Iguanid Research Articles

Scanning electron microscope studies of the auditory papillae of some iguanid lizards.

The papillae basilares of 16 species (10 general) of iguanid lizards were studied by scanning electron microscopy. Variations in the surface structures of the auditory papillae showed the following major differences: 1)papillae with localization of the unidirectional hair cells at the apical end of the papilla (anolis carolinensis); 2)papillae with absence or loss of a portion of the apical bidirectional hair-cell segment (Basiliscus basiliscus); 3)papillae with a central, short ciliated, unidirectional hair-cell segment, and 3-6 irregular rows of long-ciliated bidirectional hair cells located in the apical and basal regions (Iguana iguana, Crotaphytus collaris, C. wislizeni, Dipsosaurus dorsalis, Sauromalus obesus); 4)papillae in which the apical and basal bidirectional hair-cell segments are reduced to two rows of hair cells (Sceloporus occidentalis, S. clarki, S. orcutti, S. jarrovi, S. undulatus, S. magister, Callisaurus draconoides, Uta stansburiana). The above differences in auditory papilla structure agree closely with other anatomical differences that delineate iguanid assemblages. Thus the species in the four groups above fall respectively into the following iguanid groups: 1)anolines, 2)basiliscines, 3)iguanines, and 4)sceloporines.

Factors Affecting Activity in Sceloporus Virgatus

A population of Sceloporus virgatus, an iguanid lizard, was studied to determine the adult patterns of activity and inactivity. Activity was primarily a function of the sex and age of the individual, as well as reproductive condition. Activity was highest during the breeding season when males were active daily (97% of the days) and females were active 76% of the days. Males were also active longer and moved greater distances than females. Males lost mass during this high activity period. During the nonbreeding season, females were active more days than males. Activity levels were not substantially different for females during the breeding and nonbreeding season. Male activity decreased dramatically during the nonbreeding season and activity differed depending on the age of the lizard. Year—old males were nearly twice as active as older males (57% compared to 29% of the days). Activity was so low in these large, older males that territory maintenance was probably no longer functional. This low activity sug...

Lizard Reproduction: Habitat Specificity and Constraints on Relative Clutch Mass

The iguanid lizard Platynotus semitaeniatus is adapted morphologically and behaviorally to utilize rock crevices to escape predation. Attendant reproductive adaptations reveal an adaptive compromise in which costs incurred from reduced reproductive investment per episode are outweighed by advantages associated with use of a relatively predator-free refugium thereby increasing adult survivorship and thus lifetime reproductive success.

A New Subspecies of the Iguanid Lizard, Sceloporus grammicus, from Northeastern Mexico, with Comments on Its Evolutionary Implications and the Status of S. g. disparilis

Sceloporus grammicus tamaulipensis is described from the isolated Sierra de Tamaulipas mountain range in southern Tamaulipas, Mexico, where it is apparently restricted to oak and pine-oak habitats of high elevations. It is distinguished from other adjacent races of S. grammicus by its larger scales and, consequently, a much lower number of dorsal scales, and to a lesser extent, scales around mid-body. Males of S. g. tamaulipensis are separated from males of S. g. grammicus, some of which have low numbers of dorsals, by ventral color patterns. This new race is also distinct at two allozyme loci (esterase-1, IDH). Morphometric, color pattern, and chromosome data suggest that S. g. tamaulipensis is most closely related to S. grammicus populations inhabiting the Sierra San Carlos and lowland thorn scrub habitats of northern Tamauli- pas and southern Texas. Sceloporus grammicus disparilis is not clearly differentiated from S. g. microlepidotus and is placed in synonymy with it.

Regional specialization in retinal ganglion cell projection to optic tectum of Dipsosaurus dorsalis (Iguanidae).

Regional variation in the composition of the ganglion cell layer is a characteristic feature of vertebrate retinas. This suggests that corresponding patterns of regional variation might be expected in CNS structures which receive a direct, topographic projection from the retina. To investigate this possibility, I studied the retinotectal projection in an iguanid lizard (Dipsosaurus dorsalis), which shows a marked degree of regional variation in its retinal ganglion cell layer. Results of these experiments indicate that in D. dorsalis the optic tectum is differentiated horizontally into five regions which can be distinguished on the basis of cytoarchitecture and the patterning of retinal afferents, as visualized with silver degeneration and autoradiographic tracing techniques. These five areas are named according to their location: 1) Ventral Rim, 2) Lateral Wall, 3)Dorsolateral Area, 4) Dorsal Wall and 5) Medial Rim. Following enucleation, the Medial and Ventral Rim are characterized by fascicles of coarse degenerated fibers in layers 13, 12, and 9, by a relative absence of fine particulate debris in reduced silver material, and by the absence of silver grains in autoradiographs following intraocular injections of tritiated proline. They differ in the density of large calibre fibers and in the temporal course of degeneration. In the Lateral Wall the cellular layers are best differentiated, and nine retino-recipient layers can be distinguished below the stratum opticum. Degeneration is particularly heavy over the plexiform layers 9, 11, and 13. There is a superficial to deep gradient of degeneration density and of silver grains within layers 13 and 11. In the lower half of layer 11, argyrophilic debris and silver grains are aligned in vertical columns. The Dorsolateral Area is a circular region which covers the dorsolateral convexity of the tectum just caudal to mid tectal levels. It is characterized by a relatively low density of degenerated fibers in layers 13, 12, and especially in layer 9. Finally, the Dorsal Wall is similar to the Lateral Wall in the laminar distribution of degeneration and silver grains, except that there is an additional band of fine debris over layers 12 and 13 which is not visible in the Lateral Wall. Rostrally, the Dorsal Wall is greatly expanded (the Dorsal Expansion) and in this region a well developed plate of neurons lies immediately subjacent to the stratum opticum. This is the only tectal area which shows substantial degeneration at short survival times. These data suggest that in D. dorsalis there is horizontal variation in the morphology and patterning of retinal ganglion cell axons to the superficial tectal layers. Since Dipsosaurus retina exhibits a substantial degree of regional variation in the ganglion cell layer, and since the retina projects topographically onto the tectum, it is suggested that regional variation in the optic tectum may reflect regional variation in the ganglion cell layer of the retina.

The role of chemoreception in the iguanid lizard Sceloporus jarrovi

We examined the role of tongue extrusions for the detection of chemicals in the iguanid lizard Sceloporus jarrovi, prior to the breeding season. Most extrusions resulted in the tongue touching the substrate and are referred to as tongue-touches. A total of 2819 tongue-touches were observed for four age/sex classes of lizards. We could not demonstrate that the tongue is involved in the detection of a natural predator, the Arizona kingsnake ( Lampropeltis pyromelana), and it was clear that it was not used to find food. It did, however, seem to be involved in the exploration of temporally and spatially unfamiliar areas. The possibility that the tongue is involved in the detection of conspecifics is discussed for this study, as well as for complementary studies. Possible marking attempts in the form of chin wipes, pelvic rubs, and defaecations were examined. The latter two possibilities were not important at this time of year. Chin wiping may result in the depositing of chemical markers, although no external chin glands were found and the possibility is still uncertain.

Seasonal changes in oxygen consumption and body composition of Sceloporus occidentalis

1. 1. Oxygen consumption in the iguanid lizard Sceloporus occidentalis was recorded every hour at 25°C for at least 3 consecutive days by a coulometric technique, the principle of which is discussed. 2. 2. Metabolic data of 154 male and female lizards captured at 150 and 1500m in the Central Sierra Nevada of California are reported. Data on body composition were obtained from 489 lizards captured at 150m. 3. 3. All lizards displayed circadian changes in oxygen uptake whether placed in continuous darkness or light; the daily metabolic patterns were unimodal during spring and fall, but became bimodal in summer. 4. 4. Regardless of elevation, minimum oxygen consumption bears the same power function to body mass in both sexes, with mass exponent equal to 0.67 ± 0.03. 5. 5. Minimum oxygen consumption, expressed per body mass to the power 2 3 , displayed seasonal changes (32%) with a peak in May–June and a low level in fall. These changes appear to reflect a true metabolic phenomenon rather than only changes in body mass or composition. 6. 6. The allometric relations between body mass, fat-free dry mass, body water, fat and snout-vent length are reported. 7. 7. Body mass and body composition at constant snout-vent length display seasonal changes.

Four hormones in the pancreas of the lizard, Anolis carolinensis.

The electron microscopic localization of insulin, glucagon, somatostatin, and pancreatic polypeptide (PP) in the pancreas of the iguanid lizard, Anolis carolinensis was studied by the unlabeled antibody peroxidase-antiperoxidase immunocytochemical technique. Insulin, glucagon, and somatostatin were localized absolutely to those cells previously identified on the basis of the characteristics of their secretory granules as being beta cells, alpha cells, and D cells, respectively. The secretory granule cores of the PP-containing cells appeared to be ellipsoidal with a semi-major axis of 450 nm and a semi-minor axis of 365 nm. This previously unidentified cell type is named the F cell, in keeping with the localization of PP to the original F cell of the canine pancreas. Without immunocytochemical staining, the qualitative ultrastructural characteristics of the F cell secretory granules were inadequate to permit identification of the F cell, especially with regard to the D cell.

Membrane systems in skeletal muscle of the lizard Anolis carolinensis

The iliotibialis muscle of the iguanid lizard Anolis carolinensis is composed of fibers that display highly developed membrane systems. One of these systems is composed of the so-called “transverse” tubules, which may branch in both the horizontal and vertical planes and which usually are connected to the surface sarcolemma via intermediary passages composed of caveolar vesicles. The remaining membrane system comprises the various elements of the sarcoplasmic reticulum (SR). Three reasonably distinct yet confluent conformations of SR can be found: (1) highly developed “conventional” SR which surrounds each myofibril and is segmented into specialized regions according to the divisions of the sarcomeres, such as junctional SR at the A–I levels, “network” SR massed over the I/Z/I band complexes, and fenestrated collars at the M lines; (2) subsarcolemmal SR whose junctional SR cisternae form peripheral couplings with the inner surface of the external cell membrane; and (3) extensive masses of proliferated SR that form roughly cylindrical bodies oriented longitudinally within intermyofibrillar spaces. These last (“columnar SR”) are found at all depths of the fibers and may be collected into less discrete aggregates that lie just underneath the sarcolemma, including the soleplate regions of motor end plates. The degree of development of the Anolis skeletal muscle membrane systems may reflect the requirements for rapid movement of the fibers.

An Experimental Study of Interspecific Competition Between the Iguanid Lizards Sceloporus Merriami and Urosaurus Ornatus

Competition between the insectivorous iguanid lizards Sceloporus merriami and Urosaurus ornatus was studied in a density manipulation experiment conducted in the Grapevine Hills of Big Bend National Park, Texas, USA from 1974 through 1977. Resident lizards were individually marked and censused using standard recapture techniques on six experimental plots chosen for similarity in size, habitat, isolation from one another by habitat unsuitable for these lizards, and initial densities of these two species. All S. merriami were removed from two plots, all U. ornatus from two, and two plots functioned as controls. Recaptures of marked individuals provided data on individual growth, age—specific survivorship, size—specific fecundity, and population density. Animals collected near the study plots provided data on size—specific fecundity, individual foraging success, and total prehibernation lipid levels. Observations of marked individuals provided estimates of individual foraging success. Rainfall varied dramatically during the 4 yr of the study; in 1974 and 1976 precipitation was much greater than the 22—yr average, and in 1975 and 1977 precipitation was much less than average. Two methods of estimating arthropod abundance indicated that significantly fewer prey were available to these lizards in the dry years. Individual foraging success, growth rates, body masses, prehibernation lipid levels, and population densities were significantly lower in the control populations of both species in 1975 and 1977 than in 1974 or 1976, indicating that individuals of both species experienced stressful conditions during the dry years. The removal of S. merriami resulted in significant effects on experimental populations of U. ornatus only during 1975 and 1977. The density of U. ornatus on the experimental plots increased significantly after the removal of S. merriami, even though the control populations declined. Individual foraging success, growth rate, prehibernation body mass, and lipid levels were significantly greater in U. ornatus from experimental populations than in those from control populations in the dry years of the study. The two treatments did not differ significantly in the wet years. Experimental populations of S. merriami exhibited significantly higher adult and juvenile survival than did the control populations in 1975. This was the only significant treatment effect demonstrable in experimental populations of S. merriami. Experimental results and data on life history characteristics suggest that these species compete significantly during periods of drought—induced food scarcity but not at other times. The mechanism of this competition is probably exploitative, with the per capita effect of S. merriami on U. ornatus greater than vice versa. Temporal variation in the intensity of competitive interaction between these two species is attributable to variation in food resource abundance, and arthropod abundance in this system was shown to be a function of rainfall. Examination of 22 yr of continuous precipitation data suggests that competition between these species may be frequently absent or undetectable in this system. The results of this study demonstrate that the intensity of interspecific competition can be quite variable in systems such as this and invite caution to the uncritical acceptance of point estimates of the intensity of competitive interaction.

Field Observations on the Use of the Tongue-Jacobson's Organ System in Two Iguanid Lizards, Sceloporus jarrovi and Anolis trinitatis

Field Observations on the Use of the Tongue-Jacobson's Organ System in Two Iguanid Lizards, Sceloporus jarrovi and Anolis trinitatis

The Endemic Hispaniolan Lizard Genus Chamaelinorops

Variation, natural history, and distribution of Chamaelinorops barbouri on His- paniola are given; no subspecies are recognized, although variation suggests that there may be two populations that have differentiated. Schmidt (1919) named a new genus and species of iguanid lizard Chamaelinorops barbouri ostensibly from Navassa Island, between Hispaniola and Jamaica. The species was based upon two specimens in the collection of the American Museum of Natural History that had been collected by Rollo H. Beck in 1917. Apparently no further information or specimens of Chamaelinorops became available until Alexander Wetmore secured a third specimen in 1927 at Fond des Negres, Departement du Sud, Haiti. This specimen, in the National Museum of Natural History, Washington, served as the holotype of Chamaelinorops wetmorei Cochran (1928); the genus was thus known from two populations, one from Navassa Island, the other from the Hispaniolan south (sensu Williams, 1961) on the Tiburon Peninsula in Haiti. Thomas (1966) examined 10 additional specimens (exclusive of the holotype and paratype of C. barbouri); these few specimens were all that had accumulated in the period between 1927 and 1966. It seemed that Chamaelinorops is a rare or at least very uncommon lizard. Thomas (1966) also showed that there appeared to be no native population of these lizards on Navassa, an island which he had visited and which appeared to be ecologically unsuitable for Chamaelinorops. He did suggest, on the meager material then available, that barbouri and wetmorei were subspecifically related, with the former occurring in the Massif de la Hotte in the extreme west of the Tiburon Peninsula, the latter in the extreme eastern portion of that range, as well as in the Haitian Massif de la Selle and the Dominican Sierra de Baoruco. He presented evidence that in fact the Beck

New Endemic Iguanid Lizards from the Famatina Mountains of Western Argentina

The first herpetological information on the Sierra de Famatina massif (6250 m), La Rioja Province, Argentina, includes two new species of Phymaturus and Liolaemus living at altitudes from 3600 to 4200 m. Taxonomic and ecological relationships between these isolated tropidurine iguanids and nearby related species from the Cordilleran highlands are discussed. A montane species-group comprising Uolaemus ruibali, L. duellmani and L. famatinae sp. nov. is suggested by morphological affinities. * * *

Enterobacteriaceae isolated from iguanid lizards of west-central Texas.

The prevalence of members of the family Enterobacteriaceae in the intestines of seven species of iguanid lizards native to west-central Texas was determined. Of the 67 lizard specimens examined, 48.7% were infected with Salmonella and 9% were infected with Salmonella arizonae. Two lizard species (Sceloporus olivaceus and Crotaphytus collaris) were shown to have a 100% prevalence of Salmonella.

The Lizard Corytophanes cristatus: An Extreme "Sit-and-Wait" Predator

Observations on the diet and field behavior of the iguanid lizard Corytophanes cristatus were made in Costa Rica and Panama. Stomach-content analyses show that this lizard is a specialist, feeding on extremely large arthropods. The average prey item is sufficiently large to provide more than the daily caloric requirement of a Corytophanes. The normal foraging behavior of C. cristatus appears to consist of brief and infrequent bouts of prey capture (bipedal dashes on the forest floor were observed) alternating with long periods of immobility. By eating arthropods which are large relative to its body size, C. cristatus minimizes conspicuous feeding activities and the associated risk of attracting the attention of predators. Such behavior is adaptive in tropical rainforests where lizards are under heavy predation pressure. THE ECOLOGY OF THE THREE SPECIES of Corytophanes is poorly known because these Central American and Mexican iguanids are infrequently encountered by biologists. Not only are population densities probably very low in most places (Andrews 1971; C. W. Myers, pers. comm.), but highly cryptic coloration and behavior (Davis 1953) make them appear to be much rarer still. Information about their habits is available mostly in collection records in faunal surveys (Taylor 1956, Alvarez del Toro 1960, Duellman 1963, Stuart 1948), but also from observations of a few individuals in captivity (Davis 1953, Ream 1965). Observations are presented here on diet and field behavior of Corytophanes cristatus (fig. 1) at Rincon de Osa, Puntarenas Prov., Costa Rica (tropical wet forest of Holdridge 1967), and on Barro Colorado Island, Canal Zone, and nearby sites in the Republic of Panama (tropical moist forest of Holdridge and Budowski 1956).

A taxonomic reconsideration of some Plasmodium species from iguanid lizards.

Saurian Plasmodium populations previously identified as P. tropiduri from Panama are described as subspecies or distinct species. The nominate subspecies, P. tropiduri tropiduri parasitizes Tropidurus species from Brazil, Guyana and Venezuela. Two other subspecies occur in Panama, P. tropiduri panamense from Anolis biporcatus and P. tropiduri aquaticum from the semi-aquatic lizards Anolis lionotus and A. poecilopus. Parasites found in Anolis frenatus are described as a distinct species, P. marginatum, while those from Anolis limifrons represent a third, un-named species. A parasite of Plica plica in Guyana, previously called P. cnemidophori, is designated P. guyannense, while identification of Plica umbra parasites as P. tropiduri is corrected to P. vacuolatum and Fallisia simplex.

Melatonin affects circadian rhythmicity in lizards

Subcutaneous Silastic capsules which continuously released melatonin at low rates (10 μg/day) either (i) lengthened the period of the freerunning activity rhythm in two iguanid lizard species (Sceloporus occidentalis andS. olivaceus) exposed to either continuous illumination or continuous darkness or (ii) induced arrhythmicity inS. olivaceus exposed to continuous illumination. These results and previous observations that two melatonin synthesizing sites in lizards, the pineal organ and lateral eyes, are involved in circadian rhythmicity suggest that melatonin may be a chemical messenger between the pineal or eyes and other elements of the circadian system.

Physiology and bioacoustics in reptiles

Hearing in reptiles is of particular interest because of the diversity in the anatomy of the reptilian auditory system. This diversity is best illustrated in the lizard, where there is significant variation in cochlear anatomy across families. This review of the auditory physiology of reptiles will begin with a detailed discussion of the extensive physiological data available for the alligator lizard (Anguid family). These data include measurements of basilar membrane motion, intracellular hair cell responses, and single-unit activity of primary auditory-nerve fibers. Single-unit data from an Iguanid lizard will be compared to that for the alligator lizard and discussed in terms of the differences in cochlear anatomy of these two families. In addition, single-unit data for other lizards and other reptiles will be reviewed. The presentation will conclude with a comparison of auditory processing in the reptile and the mammal and will consider issues such as the tuning of individual fibers and the relationship of anatomical structure to physiological response.

Seasonal Changes in the Territorial Behavior of the Iguanid Lizard Sceloporus jarrovi

Territorial behavior of Sceloporus jarrovi was observed in Arizona during 3 years. Male aggression, activity and home range size increased and overlap between home ranges decreased as the fall breeding season approached. Most animals defended the entire home range. Males shifted their positions to maximize overlap with females in the fall. Females were less aggressive, occupied smaller areas and shifted positions less.

Food Availability as a Proximate Factor Influencing Individual Growth Rates in the Iguanid Lizard Sceloporus Merriami

Von Bertalanffy, logistic—by—length, and logistic—by—weight models of individual growth for 2 populations of Sceloporus merriami were estimated from 3 yr (1974—1976) of mark—recapture data using nonlinear regression. The logistic—by—weight model was found to provide the best fit to observed growth rates. Abundance of arthropod prey was estimated by 2 techniques and found to be serially correlated with seasonal precipitation. Prey abundance was correlated with annual precipitation. Individual foraging success was found to be correlated with estimated prey abundance. Parameters of logistic—by—weight growth models were compared for the 3 yr of the study and revealed that variation in food availability resulted in predictable variation in individual growth rates. Individual growth rates were positively correlated with active—season and annual precipitation and with estimates of food availability. The limitations of using stationary growth models to describe a potentially nonstationary process such as individual growth are discussed.