KARYOTYPIC VARIATION AND EVOLUTION OF THE LIZARDS IN THE FAMILY XANTUSIIDAE

Transcription

1 KARYOTYPIC VARIATION AND EVOLUTION OF THE LIZARDS IN THE FAMILY XANTUSIIDAE Item Type text; Dissertation-Reproduction (electronic) Authors Bezy, Robert L. Publisher The University of Arizona. Rights Copyright is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 12/07/ :25:51 Link to Item

2 7i-»m2 BEZY, Robert Lee, KARYOTYPIC VARIATION AND EVOLUTION OF THE LIZARDS IN THE FAMILY XANTUSIIDAE. University of Arizona, Ph.D., 1970 Zoology University Microfilms, Inc., Ann Arbor, Michigan THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED

3 KARYOTYPIC VARIATION AND EVOLUTION OF THE LIZARDS IN THE FAMILY XANTUSIIDAE by Robert Lee Bezy A Dissertation Submitted to the Faculty of the DEPARTMENT OF BIOLOGICAL SCIENCES In Partial Fulfillment of the Requirements For the Degree.of DOCTOR OF PHILOSOPHY WITH A MAJOR IN ZOOLOGY In the Graduate College THE UNIVERSITY OF ARIZONA

4 THE UNIVERSITY OF ARIZONA. GRADUATE COLLEGE I hereby recommend that this dissertation prepared under my direction by entitled Robert Lee Bezy Karvotypic Variation and Evolution of the Lizards in the Family Xari-tnisi iriab be accepted as fulfilling the dissertation requirement of the degree of, Doctor of Philosophy Dissertation Director After inspection of the final copy of the dissertation, the following members of the Final Examination Committee concur in its approval and recommend its acceptance:" : TU><± W- This approval and acceptance is contingent on the candidate's adequate performance and defense of this dissertation at the final oral examination. The inclusion of this sheet bound into the library copy of the dissertation is evidence of satisfactory performance at the final examination.

5 STATEMENT BY AUTHOR This dissertation has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library. Brief quotations from this dissertation are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author. SIGNED

6 ACKNOWLEDGMENTS I thank the many people who have generously given their time, ideas, labor, and money to aid me in what probably seemed to them an endless and foolish study of an obscure group of lizards. I am especially grateful to Dr. Charles H. Lowe, my major professor, who has not despaired in his eleven-year attempt to impart an fecophysioevolutionary perspective to my extended-boyhood interest in reptiles and amphibians; to Dr. C. Jay Cole, who has also shown unbelievable patience in trying to show me how to find my way out of corn fields, how to wash centrifuge tubes without breakage, and how to make a pastie; to Dr. J. L. Patton who has repeatedly explained to me the details of the karyotype racket; to Dr. William B. Heed who has courageously tried to give me an understanding of the relationship between Drosophila inversions and Lepidophyma karyotypes; to Dr. Philip J. Regal who has shared with me his thoughts on night lizards and related illnesses; and to Dr. David S. Hinds who has spared me from the tragedy of the double-nested do-loop. Xantusiid lizards are collected with crowbars and sweat; 1 am indebted to many blister-handed field friends: E. J. Braun, H. W. Campbell, C. J. Cole, S. R. Goldberg, C. H. Lowe, P. J. Regal, M. D. Robinson, W. C. Sherbrooke, and S. R. Telford. I express my thanks also to those.who have read and criticized this manuscript: Drs. C. H. Lowe, H. K. Gloyd, W. B. Heed, iii

7 iv L. A. Crowder, L. A. Carruth, F. G. Werner, and J. L. Fatton. The skillful editorial efforts of Dr. Gloyd are especially appreciated. I am indebted to the following persons for permitting me to examine specimens under their care: Dr. Richard G. Zweifel, American Museum of Natural History (AMNH); Dr. Jay M. Savage, University of Southern California (CRE); Dr. William E. Duellman, University of Kansas Museum of Natural History (KU); Dr. Douglas H. Rossman, Louisiana State University Museum of Zoology (LSUMZ); Dr. Sam R. Telford, Gorgas Memorial Laboratory (SRT); Dr. James R. Dixon, Texas Cooperative Wildlife Collection, Texas A & M University (TCWC); Dr. Charles L. Douglas, Texas Natural History Collection, University of Texas (TNHC), Dr. Charles H. Lowe, University of Arizona (UAZ); Dr. Donald F. Hoffmeister, University of Illinois Museum of Natural History (UIMNH); Dr. Charles F. Walker, University of Michigan Museum of Zoology (UMMZ); Dr. James A. Peters, United States National Museum (USNM); Dr. William F, Pyburn, University of Texas at Arlington (UTA). The Computer Center of the University of Arizona facilitated the data reduction. This study was partially supported hy a NASA traineeshlp at the University of Arizona.

8 TABLE OF CONTENTS Page LIST OF ILLUSTRATIONS LIST OF TABLES ABSTRACT. vi vii vili INTRODUCTION 1 MATERIALS AND METHODS 6 Karyotypes 6 Morphology 7 Specimens Examined 13 RESULTS AND DISCUSSION 16 Karyotypes 16 Description. 16 Phylogeny 27 Discussion Sex Ratios. 41 Morphology 54 SUMMARY AND CONCLUSIONS 63 Karyotypes 63 Sex Ratios 66 Morphology 67 LITERATURE CITED v

9 LIST OF ILLUSTRATIONS Figure Page 1. Karyotypes of Xantusia vigil is, X_. henshawi, and X. river slana Karyotypes of Lepidophyma flavimaculatum Karyotypes of Lepidophyma tuxtlae. L_. pajapanensis. and L,. ealgeae Karyotypes of Lepidophyma micropholis and L^. smithl Karyotype phylogeny of the family Xantusiidae Karyotype phylogeny of the family Xantusiidae superimposed on a scale of karyotypic advancement Scatter diagram of the relationship between the index of morphologic difference (IMD) and the index of karyotypic difference (IKD) based on the original karyotype phylogeny for the genus Lepidophyma Regression of the index of morphologic difference (IMD) on the index of karyotypic difference (IKD) based on the restructured karyotype phylogeny for the genus Lepidophyma 62 vi

10 LIST OF TABLES Table Page 1., Variation in the chromosomes of nine species in the family Xantusiidae Summary of karyotypic variation in the family Xantusiidae Variation in sex ratio of six species of Lepidophyma Variation in sex ratio of 11 populations of Lepidophyma flavimaculatum Indices of morphologic and karyotypic differences between six species of Lepidophyma. 56 vii

11 ABSTRACT The three species of Xantusia have a diploid chromosome number of 40 (18 macrochromosomes and 22 microchromosomes). Variation within the genus involves differences in the relative number of subtelocentric and telocentric chromosomes. Of the six species of Lepidophyma studied, the diploid chromosome number is 38 (18 macrochromosomes and * 20 microchromosomes) in four, and 36 (16 macrochromosomes and 20 microchromosomes) in two. Subtle differences between the karyotypes of the two species of Lepidophyma with 16 macrochromosomes suggest they have independently undergone centric fusion. The karyotypic variation observed to date in the family Xantusiidae can be explained by the occurrence of ten pericentric inversions, three centric fusions, and one Instance of satellite formation. A phylogeny based exclusively on karyotypic variation is consistent with biogeographic and ecologic information, except for the higher microchromosome number (more primitive character state) of the generally more derived genus Xantusia. Populations composed of 87% to 100% females occur at the northern and southern distributional limits.of Lepidophyma flavimaculaturn. Specimens from an all female population of this species in Panama have a diploid homomorphic karyotype identical to bisexual populations of this species. The possibility still remains, viii

12 ix however, that this is an allodiploid resulting from interspecific hybridization between any of the three bisexual species with this same karyotype. Until evidence of interspecific hybridization is presented, these varying sex ratios are perhaps best explained as being the result of selection favoring females, acting on some basic 'mechanism that could alter sex ratio. When an index of total morphologic difference Is plotted against an Index of total karyotypic difference for each of the 15 possible comparisons between six species of Lepidophyma. a bell-shaped curve results. If, however, one rejects the rather tenuous decision, made exclusively on karyotypic evidence, that the centric fusions of L. smlthi and L_. micropholis are independent (non-homologous), the indices of karyotypic difference resulting from the restructured phylogeny show a much higher correlation with the indices of morphologic difference.

13 INTRODUCTION In Camp's (1923) monumental classification of lizards, the morphologic gap between the two divisions, Ascalabota and Autarchoglossa, of the suborder Sauria was bridged by a single family, Xantusiidae, which was surreptitiously placed in the Autarchoglossa. Subsequent workers have also found this systematically ambivalent family annoying and have shifted it endlessly between these divisions. In actuality, these inconspicuous lizards may well be relicts of the departure point of the two major lines of saurian evolution and might conveniently be placed in a third division. At present, however, this depauperate family remains one of the major problems in the classification of the higher taxa of lizards. In addition to their morphologic intermediacy between the two divisions of Sauria, xantuslids betray their primltiveness in other ways. The family exhibits an extremely disjunct pattern of distribution characteristic of primitive, receding groups. Individuals frequently live separated from one another by relatively large distances. Wide spacing of areas with optimal microclimate produces highly disjunct local populations. Ranges of most of the species are extremely fragmented and populations are often isolated by hundreds of miles. Particularly spectacular examples are the occurrence of Xantusia vlgilis and Xantusia henshawi In Durango, Mexico, ca. 800 air-llne miles from the nearest known populations to the northwest, and the insular 1

14 2 isolation of Xantusia riversiana and Cricosaura typica. Unless truly amazing powers of dispersal are involved, this pattern of distribution indicates that the lizards of this family were at some time in the past much more widely distributed than they are today. The occurrence of the Eocene fossil, Paleoxantusia fera (Hecht, 1956) in Wyoming, ca. 300 miles north of the present northern limit of the family further underscores this viewpoint. Not only have xantusiid lizards been troublesome to students of "higher classification", but those unfortunate taxonoraists who have been lured into extensive studies of the systematics of this difficult group have suffered what can be called extreme psychological torture. Within this handful of species there occurs nearly every conceivable degree of morphologic divergence. Many problems are encountered by systematists attempting to define subspecies, species, and genera in this small family because the morphologic distances separating taxa are quite variable and do not tend to fall into discrete levels that could be assigned rank. In partitioning this array of only about 14 species into genera, one must steer between the Scylla of monotypic genera and the Charybdis of a monotypic family. Cope (1895) recognized five Recent genera, all of which were monotypic except Xantusia. and one of which (Amoebopsis gilberti) contained what is currently recognized as only a subspecies (Xantusia vigilis gilberti). Savage (1963) recognized four Recent genera of which two (Xantusia and Lepidophyma) are polytypic and two (Cricosaura and Klauberina) are monotypic. In this study only two genera are treated, Xantusia

15 3 (inclusive of Klauberina), and Lepidophyma (inclusive of Gajgeia); the genus Cricosaura has not yet been studied karyotypically. Sympatric contacts have been reported for only two species pairs in the family Xantusiidae: Xantusia henshawi and X_. vigilis in southern California (Klauber, 1931), and Lepidophyma tuxtlae and L. palapanensis in southern Veracruz (Werler, 1957). When the lack of sympatry in this family is combined with extreme variability in morphologic divergence at the population level, the task of defining evolutionarily meaningful (or even morphologically consistent) species units becomes difficult (Bezy, 1967b).- Further, strong selective pressure for morphologic adaptations in highly isolated populations of saxicolous xantusiids has lead to apparent morphologic convergence at the subspecies level (Xantusia vigilis arizonae and. v. sierrae, Bezy, 1967a,b), at the species level (Xantusia vigilis arizonae and X. henshawi. Klauber, 1931), and at the near-generic level (Xantusia and Gaigeia, Smith, 1939). An analysis of karyotypic variation has been undertaken in the hope of finding new data to help establish meaningful phylogenetlc relationships in this small but puzzling family. Karyotypes of nine species of xantusiids are reported and discussed herein: Xantusia henshawi Stejneger, X. vigilis Baird, X. riversiana Cope. Lepidophyma flavimaculatum A. Dumeril, JL. gaigeae Mosauer. L_. micropholis Walker. L.. pajapanensis Werler, L. smith! Bo court, and L_. tuxtlae Werler and Shannon. The biogeographic, morphologic, and karyotypic evidence, when considered together, indicates that these are all valid species,

16 as will be discussed In a separate paper on the systematica of the genus Lepldophyma. Karyotypic data are not yet available for six rare forms of uncertain status: Crlcosaura typica Gundlach and Peters, Lepldophyma dontomasl (Smith), 1^. radula (Smith), L_. sylvaticum Taylor, L. (smith!) occulor Smith, and an undescribed species of Lepldophyma from Guatemala..X wish to emphasize that this "new information" can be meaningfully interpreted only by comparison with other sources of data, that is, by the process which Hennig (1966) dignified with the term "reciprocal illumination." I consider the comparison of patterns emerging from radically different sources of data to be a vital step in the establishment of meaningful phylogenetic relationships, and do not accept Sokal and Sneath f s (1963) view that this is merely circular reasoning. Convergence, for example, can occur in morphology and in karyotypes, but, because of the radically different selective pressures involved in morphologic and karyotypic evolution, the probability is quite low that convergence will occur in these two parameters simultaneously (i.e., in the same population). For these reasons data on morphologic variation and sex ratio are presented and discussed In this paper where the major focus is on karyotypic evolution. Moreover, the phylogenetic relationships suggested herein are based not only on an appraisal of all these sources of data, but also on biogeographlc and ecologic field Impressions. 1 hope that the electronic computer and the phase contrast microscope now wedged between me and these fascinating relicts have

17 not completely obscured the evolutionary pathways whose fragments were discovered amidst immense boulders piled beneath the Mogollon Rim, in the winds sweeping across San Clemente Island, in the dripping blackness of caves in the Tamaullpas lowlands, along limestone ledges hidden in the montane woodlands of the Sierra Madre Oriental, and around the huge buttressed logs rotting in the darkness of Panamanian rain forests.

18 MATERIALS AND METHODS Karyotypes Chromosomes of cells from bone marrov and testicular tissue were prepared In vivo by Patton's (1967) modification of the colchicinehypotonic citrate technique of Ford and Hamerton (1956) as has been adapted for lizards by Lowe and Wright (1966) and by Lowe, Wright, and Cole (1966). The. karyotype of Lepldophyma flavimaculatum was also determined in vitro from lung tissue culture by Dr. T. C. Hsu of the M. D. Anderson Hospital and Tumor Institute of Houston. Good karyotype preparations were especially difficult to obtain from xantusiid lizards due, in part, to an unusually low level of mitotic activity in the bone marrow. By increasing the stressing of the peripheral circulatory system, mitotic activity was increased; unfortunately, this also increased mortality among the specimens. The limbs of Xantusia vigills and Lepldophyma galgeae are quite small in diameter, and the bone marrow is consequently difficult to "flush out." Pooling of the bone marrow from several individuals was necessary to obtain the somatic karyotype of L. galgeae. While the karyotype of populations of X. vigllls was derived exclusively from analysis of testicular tissue. Whenever possible, a minimum of at least ten cells was studied from each specimen "run.". For each cell studied, the permanent slide number, the cell co-ordinates, the diploid chromosome number, the 6

19 number of macrochromosomes and microchromosomes, the occurrence of secondary constrictions, and the numbers and relative sizes of metacentric, submetacentric, subtelocentric and telocentric'macrochromosomes were recorded. The karyotype of the specimen was then determined on a modal basis. For the family Xantusiidae the following classification of chromosomes was found to be the most useful and was employed throughout the study: metacentric S/L (p ratio of short to long arm of chromosome), ; submetacentric S/L ; subtelocentric S/L, ; and telocentric S/L 0.00 (see Lowe and Wright, 1966, for an alternate classification). Both pairing and classifying the chromosomes, however, was done "by eye 11 rather than by actual measurement. Morphology Twenty-seven morphologic characters were used in. the analysis of variation in the genus Lepidophyma. These characters were not selected at random but are the ones judged to have the greatest utility in defining evolutionarily meaningful species in the genus. This judgement is based on an appraisal of the species delineations of earlier workers, on my own experience with Xantusia, (Bezy, 1967a,b), and on casual observations on variation in the genus Lepidophyma. While the'selection of the characters was rather subjective, I have striven for their objective and quantitative definition. Unless otherwise noted, the following descriptions of the characters studied utilizes the scale terminology oe Savage (1963). Those marked with

20 an asterisk were not included in the index of morphologic difference: 1.* Sex: Based on internal examination of the gonads. Specimens too small to allow discrimination of ovaries from testes were recorded as juveniles. 2. Femoral pores: Counts on right and left leg were recorded separately. Total femoral pores (right plus left) were used in the. analysis.' In the females of several species, the pores are frequently reduced to faint depressions in the femoral scales. Such, "undeveloped pores" were included in the counts. 3. Tubercle rows: The number of vertical rows of enlarged tubercles on ttie side of the body between axilla and groin. The count is made along a line about two tubercles below (i.e., lateral to) the paravertebral scales. In species in which the lateral surface is covered by scales of uniform size, the count is taken of all scales along this line. 4. Interparavertebrals: The number of scales separating the rows of enlarged paravertebral tubercles. The count is taken raidbody and is recorded as the mean (to the nearest 0.5 scale) of the counts for five consecutive pairs of tubercles. 5. Interwhorls: The number of small scales (interwhorls) separating the whorls of enlarged caudal scales. Both a dorsal and a ventral count were made between the first and the second complete caudal whorl. Continuing distally, any change in either the ventral or the dorsal interwhorl count was recorded along with the whorl number (.enlarged whorls numbered consecutively beginning with the first

21 complete basal whorl) at whic h the change occurs. If the tail was Incomplete, record was made cf the whorl number at which it was broken or after which it was regene iated. From these data, analysis was made of (a) the number of dorsal interwhorls separating whorl 1 and whorl 2; Cb) maximum number of dorsal interwhorls occuring between any of the first 15 whorls; (c) the num iber of dorsal interwhorls between whorl 14 and 15; (d) maximum number of ventral interwhorls between any of the first five whorls; and (3) occuring between any of the in the index of morphologic Hi: inimum number of ventral interwhorls first five whorls. Only (a) above was used difference. 6. Median prefrontals: The number of median prefrontals. This is the "median" of Savage C1963) 7. Median prefrontal contac t: The presence or absence of a contact between the median prefrontal and the frontonasal. In the data analysis* no contact was give n a value of 1; contact, a value of Scales between postocula rs and 6-7 labial suture. The number of temporals that separate the jjostoculars from the suture between the 6th.and 7th supralabial. The sun of right plus the left side of the head was used in the analysis. 9. Intraparavertebral: Es tjimation of the distance between the enlarged tubercles along one paravertebral row. The estimation is mads by counting the number c f granules of the interparavertebral area that equals the distance betw een two consecutive tubercles in one paravertebral row. The mode of five counts was recorded.

22 Anterior loreal height vs. posterior nasal height: Comparison of the relative height of these two scales for both sides of the head. In data analysis, values were assigned as follows: loreal higher than nasal on both sides of head «1; loreal higher than nasal/loreal. same height as nasal = 2; loreal same height as nasal on both sides of head =» 3; loreal same height as nasal/nasal higher = 4; nasal higher on both sides of head = 5; loreal higher/nasal higher = Posterior nasal-prefrontal contact: Presence or absence of a contact between posterior nasal and prefrontal. Coded as follows: no contact (both sides of head) = 1; contact on one side/no contact on other side of head = 2; contact on bot'h sides of head Second lnfralabial contact: Degree of contact between second pair of infralabials. Coded as follows: clear direct contact = 1; separation by a skin fold less than one gular scale in width = 2; separation by a skin fold more than one gular scale in width =3; separation by distinct gular scales = * Inner paravertebral tubercle enlargement: Presence or absence of enlargement of the row of scales immediately medial to the row of paravertebral tubercles. Coded as: unenlarged =1; enlarged = * Inner paravertebral tubercle keels: Presence or absence of keels on the scales immediately medial to the paravertebral tubercles'. Coded as: smooth = 1; keeled = Postparietal sutures: Degree of development of sutures leading from the interparietal, posteriolaterally across the postparietals. If these sutures reach the nuchals, they are considered "complete."

23 Coded as follows: no suture on either postparietal» 1; no suture/ incomplete suture= 2; incomplete sutures on both postparietals =3; no suture/complete suture = 3; incomplete suture/complete suture = A; complete suture across both postparietals = Postocular width/ocular diameter: Ratio of the maximum width of the largest postocular scale to the maximum diameter of the orbit. Measured with an ocular micrometer to the nearest.01 mm. # 17.* Snout-vent length: Measured to the nearest whole millimeter. r* 18. Gulars: Longitudinal count of the number of transverse rows of gular scales between the gular fold and the point of mid-ventral contact of the infralabials. 19. Scales bordering the anterior supratemporal: The number of scales contacting the anterior supratemporal, exclusive of the parietals, postparietals, and posterior supratemporal. The count Includes primary temporals and "pretympanics Fretympanic diameter/auricular diameter: Ratio of the maximum diameter of the pretympanic scales to the maximum diameter of auriculars. Diameters were measured to the nearest 0.01 mm, with an ocular micrometer. 21. Minimum number of scales between the 8th supralabial and the posterior supratemporal. Count of the fewest number of scales between the end of the supralabial row and the posterior supratemporal. The count usually includes some, if not all, of the scales of the row of enlarged pretympanics.

24 22. Dorsal scales: The number of dorsal scales that are contained In one head length. The count Is made In the area between the paravertebral rows and Is centered between the axilla and the groin. 23. Enlarged paravertebral tubercles: The number of distinctly, enlarged tubercles between axilla and groin in the paravertebral row. Difficulty is sometimes encountered in distinguishing "enlarged" from "unenlarged" tubercles. Generally, the tubercle must be at least two times the average diameter of the interparavertebrals to be considered "enlarged" and thus included in the count. 24. Ventrals: Number of ventral scales from the gular fold to the vent. The count thus included both the ventrals and the pireanals of Savage (1963). It is made just to one side of the mid-line. 25. Fourth toe lamellae: Minimum number of scales on the underside of the fourth toe between its base and the claw. Proximally the count is begun at the point of attachment of the digit to the foot rather than necessarily at the occurrence of the first enlarged lamella which sometimes begin either on the sole of the foot or somewhat distal to the attachment of the toe. 26. Divided fourth toe lamellae: The number of lamellae on the undersurface of the fourth toe that are divided midventrally. The divided lamellae usually begin at the base of the toe and continue for one third to one half its length. The few divided lamellae that usually occur distal to, and isolated from, this basal series are also included in the count.

25 13 27.* Scales around body (SAB): The number of scales (excluding ventrals) at midbody. Midbody was considered as the point indicated by one-half the total ventral count. The count is.greatly reduced and its variability greatly increased when enlarged tubercles are included. To avoid this problem, an attempt was made to encounter the fewest number of tubercles in making the count, and this character was used only for species that have few or no enlarged tubercles. Specimens Examined The following specimens were used in the karyotypic analysis and are deposited in the Herpetological Collection, Department of Biological Sciences, of The University of Arizona (UAZ). Lepidophyma flavimaculatum: MEXICO: Chiapas: 25 mi. (by rd. to Malpaso) NW Ocozocoautla (UAZ ). PANAMA: Colon Province: 3 mi. (air line) SE Achiote (8 mi. NNW Escobal) (UAZ , 28826). Lepidophyma gaigeae: MEXICO: Hidalgo: 2 mi. N Durango, 13 ml. (by Hex. 85) S Jacala (UAZ ); Durango, i5 mi. (by Mex. 85) S Jacala (UAZ , , 28915). Lepidophyma micropholis: MEXICO: Tamaulipas: Cave at El Pachon 8 Km. (by rd.) NNE Antigua Morelos (UAZ 28762, ). Lepidophyma pajapanensis' MEXICO: Veracruz: Coyame, 9 mi. SE Catemaco (UAZ 28804); 2 mi. (by rd.) SE Sontecomapan, 14 mi. (by rd.) NE Catemaco (UAZ ). Lepidophyma smithi: MEXICO: Chiapas: 9 mi. (by Mex. 200) NW Escuintla (UAZ 28797); 4 ml. NW Mapastepec, 24 mi. (by Mex. 200) NW

26 14 Esculntla (UAZ ); Oaxaca: l^g mi. (by Mex. 190) E Tapanatepec (UAZ 28794). Lepidophyma tuxtlae: MEXICO: Chiapas: 25 mi. (by rd. to Malpaso) NW Ocozocoautla (UAZ ); Veracruz: 2 mi. (by rd.) SE Sontecomapan, 14 mi. (by rd.) NE Catemaco (UAZ ). Xantusia henshawimexico: Bala California del Norte; 5 to 20 mi. (by Mex. 3) NE Ensenada (UAZ ). UNITED STATES: California: Riverside Co.: Tramway parking toll booth, Chino Canyon, San Jacinto Mts. (UAZ 21617); 2 mi. (by rd. to Idyllwild) S. Banning* San Jacinto Mts. (UAZ 21653, , 21700, 21705); 3 mi. (by rd. to Idyllwild) S'. Banning, San Jacinto Mts. (UAZ 21690, 21692). Xantusia riversianat UNITED STATES: California: Channel Islands: N end of Pan Clemente Island (UAZ , , 28965). * Xantusia vigilis: MEXICO: Baja California del Norte: ca. 14 mi. (by rd.) E La Trinidad, Valle de La Trinidad (UAZ ); Sonora: ca. 0.5 mi. S El Desemboque del Rio San.Ignaclo (UAZ 24193, 24238); 1-2 mi. (by.rd.) S Desemboque del Rio San Ignaclo (UAZ 24858, 24860, 24868, , , 24860). UNITED STATES: Arizona: Mohave Co.: 7.6 mi. (by Ariz. 93) SE Burro Creek, 3200 ft. (UAZ ); Yavapai Co.: 11.3 mi. (by Ariz. 93) SE Burro Creek, ca ft. (UAZ , 21706, 21710, 24193, 24201, 24204, 24210, 24216, 24229, 24231, , 24242, 24251); 9.2 mi. (by Ariz. 93) SE Burro Creek, 3200 ft. (UAZ 24233, 24239, 24183, 24237); 0.9 mi. (by Manzanita Dr.) W of 0.8 mi. S Yamell, 4750 ft. (UAZ 21652,

27 ); vie. Yarnell, 4750 ft. (UAZ 24184, 24188, 24196, 24198, 24227, 24854, 24856, 24861, , 24902); Yuma Co.: E end of u- Palm Canyon, Kofa Mts. (UAZ

28 RESULTS AND DISCUSSION Karyotypes Description Xantusia vigills. A total of 384 cells from 16 individuals (16<?,0?) representing five populations (Yarnell, Burro Creek, Palm Canyon, Valle de La Trinidad, and Desemboque) were studied. The karyotypic analysis of this species is based exclusively on examination of meiotic and mitotic metaphase figures in testicular tissue. Bone marrow, spleen, and regenerating tail tissue preparations did not yield workable results. The diploid chromosome number in Xantusia vlgills is 40, composed of 18 macrochromosomes and 22 microchromosomes. (Tables 1-2, Fig. 1). The macrochromosome pairs are numbered from largest to smallest (left to right in Fig. 1); the microchromosome pairs are not numbered as their small size precludes recognition of individual pairs. Chromosome pair no. 1 is by far the largest pair in the complement and is metacentric to submetacentric. Fair no. 2 is about half the size of no. 1 and is consistently metacentric. Fair no. 3 is only very slightly smaller than pair no. 2 and is consistently subtelocentric. On the basis of size and centromere position these first three chromosome pairs are always clearly distinguishable from one another and are distinctly larger than the remaining six pairs that are of more similar morphology 16

29 Table 1. Variation in the chromosomes of nine species in the family Xantusiidae. Centromere position (M = metacentric, SM = submetacentric, ST = subtelocentric, T = telocentric) and presence of satellites (*) for the macrochromosome pairs. Centromere positions in parentheses are those observed less frequently for the chromosome pair. Chromosome Pair No. 12 2A Xantusia vigilis a M M - ST ST SM ST(T) ST ST T(S) vigilis 0 H M ST ST SM ST(T) ST ST ST henshawi M M ST ST SM ST ST(SM) ST ST riversiana H M ST ST SM T(ST) ST(T) ST ST aidophyma flavlmaculatum M M ST* ST SM ST ST ST T paiapanenesis M M - ST* ST SM ST. ST ST T tuxtlae M M - ' ST* ST SM ST ST ST T gaigeae M M - ST* ST SM ST SM(ST) ST ST micropholis M M M ST ST SM - SM(M) - T smithi M M M ST* ST SM - ST ST -

30 Table 2. Summary of karyotypic variation in the family Xantusiidae. Diploid chromosome number (2n); number of macrochromosomes (macros); number of microchromosomes (micros); number of pairs of metacentric (M), submetacentric (SM), subtelocentric (ST), and telocentric (T) macrochromosomes; presence (*) or absence (-) of satellites (Sats) on macrochromosome pair no. 3; and index of karyotypic advancement (IKA) for 9 real and 3 hypothetical species. 2n Macros Micros M SM ST Sats IKA Xantusia vigilis a vigilis henshawi riversiana Lepidophyma flavimaculatum paiapanensis tuxtlae gaiseae micropholis sraithi * k * * A Ancestral Xantusiid Xantusia Lepidophyma

31 Fig. 1. Karyotypes of Xantusia vigilis, X. henshawi and X_. riverslana. A. X. vigilis. karyotype B. UAZ 24861,di vie. Yarnell, 4750 ft., Yavapai Co., Arizona. B. X. vigilis, karyotype a. UAZ 24216,(T: 11,3 mi. (by Ariz. 93) SE Burro Creek, 3200 ft., Yavapai Co., Arizona. Line represents 10 y. C. X. henshawi, UAZ 21694,<T: 2 mi. (by rd. to Idyll wild) S Banning, San Jacinto Mts., Riverside Co. California. D. X_, riverslana. UAZ 21688,$: N end San Clemente Island, Channel Islands, California.

32 19 jj II II it H A #t "*» [* * J )( 11 it it ii it t» «B (I n # Aft III j II 11 it I: m Fig. 1. Karyotypes of Xantusla vlgllls. X. henshawl. and X. rlverslana.

33 V 20 and size, and thus more difficult to distinguish from one another. Pairs no. 4 and 5 are larger and more distinctly bi-armed than the last four pairs (no. 6-9). Pair no. 4 is subtelocentric and pair no. i 5 is submetacentric. Pairs no. 6, 7 and 8 are nearly identical in size and are subtelocentric; the largest (no. 6), however, has only minute short-arms and thus occasionally appears telocentric. The smallest macrochromosome pair (no. 9) varies among the populations of Xantusia vigilis studied. It appears subtelocentric in individuals'from the Yarnell and Desemboque populations (karyotype 0, Fig. 1) and telocentric (only occasionally minutely subtelocentric) in the Burro Creek, Valle de La Trinidad, and Palm Canyon populations (karyotype a, Fig. 1). It must be emphasized that this karyotypic difference is based on the modal conditions in the populations examined and the photos (Fig. 1) represent this modal difference. Since rather subtle karyotypic differences are involved, statistical comparisons of mean chromosomal arm ratios (c.f., Cole, Lowe, and Wright, 1969) would be necessary to completely document geographical variation in this smallest macrochromosome of Xantusia vigilis. The quantity and quality of the karyotype material of this species now at hand is not adequate for such an analysis. Xantusia henshawi. Based on examination of 114 cells from bone marrow and testicular tissue of 7 individuals (6(?,1!?), the diploid chromosome number of this species appears to be 40, with 18 macrochromosomes and 22 microchromosomes (Tables 1-2, Fig. 1). The karyotype appears identical to that of the B karyotype of X, vigilis except that chromosome pair no. 7 has longer short-arms and is subtelecentric to

34 21 submetacentric. The above data suggest that Matthey (1931) was in error in giving the diploid number of Xantusia henshawi as 42 (rather than 40) with 18 macrochromosomes and 24 (rather than 22) microchromosomes. Xantusia riversiana. From an analysis of 124 cells from bone marrow, testicular, and spleen tissue of 9 individuals C4(T,5$), this species also appears to have a diploid.chromosome number of 40 with 18 macrochromosomes and 22 microchromosomes (Tables 1-2, Fig. 1). The karyotype appears identical to the fi karyotype of 3C. vigilis except that chromosome pair no. 6 appears telocentric more often than subtelocentric, and chromosome pair no. 7 sometimes appears telocentric. Lepidophyma flavimaculatum. Based on an examination of 266 cells from bone marrow, as well as lung tissue of 10 individuals (0< l0j), this species has a diploid chromosome number of 38 with 18 macrochromosomes and 20 microchromosomes (rather than 22 as in Xantusia; Tables 1-2, Fig. 2). The macrochromosomes in this species appear identical in morphology to those of the a karyotype of Xantusia vigilis except that chromosome pair no. 3 bears a distinct terminal satellite. Bone marrow tissue of one individual of this species from an "all-female" population in Panama appears to be composed of both diploid (2n^38) and triploid (3ir=57) cells (Fig. 2). Eighty-two diploid and 25 triploid cells were examined from one bone-marrow \ v preparation, yielding a ratio of 3.28 diploid to 1 triploid. This condition was observed in the bone-marrow.tissue of only one of the 8 Individuals studied from this "all-female" population. The karyotype

35 Fig. 2. Karyotypes of Lepidophyma flavlmaculatum. A. Bisexual population. UAZ 28805,$: 25 mi. (by rd. to Malpaso) NW Ocozocoautla, Chiapas, Mexico. B. Unisexual population. UAZ 27642,$: 3 mi. (air line) SE Achiote, (8 mi, NNW Escobal), Colon Province, Panama. C. Unisexual population. Diploid cell from UAZ 27640,$: locality same as UAZ above. Line represents 10 y. D. Unisexual population. Triploid cell from UAZ

36 22 )I II IK IX IB «U l»! «\} 81 M «x II B II * M if Km AA * ** * * ()] IU HI M«iA.m ^ * * ** * # *» Fig. 2. Karyotypes of Lepldopkyma flavimaculatum.

37 23 of an individual from this same population was also determined in vitro from lung tissue culture by T. C. Hsu and found to be identical to the diploid bone marrow cells. Lepidophyma palapanensis. From an analysis of 87 cells from bone marrow and testicular tissue of 4 Individuals (1<?,3 ), this species appears to have a diploid chromosome number of 38 with 18 macrochromosomes and 20 microchromosomes (Tables 1-2, Fig. 3). The karyotype appears identical to that of L.. flavimaculatum. Lepidophyma tuxtlae. Analysis of 227 cells from bone marrow and testicular tissue of 9 individuals (6<?,3?) reveals that this species has a diploid chromosome number of 38 with 18 macrochromosomes and 20 microchromosomes (Tables 1-2, Fig. 3). The karyotype of this species also appears identical to that of JL. flavimaculatum. Lepidophyma gaigeae. Based on examination of 76 cells from bone marrow and testicular tissue of 4 individuals (2c?,2$), the diploid chromosome number of this species appears to be 38 with 18 macrochromosomes and 20 microchromosomes (Tables 1-2, Fig. 3), The morphology of the macrochromosomes appears identical to that in L. flavimaculatum except that: (1) chromosome pair no. 7 has longer short-arms, appearing submetacentric more often than subtelocentrlc; (2) chromosome pair no. 9 is subtelocentrlc rather than telocentric. Lepidophyma micropholis. From an analysis of 110 cells from bone marrow and testicular tissue of 3 individuals (2t?,l ), this species appears to have a diploid chromosome number of 36 with 16 macrochromosomes and 20 microchromosomes (Tables 1-2, Fig. 4).

38 24 XX" Aft ft* KK» *11 All Alt * #«i u i* M ft* A* ft* ftft» B U &ft IX A* Aft AA ft* 91 Fig. 3. Karyotypes of Lepldophyma tuxtlae. L_. pajapanensls. and L_. galgeae. A. L. tuxtlae. UAZ 28770,*?: 2 ml. (by rd.) SE Sontecomapan, 14 ml. (by rd.) NE Catemaco, Veracruz, Mexico. B. L.. palapanenals. UAZ 28810,cT: same locality as L.. tuxtlae above. Line represents 10 y. C. L. galgeae. UAZ ,$: 2 ml. N. Durango, 13 ml. (by Hex. 85) S. Jacala, Hidalgo, Mexico.

39 25 XX XX if n«xx a a a % 0 <> n 10 l IS Aft ft«* i i B Fig. 4. Karyotypes of Lepldophyma mlcropholls and L_. smlthl. A. L. mlcropholls. UAZ 28762,$: Cave at El Faction, 8 Km. (by rd.) NNE Antigua Morelos, Tamaulipas, Mexico. Line represents 10 u. B. L_. smithi. UAZ 28812,^: 4 mi. NW Mapastepee, 24 ml. (by Mex. 200) NW Escuintla, Chiapas, Mexico.

40 26 The tnacrochromosome pairs are numbered on the basis of their probable homologies with L_. flavimaculatum. Chromosome pairs no. 1 and 2 are metacentric and appear Identical to those of all the other species of the family; chromosome pair no. 2A is a large metacentric that appears to have been formed by centric fusion of two of the smaller macrochromosomes (probably pairs no. 6 and 8). Chromosome pair no. 3 is a large subtelocentric that lacks the terminal satellites which are found on this pair in all other species of Lepidophyma but which are absent in the species of Xantusia. Matching the remaining four macrochromosomes with their homologs in L_. flavimaculatum is somewhat difficult. Chromosome pair no. 2A was most probably formed by fusion of chromosome pairs no. 6 and 8. Chromosome pairs no. 4 and 5 appear identical in the two species. Pair no. 7 is submetacentric to metacentric, and resembles pair no. 7 of L. gaigeae. The smallest macrochromosome is probably homologous to pair no. 9 of L. flavimaculatum. Lepidophyma smithi. From an analysis of 151 cells from bone marrow and testicular tissue of 7 individuals (A3$), this species appears to have a diploid chromosome number of 36 with 16 macrochromosomes and 20 microchromosomes (Tables 1 2, Fig. 4). Chromosomes pairs no. 1 and 2 appear identical to those chromosomes in all other species. Chromosome 2A is a large metacentric to submetacentric and probably was formed by centric fusion of chromosome pairs no. 6 and 9; thus only its long arms are homologous with chromosome 2A of L_. micropholis. That chromosome pair no. 2A is formed by fusion of pairs

41 27 no. 6 and 8 in L,. micropholis and pairs no. 6 and 9 in L. smith! is based on the following: (1) pair no. 2A appears somewhat more submetacentric in L_. smithi than in L. micropholis; (2) the smallest chromosome pair in L. micropholis usually appears slightly smaller than the smallest pair in L. smithi, and is telocentric in the former and. subtelocentric in the latter. All of these differences could also be explained as resulting from inversions occurring after one centric fusion, except the difference in the size of the smallest chromosome pair. This could be made more concrete by comparing measurements from photomicrographs of the karyotypes of the two species, but the size differences involved are so small that truly convincing identification of homologous chromosomes would probably require observation of synapsis, in artificially produced hybrids. Phylogeny The logical establishment of phylogenetlc relationships based on a single morphologic trait is difficult at best. Hennig (1966: 88-99) recently emphasized the necessity of identifying the primitive (plesiomorphous) and advanced (apomorphous) states of all characters in order to construct a meaningful phylogeny and discusses criteria for determining the direction of character evolution. Darlington (1970) has presented rather cogent criticisms of Hennig's theory and methods. The construction of phylogenies by careful identification of primitive versus advanced character states is well illustrated in herpetology by Kluge (1967) and by Wake and Ozeti (1969).

42 28 The evolutionary relationships of the family Xantuslidae remain obscure. Morphologic evidence has been presented which ally the family with both Gekkota (McDowell and Bogert, 1954; St. Girons, 1967) and Scincoraorpha (Etheridge, 1967; Miller, 1966) thus confirming Camp's (1923) original hypothesis that xantusiids are extremely primitive lizards intermediate between the widely divergent infraorders Scincomorpha and Gekkota Otegal, 1968). This situation makes the determination of primitive character states by comparison with "sister groups" (Hennig, 1966) impossible at present. An alternate method of determining the direction of karyotype evolution in the family is by extrapolation from the pattern of karyotype evolution seen in other phylogenetic groups. Of the 147 forms of the genus Drosophila for which both metaphase and salivary gland chromosomes had been studied, one (0.7%) showed an increase in chromosome number (fission), while 76 (51.7%) showed one or more centric fusions (Patterson and Stone, 1952). Within the suborder Sauria, karyotypic evolution at the family level appears to have occurred predominately by means of centric fusion (whole arm translocation or Robertsonian fusions, Matthey, 1951j White, 1954). The same evolutionary pattern appears to hold for the genera of the family Iguanidae (Gorman, Atkins, and Holzinger, 1967); in the genus Sceloporus centric fusion appears consistent with the historical blogeography of the biotic communities of which the particular species is a member, and with behavior (Lowe, Cole and Patton, 1967; Cole, 1969); in the genus Anolis centric fusion appears consistent with

43 29 evolutionary trends based on osteology (Gorman and Atkins, 1967). In the genus Cnemidophorous of the family Teiidae, Lowe et al. (1970a) consider that a karyotypic phylogeny based on centric fusions is consistent with biogeography. Thus, by correlation with other characters (i.e., circular reasoning) the direction of karyotypic evolution can be expected to be from a higher to a lower diploid chromosome number and from a higher to a lower percentage of telocentric chromosomes in the karyotype. In spite of the fact that the paracentric inversions of Drosophila salivary chromosomes form the basis for perhaps the most concrete phylogenies yet constructed, it is difficult even to assign directionality to the unequal pericentric inversions that are presumed to be responsible for the shifts in centromere positions of the chromosomes in the karyotypes of xantusiids. However, as in the case of centric fusions, the general evolutionary trend in karyotypic evolution is that pericentric inversions tend to convert uni-armed chromosomes into bi-armed chromosomes, not vice versa (White, 1954: 192). As with centric fusions, unequal pericentric inversions reduce the number of acrocentrics and increase the number of subtelocentric to metacentric chromosomes. The major difference in the results of these two mechanisms is, of course, that fusions maintain a constant number of "major chromosome arms" (nombre fondamental) while pericentric inversions increase the number of "major chromosome arms." When, as in xantusiids, both mechanisms are operative, "asymmetrical karyotypes" result (White, 1954:192), since inversions produce

44 30 smaller bi-armed chromosomes than fusions. If Matthey (1951) is correct In considering the basic haploid karyotype of his "complex Iguanoide" to be composed of 12 major chromosome arms, the submetacentric chromosome pair no. 5 of all xantusiids must have resulted from centric fusion, while the submetacentric condition of chromosome pair no. 7 of Lepidophyma galgeae and L,. micropholis appears to have resulted from pericentric inversion. Thus, in constructing the karyotype phylogeny (Figs. 5-6), for each chromosome I have always considered the most nearly acrocentric condition observed among the various forms to be the primitive condition for that chromosome and have considered fused chromosomes to be a derived condition. From this line of reasoning, the ancestral xantusiid is hypothesized to have a diploid chromosome number of 40, with 22 microchromosomes and 18 macrochromosomes consisting of 2 metacentric, 1 submetacentric, 3 subtelocentric, and 3 telocentric pairs and without a satellite (Fig. 5). From this primitive condition I have derived the observed karyotypes by centric fusions and pericentric inversions using those pathways that would require the minimum number of chromosomal rearrangements yet produce the minimum amount of karyotypic convergence (Figs. 5-6). A total of 10 pericentric inversions, 3 fusions, and one instance of satellite formation is required to account for the chromosomal evolution observed thus far in the family Xantusiidae; a total of 6 instances of chromosomal convergences result (chromosomal convergence occurs when a specific derived state of a given chromosome

45 Fig. 5. Karyotype phylogeny of the family Xantusiidae. In each box, beneath the scientific name, is the diploid chromosome number, followed (in parentheses) by the number of macrochromosomes + the number of microchromosomes. Beneath this is the number of pairs of metacentric CM) + submetacentric (SM) + subtelocentric (ST) + telocentric (T) macrochromosomes; the.numbers in parentheses identify the macrochromosome pair nos. (as in Table 1) that have these centromere positions. All pairs of macrochromosomes are identified for the ancestral xantusiid; thereafter, numbers are given only for those macrochromosome pairs that are in a derived state (I.e., have a centromere position different from that of the ancestral xantusiid). Asterisks (*) indicate the presence of a terminal satellite on macrochromosome pair no. 3. The arrow and box that are dashed indicate an alternate derivation of smith! that is suggested by the morphological data (see text). Data from Tables 1 and 2.

46 31 L. Rnlp.cni* 38 (18+20)* 2H+2SM(7)+5ST(6,8,9)+0T 2 inv L. smith! 36 (16+20)* 3M(6+9)+lSW4ST(8)+0T Fusion (Macros) 38 (18+20)* 2M+lSMt4ST(8)+2T 1 inv L* lavimaculacuni L. pa lapgnonstis L. tuxtlae 38 (18+20)* 2M+lS»+5ST(6,8)+lT 1 inv. + satellites L. microphojis *" 36 (16+20) 3M(G+8)+2SM(7)+2ST+lT j 2 inv. + I satellites \j/ [" L* smitlil ] I 36 (16+20)* J 3M(6+8)+lSM+4ST(9)+0T Fusion (Macros) ancestral Lcpidophyma 38 (18+20) 2H+1SH+3ST+3T 1 inv. Fusion (micros) anccstral Xantusiid 40 (18+22) 2M(1,2)+lSM(5)+3ST(3,4,7)+3T(6,8,9) X, viftilis a "40 (16+22) 2H+1SM+5ST(6,8)+1T anccstral Xnntusla 1 inv. 40 (18+22) 1 inv 2M+lSM+'i ST (8)+2T X. riversiana 40 (18+22) 2ffl-lSW-5ST(8,9)+IT 1 inv 1 inv \/ X. vinilis p 40 (18+22) 2M+lShH-6ST(6, B, 9)+0T X. licnshnwl 40 (18+22) 2MUSMt6ST (6,8,9)+0T Fig. 5. Karyotype phylogeny of the family XantusUdae.

47 'fl. f lovlmaculqtum rlt pojopanensis t~ luxlloe -,L. micropholis (m,6+8,7) If-X.^glLls ^^(6,8,9). A, L. (in) X. vlguu ct. (6,8) \ A.X. «X. henshnwl (6,8,9) X. rlverslono (8,9) I Fig. 6. Karyotype phylogeny of-the family Xantusiidae superimposed on a scale of karyotypic advancement. The index of karyotypic adavantfement is indicated by the scale below the concentric rings. For each taxon,. its scientific name is followed (in parentheses) by symbols indicating the derived states occurring in its karyotype (i.e., those states that are different from that of the ancestral xantusiid); the numbers indicate the pair nos. of those macrochromosomes with derived centromere positions; asterisks (*) indicate the presence of satellites on macrochromosome pair no. 3; m indicates the occurrence of 20 rather than 22 microchromosomes. The hypothetical xantusiid (A.X.), ancestral Xantusia (A.X.) and ancestral Lepidophyma (A.L.) are included in the phylogeny (See Fig. 5; data from Tables 1 and 2).