'lly BULLETIN of the FLORIDA STATE MUSEUM Biological Science s~ VOLUME 29 1984 =Bal SCUTELLATION VARIATION IN OPHEODRYS AESTIVUS ARNOLD B. GROBMAN UNIVERSITY OF FLORIDA GAINESVILLE Numbers of the BULLETIN OF THE FLORIDA STATE MUSEUM, BIOLOGICAL SCIENCES, are published at irregular intervals. Volumes contain about 300 pages and are not necessarily completed in any one calendar year. OuvER L. AusTIN, JR ., Editor RHODA J. BRYANT, Managing Editor Consultants tor this issue: JAMES E. B6HLKE VICTOR G. SPRINGER Communications concerning purchase or exchange of the publications and all manuscripts should be addressed to: Managing Editor, Bulletin; Florida State Museum; University of Florida; Gainesville, FL 32611, U.S.A. Copyright © by the Florida State Museum of the University of Florida This public document was promulgated at an annual cost of $1,507.00 or $1.507 per copy. It makes available to libraries, scholars, and all interested persons the results of researches in the natural sciences, emphasizing the circum-Caribbean region. Publication date: Price: $1.55 SCUTELLATION VARIATION IN OPHEODRYS AESTIVUS ARNOLD B. GROBMAN1 ABSTRACT: Variation in the scutellation of Opheodrys aestiVUs is analyzed. North-south clines are demonstrated in the number of ventrals and eaudals and the pattern of scale row reduction. Sexual dimorphism is described for the number of ventrals, the number of caudals, the locus of dorsal scale row reduction, and the locus of the umbilical scar. Taxonomic considerations result in the recognition of four races; two are newly described (cari,uitus and conanti); one is resurrected (majalis Baird and Girard 1853); and the nominate race is redefined. Two additional variant populations are noted but are not given taxonomic recognition. RESUMEN: Se analiz6 la variaci6n en la escamaci6n de Opheodrys aestivus. Se demonstr6 clinas de norte a sur en el numer6 de escamas ventrales y caudales, asT como en el modelo de reducci6n en filas de escamas. Se describi6 el dimorfismo sexual de acuerdo al numer6 de escamas ventrales, caudales, el locus de reducci6n de filas de escamas dorsales, y el locus de la marca umbilical. Consideraciones taxon6micas permiten reconocer 4 razas; dos son descritas por primera vez (carinatus y conantg una ha sido restaurada (majalis Baird y Girard 1853); y la raza nominal es redefinida. Se menciona dos poblaciones variantes adicionales pero no se les da reconocimiento taxon6mico. TABLE OF CONTENTS INTRODUCTION...... ... ..... .. 153 ACKNOWLEDGEMENTS . .. ........... ... ·· 154 MATERIALS STUDIED . ........... ... ........ ·· 154 METHODs ................. .. ......... .. .. 155 RESULTS. ... .. ..155 1, Clinal Variation . .......... .. . 155 Sexual Dimorphism ... .......... ..... .. 157 TAXONOMIC CONSIDERATIONS . ............ .. .. ·· 160 Opheodrys aestivus aestivus (Linneaus). ..160 Opheodrys aestivus majatis (Baird and Girard). ..162 Opheodrys aestivus carinatus, new subspecies ......... ..164 Opheodrys a€stious conanti, new subspecies...... .166 TAXONOMICSUMMARY. .. .. ............... ..167 LrrERATURE CITED .. .......... ............. . 170 INTRODUCTION Since Cope's (1900) extensive compendium on the reptiles of North America, virtually all the wide-ranging species of snakes in the United States have been the subjects of variational studies. Over 40 years ago, I (Grobman 1941) prepared a paper on the variation in the scutellation of the Smooth Green Snake, Opheodrys vernalis. In the present ac- 'Professor of Biology and Chancellor, University of Missouri, St. Louis, Missouri 63121, and Acliuncl Curator, Depart- ment of Natural Sciences, Florida State Museum, University of Florida, Gainesville, Florida 32611. GRoBMAN, A. B. 1984. Scutellation Variation in Opheodrys aestilms. Bull. Florida State Mus., Biol. Sci. 29(4): 153-170. 154 BULLETIN FLORIDA STATE MUSEUM VOL. 29, NO. 3 count , I offer a similar analysis of the Rough Green Snake , Opheodrus aestivus, one ofthe few remaining species of United States snakes for which no such report exists. ACKNOWLEDGEMENTS I am pleased to acknowledge the generous cooperation of many individuals and their institutions for the loan of specimens and for responses to my queries, thereby greatly facilitating my investigations. Acronyms are provided for the collections containing specimens used in this study. The addresses of persons given are those that were cur- rent at the time of our correspondence. In particular, I wish to thank: Robert W. Bowker and Douglas Rossman, Museum of Zoology, Louisiana State University (LSU); W. Leslie Burger, Japan Snake Institute; Steven P. Christman, U.S. National Fish and Wildlife Laboratory, Gainesville, F16rida (formerly of the Department of Zoology, University of Florida); F. Wayne King and Peter A. Meylan, Florida State Museum, University of Florida (FSM); Joseph T. Collins, Museum of Natural History, University of Kansas (KID; Ronald I. Crombie, National Museum of Natural History, Smithsonian Institution (USNM); James R. Dixon, Texas Cooperative Wildlife Collection, Texas A&M University (TCWC); Carol Fieber, Dennis M. Harris, Alan Jaslow, A. G. Kluge, and Ronald Nussbaum, Museum of Zoology, University of Michigan (UMMZ); Dean Metter and Walter A. Schroeder, University of Missouri-Columbia; George W. Foley, American Museum of Natural History (AMNH); Michelle Hudson, Department of Archives and History, Jackson, Mississippi; C. J. McCoy, Carnegie Museum (CM); Bproamin Shreve and Ernest E. Williams, Museum of Comparative Zoology, Harvard University (MCZ); Dorothy Smith, Museum of Natural History, University of Illinois (UIMNH); and Phillip W. Smith, Illinois Natural History Survey (INHS). I am grateful also to the authorities of the Chicago Academy of Sciences (CA) and the Field Museum of Natural History (FMNH), who graciously permitted examination of specimens in their laboratories. Most of the demanding work of recording scale counts was performed by Allan Markezich who, at the time that phase of the study was pursued, was a graduate stu- dent at the University of Illinois at Chicago Circle. I am deeply indebted to him for his careful recording of data and for his many valuable and thoughtful suggestions. Hobart M. Smith, Department of Biology, University of Colorado, and Roger Conant, Depart- ment of Zoology, University of New Mexico, were especially helpful in reviewing early drafts of the manuscript. I acknowledge, also, the helpful suggestions of anonymous reviewers. MATERIALS STUDIED The Opheodrys aestivus material available in major American collections made it possible to extract scutellation data from 1154 specimens with precise locality (county or better) data. This report is the result of an analysis of those data. Two cataloged specimens with specific locality data have been excluded from the analysis. They are: CM 1322, Ninveh, Green Co., PA, D. A. Atkinson, 31 May 1922. The nearest records to Ninveh I know of are 110 miles to the southwest and 130 miles to the east. Apparent- ly no additional specimens have been collected in the intervening region despite the ac- tivities of local herpetologists over many years. I have given reasons (Grobman 1950) for questioning the authenticity of a specimen of 0. vernalis (CM 422) Atkinson collected. It appears prudent to discard locality data accompanying CM specimens Atkinson collected. USNM 7196, Cimmaron, NM, S. A. Clark. Mr. R. I. Crombie (in litt., 13 November 1974) advised that no other specimens (which might assist in identifying the region of collee- tion) are associated with this shake nor has the collector donated other materials. Fur- 1984 GROBMAN: OPHEODRYS AESTIVUS SCUTELLATION VARIATION 155 ther, the scale counts for this male specimen (ventrals 153, caudals 129) resemble those of eastern specimens somewhat more than those of western specimens of 0. aestivlts. The same specimen is listed by Cope (1900) as from the Cimmaron River, and one with an adjacent catalogue number (USNM 7197) is listed as Ft. Bliss, New Mexico, but Crom- bie suggested the latter may be from Texas. Cope also listed a specimen (USNM 11825) as donated by E. Palmer and gave the locality as Old Fort Cobb, New Mexico. As the "New Mexico" of the nineteenth century was a very inclusive term; as collec- tors along the Cimmaron River in Oklahoma (where 0. aestivus occurs)may have sent their collections to army forts in New Mexico and elsewhere f6r shipment to Washington; and as the nearest point in the present State of New Mexico is more than 150 miles west of the westernmost specimen of Opheodrys aestivus, I do-not consider those cited 19th century "New Mexico" locality records to represent sites in the present State of New Mexico. METHODS Oph€odrys aestivus is a green snake with no dorsal or ventral color pattern, and so a study of its external morphology must rest almost exclusively on an examination of meristic characters. I examined a variety of these characters in some detail, and those I found to be useful are the number of ventrals, the number of caudals, the degree of keeling of the dorsal scales, the method of dorsal scale row reduction (from 17 rows anteriorly to 15 rows posteriorly), and the locus (i.e. opposite which ventral) of dorsal scale row reduction. Head plate arrangements did not vary significantly in the specimens examined, and body and tail length measurements were not recorded. RESULTS Clinal variation (north/south; not east/west), beyond that ascribable to race, occurs in number of ventrals and caudals and pattern of dor- sal scale row reduction. Sexual variation occurs in the number of ventrals, number of caudals, locus of dorsal scale row reduction, and locus of the umbilical scar. Geographic variation (not primarily clinal) suggests the recognition of four races of Opheodrys aestivus. Two additional populations are identified through scutellation characteristics but are not given tax- onomic recognition. CLINAL VARIATION 1. VENTRALS AND CAUDALS Ventrals and caudals exhibit a geographic gradient, with the southern specimens of Opheodrys a€stivus having a larger number than northern specimens. In order to minimize the effect of other trends (discussed below) on an analysis of possible clinal variation, the samples selected for a preliminary study were restricted to specimens collected in Illinois, In- diana, Ohio, Kentucky, West Virginia, and Tennessee (northwestern quadrant); Alabama, Mississippi, and Louisiana (southwestern quadrant); New Jersey, Delaware, Maryland, the District of Columbia, and Virginia (northeastern quadrant); and Georgia, South Carolina, and 156 BULLETIN FLORIDA STATE MUSEUM VOL. 29, NO. 3 North Carolina (southeastern quadrant). Comparisons of ventral and caudal counts between northern and southern samples show higher values for the southern specimens, with southern snakes having about 2.75 more ventrals and about 7 more caudals than northern snakes. In similar comparisons between western and eastern specimens, the sample value for ventrals for the western specimens is about 1.25 higher and for caudals about 1.67 lower than for the eastern specimens. The data (summarized in Table 1) do not support a suggestion that a demonstrable east-west cline exists in the number of ventrals plus caudals. TABLE 1.-Mean number of ventrals and caudals, with number of specimens indicated in parentheses, in selected samples (see text). Western Eastern Northern Male ventrals 153.5 (113) 161.9 (71) Female ventrais 156.0 (93) 154.4 (67) Male caudals 131.9 (97) 131.3 (59) Female caudals 124.7 (63) 124.5 (45) Southern Male ventrals 1'55.4 (64) 154.8 (63) Female ventrals 159.3 (57) 157.4 (60) Male caudals 135.5 (48) 139.0 (42) Female caudals 130.8 (44) 132.7 (44) To study the north-south cline in ventrals plus caudals more closely, and to reduce heterogeneity associated with racial differences (see below), an analysis was made of specimens collected from alllocalities other than those in Missouri, Kansas, Arkansas, Oklahoma, Texas, and Mexico; and the offshore islands of Virginia. Table 2 gives the modal latitude of collections by localities and the mean number of ventrals plus caudals of specimens in those collections. The latitudes are representative of the collection samples, and the scutellation data are the weighted means of the total ventral and caudal counts for males and females combined. A best-fit regression line indicates 296 ventrals plus caudals to be typical of snakes living near the 30 ° parallel and 281 ventrals plus caudals to be typical at the 40 ° parallel. Thus it appears that a decrease of one degree of latitude is accompanied by an increase of about 1.5 ventrals plus caudals. 2. SCALE Row REDUCTION Ophedrus aestivus typically has 17 rows of dorsal scales , and that number reduces posteriorly to 15 about two-thirds of the distance from 1984 GROBMAN: OPHEODRYS AESTIVUS SCUTELLATION VARIATION 157 Table 2.-North-south cline in ventrals plus caudals. Mean No. of ventrals plus No. of Latitude caudals Specimens States Included 30 ° 30' 295.3 34 FL 31° 289.9 51 LA 32 ° 30' 294.0 65 AK, GA, MS 33 ° 36' 294.0 33 SC 35 ° 30' 288.5 30 NC 36° 284.5 53 TN 37 ° 30' 284.9 62 VA, KY 38° 285.4 43 IL 38° 30' 281.5 39 WV, IN 39° 283.1 35 DC, MD 40° 286.6 8 NJ the head. The patterns of reduction and the percentages of occurrence of those patterns, based on 1875 observations, are as follows: fusion of rows 3+4 (78.2%), fusion of rows 2+3 (14.7%), elimination of row 3 (5.6%), fusion of rows 4 + 5 (0.8%), elimination of row 4 (0.6%), and elimination of row 2 (one instance). Considerable geographic variation occurs in the patterns of reduc- tion, and though there appears to be some sexual dimorphism (the males being slightly less variable, a higher proportion having the 3 + 4 pat- tern), the degree of that dimorphism is slight compared to the observ- ed geographic variation. The fusion of rows 2+3 occurs more often in northern specimens, less often in southern specimens, and the converse is true of the fu- sion of rows 3 + 4. The trend is exhibited in Table 3, which shows the percentage of specimens in which scale row reduction involves dorsal row 4 (either through fusion or elimination) from localities in states bordering the East Coast. Table 3.-Percentage of specimens in which dorsal row four is involved in scale row reduction. Mean Locality Number Latitude Percent NJ-MD 70 39 ° 52.9 VA 51 37° 66.7 NC-SC 84 350 72.6 GA-N. FL 132 32° 85.6 S. FL 241 27° 89.6 SEXUAL DIMORPHISM 1. VENTRALS AND CAUDALS Males appear to have approximately 3 fewer ventrals and 7 more 158 BULLETIN FLORIDA STATE MUSEUM VOL. 29, NO. 3 caudals than females. The mean number of ventrals in 569 males is 155.3 * 0.31 and in 576 females, 158.5 i 0.32. The mean number of caudals in 427 males is 132.9 i 0.58 and in 411 females, 125.2 i 0.59. With the more attenuated tailin males, it might reasonably be assum- ed that among museum specimens their proportion of broken and therefore incomplete tails would be slightly higher than in females. The data do not support that assumption. Among 569 specimens of males examined, 427 had complete tails, and thus about 25% of the tails were incomplete; in the samples of females, 29% had incomplete tails. A Chi- square value of 0.19 supports the interpretation that the observed dif- ference could well be due to chance sampling errors. 2. SCALE ROW REDUCTION The place where the dorsal scale rows reduced from 17 to 15 rows was recorded as the number of the ventral scale opposite the place of reduction. During a preliminary part of this study I used a ratio, calculated for each side of a specimen, simply by dividing the number of the ventral scale at the reduction point by the total number of ven- trals. As the resulting ratios are similar in the four subspecies iden- tified below, the place of scale row reduction reflects no obvious dif- ferences among those races. To investigate whether clinal or other geographic differences might be associated with the place of scale row reduction, the data were segregated into geographic samples, as defined earlier, representing specimens from northwestern, northeastern, southwestern, and southeastern quadrants. No differences of consequence were noted that could be related to geography, but in all four samples the ratio was lower in females than in males. In males the mean ratio at the point of reduction is 63.6 i 0.17 and in females it is 61.7 f 0.18. The difference is small, 1.9, but contain- ing its standard error, 0.25, more than seven times, is statistically significant. A subsequent means of analysis was through the use of the locus of Table 4.-Mean locus, by ventral number, of reduction of dorsal scale rows in O. a a€stivus. Sex Males Females Number of Specimens 333 331 Mean number of ventrals anterior to reduction 97.7 96.8 Mean number of ventrals posterior to reduction 56.5 60.2 Mean total number of ventrals 154.2 157.0 1984 GROBMAN: OPHEODRYS AESTIVUS SCUTELLATION VARIATION 159 reduction by actual ventral number instead of by ratios. The data of Table 4 were obtained by restricting that analysis to 0. a. aestivus (see below for definition of races) to reduce heterogeneity. These data are consistent with the following: In 0. a. aestivus females have about 3 more ventrals than males. The corresponding elongation in the females occurs primarily in the posterior third of the body be- tween the anal plate and the point of dorsal scale row reduction. Females show a slight increase in body length, as reflected by the number of ventrals, that may be associated with the retention of matur- ing ova, but no comparable accommodation in girth is apparent, for the length of the body with a reduced number of dorsal scale rows ac- tually is greater in females than males. Little bilateral variation occurs. The locus of reduction on the left side of a specimen is about 2.3 ventral scales from the place of reduc- tion on the right side of that specimen. The observed bilateral varia- tion is summarized in Table 5. Table 5.-Bilateral variation in locus of scale row reduction in 941 specimens; difference indicates the number of ventrals between the locus of reduction on one side of the specimen and the locus on the other side. Difference Percentage 0 18.8 1 25.3 2 21.6 3 12.5 4 9.8 5 3.9 6 2.9 7 1.7 8+ 3.5 3. UMBILICAL SCAR Four specimens, two of which were litter mates, had visible umbilical scars; the data are given in Table 6. Although the data at hand are scant, they support the view that geographic and sexual variation in the number of ventrals occurs primarily anterior to the umbilicus, for the number of ventrals between the umbilicus and the anal plate appears to be relatively constant at about 20. Tinkle (1960) made a similar obser- vation based on a study of 142 specimens of 0. aestivus from Jeffer- son Parish, Louisiana. The locus for most of the sexual variation in the number of ventrals in 0. aestivus appears to be the region between the place of scale row reduction and the umbilicus. The region of greatest variability in the number of ventrals in aestivus seems to lie between ventrals 97 and 136. In an idealized male specimen of Opheodrys aestivus with 155 ven- 160 BULLETIN FLORIDA STATE MUSEUM VOL. 29, NO. 3 trals, scale row reduction is opposite the 98th ventral and the center of the umbilicus is at the 135th ventral. TAXONOMIC CONSIDERATIONS An analysis of the data suggests that Opheodrys aestivus contains no less than four subspecies. This report recognizes subspecies if'75% of the available specimens can be correctly assigned to their geograDhic provenience by scutellation characters. Geographic discontinuities in the scutellation characters are the basis for the generalized racial distributions shown in Figure 1. Each spot on the map indicates a coun- ty or parish (or specific location in Mexico) from which one or more specimens have been examined. The dashed lines separating the races pass through areas of intergradation. < ~r:h--v