were examined, and the species present, is included as
an Appendix.
This systematic investigation, in addition to the results which form the substance of this mono
graph, has provided further insight into the nature of some of the phenomena which make the
biology of Daphnia so interesting—and their systematics so difficult. Chief among these phenomena,
which are only mentioned in this monograph, are the extraordinary phenotypic variation, the
frequent co-existence of several species in the same body of water, and the not infrequent occur
rence of introgressive hybridization. But possibly the most interesting theoretical outcome of
this study has been the suggestion that it gives of the adaptive significance of extensive pheno
typic variation (cyclomorphosis). As each of these topics merits detailed consideration, they will
be considered at a later time.
Any systematic study is in part historical, not only in the sense that it deals with the history
of the organisms, but also because it is concerned with the history of the human endeavor to
understand this particular aspect of the natural world. The published accounts of such endeavors
do not always provide sufficient information about the materials studied. Through good fortune
and the generosity of several people it has been possible for the author to examine ancillary
evidence (both specimens and preliminary data), which permits meaningful interpretation of
several published results that would otherwise be of uncertain value.
It seems appropriate to indicate here the nature of this heretofore unrecorded material and
its sources. These materials relate to the work of two pioneer American students of the Cladocera,
S. A. Forbes and C. L. Herrick, and that of three European investigators, S. Fischer, J. Richard,
and G. O. Sars. The source of most of this data is the collection of material relating to the Clado
cera which the late E. A. Birge had accumulated. After Birge's death, this collection was sent
to the author by Professor A. D. Hasler, of the Department of Zoology, University of Wisconsin.
It is a pleasure to record my indebtedness to him and to the department.
The Birge collection included slides of some of Forbes' type specimens. These were greatly
supplemented by slides of specimens that Forbes had collected, which were kindly lent by
Professor Samuel Eddy and the late Professor Harley J.Van Cleave. Specimens from these three
sources made possible the re-description of Forbes' type material (Brooks, 1953 a, b). However,
a proper evaluation of the status of Forbes' names was not possible until the present investiga
tion. (See taxonomic notes on D. pulex, D. schodleri, D. rosea, and D. thorata.)
Also among the Birge collection were the work notebooks which Herrick kept during his study
of the Cladocera. These rough drawings and notes, which are unquestionably the source for the
published drawings, are more accurate and complete than the latter, and have served unequi
vocally to establish the identity of certain of his specimens and the names he proposed for them.
Two pages from these notebooks are here reproduced as Plate 43. (See taxonomic notes on
D. dubia and D. laevis for details.)
An even more unexpected inclusion in the papers of the Birge collection was a portfolio of
rough camera lucida drawings by Richard. These large drawings are unquestionably the source
of the small lithographs that accompanied his 1896 revision of the Cladocera. Some of these
drawings are particularly valuable because they depict specimens from the type collections of
JOHN LANGDON BROOKS 7
both Sars and Fischer, whose original descriptions either were without illustrations (Sars) or
inadequately illustrated (Fischer). (It should be noted that Sars made careful drawings to ac
company his later descriptions, and these are among the best ever made of Cladocera.) The
pertinent camera lucida drawings are photographically reproduced in Plates 10 and 11, and
they are discussed under the taxonomic history of the species concerned. The skill with which
Mr. Emiddio De Cusati, Photographer at the Yale School of Fine Arts, used infra-red photography
to intensify these faint pencil lines on paper brown with the age of sixty years deserves special
mention.
As was noted above, most of the material examined in this investigation was not collected by
the author, but was lent or given for examination by many people. To all of these, whose names
are indicated in the locality list (Appendix), the author wishes to express his gratitude and
indebtedness. Some of those contributors have been so generous with their time and interest
as well as the collections, that the author would like to record his thanks here as well. These are :
Fenner Chace, Jr. (loan of S. F. Light collection from U. S. National Museum); R. E. Coker
(University of North Carolina); E. S. Deevey, Jr. (Yale University); W. T. Edmondson (University
of Washington); A. D. Hasler (University of Wisconsin); W. Jones (University of Oklahoma);
R. W. Kiser (Centralia Junior College, Washington); J. E. Lynch (University of Washington);
Mildred S. Wilson (for collections by personnel of Arctic Health Research Center; these collec
tions are property of U. S. National Museum); J. G. Mackin (Agricultural and Mechanical College
of Texas); M.Meyer (University of Maine, for material collected by staff of Department of
Zoology on biological surveys conducted for Maine Department of Inland Fisheries and Game);
J. E. Moore (University of Alberta); R.W. Pennak (University of Colorado); D. S. Rawson
(University of Saskatchewan). For the opportunity of examining non-North American material,
the author is indebted to J. H. Barrow, Jr. (Huntingdon College, Alabama)—England; Sidney
Hsaio (University of Hawaii)—China; G. E. Hutchinson (Yale University)—South Africa,
Sweden; A. F. O'Farrell (New England College, Australia)—Australia; V. Tonolli (Istituto
Italiano di Idrobiologa, Pallanza)—Italy.
It is a pleasure to express my thanks to Professor J. S. Nicholas, Director of the Osborn
Zoological Laboratory, Yale University, for the facilities of the laboratory and for reimbursement
for local field work. To Professor Edmund W. Sinnott, Director of the Sheffield Scientific School,
are due thanks for the financial support of field work in southern Ohio. I wish to record my
thanks for the kind and helpful cooperation of Dr. Dorothea Rudnick, Secretary of the Connec
ticut Academy of Arts and Sciences, in the preparation of the manuscript for publication. To the
student assistants provided by the Committee on Bursary Appointments of Yale University fell
much of the routine work associated with a systematic study of this scope; to three of them in
particular I wish to express my thanks for perseverance in dull work — G. W. Davis, III, G. Lan
der, and N. Zlotsky. The greatest debt I bear my wife, Yvette D. G. Brooks, for moral support
and encouragement, and for assistance in the uninspiring task of checking manuscript and
Pr0°f- J.L.B.
Osborn Zoological Laboratory
Yale University
15 February 1956
CONTENTS
Page
PREFACE . . . 5
LIST OF ILLUSTRATIONS 9
LIST OF TABLES 10
:
CHAPTER I
A General Account of the Systematics of North American Daphnia 11
COMPARISON OF THE TWO CLASSIFICATIONS ......... 12
ON THE CLASSIFICATION OF THE SUBGENUS DAPHNIA 13
AFFINITIES OF THE NORTH AMERICAN SPECIES. .. . .. .. 15
HOLARCTIC SPECIES . .....' 16
NEW WORLD SPECIES ... 20
CONTRIBUTIONS TOWARD THE CLASSIFICATION OF DAPHNIA . . . . 23
CHAPTER II
Identification of North American Species of Daphnia 27
KEY TO NORTH AMERICAN DAPHNIA 30
CHAPTER III
Descriptions of Species Found in North America 32
SUBGENUS CTENODAPHNIA: D. SIMILIS... 32
D. MAGNA.... 44
SUBGENUS DAPHNIA: D. MWDENDORFFIANA 47
D. PULEX 58
D. SCH0DLERI 66
D. CATAWBA.... 76
D. PÁRVULA .... . 82
D. RETROCURVA 88
D. AMBIGUA..... 96
D.LONGIREMIS ..."." 105
D. ROSEA. 110
D. LAEVIS 117
D. DUBIA. 123
D. GALEATA MENDOTAE 132
D. THORATA 138
CHAPTER IV
Regional Aspects of Daphnia Systematics. 145
BIBLIOGRAPHY 165
LIST OF LOCALITIES 168
INDEX 177
LIST OF ILLUSTRATIONS
Plate Page
1. Convergence in helmet shape, (A) in the "cephalata" form of Daphnia carinata King, (B) in Daphnia
gibba Methuen. (After Wagler.) .. 25
2. Daphnia similis Claus. Variation in adult females; neonata, male, and ephippial female 36
3. Daphnia similis Claus. Continuation of Plate 2 . 37
4. Dorsal and lateral views of (A) Daphnia atkinsoni Baird and (B) Daphnia triquetra Sars. (After Wagler; Sars.) 39
5. Daphnia similis Claus. Postabdomens of female and male; claw 40
6. Daphnia similis Claus. Rostra, female and male 41
7. Distribution map. for Daphnia similis Claus and Daphnia magna Straus in North America 43
8. Daphnia magna Straus. Dorsal and lateral view of female; postabdomens of female and male; claw , 45
9. Daphnia magna Straus. Ephippial female; rostra of female and male 46
10. Daphnia middendorfftana Fischer. Richard's camera lucida drawings (unpublished) of Fischer's "types"
with accompanying notes Following page 48
11. Richard's camera lucida drawings (unpublished) of Sars' "types" of D. schodleri and D. rosea, and of a
specimen Sars considered to be Daphnia longispina, Müller Following page 48
12. Daphnia middendorfftana Fischer. Females from Alaska, Canada, California 50
13. Daphnia middendorfftana Fischer. Parthenogenetic and ephippial females, and male from Washington... 51
14. Daphnia middendorfftana Fischer. Rostra, male and female, Washington specimens 53
15. Distribution map for Daphnia middendorfftana Fischer in North America 57
16. Daphnia pulex Leydig. Females and male from Alaska and Canada 60
17. Daphnia pulex Leydig. Females from central and eastern United States 62
18. Daphnia pulex Leydig. Hybrid (?) populations from eastern Oregon and Washington 64
19. Distribution map for Daphnia pulex Leydig emend. Richard in North America 65
20. Daphnia schodleri Sars. Females and males from Alaska, Canada, and Wisconsin 68
21. Daphnia schedleri Sars. Females showing transition to "arcuata" form; Washington, Wyoming, California 70
22. Daphnia schedleri Sars. Females with dorsal helmets; Oklahoma, Texas 71
23. Distribution map for Daphnia schodleri Sars and Daphnia catawba Coker in North America .... 75
24. Daphnia catawba Coker. Seasonal variation in Tucker Pond, Rhode Island 78
25. Daphnia catawba Coker. Geographical variation 80
26. Daphnia párvula Fordyce. Seasonal variation; Oklahoma, North Carolina 85
27. Distribution map of Daphnia párvula Fordyce and Daphnia retrocurva Forbes in North America 87
28. Daphnia retrocurva Forbes. Females from type localities (?); seasonal variation in Bantam Lake, Connecticut 91
29. Daphnia retrocurva Forbes. Geographical variation in central part of continent; "breviceps" and helmeted
individuals from a single population in a New York lake 93
30. Seasonal variation of Daphnia retrocurva Forbes in a Connecticut lake 95
31. Daphnia ambigua Scourfleld. Females and males 99
32. Daphnia ambigua Scourfleld. Scourfleld's drawings 101
33. Seasonal variation of Daphnia ambigua Scourfleld in a Connecticut lake 102
34. Distribution map of Daphnia ambigua Scourfleld and Daphnia longiremis Sars in North America 104
35. Seasonal variation in Daphnia cristata Sars and Daphnia longiremis Sars in Lake Oren, Sweden. (After
Friedenfelt.) 106
36. Daphnia longiremis Sars. Various head shapes in females of North America; male from Shuswap Lake,
British Columbia 107
37. Daphnia longiremis Sars. Lilljeborg's drawing of a helmeted Swedish specimen 108
38. Daphnia rosea Sars. Typical and "robusta" forms of female; male 113
39. Distribution map of Daphnia rosea Sars in North America 116
40. Daphnia laevis Birge (after Banta); related African species (after Wagler) 119
41. Daphnia laevis Birge. Females and male 121
42. Distribution map of Daphnia laevis Birge and Daphnia dubia Herrick in North America 124
43. Daphnia dubia Herrick. Unpublished sketches from Herrick's notebook. 126
Plate Page
44. Daphnia dubia Herrick. Seasonal variation in females 127
45. Daphnia dubia Herrick. Geographical variation in females; male 131
46. Daphnia galeata mendotae Birge. Specimen from type-locality of subspecies; seasonal variation in a Con
necticut lake; male 135
47. Daphnia galeata mendotae Birge. Geographical variation in female 136
48. Daphnia galeata galeata Sars. (After Lilljeborg.) 137
49. Distribution map of Daphnia galeata mendotae Birge and Daphnia thorata Forbes in North America ... 139
50. Daphnia thorata Forbes. Variation in female 143
51. Map showing the division of North America into ten areas on the basis of their distinctive assemblages
of Daphnia species 146
52. Species assemblage of Area A 148
53. Species assemblage of Area B 149
54. Species assemblage of Area C 150
55. Species assemblage of Area D 152
56. Species assemblage of Area E 154
57. Species assemblage of Area F 156
58. Species assemblage of Area G 158
59. Species assemblage of Area H 160
60. Species assemblage of Area I 162
61. Species assemblage of Area J 163
LIST OF TABLES
Table Page
I. Comparison of characteristics of middendorjfiana and pulex 49
II. Comparison of characteristics of catawba and schodleri 77
III. Comparison of characteristics of galeata and hyalina 133
IV. Comparison of characteristics of thorata, hyalina, and galeata mendotae 140
V. Comparison of characteristics for diagnosis between galeata mendotae and thorata 142
VI. Distribution of species in saline lakes of southern Saskatchewan 152
VII. Frequency of occurrence in Maine lakes 157
CHAPTER I
A General Account of the Systematics of
North American Daphnia
D
APHNIA are particularly suitable material for a study of the ecological aspects of evolution
(or the evolutionary aspects of ecology). The genus enjoys a world-wide distribution, yet
comprises a manageable number of species—probably around 50, of which 30 are adequately
characterized. The extreme variability within most species bedevils the taxonomy, yet is in its
own right a phenomenon well worth the close attention of the ecologist. The seasonal variation
in body form, which often produces bizarre shapes, is determined in large part by environmental
changes because parthenogenesis of the type found in Daphnia keeps the genotype similar from
generation to generation. Such evolutionary and ecological studies, while an integral part of
Daphnia systematics, have to be based on a sound classification.
Unfortunately the scheme for the classification of Daphnia proposed by Birge (1918), which
was quite adequate in its day, will no longer suffice. The philosophy of systematics has changed
considerably in the 45 years since Birge prepared his key to the North American Cladocera.
(He had finished his section on Cladocera in 1910, although it was not published until 1918.)
The trinomials and quadrinomials which he employed, as had been done for two decades before
him, are no longer justifiable. When the nature and limits of each species are discovered, there
is no longer need for polynomials. In the past these have been employed both to designate
morphological variants within a species (usually not geographical variants in the modern sense
of the term), and to indicate intergroup relationships. Both of these usages are not only unsound
but also unnecessary.
A large part of the trouble, as we shall see, has come from the tenacious adherance to the
idea that all species of the subgenus Daphnia that have large teeth in the middle pectén of the
postabdominal claw must be assigned to Daphnia pulex, and all species without these large teeth
must be assigned to Daphnia longispina. This lumping, which has characterized most of the
Daphnia taxonomy since the early years of this century, has resulted in the inclusion of at least
six species (considering the entire world) under the name "Daphnia pulex" and at least nine
under "Daphnia longispina." Although the species in each group have but the single claw character
in common (and many differences between them) they were retained without question under
the names "pulex" and "longispina." But as the distinctness of some of the species included
in these two groupings was recognized they had to be designated by a trinomial, or often a
quadrinomial. A few workers have recognized this as an unsatisfactory taxonomy (Mackin, 1931
in this country; Scourfield, 1942, 1946; and Johnson, 1952 in England). But on the other hand
there are a few who, because of the difficulty of distinguishing between some "pulex" and some
"longispina," would lump both into one species! This is simplification but not classification.
