Search

Unisexual vertebrates typically form through hybridization events between sexual species in which reproductive mode transitions occur in the hybrid offspring. This evolutionary history is thought to have important consequences for the ecology of unisexual lineages and their interactions with congeners in natural communities. However, these consequences have proven challenging to study owing to uncertainty about patterns of population genetic diversity in unisexual lineages. Of particular interest is resolving the contribution of historical hybridization events versus post formational mutation to patterns of genetic diversity in nature. Here we use restriction site associated DNA genotyping to evaluate genetic diversity and demographic history in Aspidoscelis laredoensis, a diploid unisexual lizard species from the vicinity of the Rio Grande River in southern Texas and northern Mexico. The sexual progenitor species from which one or more lineages are derived also occur in the Rio Grande Valley region, although patterns of distribution across individual sites are quite variable. Results from population genetic and phylogenetic analyses resolved the major axes of genetic variation in this species and highlight how these match predictions based on historical patterns of hybridization. We also found discordance between results of demographic modelling using different statistical approaches with the genomic data. We discuss these insights within the context of the ecological and evolutionary mechanisms that generate and maintain lineage diversity in unisexual species. As one of the most dynamic, intriguing, and geographically well investigated groups of whiptail lizards, these species hold substantial promise for future studies on the constraints of diversification in unisexual vertebrates.

(225)Biodiversity in southwestern North America has a complex biogeographic history involving tectonism interspersed with climatic fluctuations. This yields a contemporary pattern replete with historic idiosyncrasies often difficult to interpret when viewed from through the lens of modern ecology. TheAspidoscelis tigris(Tiger Whiptail) complex (Squamata: Teiidae) is one such group in which potential taxonomic boundaries have been confounded by a series of complex biogeographic processes that have defined the evolution of the clade. To clarify this situation, we first generated multiple taxonomic hypotheses, which were subsequently tested using mitochondrial DNA sequences (ATPase 8 and 6) evaluated across 239 individuals representing five continental members of this complex. To do so, we evaluated the manner by which our models parsed phylogenetic and biogeographic patterns. We found considerable variation among species ‘hypotheses’, which we suggest in part reflects inflated levels of inter-population genetic divergence caused by historical demographic expansion and contraction cycles. Inter-specific boundaries withA. marmoratusjuxtaposed topographically with the Cochise Filter Barrier that separates Sonoran and Chihuahuan deserts (interpreted herein as case of ‘soft’ allopatry). Patterns of genetic divergence were consistent across the Cochise Filter Barrier, regardless of sample proximity. Surprisingly, this also held true for intraspecific comparisons that spanned the Colorado River. These in turn suggest geomorphic processes as a driver of speciation in thetigriscomplex, with intraspecific units governed locally by demographic processes.HIGHLIGHTSPhylogeographies of vertebrates within the southwestern deserts of North America have been shaped by climatic fluctuations imbedded within broad geomorphic processes.The resulting synergism drives evolutionary processes, such as an expansion of within-species genetic divergence over time. Taxonomic inflation often results (i.e., an increase in recognized taxa due to arbitrary delineations), such as when morphological divergences fail to juxtapose with biogeographic hypotheses.However, isolated groups can be discriminated within-species by mapping genetic variability onto geographic distances. This approach can often diagnose ‘hard’ barriers to dispersal, or alternatively, strong selection acting against hybridization. On the other hand, elevated genetic divergences among groups less-isolated would underscore isolation-by-distance (i.e., an increase in genetic differentiation concomitant with geographic distance).The biogeographic patterns we identified in Tiger Whiptail are largely synonymous with those found in other regional species, particularly given the geomorphic separation of Mohave and Sonoran deserts by the Colorado River, and Sonoran/ Chihuahuan deserts by the Cochise Filter Barrier.Our results for the Tiger Whiptail complex broaden and extend the context within which polytypic species are conserved and managed, particularly those that reflect an incongruence among molecular and morphological standards.

Aspidoscelis velox is a triploid parthenogenetic species with clonal inheritance. We studied karyotypes of population samples representing diverse localities from much of its range. All specimens were triploids, but six different karyotypes were found with small differences among them, apparently resulting from chromosomal mutations that occurred after the origin of the species. As in other parthenogens, karyotypes and allozymes reveal variant clones in A. velox, but we do not recommend naming any of these genetic lineages as separate species. Specimens from the vicinity of Kanab, Kane County, Utah, have been treated by other herpetologists as a separate but morphologically similar species, Aspidoscelis innotatus, based on the assumption that they represented a diploid species. That assumption, made without any genetic evidence of ploidy, was recently based on evidence of histoincompatibility among certain population samples, but that could have been caused by factors other than ploidy (e.g., mutations at histocompatibility loci). We have examined specimens from Kane County, Utah, and all individuals were triploids similar to other population samples of A. velox from Arizona and New Mexico.

Abundância, variacao no padrao de coloracao, ciclo de vida e reproducao no lagarto partenogenetico triploide Aspidoscelis uniparens (Squamata: Teiidae) in Chihuahua, Mexico. Nos observamos o lagarto triploide partenogenetico Aspidoscelis uniparens em sintopia, bem como em alopatria, com muitos congeneres, dentro de uma area em partes do Arizona, Novo Mexico e Texas (EUA) e Chihuahua e Sonora (Mexico). Em julho de 2000, descobrimos grupos de A. uniparens com padroes distinto de coloracao dorsal, em alopatria com especies congeneres, em um agrupamento de tres localidades do noroeste de Chihuahua. Esses grupos foram distinguidos com base em padroes de coloracao dorsal marcadamente diferentes. Desse modo, nos designamos especimes de duas localidades mapeadas no municipio de Casas Grandes e de um local mapeado nas proximidades no municipio de Nuevo Casas Grandes como lagartos com listras vividas (VSL). Os especimes de outras localidades mapeadas foram chamados de lagartos com listras normais (NSL). Observamos que as tres localidades VSL ao longo da base dos sopes da encosta leste de Sierra Madre Ocidental foram ecologicamente diferentes das localidades NSL tais como El Sueco e Pradera de Janos, no centro e no noroeste de Chihuahua, respectivamente. Todos os especimes VSL exibiram listras primarias mais largas e mais nitidas, enquanto as listras se mostraram de largura normal e coloracao de pouco contraste nas amostras NSL-1 e NSL-2. Nos usamos as amostras NSL-1, NSL-2 e VSL para comparacoes estatisticas de medias ± 1 SE para os seguintes caracteres: comprimento rostro-cloacal (os tres grupos tiveram medidas similares de SVL maximo e diferencas medias atribuiveis a estrutura de classes etarias das amostras); numero de escamas granulares entre as listras paravertebrais no meio do corpo (revelando diferencas signifcativas entre algumas amostras); porcentagem de escamas granulares em torno do meio do corpo situadas entre as faixas paravertebrais no meio do corpo (revelando diferencas signifcativas entre todas as amostras); porcentagem de campo paravertebral com uma listra vertebral (revelando diferencas signifcativas entre algumas amostras); e tamanho da desova (revelando diferencas signifcativas entre algumas amostras). Nos concluimos que os caracteres qualitativos diagnosticos da amostra VSL de A. uniparens nao foram acompanhados por caracteres quantitativos exclusivos.

Subspecies have most often been described qualitatively with small sample sizes as excerpted from geographic continua. They present a long-standing conflict with evolutionary and statistical principles as well as conservation planning that often relies upon a phylogenetic perspective. Herpetological subspecies have been recognized in the literature as exceeding numerical expectations and subsequent reevaluations during the last decade have decreased their numbers ,50%, the exception being whiptail lizards (Aspidoscelis, family Teiidae). Here we used 842 base pairs of mitochondrial (mt) DNA to examine potential taxonomic and conservation boundaries among two putative species and four subspecies of the abundantly polytypic Aspidoscelis inornata (Little Striped Whiptail Complex, LSWC) of southwestern North America. Body coloration, but not mtDNA, distinguished two putative species inhabiting alkali deposits, whereas neither dataset could diagnose three paraphyletic subspecies. A trend to elevate putative subspecies following a more contemporary evaluation is premature for the LSWC: we suggest that two species (arizonae, pai) and three subspecies (gypsi, junipera, llanuras) lack molecular and morphological differentiation and thus should be rescinded in taxonomic rank. These uncertainties concerning the LSWC with regard to its distributions and relationships impinge upon conservation proposals that, for example, seek to list A. arizonae as ‘threatened’ under the Endangered Species Act.

Parthenogenetic reproduction in several all-female species of whiptail lizards (genus Aspidoscelis) does not preclude the occasional production of extreme variants. An adult lizard with a unique combination of dorsal color pattern, scutellation, and meristic characters captured 20 August 2013 approximately 200 m east of the Rio Grande in Bosque Farms, Valencia County, New Mexico, was inferred to be an extreme variant of triploid, hybrid-derived Aspidoscelis exsanguis which was also observed near the point of capture. There was no basis for identifying the specimen as a tetraploid hybrid because morphology did not reflect that origin and no gonochoristic species (e.g., Aspidoscelis marmorata or Aspidoscelis inornata) was known to occur at the site. Morphological analyses also ruled out the possibility that it could be an extreme variant of diploid parthenogenetic Aspidoscelis neomexicana, which is syntopic with A. exsanguis in Bosque Farms.

Lizards of the gonochoristic Aspidoscelis inornata (Little Striped Whiptail) complex are ubiquitous components of vertebrate faunas in diverse habitats in the southwestern United States and northern Mexico. One of these, Aspidoscelis arizonae ( = A. inornata arizonae, Arizona Striped Whiptail), is extant at only a few grassland areas in southeastern Arizona, but nonetheless played an important evolutionary role in the hybrid origins of seven obligatory parthenogenetic species. Although recognized as a distinct species by many, A. arizonae lacks a valid species description and only anecdotal data argue for its recognition. We were unable to separate it from geographically proximate A. inornata in southwestern New Mexico, using diagnostic morphological features (i.e., number of stripes, dark field coloration, sky blue ventral suffusion) previously used to delineate aspidoscelids. Furthermore, we evaluated additional diagnostic characters (i.e., body size plus ten meristic characters) in samples of A. arizon...

Is it correct, as is often assumed, that the clonal form of inheritance in parthenogenetic lizards results in less variability than occurs with genetic recombination in their sexually reproducing (gonochoristic) relatives? We tested this hypothesis by comparing morphological variability in samples of parthenogenetic Aspidoscelis tesselata and several gonochoristic species of whiptail lizards. To control for environmental factors that might differentially affect embryonic development of morphological characters, we compared samples obtained from the same or geographically adjacent localities. In addition, we compared apparently “uniclonal” and multiclonal samples from each of two color-pattern classes (C and E) of A. tesselata. For univariate meristic characters, parthenogenetic A. tesselata matched the variability of a sympatric gonochoristic species in 11 of 20 comparisons, had lower variability in six comparisons, and was more variable in three. For multivariate characters derived from principa...

Parthenogenetic Aspidoscelis tesselata (pattern class C) reaches the northern limit of its distribution in Ninemile Valley, Otero County, Colorado. Its coexistence with gonochoristic A. sexlineata permitted comparison of diets between species of different sizes, reproductive modes, and evolutionary histories. Based on numbers of prey in stomachs, A. sexlineata had a broader diet than A. tesselata C in June and July; however, breadth of diets calculated from volumes of prey were nearly the same for the two species. Despite the larger size of A. tesselata C, dietary resources were not partitioned by size and foods present exclusively in one species were rare in its diet. Overlap of diets in June could be explained by chance, but this was not true for July. Remarkably high dietary overlap in July resulted from both species taking advantage of an annual surge in abundance of grasshoppers. There was no evidence that either species was affected adversely by presence of the other.

We report on Aspidoscelis sexlineata (six-lined racerunner) from the four known sites of occurrence in Mexico, one being a southward range extension of 74.3 km for the species. These sites are situated in the extreme eastern part of the municipality of Matamoros, Tamaulipas, and are nearest to records for the species in the United States for Brazos Island-South Padre Island, Cameron County, Texas. In both regions, A. sexlineata occurs a short distance from the seashore in habitats formed and influenced by perturbations of hurricanes and the maritime climate of the Gulf of Mexico (e.g., sand dunes devoid of congeners with openings in halophytic vegetation). Samples of A. sexlineata from Tamaulipas are statistically similar to those from South Padre Island in two meristic characters, one ratio, and snout–vent length, but significantly different in one meristic character and one ratio involving color pattern. Because similarities among specimens from the plains of southern Texas, South Padre Island,...

Studies of distributional ecology of whiptail lizards near the Rio Grande in Presidio County, Texas, have resulted in discovery of Aspidoscelis neomexicana at three of >20 sites investigated. Records of A. neomexicana in Presidio County are >225 km southeast of sites inhabited by the species in El Paso, El Paso County. Observations made during 1988–2008 indicate that A. neomexicana in Presidio County inhabits only a few areas of floodplain where there is intermingling of several microhabitats characterized by loamy, gravelly alluvium with various combinations of trees, shrubs, Russian thistle (Salsola kali), Spanish dagger (Yucca torreyi), cacti, grasses, and forbs. Each species of whiptail lizard (i.e., A. exsanguis, A. tesselata, and A. tigris) that is syntopic with A. neomexicana is widely distributed in Presidio County and elsewhere in the United States and Mexico. Despite range maps to the contrary, A. neomexicana has not been recorded in Mexico; forays in 1993 to San Antonio, Chihuahua, acr...

The genus Unionicola Haldeman, 1842 contains 56 subgenera (Smit, 2008). The subgenus Polyatacides Lundblad, 1941a was originally created as a genus. Cook (1974) reduced the taxon to subgenus. Vidrine (1986a) eliminated the subgenus, and placed its only species, U. prominens Koenike, 1914, into the subgenus Atacella Lundblad, 1937. Vidrine (1996) resurrected the subgenus Polyatacides in the genus Unionicola. This paper supports that change and re-evaluates Polyatacides, Atacella, and Berezatax Vidrine 1986b: the three subgenera have dorsoventrally flattened pedipalps and form a distinctive Artenkreis of gill mites in the Americas.

The whiptail lizard Aspidoscelis dixoni (Teiidae) comprises three distinctive color pattern classes (i.e., variants); A and B are restricted to Presidio County, Texas, and C is isolated over 500 km to the west-northwest in Hidalgo County, New Mexico. Pattern class E of A. tesselata is widely distributed in Chihuahua, Texas, and New Mexico. Genetic data have verified that these parthenogenetic species are hybrid-derivatives of A. tigris marmorata ♀ X A. gularis septemvittata ♂; however, the number of hybridization events involved in their origin has remained problematic. We used 19 lizards in laboratory skin-grafting experiments to test the histoincompatibility responses among A. dixoni A, B, C, and A. tesselata E. The results of these graft exchanges indicated that individuals of all four pattern classes were mutually histocompatible to skin grafts, a level of genetic homogeneity indicative of the origin of A. dixoni and A. tesselata from the same hybrid lizard. Thus, the color pattern variants A...

We compared several life history characteristics between 2 syntopic color pattern classes (Conchas C-E and Conchas D) of parthenogenetic Aspidoscelis tesselata from Conchas Lake, New Mexico. These pattern classes lacked significant differences in mean clutch size, mean size of gravid females, SVL frequency distributions of gravid females, and SVL frequency distributions of complete samples. We then compared the Conchas Lake assemblage to the other 2 pattern class assemblages (Higbee, Colorado, and Sumner Lake, New Mexico) whose life history characteristics had been previously reported. Comparisons of life history attributes within and between the 3 assemblages augment morphological and genetic evidence that each population of pattern class D was derived by mutation from individuals of pattern classes C or C-E in different geographic areas.

Sumner Lake State Park, De Baca County, New Mexico, is the only known locality where three pattern classes of diploid, parthenogenetic Aspidoscelis tesselata (Sumner C, Sumner D, and Sumner E) coexist in syntopy. Reciprocal skin transplants confirmed that the pronounced phenotypic differences between Sumner C and Sumner E represent postformational genetic changes rather than separate hybridization origins. Sumner D is meristically indistinguishable from Sumner C and is considered to be a recent mutational derivative of the latter. In contrast, Sumner E is distinctly different from Sumner C in multivariate meristic characters and several important life-history characteristics. Discordant patterns of phenotypic variation characterize many geographically disjunct groups of A. tesselata classified as pattern class E, thus defying a cohesive diagnosis. Therefore, based on the evolutionary species concept (ESC), we consider Sumner C and Sumner E to be divergent clonal groups in the same species. We contrast this example with a parthenogenetic complex on the Yucatan Peninsula in which formal recognition of Aspidoscelis maslini and Aspidoscelis cozumela can be accommodated under the ESC.

At Conchas Lake State Park, San Miguel County, New Mexico, four allozymic variants of parthenogenetic Cnemidophorus tesselatus pattern class C and three allozymic variants of C. tesselatus D are syntopic with one gonochoristic and two parthenogenetic congeners. Our study of 14 individuals revealed that C. tesselatus C and D from this site are histoincompatible with both their maternal, Cnemidophorus tigris marmoratus, and paternal, Cnemidophorus gularis septemvittatus, progenitors. Evidence of skin histocompatibility between these combinations of C. tesselatus pattern class C and D lizards supports the hypothesis of a single hybrid origin for representatives of this species at the study site.

Parthenogenetic reproduction has not precluded the genesis of extensive genetic variation in the whiptail lizard, Cnemidophorus tesselatus. In Conchas Lake State Park, San Miguel County, New Mexico, the population of C. tesselatus includes pattern class C, with 4 allozyme variants, and pattern class D, with 3 allozyme variants. In 1988, we obtained a lizard in the park, described herein, with a unique color pattern and unusual meristic characters, which indicate that occasional females of C. tesselatus continue to be capable of producing neonates phenotypically different from the mother.

We searched for areas of syntopy between hybrid-derived clonal complexes A and B of Cnemidophorus laredoensis and both of their gonochoristic progenitors, C. sexlineatus and C. gularis, in Texas and Mexico from 1983 through 2000. We discovered that all sites inhabited syntopically or separately by these two clonal complexes of lizards are contained within the vast binational range of C. gularis, a widely tolerant species that is either present, or exists in neighboring plant communities, at all sites inhabited by these parthenogenetic forms. Conversely, the only sites of syntopy between C. laredoensis A and B and C. sexlineatus discovered during our study were clustered in a small area of northern Webb County, Texas. The basis for extensive syntopy between C. laredoensis A and B and maternal progenitor C. gularis and limited syntopy between these parthenogenetic forms and paternal progenitor C. sexlineatus includes components of both species-specific ecological adaptations and zoogeographical his...

The Cnemidophorus laredoensis subgroup of parthenogenetic whiptail lizards comprises clonal complexes A and B, with each form having a mostly allopatric distribution area that includes only a few sites of syntopy with the other form and a distinctive ensemble of morphological characters. The evolution of these clonal complexes is most readily explained by the hypothesis of a hybrid C. gularis × C. sexlineatus derivation for form A, originally described from Laredo, Webb County, Texas, and a second hybridization involving these species to account for form B. Reciprocal skin-grafting, previously used in studies of genetic structure in the parthenogenetic species C. tesselatus, C. neomexicanus, C. uniparens, and C. velox, provides a methodology for differentiating between the descendants of different parthenogenetically capable interspecific hybrids. We used individuals of C. laredoensis A from six sites in Texas and individuals of form B from three of these sites in reciprocal skin-grafting experim...

Two hundred and one whiptail lizards, Cnemidophorus spp., from Texas and Colorado (USA), were examined for Mesocestoides sp. tetrathyridia. Eleven (5%) were infected, including three of 58 (5%) C. dixoni, six of 70 (9%) C. gularis septemvittatus, one of 35 (3%) C. marmoratus, and one of 34 (3%) C. tesselatus; four C. inornatus heptagrammus were not infected. In addition, 41 non-cnemidophorine lizards from the same study area were not infected. Free tetrathyridia were found in the body cavity of lizards and encapsulated tetrathyridia were observed in the heart, liver, stomach, mesenteries, ovaries, intestines, and lungs. None of the Mesocestoides sp. exhibited any evidence of asexual proliferation such as multiple scoleces or buds. This note, the fifth in a series of reports on helminths of Cnemidophorus spp., represents the first time Mesocestoides sp. has been reported from these four taxa, and Colorado is a new geographic locality record for this parasite.

Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas 72701, USA (JMW) Division of Sciences, Louisiana State University at Eunice, Eunice, Louisiana 70535, USA (JEC) Department of Biology, Regis University, Denver, Colorado 80221, USA (HLT) Area de Recursos Naturales-Instituto Tecnologico Agropecuario No. 6 (SEP-DGETA-SEIT), km. 5.5 Carretera Huejutla-Chalahuiyapa, 4300 Huejutla de Reyes, Mexico (FMQ)

KLAWINSKI, P. D., R. K. VAUGHAN, D. SAENZ, AND W. B. GOODWIN 1994. Comparison of dietary overlap between allopatric and sympatric geckos. J Herpetol. 28:225-230. PIANKA, E. R. 1986. Ecology and Natural History of Desert Lizards. Princeton Univ Press, Princeton, New Jersey. SAENZ, D. 1996. Dietary overview of Hemidactylus turcicus with possible implications of food partitioning. J. Herpetol. 30:461-466. SAS INSTITUTE, 1988. SAS User's Guide: Statistics. SAS Institute, Cary, North Carolina. SELCER, K. W. 1986. Life history of a successful colonizer: the Mediterranean gecko, Hemidactylus turcicus, in southern Texas. Copeia 1986:956-962. T. C. I., 1993. Guida d'Italia, Roma. VIII edition, Touring Club Italiano, Milano. VAUGHAN, K. R. 1991. Competitive interference for habitat space among three species of Texas geckos. Unpubl. Ph.D. Thesis, Texas A&M Univ., College Station, Texas. , J. R. DIXON, AND J. L. COOKE 1996. Behavoural interference for perch sites in two species of introduced house geckos. J. Herpetol. 30:46-51.

Cnemidophorus tesselatus is an allodiploid, parthenogenetic lizard comprised of a number of distinctive tokogenetic arrays (Frost and Hillis, 1990) presently identified by four color pattern class descriptors: C, Colorado D, New Mexico D, and E (Taylor et al., 1996; Walker et al., 1997). The macrogeographic relationships of these pattern classes were outlined in Zweifel's (1965) pioneering study of geographic variation in Cnemidophorus tesselatus. Pattern class C was known to exist isolated from the other pattern classes in parts of southeastern Colorado, northwestern Oklahoma, and northwestern Texas. Sympatry between pattern classes C and D was known to occur only in the vicinities of the historic townsite of Higbee, Otero County, Colorado, and Conchas Lake, San Miguel County, New Mexico. Pattern class E occurred to the south, with specimens from Fort Sumner, De Baca County, New Mexico, approximately 105 km south of the Conchas Lake locality, documenting the closest proximity of pattern class E to pattern classes C and D.

At times over 30 years, various authors have expressed conflicting opinions on the composition of the parthenogenetic Cnemidophorus tesselatus complex at Higbee, Otero County, Colorado, the only known site of sympatry between diploid and triploid members of this complex. Recently, some workers have stated that two rather than three distinctive parthenogens occur at Higbee, one being an undescribed triploid species (tentatively designated pattern class C), which resulted from hybridization between C. tesselatus D(2n) and gonochoristic C. sexlineatus. Alternatively, our study identified two diploid pattern classes [C(2n) and D(2n)] and one triploid pattern class [B(3n)] among specimens of C. tesselatus from Higbee (including those with electrophoretically determined ploidy levels). We used two canonical variate analyses (CVA) to test hypotheses concerning the identity and origin of the triploid form. CVA1 suggested that specimens of the Higbee triploid form represented C. tesselatus B(3n), not an undescribed species. CVA2 suggested that C. tesselatus B(3n) was derived from a C. tesselatus C(2n) x C. sexlineatus hybrid, not a hybrid involving C. tesselatus D(2n).

Canonical variate analysis (CVA) of color pattern and scutellation characters in lizards collected in Ninemile Valley of the Purgatoire River at Higbee, Otero Co., Colorado graphically depicted two forms of parthenogenetic Cnemidophorus tesselatus (diploid color pattern class C and triploid color pattern class B), gonochoristic C. sexlineatus, and hybrid C. tesselatus x C. sexlineatus as four morphologically distinctive groups. A newly obtained male specimen with a C. tesselatus-like color pattern entered as an unknown was classified to the hybrid group in the CVA. It represented the fourth tetraploid hybrid C. tesselatus B(3n) x C. sexlineatus collected in the valley. A female specimen was also classified to the hybrid group by the CVA. A triploid karyotype (3n = 69) and color pattern identified this female as a putative C. tesselatus C(2n) x C. sexlineatus hybrid. Whereas male hybrids are presumably sterile and biological novelties at most, the possibility remains that a female hybrid could be the founder of a new parthenogenetic lineage. Zweifel (1965) informally described six color pattern classes of parthenogenetic lizards (A, B, C, D, E, F) in the Cnemidophorus tesselatus complex (family Teiidae) of which four (A-D) were reported from Colorado. Wright and Lowe (1967a) found that pattern classes A and B were triploid hybrid derivatives and pattern classes CF were diploid hybrid derivatives. Analyses of morphology (Walker et al., 1990) and karyology (Cordes, 1991) identified three of Zweifel's pattern classes of C. tesselatus in sympatry in Ninemile Valley of the Purgatoire River at Higbee, Otero Co., Colorado rather than two as indicated by Zweifel (1965), Densmore et al. (1989), and Wright (1993). These included diploid C. tesselatus C and D and triploid B, not triploid pattern class C as indicated by Parker and Selander (1976), Densmore et al. (1989), Wright (1993), and Leuck (1993). We found that the Ninemile Valley triploid population was morphologically indistinguishable from the pattern class B population described by Zweifel (1965) from Pueblo Co., Colorado. In samples collected in the valley since 1960 by various workers, diploid C. tesselatus outnumbered triploid C. tesselatus by a combined ratio of over 7:1. Moderate numbers of the gonochoristic species C. sexlineatus, the paternal parent of triploid C. tesselatus B (Wright and Lowe, 1967a; Parker and Selander, 1976), were also found in many parts of the area sampled. Four hybrid male C. tesselatus x C. sexlineatus were included in these collections. Three of these were described, and their probable parental forms identified as triploid C. tesselatus B x C. sexlineatus, by Walker et al. (1990). In the present study we describe the most recently collected hybrid male Cnemidophorus, infer its putative parentage on the basis of critical morphological characters, and evaluate the possibility of a hybrid origin for a female specimen displaying an ambiguous combination of classification characters. MATERIALS AND METHODS-Characters of scutellation that were quantitatively analyzed included: number of granules around midbody (GAB), number of granules from occiput to rump (OR), sum of left and right femoral pores (FP), number of subdigital lamellae on the longest toe of the left pes (SDL), sum of left and right circumorbital scales (COS), sum of This content downloaded from 207.46.13.57 on Mon, 08 Aug 2016 05:24:23 UTC All use subject to http://about.jstor.org/terms 236 The Southwestern Naturalist vol. 39, no. 3

nithol. Union, Washington, D.C. AVERY, M. L., AND C. VAN RIPER III. 1986. Bird community survey at Pinnacles National Monument. U.S. Natl. Park Serv., Coop. Natl. Park Resourc. Stud. Unit Tech. Rep. 24, Davis, California, 83 pp. BALTOSSER, W. H. 1989. Costa's hummingbird: its distribution and status. West. Birds, 20:41-62. BOLTEN, A. B., P. FEINSINGER, H. G. BAKER, AND I. BAKER. 1979. On the calculation of sugar concentration in flower nectar. Oecologia, 41:301-304. CARPENTER, F. L. 1983. Pollination energetics in avian communities: simple concepts and complex realities. Pp. 215-234, in Handbook of experimental pollination ecology (C. E. Jones and R. J. Riddle, eds.). Van Nostrand Reinhold Co., New York. HIXON, M. A., AND F. L. CARPENTER. 1988. Distinguishing energy maximizers from time minimizers: a comparative study of two hummingbird species. Amer. Zool., 28:913-925. JOHNSGARD, P. A. 1983. The hummingbirds of North America. Smithsonian Institution Press, Washington, D.C. LEVALLEY, R., AND K. F. CAMPBELL. 1984. The spring migration: March 1-May 31, 1984, middle Pacific Coast region. Amer. Birds, 38:952-957. SPIRA, T. P. 1980. Floral parameters, breeding system and pollinator type in Trichostema (Labiatae). Amer. J. Bot., 67:278-284. STILES, F. G. 1971. On the field identification of California hummingbirds. Calif. Birds, 2:41-54. 1972. Food supply and the annual cycle of the Anna hummingbird. Univ. Calif. Publ. Zool., 97:1-109.

Wright and Lowe (1968) and Cuellar (1977) suggested that parthenogenetic Cnemidophorus can survive only in isolation from their bisexual congeners because the latter would otherwise eliminate the parthenoforms through competition and/or destabilizing hybridization. Data from studies of the parthenogenetic clone LAR-A of the Cnemidophorus laredoensis subgroup suggest this hypothesis is not correct. The bisexual species C. gularis occurs at 24 of the 39 sites at which LAR-A has been found, and neither form is consistently more abundant than the other at syntopic sites. The literature documents many cases where parthenogenetic whiptails coexist with their bisexual congeners, suggesting parthenoforms do not require isolation as previously believed. One of two things must be happening to allow parthenoforms to coexist with bisexuals: (1) competition and destabilizing hybridization do not occur; or (2) these processes do occur but some other factor counteracts their effect. At present, too little data exist to evaluate which of these alternatives is correct. However, analysis of lizard diets at three sites of syntopy and data reported in studies of other parthenoforms are used to advance testable hypotheses in the hope of stimulating future research. The lizard genus Cnemidophorus (Teiidae) includes several forms that reproduce by true parthenogenesis in addition to many bisexual species. The parthenoforms originate as hybrids between bisexual species; the hybrids then reproduce asexually to generate clones of genetically identical individuals (Wright, 1978; Cole, 1979). The existence of parthenoforms presents biologists with an interesting evolutionary problem: how do such forms persist in a world dominated by sexually reproducing species that are presumably better adapted to the environment through natural selection? In their classic paper, Wright and Lowe (1968) proposed the weed hypothesis, which states that parthenogenetic whiptails can become established only in disturbed, marginal, or ecotonal habitats because such habitats are unsuitable for bisexual whiptails. A slightly different view was proposed by Cuellar (1977) who suggested parthenogenetic whiptails occupy only floodplain, beach, or lakeside habitats because parthenoforms can rapidly colonize areas where natural disasters periodically eliminate lizard populations, and because bisexual species are usually absent from such habitats. The implication of both hypotheses is that parthenoforms are poor competitors, presumably because their limited genotypic diversity translates into narrow ecological breadth (Bell, 1982; Case and Taper, 1986). Therefore parthenoforms can avoid competitive exclusion by their bisexual congeners only by occupying disturbed habitats. Cuellar (1977) also emphasized that isolation from bisexual forms ensures that a parthenoform will not lose its genetic identity through hybridization, a phenomenon termed "destabilizing hybridization" by Lynch (1984). This occurs if diploid parthenoforms mate with males of bisexual species to produce triploid hybrids that are either sterile or are parthenogenetic themselves (Lynch, 1984; Vrijenhoek, 1989). The latter case should lead to the replacement of diploid parthenoforms by triploid parthenoforms. Hybridization with bisexual species might also be detrimental to a parthenoform if the fertilization of a parthenogenetic egg caused the egg to fail to develop, resulting in waste of reproductive effort (White and Contreras, 1979). Both Wright and Lowe (1968) and Cuellar (1977) suggested that parthenoforms should rarely be found at site where bisexual species occur, and in those ra e instances where the two forms do co-occur, the bisexual species should be rare enough that it does not exert a strong impact on the parthenoform. However, these hypotheses have not been tested rigorously. The parthenogenetic Cnemidophorus laredoensis subgroup comprises several allodiploid clones that occupy a narrow zone on either side of the Rio Grande from Del Rio (Val Verde County), Texas, to within 16 km of the Gulf of Mexico (Walker, 1987a, b). The subject of this paper is the clone LAR-A, (originally described as Cnemidophorus laredoensis by McKinney et al., 1973). A second major clone, named LAR-B, discovThis content downloaded from 207.46.13.160 on Mon, 17 Oct 2016 05:18:30 UTC All use subject to http://about.jstor.org/terms M. A. PAULISSEN ET AL. TABLE 1. Snout-vent lengths (SVL) and mass of LAR-A and C. gularis at three sites in Texas. Values are mean + standard deviation, sample sizes are given in parentheses. Statistically significant differences, as evaluated by Mann-Whitney U tests, are indicated by an asterisk. The sample sizes for SVL and mass at Garceno differ because lizards were not weighed during the 1 May collection.

Parthenogenetic Cnemidophorus dixoni, consisting of color pattern classes A and B, is limited to a small area in the Chinati Mountains in southwestern Presidio Co., Texas, and a disjunct area in Hidalgo Co., New Mexico. In Presidio County lizards emerged from winter inactivity in April. Thereafter, adult lizards remained active into late August or early September; postneonates remained active until late October. Activity in C. dixoni A and/or B was observed on one or more occasions during every 15-min interval between 1020 h and 1930 h CDT during a 46-day field study between June 1989 and June 1990. No differences in mean cloacal body temperature were observed between juvenile and adult C. dixoni A or B, or among monthly samples. Mean cloacal body temperature for all individuals was 39.89 C ? 0.15 (n = 113). Neonatal Cnemidophorus dixoni A and B hatched in July and August; they grew rapidly, became inactive for about 5 mo (November-March) and matured early in their 2nd summer at 67-73 mm snout-vent length. The life expectancy of C. dixoni appeared to involve parts of three activity cycles, or about 2 calendar yr. Clutch size varied from 1-5 with a mean of 2.90 ? 0.08 for 94 clutches; snout-vent lengths of preserved gravid females varied from 6797 mm with a mean of 82.12 ? 0.57. Larger females had significantly larger clutches than smaller females; the model for the relationship is egg count = 0.09SVL 4.51.

Both triploid (TES-B(3n)) and diploid (TES-C(2n) and TES-D(2n)) lineages of all-female, normally parthenogenetic Cnemidophorus tesselatus are sympatric with gonochoristic C sexlineatus viri- dis in Ninemile Valley of the Purgatoire River at Higbee, Otero County, Colorado. An adult, a subadult, and a juvenile hybrid male C. tesselatus x C. sexlineatus were collected in 1973,1988, and 1989, respectively, in microhabitats where all of the possible parental forms were found. Scutellation, color pattern, and electrophoretic data identified TES-B(3n) as the maternal parent of the adult hybrid, and the presence of four bands at the albumin locus confirmed that it is tetraploid. The subadult and juvenile males also appear to represent tetraploid hybrid TES-B(3n) x C. sexlineatus based upon color pattern and univariate and multivariate analyses of scutellation data. Female TES-B(3n) achieve sexual maturity at a significantly smaller size than either TES-C(2n) or TES-D(2n) at Higbee; this makes insemination of female TES-B(3n) by adult male C sexlineatus more likely, and also favors the hypothesis of TES-B(3n) parentage for the two hybrids. All evidence of continuing hybridization between any of these all-female forms and C. sexlineatus is significant since it provides a basis for the inference that hybrid females with the potential of founding new parthenogenetic lineages of Cnemidophorus may also be produced.

from a local nest. The young are capable of considerable upstream and downstream movement (Brown, 1985) and could have moved some distance from their nest site to the observation locality. Nineteen other common mergansers (7 pairs, 4 single males, 1 single female) were observed along the river during the survey. Bellrose (1976) states that the males abandon the females and leave the breeding area early in incubation, but males were clearly in evidence along the Rio Conchos. These sightings suggest that additional nesting pairs were present in the study area, as most wintering common mergansers have departed fro the latitude of southern Chihuahua by that time (G. Monson, pers. comm.; S. M. Russell, pers. com .). The probable peak of hatching at this locality is midMay (D. E. Brown, pers. comm.), so that most of the other pairs observed could have been involved with nesting activities. These nesting records from the Rio Conchos suggest that common mergansers could nest along streams in the Sierra Madre Occidental of Chihuahua more often

The first descriptions of food habits and activity patterns of two clonal complexes of Cne- midophorus 'laredoensis', designated LAR-A and LAR-B, are presented from a site of syntopy near Los Ebanos, Hidalgo Co., Texas. Termites were the numerically dominant prey for both clonal complexes in April, May and July 1986. However, LAR-A consumed a greater volume of orthopterans than termites, with insect larvae and spiders also being important. LAR-B consumed a greater volume of termites than other prey though orthopterans, insect larvae, spiders and beetles were also important. Both clonal com- plexes showed a significant increase in the volume consumption of termites from April to July and peak consumption of orthopterans and insect larvae in May suggesting shifts in diet with seasonal changes in prey availability. On the year LAR-B consumed larger numbers of small prey (especially termites), whereas LAR-A consumed smaller numbers of larger prey (especially orthopterans). LAR-A was active all day in May but LAR-B was active primarily before 1300; the activity of both clones peaked during morning hours in July. Overall the data support two hypotheses concerning clonal ecology: both LAR-A and LAR-B show phenotypic flexibility predicted by the general-purpose genotype hypothesis; and the niche characteristics of the two clonal complexes differ (at least as much as niche characteristics of other syntopic Cnemi- dophorus) as predicted by the frozen niche variation model. We suggest that LAR-A has the potential for competitive superiority to LAR-B at Los Ebanos because diet overlap is high, LAR-A has a broader diet and activity breadth than LAR-B and preliminary data indicate that the LAR-A complex comprises two cryptic clones, whereas LAR-B is uniclonal. The high population densities of both clones suggest super- abundant resources and/or niche differences alleviate competition. The Laredo whiptail, Cnemidophorus 'la- redoensis' is an all-female, parthenoge- netic form first described by McKinney et al. (1973) from two localities in Webb Co.

Cnemidophorus laredoensis comprises two allodiploid parthenogenetic clonal complexes. LAR-A(2n) includes C. laredoensis as originally described from Laredo and many recently discovered populations in other parts of Texas and Mexico. LAR-B(2n), discovered in 1984, also has been recently reported from both sides of the Rio Grande, including many sites here LAR-A(2n) does not occur. Seven hybrid female and 16 hybrid male LAR-A(2n) x C. gularis (gonochoristic) were collected at 11 sites in Texas and Mexico; three hybrid female LAR-B(2n) x C. gularis were collected at three sites in Texas and Mexico. All hybrids were distinguishable on the basis of color pattern and scutellation. Also, two unusually large females exhibited the effects of heterosis in body size, and one putative hybrid captured alive was triploid. Cytogenetic and/or behavioral mechanisms in LAR-B(2n) are apparently more resistant to hy- bridization than in LAR-A(2n) under identical habitat conditions. The production of hybrids, especially those of LAR-A(2n) x C. gularis, is closely related to disturbed habitat structure and/or relative abundance of syntopic whiptail forms, allowing increased contact between the parental forms. Hybrid LAR-A(2n) x C. gularis were most often found at sites where confined space intensified the interactions between the parental forms, at sites where large numbers of male C. gularis came into contact with the few female LAR-A(2n) present, and at sites where large numbers of female LAR-A(2n) came into contact with the few male C gularis present.