Parthenogenetic reproduction in lizards: Histological evidence

Hermaphroditism and sex reversal have not previously been ruled out adequately as possible explanations for the existence of unisexual species of reptiles. Therefore, we examined serial histological sections of the complete urogenital systems of nine F₂ specimens belonging to two ontogenetic series of Cnemidophorus exsanguis raised in captivity in isolation from males, as well as the urogenital system of the F₁ mother of one of these series. No evidence of spermatozoa or testicular tissue was found in any specimen. Comparative material reveals that the histology of the urogenital tract, including the mesonephric kidney in adults, is similar to that of females of bisexual species of Cnemidophorus. We conclude that C. exsanguis is a unisexual, parthenogenetic species whose normal reproduction does not involve sex reversal, self-fertilization, gynogenesis, hybridogenesis, or spermatozoa in any way whatsoever.     

The effects of progesterone on sexual behavior in male green anole lizards (Anolis carolinensis)

It is well known that androgen-dependent sexual behaviors in male mammals and birds are inhibited by exogenous progesterone (P). However, recent research on male whiptail lizards (Cnemidophorus inornatus) indicates that P can stimulate sexual and copulatory behavior. We report here both antiandrogenic and synandrogenic actions of P on sexual behavior in males of another reptile, the green anole lizard (Anolis carolinensis). Earlier reports on birds and mammals are reviewed and discussed in relation to a possible physiological role of P in influencing sexual behavior in male vertebrates.     

The reproductive cycle of the western whiptail lizard (Cnemidophorus tigris) in Southern Arizona

Reproduction in Cnemidophorus tigris at Tucson, Arizona follows a seasonal cycle in which gonadal size is minimal in September-October. Male reproductive organs gradually recrudesce during the winter months spent underground. After the lizards emerge from hibernation in March-April the testis, seminiferous epithelial height and tubule diameter gradually increase in size through April and May, reaching maximum size in June-July followed by rapid regression in August. Mating is first observed in the field in May. The ovaries undergo a period of heavy yolk deposition from early April to May, and remain functional until August. A thick circumtesticular subtunic layer of equivalent interstitial material (Leydig cells) is reported and described for the testis of Cnemidophorus.     

St Lucia Whiptail Lizard Cnemidophorus vanzoi (Sauria: Teiidae) microsatellite primers

Eight polymorphic microsatellite loci have been characterized for the endangered St Lucia Whiptail Lizard Cnemidophorus vanzoi. Endemic to two small islets, Maria Major and Maria Minor, off the coast of St Lucia, Lesser Antilles, the world population is estimated at < 1000 individuals. However, representatives of the systematically complex genus Cnemidophorus, containing sexual species and parthenogenetic allopolyploids, are distributed widely in North, Central and South America, and on several islands in the Caribbean Sea. These microsatellite markers are being used to monitor the genetic structure of a population of St Lucia Whiptails, recently founded through translocation, on the nearby Praslin Island.     

The reproductive morphology of Cnemidophorus neomexicanus X Cnemidophorus inornatus hybrid males

The morphology of the gonads and epididymides, and an analysis of selected scale characters of six hybrid males presumed to be the result of the natural mating of the all-female whiptail lizard species Cnemidophorus neomexicanus and the bisxual species C. inornatus are presented. The histological appearance of the gonads and epididymides reveals a seasonal cyclicity with respect to the production and storage of spermatogenic elements. On the basis of the limited sample, it is postulated that some abnormality may be present in gametogenesis of these hybrid males which could be related to their chromosomal number. The data on scale characters support the interpretation that these hybrids are intermediate with respect to the parental species.     

MITOCHONDRIAL-DNA ANALYSES AND THE ORIGIN AND RELATIVE AGE OF PARTHENOGENETIC LIZARDS (GENUS CNEMIDOPHORUS). III. C. VELOX AND C. EXSANGUIS

Mitochondrial DNAs (mtDNAs) of two unisexual, parthenogenetically reproducing species of whiptail lizards (Cnemidophorus velox and C. exsanguis) and their bisexual relatives were compared by restriction-enzyme analysis to assess levels of mtDNA variation and to establish the maternal ancestry of the unisexuals. No cleavage-site differences were found to be diagnostic between C. velox and C. exsanguis mtDNAs, suggesting an ancestry rooted in the same maternal lineage. The mtDNA of the unisexuals is relatively homogeneous, indicating that these lineages are of recent origin. Phylogenetic analysis revealed that the maternal ancestor of both C. velox and C. exsanguis was most probably C. burti stictogrammus, C. costatus barrancorum, or an unidentified taxon closely related to them. In addition, the mtDNA analyses demonstrate conclusively that the triploid species C. velox could not have been formed by the fertilization of an unreduced (diploid) C. inornatus egg, further strengthening the hypothesis that parthenogenesis in Cnemidophorus results from hybridization.     

Lizard assemblages in the Vizcaino Biosphere Reserve, Mexico

Lizard assemblages were surveyed in eight selected habitats in the Vizcaino Biosphere Reserve in Baja California Sur, Mexico. We compared the species composition and relative abundance among habitats, considering habitat characteristics, such as vegetation type, vegetation ground coverage, and soil types. Thirteen lizard species were recorded. The most abundant species in almost all habitats was Uta stansburiana, accounting for 59% of all observations. Cnemidophorus tigris was the second most abundant species, accounting for 12% of all observations. The richest habitat was the rocky lower elevations of the Sierra de San Francisco (nine species). However, the habitat with the highest diversity value was Scammon's dunes. Implications of our findings for lizard conservation in this biosphere reserve are discussed.     

Ecological organization of a Chihuahuan desert lizard community

Summary Niche relationships among 11 diurnal lizard species were studied for 3 years. The community appeared to be subdivided spatially into different subsets of only four to six species. Coexisting species of each subgroup were separated further by differential utilization of microhabitats. In late spring and early summer, when food shortage is likely, dietary overlaps between syntopic species were generally low but increased broadly after the rains, when food became plentiful. Because of the high similarity in prey-size utilization among large and medium species, effects of prey selection according to size were generally slight except for very different-sized species. Overlap in the three-dimensional resource space was high between Cnemidophorus scalaris and C. tigris, but close observation of the ecology of the two populations showed many small differences between them. We suggest that the very diversified ecological opportunism of C. scalaris allows it to coexist with C. tigris in a very heterogeneous ecosystem. Several hypotheses are discussed to explain the ecological determinism of resource partitioning within such a community.     

A histochemical study of the circumtesticular Leydig cells of a teiid lizard, Cnemidophorus tigris

Several oxidative enzymes in the testis of the teiid lizard Cnemidophorus tigris were studied histochemically. The cells of the circumtesticular sheath (Leydig cell tunic) are functionally equivalent to Leydig cells of the interstitium on the basis of similar histochemical reactions for the five enzyme systems studied. Both groups of cells were positive for 3β-hydroxysteroid dehydrogenase, 17β-hydroxysteroid dehydrogenase, NADH diaphorase, NADPH diaphorase, and glucose-6-phosphate dehydrogenase. These results support the hypothesis that the circumtesticular sheath has endocrine function as indicated by its vascularity and its ability to catalyze histochemical reactions involving steroid biosynthesis.     

Sexual selection versus alternative causes of sexual dimorphism in teiid lizards

Summary The presence and extent of sexual dimorphisms in body form (size and shape) of adult macroteiid lizards were investigated. Males were significantly larger than females in the temperate species, Cnemidophorus tigris, and in the tropical species, Ameiva ameiva and C. ocellifer. Young adult C. tigris males grew faster than young adult females within and between reproductive seasons. Adult males of all species had larger heads than adult females of the same body size; this difference increased with body size. Moreover, male C. tigris were heavier than females of the same snout-vent length. The causes and consequences of the sexual dimorphisms were also examined. The possible causes of body size are especially numerous, and distinguishing the relative influences of the various causal selection factors on body size is problematical. Nevertheless, observational field data were used to tentatively conclude that intrasexual selection was the cause of larger body size of C. tigris males relative to females because (1) larger males won in male aggressive interactions, (2) the winning males gained access to more females by repelling competitors and by female acceptance, (3) larger males consequently had higher reproductive success, and (4) other hypothetical causes of larger male size were unsupported.     

MITOCHONDRIAL-DNA ANALYSES AND THE ORIGIN AND RELATIVE AGE OF PARTHENOGENETIC LIZARDS (GENUS CNEMIDOPHORUS). II. C. NEOMEXICANUS AND THE C. TESSELATUS COMPLEX

Restriction-endonuclease analyses of mitochondrial DNAs from all six color-pattern classes (A–F) of the parthenogenetic lizard Cnemidophorus tesselatus yield estimates of nucleotide divergence that are extremely low (π = 0.06%). In digests of 75 C. tesselatus mtDNAs with 20 different restriction enzymes, only four cleavage-site differences were noted, three of which were found only in pattern class F. The near-identity of these mitochondrial DNAs with those from C. tigris marmoratus shows unequivocally that C. t. marmoratus was the species to which the maternal parent(s) of all C. tesselatus belonged. Mitochondrial-DNA analyses of another unisexual species, C. neomexicanus, led to the same conclusion. Mitochondrial DNAs from 96 individuals of these three species were extensively analyzed for cleavage-site differences; only 13 were found. The low interspecific sequence diversity found within C. neomexicanus and the C. tesselatus complex suggests a recent origin for both. Based on diversity data for mitochondrial DNA and allozymes, we estimate that a minimum of two hybridizations were required to produce all diploid C. tesselatus (C–F), followed by at least two more to generate the triploids (A and B). These data and those presented in the two accompanying papers indicate that events leading to parthenogenesis in Cnemidophorus are rare and strengthen the hypothesis that interspecific hybridization is a necessary, causal event in its establishment.     

A comparative ultrastructural study of spermatozoa of the teiid lizards Cnemidophorus gularis gularis,Cnemidophorus ocellifer,and Kentropyx altamazonica (Reptilia,Squamata, Teiidae)

The ultrastructure of the spermatozoa of Cnemidophorus gularis gularis, Cnemidophorus ocellifer, and Kentropyx altamazonica is described for the first time. Mature spermatozoa of Cnemidophorus spp. and K. altamazonica differ in the occurrence of a perforatorial base plate, the enlargement of axonemal fibers 3 and 8, and shape of mitochondria. The comparisons of the ultrastructure sperm of Cnemidophorus spp. and K. altamazonica with Ameiva ameiva [J. Morphol. (2002) in press] suggest that Ameiva and Cnemidophorus are more similar to each other than either is to Kentropyx. Statistical analyses reveal that sperm of all three species studied are significantly different in the following dimensions: head, acrosome, distal centriole length, and nuclear shoulders width. There was no variable statistically different between the Cnemidophorus spp. only. The length of the tail, midpiece, entire sperm, and nuclear rostrum are significantly different between K. altamazonica and Cnemidophorus spp. Our results indicate that sperm ultrastructure presents intra and intergeneric variability.     

Experimental infection of New World lizards with Old World lizard Leishmania species

A total of 197 North and Central American lizards representing 11 genera and 4 families was examined for presence of Leishmania by culture of heart blood. None of the lizards (obtained from supply houses, collectors, and live-trapped by the authors) was found to be infected.Subsequent to the determination that they were negative for leishmaniasis, lizards in the family Teiidae (Cnemidophorus sexlineatus, and Ameiva quadrilineata) and the family Iguanidae (Anolis carolinensis, Dipsosaurus dorsalis, and Basiliscus vittatus) were inoculated with Old World lizard leishmanias. Culture forms of Leishmania adleri, Leishmania agamae, and Leishmania tarentolae were inoculated intracardially into the lizards and sampling for the parasites was by direct observation of blood slides and by examination of cultures of heart blood.Leishmania adleri was recovered from Basiliscus vittatus (Central American) for up to 56 days and from Ameiva quadrilineata (also Central American) for up to 10 days. Dipsosaurus dorsalis (North American) retained this parasite for up to 24 hr. Cnemidophorus sexlineatus (North American) maintained Leishmania agamae for periods of up to 10 days as detected by the described techniques. Leishmania tarentolae did not become established in any of the lizards, and Anolis carolinensis maintained parasites for 12 hr or less.     

Speciation with gene flow in whiptail lizards from a Neotropical xeric biome

Two main hypotheses have been proposed to explain the diversification of the Caatinga biota. The riverine barrier hypothesis (RBH) claims that the São Francisco River (SFR) is a major biogeographic barrier to gene flow. The Pleistocene climatic fluctuation hypothesis (PCH) states that gene flow, geographic genetic structure and demographic signatures on endemic Caatinga taxa were influenced by Quaternary climate fluctuation cycles. Herein, we analyse genetic diversity and structure, phylogeographic history, and diversification of a widespread Caatinga lizard (Cnemidophorus ocellifer) based on large geographical sampling for multiple loci to test the predictions derived from the RBH and PCH. We inferred two well‐delimited lineages (Northeast and Southwest) that have diverged along the Cerrado–Caatinga border during the Mid‐Late Miocene (6–14 Ma) despite the presence of gene flow. We reject both major hypotheses proposed to explain diversification in the Caatinga. Surprisingly, our results revealed a striking complex diversification pattern where the Northeast lineage originated as a founder effect from a few individuals located along the edge of the Southwest lineage that eventually expanded throughout the Caatinga. The Southwest lineage is more diverse, older and associated with the Cerrado–Caatinga boundaries. Finally, we suggest that C. ocellifer from the Caatinga is composed of two distinct species. Our data support speciation in the presence of gene flow and highlight the role of environmental gradients in the diversification process.     

Banding patterns and chromosomal evolution in five species of neotropical Teiinae lizards (Squamata: Teiidae)

Karyotypes of five species of South American teiid lizards from subfamily Teiinae: Ameiva ameiva, Kentropyx calcarata, K. paulensis, K. vanzoi (2n = 50, all acrocentric), and Cnemidophorus ocellifer (2n = 50, all biarmed), are herein described and compared on the basis of conventional and silver staining, and CBG and RBG banding patterns. Meiotic data are also included. Karyotypes of K. paulensis, K. vanzoi, and C. ocellifer are reported here for the first time. Inter-generic variability in Ag-NORs location was detected with NORs occurring at the end of long arm of pair 1 in K. calcarata, K. paulensis, and K. vanzoi; pair 5 in C. ocellifer and pair 7 in A. ameiva. The location of NORs, along with the karyological differences between A. ameiva and the Central American species (A. auberi), corroboretes the molecular-based hypothesis that the genus Ameiva is paraphyletic. Inter-populational heteromorphism in Ag-NORs size was detected between populations of C. ocellifer. RBG and CBG banding data demonstrated that the biarmed condition of the C. ocellifer chromosomes is due to multiple pericentric inversion events instead of addition of constitutive heterochromatin. Differential-staining techniques used here revealed valuable information about Teiinae karyotypic diversity and made it possible to compare these species, contributing to both the better comprehension of their chromosomal evolution and issues on taxa systematics.     

THE EVOLUTIONARY HISTORY OF PARTHENOGENETIC CNEMIDOPHORUS LEMNISCATUS (SAURIA: TEIIDAE). II. MATERNAL ORIGIN AND AGE INFERRED FROM MITOCHONDRIAL DNA ANALYSES

Restriction endonuclease analyses were performed on mitochondrial DNAs (mtDNAs) representing unisexual parthenogenetic (cytotypes A, B, and C) and bisexual (cytotypes D and E) populations of Amazonian lizards presently regarded as Cnemidophorus lemniscatus. The results of mtDNA cleavage map comparisons among these C. lemniscatus indicated that (1) there was no cleavage site variation among the unisexuals, (2) mtDNAs from the bisexual cytotypes D and E differed in sequence from one another by about 13%, and (3) mtDNAs from cytotypes A–C differed from those of cytotype D by about 5% and from those of cytotype E by about 13%. Higher resolution restriction fragment size comparisons confirmed the high degree of similarity among the unisexual mtDNAs, but identified 12 cleavage site variants among the 13 cytotype D mtDNAs examined. Both cladistic and phenetic (UPGMA) analyses of the data indicate that the unisexual and cytotype D mtDNAs form a single clade, suggesting that a female of cytotype D was the maternal progenitor of the unisexuals. The similarity among the unisexual mtDNAs and the variability among those of cytotype D suggest that the three unisexual cytotypes arose recently from a common maternal lineage. The mtDNA variability observed among cytotype D individuals has a strong geographic component, suggesting that the unisexuals arose from one or a few geographically proximal populations. The mtDNA comparisons also support the conclusion, based on allozyme comparisons (Sites et al., 1990, this issue), that cytotypes D and E, although presently allocated to C. lemniscatus, are separate species.     

Thermal ecology of five Cnemidophorus species (Squamata: Teiidae) in east coast of Brazil

In this study we compared the body temperature of 16 populations belonging to five species of the genus Cnemidophorus from restinga habitats along the eastern coast of Brazil in order to evaluate the importance of how some environmental factors affect lizard body temperatures. Cloacal body temperatures (T_b) were taken immediately after capture with a quick-reading thermometer (Schultheis). Substrate temperatures (T_s) and air temperatures (T_a; approximately 1 cm above the substrate) were taken as close as possible to the point when each lizard was initially sighted. Most of the mean body temperatures in activity of the different populations and species of Cnemidophorus along the coast of Brazil ranged from 36.5 to 39.3 °C, except for Cnemidophorus lacertoides (T_b=35.2 °C) in the restinga of Joaquina, SC and for Cnemidophorus ocellifer (T_b=34.8 °C ) in the restinga of Praia do Porto, SE. Some studies show that the body temperature of lizards is more related to phylogenetic than ecological factors, suggesting that species of the same genus tend to have similar body temperatures even occurring in different types of environments. In general, regardless of the locality and latitude along the eastern coast of Brazil, the different species of lizards of the genus Cnemidophorus and their respective populations have similar body temperatures in activity and the apparent differences result from the influence of the local thermal environment of each restinga.     

THE EVOLUTIONARY HISTORY OF PARTHENOGENETIC CNEMIDOPHORUS LEMNISCATUS (SAURIA,TEIIDAE). I. EVIDENCE FOR A HYBRID ORIGIN

Chromosomes and allozymes were studied from chromosomally distinct unisexual (races B and C) and bisexual (races D and E) populations of the teiid lizard Cnemidophorus lemniscatus, and from selected outgroup taxa (C. murinus, C. nigricolor, Ameiva ameiva, and A. auberi). Karyotyping confirmed the racial identity of individuals and showed that the chromosomal composition of populations at specific localities has remained the same for 20 years. All individuals of both unisexual populations were heterozygous for a pericentric inversion that distinguishes D and E bisexuals. Also, the unisexuals were all heterozygous for 8 of 11 protein loci for which D and E were fixed or nearly fixed for different alleles. Most of these alleles represent derived states relative to the other Cnemidophorus and Ameiva analyzed, and the fixed heterozygote condition at these nine markers provides unequivocal support for the hypothesis that the unisexual C. lemniscatus arose by hybridization between ancestors genetically similar to extant D and E populations. At the remaining three loci for which D and E show fixed differences, the unisexuals were homozygous rather than heterozygous. This suggests that either (1) allozymes have been lost by mutations to null, silent, or convergent mobility states, (2) ancestral genotypes were similar to but not identical with the extant D and E races, and/or (3) limited recombination may occur between unisexual genomes. Allozyme-based genetic distances between D and E were large, suggesting that bisexual races D and E are genetically isolated; each race should be accorded full species status. This conclusion is supported by the absence of any clear biochemical evidence for their monophyly with respect to the other Cnemidophorus examined. Cladistic analyses of 17 phylogenetically informative loci revealed two equally parsimonious shortest trees, one supporting monophyly and the other paraphyly of the C. lemniscatus complex. Further testing of the monophyly of C. lemniscatus requires additional data. With the present study, the evidence that all parthenogenetic Cnemidophorus are of hybrid origin is complete.     

Phylogeography of the endemic St. Lucia whiptail lizard Cnemidophorus vanzoi: Conservation genetics at the species boundary

Vicariance and isolation leading to speciation of reptiles on islands is well exemplified in a number of taxa in the Caribbean. The St. Lucia whiptail (Cnemidophorus vanzoi), considered a single species, is found on two small islets (Maria Major and Maria Minor) off the main island of St. Lucia. From lizards collected from both localities, we gathered morphological measurements and analysed the genetic divergence between populations, using a molecular survey of ∼ ∼2800 mtDNA base pairs and 8 microsatellites. There are significant differences in body size and general form and fixed but small mtDNA differences between island populations. Microsatellites reveal low diversity within populations but very high differentiation between islands with non-overlapping allele size ranges at all except one microsatellite and two loci exhibiting single-base polymorphism, fixed between islands. Based on these results, we examine published criteria to determine whether the studied island forms could be considered true species. According to the phylogenetic species concept and Moritz’s evolutionary significant unit (ESU) criteria, the two lizard populations can be considered separate entities. Crandall et al.’s (2000, Trends Ecol. Evol., 15, 290–295) broader categorization of population distinctiveness, based on concepts of ecological and genetic exchangeability, produces conflicting results depending on the interpretation of the observed ecological data. Following Fraser and Bernatchez’s (2001, Mol. Ecol., 10, 2741–2752) framework for management decisions when ecological data are not sufficient we propose that the lizard populations on the Maria islands are on differing evolutionary trajectories and thus at the species boundary. The populations are of high priority to conservation, thus meriting separate management.