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Americana
A Journal of Entomology.
Volume XLI (New Series) for 1961
PUBLICATION COMMITTEE
JAMES A. SLATER, EDITOR GEORGE S. TULLOCH JOHN HANSON
PUBLISHED BY THE
BROOKLYN ENTOMOLOGICAL SOCIETY 1961
ENTOMOLOGICA AMERICANA
Vol. XLI (N.S.), for 1961 CONTENTS
A Revision of the Genus Copris Muller of the Western Hemisphere (Coleoptera, Scarabaeidae). Eric G. Matthews
j
Pages
1-137
VOL. XLI (NEW SERIES)
A Journal of Entomology.
PUBLISHED BY THE
BROOKLYN ENTOMOLOGICAL SOCIETY
PUBLICATION COMMITTEE
JAMES A. SLATER, EDITOR GEORGE S. TULLOCH JOHN HANSON
Published for the Society by the Business Press Inc.
N. Queen St. and McGovern Ave., Lancaster, Pa. Subscription $6.00 Per Year Date of Issue April 9, 1962
AmerigAna
VOLUME XLI
A REVISION OF THE GENUS COPRIS MULLER OF THE WESTERN HEMISPHERE (COLEOPTERA. SCARABAEIDAE)
By Eric G. Matthews1
TABLE OF CONTENTS
Page
Introduction 2
Materials and Methods 6
Acknowledgements 7
Morphology 8
Microsculpture 8
Head 9
Mouthparts 10
Prothorax 10
Pterothorax 11
Elytra 12
Legs 12
Abdomen 13
Genitalia 13
Sexual Dimorphism 13
The Sexual Armament in Copris 14
Intraspecific Variation in Horn Height 15
Interspecific Variation in Horn Height 26
Biology 27
Taxonomy 33
Genus Copris Muller, 1764 35
Key to the Species of the Genus Copris in the Western Hemisphere Based
on the Major Males 35
Key to the Species of the Genus Copris in the Western Hemisphere Based
on the Males and Females 39
Group I. The minutns group " 43
Complex 1. The incertus complex 44
1 Dept, of Biology, U. of Puerto Rico, Rio Piedras, formerly at Cornell University, Ithaca, New York.
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Complex 2. The minutus complex 56
Group II. The fricator group 63
Complex 1. The armatus complex 64
Complex 2. The arizonensis complex 84
Complex 3. The remotus complex 87
Complex 4. The rebouchci complex 98
Complex 5. The fricator complex 107
Literature Cited 118
Plates 121
INTRODUCTION
Copris Muller is a genus of principally Old World coprophagous scarabs represented in the New World primarily in North and Central America. The present work deals only with the adults of the Western Hemisphere species.
The name Copris is fairly old; it was coined by Geoffroy (1764) to include all those species in the Linnaean genus Scarabaeus characterized by the absence of a visible scutellum. However, since Geoffroy ’s work has been discarded for nomenclatorial pur- poses*, the first valid user of the name was Muller (1764), who included an indication but no species. The first valid inclusion of species was by Fourcroy (1785), who included ten species, the first of which was lunaris L. Fabricius did not adopt the name Copris until 1798 in the Supplementum Entomologiae Systematicae. Thereafter the name was in wide use but the first valid type designation appears to be that of Curtis (1832), who designated Scarabaeus lunaris Linnaeus as the type of the genus.
Following Olivier’s (1790) very broad concept of the genus (including even many scutellate dung beetles) numerous groups were separated off as independent genera and by the end of the first third of the 19th century the name Copris had become re- stricted to a fairly homogeneous assemblage. In 1837 Hope pro- posed the first of several further subdivisions, in which he was followed by Burmeister (1846) and Erichson (1847). These sub- divisions Lacordaire (1856) did not accept, preferring to go back to the broader concept. Nevertheless, the genera and subgenera proposed by Hope, Burmeister, and Erichson subsequently became largely accepted and it was the latter author who formulated the restricted concept of Copris which exists, in largely unmodified form, today, although several additional small genera have been separated off since. Recently Balthasar (1958) divided the genus into four subgenera (one of which is Litocopris Waterhouse, 1891).
* Opinions and declarations rendered by the International Commission on Zoological Nomenclature, Vol. 4, Opinion 228, 1954.
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All the American species belong to the subgenus C opr is as under- stood by Balthasar.
There have been very few attempts at any revisional study of the large genus Copris and these have been restricted to relatively small geographical areas. The American species of the genus have been investigated very perfunctorily from two geographical vantage points — the United States and Central Mexico — with no attempt, until now, at coordinating the results. Fortunately, the two areas are sufficiently distinct zoogeographically that a minimum of synonymization has resulted. All the literature consists of scat- tered new species descriptions with four exceptions : Harold (1869), while describing most of the Mexican species, presented a key to them with short discussions of means of distinguishing them ; Horn (1873) presented a key and descriptions of the four United States species known at the time; Bates (1887-1889), in the Biologia Centrali Americana, reviewed the Mexican and Central American species known to him; and Schaeffer (1906) presented a short but quite usable key to the United States species known at that time. In his review, Bates used only Harold’s names, even though he was looking at several undescribed species which he attempted to fit into Harold’s descriptions. As a result, the range extensions given by Bates for Harold’s species, repeated in all subsequent catalogues and lists, are largely erroneous. There followed some individual species descriptions and Gillet (1911), in the Coleoptero- rum Catalogus, lists 16 species and two “varieties” for the Western Hemisphere. Thereafter there were several more species descrip- tions. The Leng Catalogue and Supplement (1920-1948) list eight species for the United States and Canada, while Blackwelder (1944) lists 12 species and two varieties for America exclusive of these two countries, of which one species and one variety are listed as common to both areas. Subsequently Pereira and d’An- dretta (1955) synonymized one name, Matthews and Halffter (1959) described five new species and synonymized one name, and Matthews (1959) described one additional species and elevated one variety to species rank, presenting a key to the males of the Mexi- can species.
There were until now, therefore, 24 species and one variety known from the Western Hemisphere. The present work describes one new species and three new subspecies, elevates the one re- maining variety to species rank, lowers two species to subspecies level, synonymizes two names and resurrects one, bringing the total to 23 species and five subspecies known for this hemisphere at present.
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In the world as a whole the genus at present contains ap- proximately 160 described species which are distributed about as follows among the zoogeographical regions (with some species counted twice) : Ethiopian — 77, Oriental — 46, Palaearctic — 27, Ne- artic — 16, Neotropical — 8. It does not occur in Madagascar or in Australia. The northern limits of the genus in the Eastern Hemi- sphere appear to coincide approximately with the 50th parallel (Kolbe, 1905), except that one species occurs very locally in southern England. Of the Coprini, this is by far the most boreal of the genera, all the others being rather strictly tropical (except Synapsis) .
In the Western Hemisphere (map, fig. 1) Copris is represented in the United States east of the 100th meridian, in all of Mexico and U. S. territory immediately bordering on Mexico (except Cali- fornia), and in all of Central America to Panama. In South America it is represented by a single species from North and Cen- tral America occurring in the mountains of Colombia and Ecua- dor. It is absent from the Antilles and the Galapagos Islands. One species has been introduced by man into Hawaii.
The American forms are distributed by countries as follows :
Canada: /. fricator (F.).
United States: arizonensis Sch., f. fricator (F.), /. cartwrighti Rob., gopheri Hubb., kowdeni M. and H., incertus Say, inemargina- tus Blatch., 1. lecontei n. sp., minutus Dru., r. remotus Lee.
Mexico : arizonensis Sch., armatus Har., boucardi Har., costari- censis dolichocerus n. subsp., halffteri Matt., incertus Say, k. klugi Har., k. sierrensis n. subsp., laeviceps Har., 1. lecontei n. sp., 1. isth- miensis n. subsp., lugubris Boh., megasoma M. and TI., mexicanus M. and H., moechus Lee., rebouchei Har., r. remotus Lee. r. dicyrtus M. and II., sallei Har.
Guatemala: aspericollis Gill., boucardi Har., costaricensis do- lichocerus n. subsp., laeviceps Har., lugubris Boh.
Belize : laeviceps Har., lugubris Boh.
El Salvador: boucardi Har., lugubris Boh.
Honduras : laeviceps Har., lugubris Boh.
Nicaragua: lugubris Boh.
Costa Rica: c. costaricensis Gahan, incertus Say, laeviceps Har., lugubris Boh., subpunctatus Gill.
Panama : c. costaricensis Gahan, lugubris Boh., subpunctatus
Gill.
Colombia : incertus Say.
Ecuador : incertus Say.
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Fig. 1. The apparent distribution, based on material in collec- tions, of the genus C opr is in the Western Hemisphere.
5
SMITHSONIAN Ann , _
MsmuTioN APR 27
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MATERIALS AND METHODS
The present study was based on the collections of several institutions and individuals and was supplemented by field ex- cursions into certain critical areas from which adequate material was found to be lacking.
The methods used were those standard to taxonomic procedure. An attempt was made to investigate cryptic characters for use in classification by examining one specimen of both sexes of each species in minute detail, dissecting it to its minimum component parts and examining all interior as well as exterior surfaces. In this manner the possible taxonomic significance of the mouthparts, antennae, wing venation, dorsal abdominal surface, metendosternite, male genitalia and female spermathecum was investigated. The results were disappointingly negative; although some characters, such as the male genital capsule, reflected species differences to a slight extent, these could be much more easily seen using ex- ternal features. Consequently, the use of cryptic characters was abandoned and the study was confined to those external ‘ 1 classical ’ 5 characters familiar to investigators for centuries.
In the descriptions, characters cited in the group and complex descriptions are not repeated under the species.
In the present classification the use of the male armament has been avoided completely in arriving at a natural system. However, the male armament, when developed, provides one of the easiest ways of identifying a species quickly; for this purpose facies illustrations have been provided on plates IV-VII and the first key to the species is based largely on male secondary sexual ornamentation. It is recommended that, if a series includes some major males, the first key be used for determination. However, all forms of both sexes should key through the second key.
With regard to the geographical localities cited on labels, some judicious elimination has proved necessary. If a locality written on a label appeared to be unreliable for any reason, it was disregarded. A certain amount of difficulty was experienced in locating many Mexican and Central American localities on a map. It would greatly faciliate the work of future investigators if collectors in these areas would confine themselves to citing localities which are listed in the Index to the Map of Hispanic America, 1:1,000,000 (1943, 1944). In Central America, the Department in which a town is located is essential information. In the “material examined” section, localities for which the department or state was given but which could not be found on any map are preceded by a question mark. Additional pertinent
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information not provided on the label, snch as the altitude, was added to the citation in brackets. Information added to the Champion localities was obtained from Champion (1907).
In the case of certain groups of insects, such as the present one, much useful biological information can be gleaned from the data on labels if the collector includes a word about how the insect was collected. The only collector in this group who has consistently done this is the late F. Nevermann of Costa Rica.
All illustrations are by the author. The facies illustrations (plates IV— VII) showing the male armament were drawn by eye with the aid of proportional dividers. These illustrations are meant to show only the overall aspect of the forebody of a major male of each species and a general indication of the distribution of simple and complex punctures. Such details as the distribution of setae and the proportions of the mouthparts are only roughly indicated and not meant to be exact. The mouthparts and genitalia illustrated were mounted on slides and projected on paper with a standard projector. All other illustrations except the nest diagrams were done with the aid of an ocular grid and cross-lined paper. The nest diagrams were redrawn from field sketches and measurements.
A total of 3,400 specimens was examined, including the holo- types of 14 names. Many of the Mexican species were described by the Baron de Harold. Harold’s types are presumed to be in the Paris Museum, but I was unable to obtain verification from that institution. Fortunately, Harold’s descriptions, although short, are excellent and little doubt remains in my mind as to which of his names belongs to which species.
ACKNOWLEDGEMENTS
I wish to thank the curators of the collections at the following institutions for the loan or examination of material : American Museum of Natural History (AMNH), British Museum (Natural History) (BM), California Academy of Sciences (CAS), Carnegie Museum (CM), Cornell University (CU), Defensa Agricola (Mexico) (DA), Department of Agriculture (Canada) (CNC), Musee Royal d’Histoire Naturelle (Brussels) (MRHN), Museum of Comparative Zoology (MCZ), Naturhistoriska Ricksmuseum (Stockholm) (NR), Instituto Rockefeller (Mexico) (IR), Phila- delphia Academy of Sciences (PAS), United States National Museum (USNM), University of Kansas (UKs), University of Michigan (UMich).
ENTOMOLOGICA AMERICANA
In addition, the following individuals generously made avail- able material from their private collections : 0. L. Cartwright (Washington) (OLC), G. Halffter (Mexico) (GH), H. F. Howden (Ottawa) (HH).
I am particularly indebted to the following scarab specialists for invaluable advice and encouragement: V. Balthasar (Prague), 0. L. Cartwright (Washington), G. Halffter (Mexico), H. F. Howden (Ottawa), A. Martinez (Buenos Aires), F. S. Pereira (Sao Paulo).
Mr. R. A. Crowson of Glasgow kindly made comparisons of specimens with a Fabrician type in the Hunterian Collection.
Drs. S. E. Neff and 0. S. Flint, formerly at Cornell University, provided much help in the field work in Central America and North Carolina respectively.
MORPHOLOGY
The morphology of the adult Scarabaeinae has been the subject of some investigations. Hardenberg (1907) presented an excellent discussion of the mouthparts of Pinotus carolinus (L.), Co'pris fricator (F.), Canthon pilularius (L.), and several other Coprini, plus many other scarabs. Mohr (1930) compared the external morphology of Canthon pilularius (L.) with that of an aphodiine and a geotrnpine. Plalffter (1952) discussed aspects of the ex- ternal morphology of Phanaeus quadridens Say. Pereira and Martinez (1956) presented illustrations of the mouthparts and genitalia of many Canthonini and Matthews and Halffter (1959) discussed the external morphology of a species of Copris. For purposes of comparison, frequent mention is made below of some of these papers and of one on a melolonthine ( Amphimallon majalis Razoumowski) by Butt (1944) because of the detail in which the morphology of this species is there treated.
The following discussion is confined to those features of the external morphology of adult Copris which are of taxonomic significance, i.e. which may serve to distinguish the genus from others closely related or which vary among the species.
Microsculpture
The interpunctural surfaces are generally quite smooth in the American species except in fricator and howdeni, where the surfaces show a very fine shagreening.
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The punctures are of two basic types which in turn vary importantly among the species groups and complexes :
1. Simple punctures. This term refers to simple surface de- pressions which have no raised areas within them and which usually have indistinct edges. They are found on the dorsal head surface and on the convex portions of the pronotum and elytra in all species.
2. Complex punctures. These are of varying type but always show a raised area within them and sharp edges. The raised area may or may not bear a seta ; in the former case the puncture is said to be setigerous or umbilical and setigerous ; in the latter it is said to be simply umbilical or, if very large, annular.
The following areas show round setigerous punctures with the seta more or less erect (fig. 23) : along the posterior margin of the inner, smooth area of the proepimeron, on the sternellum, the mesosternum, the mesepimeron, occasionally the median lobe of the metasternum and the median coxae, and the abdominal sterna.
All other areas with setigerous punctures show a reniform type (fig. 21), which is a setigerous puncture one side of which has been pushed in with the result that the seta appears to issue from the side of the puncture and is recumbent, being directed away from the pushed-in edge.
The following areas normally show round or oval umbilical punctures which are not setigerous (figs. 20, 22) : the dorsal surface of the genae, the frontal area behind the horn, all depressions on the pronotum and the pygidial surface.
Finally, some species complexes show a remarkable modification of the inside surface of the punctures, which is distinctly granu- late (when seen at above 90 x magnification) (figs. 20, 21). This type of surface is seen inside all complex punctures, of whatever type, which are large enough to show the inner surface, on both the dorsal and ventral body surfaces. Punctures of this type are said to be granular and occur throughout the minutus species group, recurring in the fricator group only to a lesser extent in the rebouchei complex.
Head
The cephalic taxonomic characters which are not self-explana- tory are the following :
Posterior oblique carina.- — This is a carina on the dorsal surface which runs from just behind the eye obliquely inward towards the base of the horn. When present, it is usually very sharp immediately near the eye and then stops abruptly, being continued
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inward and forward by a raised ridge of varying sharpness (fig. 25, poe).
Transverse occipital groove. — Running very near the edge of the dorsal portion of the occipital margin is a groove bearing short, closely set setae (figs. 24, 25, tog). This groove may be complete across the entire occipital margin, or it may be divided into three approximately equal parts with the lateral ones displaced slightly forward (fig. 25). Occasionally the median section is missing.
Transverse occipital carina. — This is a carina of varying sharp- ness which runs in front of and closely parallels the transverse occipital groove (fig. 24, toe). It is found only in the incertus complex.
Immediately behind the front margin of the head dorsally is a row of seta tufts which are most conspicuous medially but which extend for varying distances laterally and posteriorly, sometimes extending onto the genae. The extent of this row of tufts ap- parently varies significantly among the species, but this character was not used in the classification because of the difficulty of seeing the setae in worn specimens.
The mouth cavity is rectangular in shape and is margined with a very broad, smooth margin which is anteriorly drawn out into a point. The shape of the mouth cavity differs somewhat in different coprine genera.
Mouthparts
The mouthparts of Copris and all other Scarabaeinae are quite remarkable for their modification of a basically primitive type towards very highly sensory and membranous appendages (plate II). A good description of the mouthparts of Copris fricator (F.) (= C. anaglypticus Say) is given by Hardenberg (1907). Since the mouthparts do not appear to provide useful taxonomic characters at the species level in this genus, they will not be further discussed here.
Prothorax
The prothoracic taxonomic characters which are not self-ex- planatory are the following:
Lateral pronotal carina. — This is a carina which runs from an anterior point on the pronotal lateral margin upwards and back- wards to pass just under the lateral fossa, after which it dis- appears. It is absent in the minutus group.
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Prosternal-proepisternal suture (fig. 26. pp). — This is the suture between the anterior portion of the prosternum and the pleuron. In the incertus complex it appears carinate because of a deep depression of the pleural surface immediately next to it.
Pleural elements. — The interpretation of the lower surface of the prothorax adopted here differs radically from that of many coleopterists (who call the entire lower surface the sternum) and that of Butt for Amphimallon, but agrees with that of Mohr and Ilalffter. Butt considers the lateral portions of the lower surface as parts of the pronotum, which is therefore believed to join directly with the sternum with a resultant complete inflection of the pleural elements, which Butt considers to be represented only by a tiny sclerite fused to the dorsolateral wall of the prono- tum on the inside.
In my opinion, it is more logical to assume merely that the sutures delimiting the pleural sclerites, seen in the primitive Coleoptera, have become completely fused and effaced in order to reinforce the prothorax. This would mean that most of the under surface lateral to the sternum in scarabs is made up of pleural elements fused together.
On this pleural area in Copris there is seen a distinct oblique carina running from the coxal cavity outward (fig. 26, pc). This carina is absent in many coprines and other scarabs and may be assumed to be a secondary modification evolved to further rein- force the prothorax. For the purposes of convenience, the area anterior to this carina is called the proepisternum, and that pos- terior to it is called the proepimeron. However, it should be understood that these areas do not in all probability correspond to the true morphological sclerites called by these names.
The longitudinal proepimeral carina. — The proepimeron in Copris and a few closely allied genera bears another characteristic carina which arises perpendicularly from the posterior proepimeral margin and quickly fades out (fig. 26, lpc). This carina serves to partly delimit a densely, setigerously punctate outer area of the proepimeron from an almost smooth inner one (except in C. minutus).
Pterothorax
Very few taxonomic characters have been found in the ptero- thorax and all are self-explanatory. The proportions and shapes of the sclerites do not differ among the American species of Copris .
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Elytra
There are ten distinct elytral striae in the genus Copris, of which the ninth is practically always present only for its pos- terior half and lies very close to the tenth. The eighth stria is of great taxonomic importance and may be present merely as a short segment near the middle of the sides, in which case it is said to be obsolescent, as a line more or less interrupted posteriorly at the hind angles, in which case it is said to be incomplete, or as a complete, uninterrupted line.
Legs
The general shape and proportion of the legs in Copris may be seen in fig. 26. There is one strong spur terminally on the anterior tibia, called the forespur, the shape of which is of great taxonomic significance.
The fore coxae are elongated cylinders very deeply sunk into the prothorax (fig. 27). They are rigidly pivoted at the two opposite ends of this cylinder such that the only possible move- ment is a rotation. The outer pivot consists of a knob formed by an invagination of the pronotal surface, called the lateral fossa of the pronotum.
The median coxae are oriented parallel to the body axis and widely separated. Their ventral (visible) surfaces are longi- tudinally obtusely carinate. The area exterior to this carina is called the outer face of the median coxa.
The arrangement of setae on the middle and hind tibiae was found to be of taxonomic significance with regard to two sets of setae, as follows :
Ventral seta tufts, also called distal seta tufts (fig. 49, st). — These terms refer to a row of tufts on the lower surface of the tibiae. The tibia is seen to be quadrate in cross section with a row of teeth and setae running down each ridge forming the corners. The ventral seta tufts are situated along the middle of the ventral face between the usual ridge setae and are usually confined to the distal end.
Supplementary setae (fig. 50, ss). — These are confined to the incertus complex and consist of an oblique row of very few, in- distinct setae near the distal end of the dorsal tibial surface.
The tarsi are unmodified and always present. Each segment is somewhat expanded distally and gradually diminishes in size apically. There is some variation in the comparative width of
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the tarsal segments in different species, but this character was not used in the taxonomy. The tarsal claws are small, parallel, and equally developed, with a small plate-like empodium at their base.
Abdomen
The only taxonomic characters on the abdomen involve the pygidium, which may be incompletely margined ventrally. The visible sternites are six in number and do not merge together along the ventral mid-line.
The tergites of segments VII and VIII are of particular interest because they make up the ventral portion of the stridula- tory apparatus. The dorsal portion of tergite VIII (the pro- pygidium) is heavily sclerotized and bears a deep longitudinal groove medially. This groove firmly holds the down-turned median edges of the elytra in repose. The actual stridulatory surface is not on this segment, however, but on the preceding one, where it consists of a finely sclerotized median area bearing some extremely fine transverse ridges. These ridges rub against some similar ridges or teeth on the elytral ribs when the abdomen is moved against the inside elytral surface, the groove on tergite VIII serving to keep the two parts in line.
Both sexes of every species of Copris I have examined show this apparatus and all those which I have collected in the field could be induced to squeak. For a discussion of stridulation in the lamellicornia the reader is referred to Arrow (1904).
Genitalia
On the whole, the male genitalia in this genus are not of any use in determining the species, at least as far as their gross aspect is concerned. The possibility that the internal sac may bear taxo- nomic characters was not examined.
SEXUAL DIMORPHISM
The phenomenon of sexual dimorphism in the lamellicorn beetles has been the subject of much speculation but, unfortunately, little organized investigation. Darwin (1871) used the scarabs as examples for his celebrated theory of sexual selection. Since then the diversity and possible uses of the horns or enlarged mandibles in the lamellicorns have been discussed in numerous works. It is
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not the purpose of this discussion to review this voluminous litera- ture; for a recent survey the reader is referred to Arrow (1951). For some of the theoretical implications of horn allometry in the scarabs see Huxley (1932) and Paulian (1935). An excellent recent quantitative survey of horn allometry in a single dynastine species is presented by Bowden (1959).
However, no one has examined the nature of the variation in horn size among related species of a single genus. It is the purpose of this survey to examine intra- and interspecific variation in horn size and general qualitative differences in armament among all the American species of Copris.
The Sexual Armament in Copris
Nearly all the males of the American species display armament of a single type : there is one horn arising from the middle of the frontoclypeal suture on the head and the pronotum bears four forwardly directed prominences in a transverse row (plates IV- VII). The median two of these prominences are variable in shape (blunt, acute, or truncated) and sometimes merge into a single process. The lateral pronotal prominences are always strongly compressed and acute when developed.
The females typically bear a transverse crest on the fronto- clypeal suture of the head. This crest is low and truncate apically, transversely oval and slightly excavate in dorsal view, and its sides converge apically, are parallel, or diverge, depending on the species or degree of development. The pronotum of the female does not bear any corniform prominences but does bear a median transverse carina (sometimes interrupted medially) and a small tumosity to either side of this carina. In the species descriptions female armament of this type is simply described as “ normal for the genus. ’ ’
Following the established custom among scarabaeidists I have called specimens (male or female) showing very little or no development in sexual armament “minor” individuals, and those showing strong development “major”. It should on no account be inferred that these are clear-cut categories, but rather that they represent the two extremes of a spectrum of variation. Alternately I have called these specimens poorly developed and well developed, respectively.
The following exceptions to the above descriptions of armament are seen in the American species :
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In the minutus group, the female head horn (or crest) is narrow, high, and rather corniform but still apically truncate in the incertus complex, completely corniform (apically acute) in the minutus complex. In the latter complex, in fact, it is very difficult to distinguish between the sexes, since the pronotal arma- ment is often scarcely developed. The incertus complex is further distinguished by the presence of a corniform tubercle on the frons of the male behind the head horn.
In the species halffteri Matthews an extraordinary reversal has taken place : the male has acquired female armament. This phe- nomenon must not be confused with the similarity to females shown by very minor males of many species. In halffteri the males I have seen are well developed and show strong armament, but this is always of an exaggerated female type (fig. 77) which few females of any species ever achieve, because they are seldom so developed. This species is apparently very localized and shows strong affinities with a common and widespread species ( C . rebouchei Harold), from which it evidently evolved. It is interesting that this form, which is most certainly a separate species, is completely sympatric with its parent species, both having been found in the same pile of cow dung.
Intraspecific Variation in Horn Height
The measurements used in the following analysis represent the height of the male head horn from the edge of the clypeus to the tip of the horn in direct front view. This is compared with the maximum length of the hind femur in ventral view. The measure- ments were carried out with an ocular micrometer at 9 x magnifi- cation, the units used being one micrometer unit or .097 mm in this case. Since only ratios are dealt with, the measurements were not converted to millimeters. For calculating curvilinear regres- sion lines, a constant factor was subtracted from each measurement of horn height to insure that the horn itself, and not also the height of the frons, was being taken into consideration. This factor was taken as the height from the clypeal edge to the tip of the frontal protuberance in the least developed specimens (those with no horn as such) of the species involved.
The mathematical interpretations of the curves obtained were taken to be either the “simple heterogony” formula of Huxley (1932) (y = bxk, where y represents the magnitude of the differen- tially growing organ — in this case, the horn, x represents the magni- tude of the animal or some reference structure — the femur, and b
15
Table I. Regression of Male Cephalic Horn Height (y) on Length of Hind Femur (x) in 14 Species of Copris.
1 unit = .097 mm
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ENTOMOLOGICA AMERICANA
and k are constants) or a simple linear relationship (y = ax + b') such as that found by Bowden (1959), whichever seemed to fit best. These different interpretations are of no real significance, in my opinion, the linear curve probably being merely the top part of a power function curve. In the case of C. moechus, it seems that both a power function and a linear curve fit the data (fig. 4 and table I), with the break occurring near the middle.
It may be objected that the material measured here was taken from museum collections and therefore not collected under proper statistical sampling procedure. To this it should be pointed out that we are concerned here with the positions of curves only, not with their slope or the positions of their origins of deviation (the common mean of the two variables) . It should, theoretically, make no difference where along a common curve a sample is taken; the subsequent plotting of these samples should reveal the position of the curve.
One of the main purposes of this study is to determine whether significant differences can be found in horn development patterns within a single species and to analyze the nature of these differences if they occur. When plotted on a graph, the data points represent- ing horn height to femoral length ratios for an intraspecific group- ing, such as a population or geographical race, could differ from those representing another grouping, or the rest of the species, in two quite different respects : 1 ) they could fall along only a section of a common species curve, that is to say, a race may fall near the bottom of the curve, another near the top, etc. or 2) much more significantly, one or more populations may fall along a recognizably different curve, thus showing a different allometric relationship with at least a different value of 1).
Individual populations could not be examined in this respect since they were almost never represented in sufficient numbers. With regard to geographical groupings, however, significant dif- ferences were found within five of the 14 species examined. In minutus (Drury) (fig. 2) specimens from a relatively small area of the range, represented by Mobile and Montgomery, Ala. and Clarksville, Fla. (in the Florida panhandle), are seen to fall almost entirely along the extreme upper portion of the curve (open circles) with little overlap with the rest of the species (dots). Mysteriously, two specimens from this area fall near the bottom of the species curve. It will be noted, however, that all specimens from this area give every appearance of falling along the common species curve. Visually these specimens are conspicuous for their great size and horn development.
17
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ENTOMOLOGICA AMERICANA
minutus
o specimens from
length of hind femur I unit =.097 mm
* ■ - L. i l l I . i I
22 24 26 28 30 32 34 36 38
ig. 2. C. minutus (Drury). Plot of horn height (y) against *al length (x) ; k = 9.40 for random 25% sample (N = 53). For nd the following figures refer to text and table I for explana- of the symbols used.
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ENTOMOLOGICA AMERICANA
In fricator (F.), on the other hand (fig. 3), specimens from a wide geographical area in the southwestern portion of the range (open circles) are all grouped in the lower part of the common curve. Visually these specimens also stand out, but in this case for their hornless condition and small size. Here, however, there is a suggestion that these specimens fall along a slightly different curve situated higher than the common species curve.
fricator
o specimens from Ks.,
Fig. 3. C. fricator (F.), k = 15.09 for x = 42 to 50. Interrupted lines estimated.
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ENTOMOLOGICA AMERICANA
The previous two examples of geographical variation come under category (1) above. The geographical race falls along a special part of the common species curve, with little or no evidence for any different allometric relationship.
The most interesting and significant type of variation is the one in which a geographical grouping falls along a totally cliferent curve from the one which characterizes the rest of the species. This is unmistakably seen in three species of the genus (figs. 6-8). In the first ( klugi Harold), when the data from specimens origi- nating in the Sierra Madre Occidental are plotted, they are seen to fall along a line which is significantly to the right of those from the rest of the species, orignating in the Transverse Volcanic Range. The degree of significant separation may be judged by noting the extent of overlap of the 95% confidence intervals shown. Visually this difference is expressed by the northern specimens possessing consistently shorter horns for their size, in comparison with the southern form, but this difference is so slight as to be all but undetectable to the eye. This is in sharp contrast to the visually conspicuous but much less important difference in cate- gory (1) above.
This shift in the position of the relationship curve in different geographical groupings is much more strongly accentuated in two additional species : in costaricensis Gahan, comparing specimens from Chiapas with those from Costa Rica (fig. 7), and in lecontei n. sp., comparing specimens from north and south of Cabo Corrientes on the west coast of Mexico (fig. 8). For each of these three species there are therefore two separate relationship curves (table I).
In the last three examples the differences in allometric rela- tionship are reflected in morphological differences only in the first species (klugi). Here the northern