Color and Color-Pattern Mechanism of Tiger Beetles
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University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Papers in Entomology Museum, University of Nebraska State June 1917 Color and Color-Pattern Mechanism of Tiger Beetles Victor E. Shelford University of Illinois Follow this and additional works at: https://digitalcommons.unl.edu/entomologypapers Part of the Entomology Commons Shelford, Victor E., "Color and Color-Pattern Mechanism of Tiger Beetles" (1917). Papers in Entomology. 131. https://digitalcommons.unl.edu/entomologypapers/131 This Article is brought to you for free and open access by the Museum, University of Nebraska State at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Papers in Entomology by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. ILLINOIS BIOLOGICAL MONOGRAPHS April, 19 1 7 No. 4 EDITORIALCOMMITTEE COPYRIGHT,1917 BY THE UNIVERSITYOF ILLINOIS DISTRIBUTEDJUNE 30, 1917 COLOR AND COLOR-PATTERN MECHANISM OF TIGER BEETLES WITH TWENTY-NINE BLACK AND THREE COLORED PLATES BY VICTOR E. SHELFORD Contributions from the Zoological Laboratory of the University of Illinois, No. 93 TABLE OF CONTENTS PAGE Introduction .............................................................................................................................. 5 Materials and methods ................................................................................................ 6 Analysis of Color Patterns .................................................................................................. 13 Color Patterns and Elytral Structures .................................................................. I3 The Color Pattern Plan ................................................................................................ 19 Color Pattern and Pigment Development .............................................................. 21 Experimental Modification of Patterns .................................................................. 38 Geographic Variation of Patterns ............................................................................ 40 Colors of Tiger Beetles ........................................................................................................ 46 Causes of Colors .............................................................................................................. 46 Ontogeny of Color .......................................................................................................... 47 Relation of Ontogenetic Stages to Geographic Races ....................................... 49 Geographic Variation in Color .................................................................................. 52 Experimental Modification of Color ....................... ... ...................................... 55 Relation of Colors and Color Patterns to Climate .............................................. 56 Geographic Center of the Group on the B'asis of Patterns ................................ 57 General Discussion .................................................................................................................. 58 Pattern Tendencies .......................................................................................................... 58 Bearing of the Color Pattern Mechanism on Orthogenesis................................ 63 Bearing of the Pattern Mechanism on the Biogenetic Law.............................. 65 Summary of Conclusions ..................................................................................................... 66 Patterns .............................................................................................................................. 66 Color ................................................................................................................................... 67 Geography ............................................................................................................................ 67 Bibliography ............................................................................................................................ 68 Explanation of Plates ............................................................................................................ 71 3991 COLORS OF TIGER BEETLES-SHELFORD 5 INTRODUCTION In the analysis of characters made the basis of studies of variation, orthogenetic trends, experimental modification and heredity, noteworthy advantages are assbciated with the study of large groups of species in which divergence and modification have proceeded in various direc- tions. The material should be plastic so that the laws governing response in characters can be determined. The ontogeny of the char- acters should be of such a character as to show the general ground plan of the system and its relation to the existing adult characters and their variations. It is further desirable to be able to breed the organ- ism, segregate pure lines, and cross various species. There is a strong tendency of late years to regard the breeding and the breeding results as superior to the other attempts at character analysis. This has pro- ceeded to such an extent without adequate physiological analysis that one writer (Riddle, 1909) designated the method of cross breeding "the mixing of unknowns". The primary object of this paper is to show the nature of the color and color-pattern mechanism of the elytron. In the matter of qualifications of material the tiger beetles are admirably adapted to all the needs enumerated above, but since one year at least and normally two are necessary for a generation, only a few single generations have been bred. For this reason the idea of breeding them was abandoned. It is also a purpose of this paper to show that breeding is not the only method by which adequate analysis can be reached, i.e., unless the laws governing heredity are a system entirely a part from those governing the modifbation of parts during ontogeny and the normal course of variation, which seems to be the tacit assumption of various students of heredity in the not too distant past. I shall indicate further that orthogenetic tendencies, if directive tendencies are to be so named, are numerous and in a large series of species present a confusing set of groups which are excessively com- plicated and reduced to any simple system, as claimed by Eimer and van Linden for Lepidoptera or for a limited number of species by Whitman, with difficulty. Still, large tendencies with numerous minor ones within them may be detected. It will be shown that the laws governing the modification of patterns apply alike to general, probably !I rctiitary !~r(I.ei~c;P 21-11 (iet~iltd <p~:cJ UIIGCI r.peri~~tt~italc31~- 6 ILLINOIS BIOLOGICAL. MONOGRAPHS [rn ditions. It will be shown that biogenetic law must be applied with caution and is not of such broad application as is held in some quar- ters, being inapplicable to various characters altogether. The brilliant colors of the group are due to physical phenomena determined by Professor Michelson, and leave no place for the bioge- netic law in connection with the development of color during ontogeny. It will be shown further that color is closely correlated with general physiological condition and is modifiable by conditions which affect gmeral metabolism. The results here presented are based on several J ears of observation. In 1903 the writer undertook a study 04 variation of the tiger beetles. The work here presented is the outgrowth of this beginning, and indeed includes some small portions regarding color patterns that were written in that year. The work has been prolonged for many reasons, but chief of these was the' very large number of species in the group and the fact that an adequate understanding of the mate- rial could not be attained without consulting many large collections. ' Further, the experimental results obtained in 1906 demanded a first- hand study of the variations of the species concerned and their natu- ral habitats. The accumulation of material and data was not com- pleted until 1911. Some of this had to be studied, drawings made, etc., which with numerous other duties and enterprises under way made necessary much time to put it into the present form. A family with upwards of 1300 species of which more than 600 are in one genus and with characters which can be studied and analyzed, appeared to afford material which was sufficiently promis- ing to justify' delay. In the fourteen years that have elapsed since the problem was first undertaken at the suggestion of Dr. C. B. Dav- enport, the attention of biologists has shifted from variation, which was then the chief topic of interest, to experimental modification of characters, and finally to the methods of modern genetics. Various men have made numerous suggestions regarding the work, but in its Gnal preparation the writer has been able to use only a few of them in a general way, and an attempt is made to present the facts and conclusions growing out of the material as simply as possible. MATERIALS AND METHODS The material which has been used as the basis of this work has consisted of collections in the family Cicindelidae of the world, exten- sive collections of several North American species, repeated year-to-year collections of a few species in Illinois and Indiana, series of observations ' on the ontogeny of color in a small number of North American species, 401 1 COLORS OF TIGER BEETLES-SHELFORD 7 and experimental modification of a number of species which has assisted in