Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 62
Filtrar
Mais filtros










Intervalo de ano de publicação
1.
J Hered ; 109(4): 426-437, 2018 05 11.
Artigo em Inglês | MEDLINE | ID: mdl-29471487

RESUMO

The Lesser Antillean Iguana (Iguana delicatissima) is an endangered species threatened by habitat loss and hybridization with non-native Green Iguanas (Iguana iguana). Iguana delicatissima has been extirpated on several islands, and the Green Iguana has invaded most islands with extant populations. Information is essential to protect this species from extinction. We collected data on 293 iguanas including 17 juveniles from St. Eustasius, one of the few remaining I. delicatissima strongholds. Genetic data were leveraged to test for hybridization presence with the Green Iguana using both mitochondrial and nuclear genes, including 16 microsatellite loci. The microsatellites were also analyzed to estimate genetic diversity, population structure, and effective population size. Using molecular and morphological data, we identified 286 I. delicatissima individuals captured during our first fieldwork effort, and 7 non-native iguanas captured during a second effort, showing hybridization occurs within this population. Comparing homologous microsatellites used in studies on Dominica and Chancel, the I. delicatissima population on St. Eustatius has extremely low genetic diversity (HO = 0.051; HE = 0.057), suggesting this population is genetically depauperate. Furthermore, there is significant evidence for inbreeding (FIS = 0.12) and weak spatial genetic structure (FST = 0.021, P = 0.002) within this population. Besides immediate threats including hybridization, this population's low genetic diversity, presence of physiological abnormalities and low recruitment could indicate presence of inbreeding depression that threatens its long-term survival. We conclude there is a continued region-wide threat to I. delicatissima and highlight the need for immediate conservation action to stop the continuing spread of Green Iguanas and to eliminate hybridization from St. Eustatius.


Assuntos
Variação Genética , Genética Populacional , Iguanas/genética , Repetições de Microssatélites/genética , Animais , Cruzamento , Conservação dos Recursos Naturais , Ecossistema , Espécies em Perigo de Extinção , Feminino , Hibridização Genética , Ilhas , Masculino , Densidade Demográfica
2.
Gen Comp Endocrinol ; 255: 90-101, 2018 01 01.
Artigo em Inglês | MEDLINE | ID: mdl-28974369

RESUMO

The somatotropic axis (SA) regulates numerous aspects of vertebrate physiology such as development, growth, and metabolism and has influence on several tissues including neural, immune, reproductive and gastric tract. Growth hormone (GH) is a key component of SA, it is synthesized and released mainly by pituitary somatotrophs, although now it is known that virtually all tissues can express GH, which, in addition to its well-described endocrine roles, also has autocrine/paracrine/intracrine actions. In the pituitary, GH expression is regulated by several hypothalamic neuropeptides including GHRH, PACAP, TRH and SST. GH, in turn, regulates IGF1 synthesis in several target tissues, adding complexity to the system since GH effects can be exerted either directly or mediated by IGF1. In reptiles, little is known about the SA components and their functional interactions. The aim of this work was to characterize the mRNAs of the principal SA components in the green iguana and to develop the tools that allow the study of the structural and functional evolution of this system in reptiles. By employing RT-PCR and RACE, the cDNAs encoding for GHRH, PACAP, TRH, SST and IGF1 were amplified and sequenced. Results showed that these cDNAs coded for the corresponding protein precursors of 154, 170, 243, 113, and 131 amino acids, respectively. Of these, GHRH, PACAP, SST and IGF1 precursors exhibited a high structural conservation with respect to its counterparts in other vertebrates. On the other hand, iguana's TRH precursor showed 7 functional copies of mature TRH (pyr-QHP-NH2), as compared to 4 and 6 copies of TRH in avian and mammalian proTRH sequences, respectively. It was found that in addition to its primary production site (brain for GHRH, PACAP, TRH and SST, and liver for IGF1), they were also expressed in other peripheral tissues, i.e. testes and ovaries expressed all the studied mRNAs, whereas TRH and IGF1 mRNAs were observed ubiquitously in all tissues considered. These results show that the main SA components in reptiles of the Squamata Order maintain a good structural conservation among vertebrate phylogeny, and suggest important physiological interactions (endocrine, autocrine and/or paracrine) between them due to their wide peripheral tissue expression.


Assuntos
Hormônio Liberador de Hormônio do Crescimento/genética , Iguanas/genética , Fator de Crescimento Insulin-Like I/genética , Polipeptídeo Hipofisário Ativador de Adenilato Ciclase/genética , Somatostatina/genética , Hormônio Liberador de Tireotropina/genética , Sequência de Aminoácidos , Animais , Sequência de Bases , Hormônio Liberador de Hormônio do Crescimento/química , Hormônio Liberador de Hormônio do Crescimento/metabolismo , Fator de Crescimento Insulin-Like I/química , Fator de Crescimento Insulin-Like I/metabolismo , Filogenia , Polipeptídeo Hipofisário Ativador de Adenilato Ciclase/química , Polipeptídeo Hipofisário Ativador de Adenilato Ciclase/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Somatostatina/química , Somatostatina/metabolismo , Hormônio Liberador de Tireotropina/química , Hormônio Liberador de Tireotropina/metabolismo
3.
Zoology (Jena) ; 126: 98-102, 2018 02.
Artigo em Inglês | MEDLINE | ID: mdl-29287619

RESUMO

Once believed to be restricted only to endotherms (mammals and birds), several poikilothermic amniote lineages have recently been documented to possess long-term evolutionary stability in their sex chromosomes. However, many important lineages were not included in these tests. Previously, based on molecular evidence, we documented the homology of well-differentiated sex chromosomes among seven families of iguanas (Pleurodonta), with basilisks (Corytophanidae) being the only exception, as the tested genes linked to X, but missing on the Y chromosome, in other iguanas were autosomal or pseudoautosomal in basilisks. In this study, we test the homology of sex chromosomes in the remaining, previously unstudied iguana families (Hoplocercidae, Leiosauridae, Liolaemidae, Polychrotidae) and in the basilisk genus Corytophanes. Our results show that 12 currently recognized families of iguanas share X-specific gene content conserved from the common ancestor living in the Cretaceous period. However, the results in the genus Corytophanes indicate the loss of the ancestral differentiated sex chromosomes from the ancestor of basilisks. Our new data further confirm the extensive stability of sex chromosomes in iguanas, thus enabling molecular sexing based on the comparison of the number of X-specific genes by quantitative PCR (qPCR) in all but one family of this widely diversified clade.


Assuntos
Iguanas/genética , Cromossomos Sexuais/genética , Animais , Feminino , Dosagem de Genes/genética , Cariótipo , Masculino , Filogenia , Reação em Cadeia da Polimerase em Tempo Real/veterinária , Cromossomo X/genética
4.
J Hered ; 108(6): 640-649, 2017 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-28821185

RESUMO

Understanding the factors that explain the patterns of genetic structure or phylogeographic breaks at an intraspecific level is key to inferring the mechanisms of population differentiation in its early stages. These topics have been well studied in the Baja California region, with vicariance and the dispersal ability of individuals being the prevailing hypothesis for phylogeographic breaks. In this study, we evaluated the phylogeographic patterns in the desert iguana (Dipsosaurus dorsalis), a species with a recent history in the region and spatial variation in life history traits. We analyzed a total of 307 individuals collected throughout 19 localities across the Baja California Peninsula with 15 microsatellite DNA markers. Our data reveal the existence of 3 geographically discrete genetic populations with moderate gene flow and an isolation-by-distance pattern presumably produced by the occurrence of a refugium in the Cape region during the Pleistocene Last Glacial Maximum. Bayesian methods and ecological niche modeling were used to assess the relationship between population genetic structure and present and past climatic preferences of the desert iguana. We found that the present climatic heterogeneity of the Baja California Peninsula has a marked influence on the population genetic structure of the species, suggesting that there are alternative explanations besides vicariance. The information obtained in this study provides data allowing a better understanding of how historical population processes in the Baja California Peninsula can be understood from an ecological perspective.


Assuntos
Clima Desértico , Genética Populacional , Iguanas/genética , Animais , Teorema de Bayes , Ecossistema , Fluxo Gênico , México , Repetições de Microssatélites , Modelos Genéticos , Filogenia , Filogeografia , Análise de Sequência de DNA
5.
Mol Phylogenet Evol ; 115: 27-39, 2017 10.
Artigo em Inglês | MEDLINE | ID: mdl-28716742

RESUMO

Spiny tailed iguanas are highly diverse clade of lizards in Mesoamerica, ranging from northern Mexico through Panama. Utilizing 2 regions of mitochondrial DNA (1948bp) and 4 nuclear loci (2232bp) we explored the relationships between these species and the phylogeographic history of the major clades. We discovered that the lineage endemic to the Yucatan Peninsula renders the genus Ctenosaura paraphyletic. To resolve this non-monophyly, we resurrect the taxon Cachryx Cope, 1866, and provide a new diagnosis for the genus. We also find that small body-size and highly spinose tails in the species previously referred to the subgenus Enyaliosaurus, have evolved independently 3 times. Cachryx were recovered as sister to the lineage of iguanines endemic to the Galapagos Islands, and we discuss biogeographic scenarios to explain this relationship as well as those among the primary clades of Ctenosaura in Mesoamerica.


Assuntos
Iguanas/classificação , Animais , Evolução Biológica , DNA Mitocondrial/genética , DNA Mitocondrial/metabolismo , Haplótipos , Iguanas/genética , México , Proteínas MutL/classificação , Proteínas MutL/genética , NADH Desidrogenase/classificação , NADH Desidrogenase/genética , Panamá , Filogenia , Filogeografia , Análise de Sequência de DNA
6.
PLoS One ; 12(5): e0176434, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28459829

RESUMO

The extent to which evolution is deterministic (predictable), or random, is a fundamental question in evolution. This case study attempts to determine the extent to which interspecific divergence can be predicted from intraspecific trends related species. The mountainous Lesser Antilles are occupied by one or two anole species with very substantial intraspecific differences in the quantitative traits between xeric and rainforest habitats. These ecologically determined differences tend to be in parallel in each island species. A related species (Anolis bonairensis) lives on the far more xeric island of Bonaire, and this study tests the extent to which its interspecific divergence in hue and pattern traits can be predicted from the parallel intraspecific variation exhibited in Lesser Antillean anoles. Regression against a multivariate climate variable suggests that the hue and pattern of the Bonaire anole are consistently predicted from the ecologically determined intraspecific variation of its Lesser Antillean relatives. However, this predictability may be less consistent with other character systems, for example, scalation.


Assuntos
Evolução Biológica , Ambientes Extremos , Iguanas/genética , Animais , Clima , Iguanas/anatomia & histologia , Iguanas/fisiologia , Ilhas , Modelos Genéticos , Análise Multivariada , Filogenia , Análise de Regressão , Pigmentação da Pele/genética , Especificidade da Espécie
7.
Gen Comp Endocrinol ; 230-231: 76-86, 2016 05 01.
Artigo em Inglês | MEDLINE | ID: mdl-27044512

RESUMO

Growth hormone (GH), together with thyroid hormones (TH), regulates growth and development, and has critical effects on vertebrate metabolism. In ectotherms, these physiological processes are strongly influenced by environmental temperature. In reptiles, however, little is known about the direct influences of this factor on the somatotropic and thyroid axes. Therefore, the aim of this study was to describe the effects of both acute (48h) and chronic (2weeks) exposure to sub-optimal temperatures (25 and 18°C) upon somatotropic and thyroid axis function of the green iguana, in comparison to the control temperature (30-35°C). We found a significant increase in GH release (2.0-fold at 25°C and 1.9-fold at 18°C) and GH mRNA expression (up to 3.7-fold), mainly under chronic exposure conditions. The serum concentration of insulin-like growth factor-I (IGF-I) was significantly greater after chronic exposure (18.5±2.3 at 25°C; 15.92±3.4 at 18°C; vs. 9.3±1.21ng/ml at 35°C), while hepatic IGF-I mRNA expression increased up to 6.8-fold. Somatotropic axis may be regulated, under acute conditions, by thyrotropin-releasing hormone (TRH) that significantly increased its hypothalamic concentration (1.45 times) and mRNA expression (0.9-fold above control), respectively; and somatostatin (mRNA expression increased 1.0-1.2 times above control); and under chronic treatment, by pituitary adenylate cyclase-activating peptide (PACAP mRNA expression was increased from 0.4 to 0.6 times). Also, it was shown that, under control conditions, injection of TRH stimulated a significant increase in circulating GH. On the other hand, while there was a significant rise in the hypothalamic content of TRH and its mRNA expression, this hormone did not appear to influence the thyroid axis activity, which showed a severe diminution in all conditions of cold exposure, as indicated by the decreases in thyrotropin (TSH) mRNA expression (up to one-eight of the control), serum T4 (from 11.6±1.09 to 5.3±0.58ng/ml, after 2weeks at 18°C) and T3 (from 0.87±0.09 to 0.05±0.01ng/ml, under chronic conditions at 25°C), and Type-2 deiodinase (D2) activity (from 992.5±224 to 213.6±26.4fmolI(125)T4/mgh). The reduction in thyroid activity correlates with the down-regulation of metabolism as suggested by the decrease in the serum glucose and free fatty acid levels. These changes apparently were independent of a possible stress response, at least under acute exposure to both temperatures and in chronic treatment to 25°C, since serum corticosterone had no significant changes in these conditions, while at chronic 18°C exposure, a slight increase (0.38 times above control) was found. Thus, these data suggest that the reptilian somatotropic and thyroid axes have differential responses to cold exposure, and that GH and TRH may play important roles associated to adaptation mechanisms that support temperature acclimation in the green iguana.


Assuntos
Hormônio do Crescimento/metabolismo , Iguanas/metabolismo , Temperatura Ambiente , Glândula Tireoide/metabolismo , Hormônio Liberador de Tireotropina/metabolismo , Animais , Glicemia/análise , Corticosterona/sangue , Hormônio do Crescimento/genética , Hipotálamo/efeitos dos fármacos , Hipotálamo/metabolismo , Iguanas/sangue , Iguanas/genética , Fator de Crescimento Insulin-Like I/genética , Iodeto Peroxidase/metabolismo , Fígado/efeitos dos fármacos , Fígado/metabolismo , Polipeptídeo Hipofisário Ativador de Adenilato Ciclase/genética , RNA Mensageiro/metabolismo , Receptores de Superfície Celular/sangue , Somatostatina/genética , Glândula Tireoide/efeitos dos fármacos , Hormônios Tireóideos/sangue , Hormônios Tireóideos/genética , Hormônios Tireóideos/metabolismo , Tireotropina/genética , Hormônio Liberador de Tireotropina/administração & dosagem , Hormônio Liberador de Tireotropina/genética , Hormônio Liberador de Tireotropina/farmacologia
8.
Mitochondrial DNA A DNA Mapp Seq Anal ; 27(5): 3699-700, 2016 09.
Artigo em Inglês | MEDLINE | ID: mdl-26357924

RESUMO

The Galápagos iguanas are among the oldest vertebrate lineages on the Galápagos archipelago, and the evolutionary history of this clade is of great interest to biologists. We describe here the complete mitochondrial genomes of the marine iguana, Amblyrhynchus cristatus (Genbank accession number: KT277937) and the land iguana Conolophus subcristatus (Genbank accession number: KT277936). The genomes contain 13 protein-coding genes, 22 transfer RNAs, and two ribosomal RNAs genes, as well as a control region (CR). Both species have an identical gene order, which matches that of Iguana iguana. The CR of both Galápagos iguanas features similar tandem repeats units, which are absent in I. iguana. We present a phylogeny of the Iguanidae based on complete mitochondrial genomes, which confirms the sister-group relationship of Galápagos iguanas. These new mitochondrial genomes constitute an important data source for future exploration of the phylogenetic relationships and evolutionary history of the Galápagos iguanas.


Assuntos
Genoma Mitocondrial , Iguanas/genética , Animais , Iguanas/classificação , Região de Controle de Locus Gênico , Fases de Leitura Aberta , Filogenia , RNA Ribossômico/genética , RNA de Transferência/genética , Sequências de Repetição em Tandem
9.
Genome Biol Evol ; 7(12): 3322-36, 2015 Nov 19.
Artigo em Inglês | MEDLINE | ID: mdl-26590214

RESUMO

Compatibility between the nuclear (nDNA) and mitochondrial (mtDNA) genomes is important for organismal health. However, its significance for major evolutionary processes such as speciation is unclear, especially in vertebrates. We previously identified a sharp mtDNA-specific sequence divergence between morphologically indistinguishable chameleon populations (Chamaeleo chamaeleon recticrista) across an ancient Israeli marine barrier (Jezreel Valley). Because mtDNA introgression and gender-based dispersal were ruled out, we hypothesized that mtDNA spatial division was maintained by mito-nuclear functional compensation. Here, we studied RNA-seq generated from each of ten chameleons representing the north and south populations and identified candidate nonsynonymous substitutions (NSSs) matching the mtDNA spatial distribution. The most prominent NSS occurred in 14 nDNA-encoded mitochondrial proteins. Increased chameleon sample size (N = 70) confirmed the geographic differentiation in POLRMT, NDUFA5, ACO1, LYRM4, MARS2, and ACAD9. Structural and functionality evaluation of these NSSs revealed high functionality. Mathematical modeling suggested that this mito-nuclear spatial divergence is consistent with hybrid breakdown. We conclude that our presented evidence and mathematical model underline mito-nuclear interactions as a likely role player in incipient speciation in vertebrates.


Assuntos
Genes Mitocondriais , Especiação Genética , Iguanas/genética , Animais , Evolução Molecular , Modelos Genéticos , Polimorfismo Genético
10.
Sci Rep ; 5: 16963, 2015 Nov 23.
Artigo em Inglês | MEDLINE | ID: mdl-26593239

RESUMO

Restriction-enzyme (RE)-based next-generation sequencing methods have revolutionized marker-assisted genetic studies; however, the use of REs has limited their widespread adoption, especially in field samples with low-quality DNA and/or small quantities of DNA. Here, we developed a PCR-based procedure to construct reduced representation libraries without RE digestion steps, representing de novo single-nucleotide polymorphism discovery, and its genotyping using next-generation sequencing. Using multiplexed inter-simple sequence repeat (ISSR) primers, thousands of genome-wide regions were amplified effectively from a wide variety of genomes, without prior genetic information. We demonstrated: 1) Mendelian gametic segregation of the discovered variants; 2) reproducibility of genotyping by checking its applicability for individual identification; and 3) applicability in a wide variety of species by checking standard population genetic analysis. This approach, called multiplexed ISSR genotyping by sequencing, should be applicable to many marker-assisted genetic studies with a wide range of DNA qualities and quantities.


Assuntos
Genoma , Técnicas de Genotipagem/métodos , Filogenia , Reação em Cadeia da Polimerase/métodos , Polimorfismo de Nucleotídeo Único , Agaricales/classificação , Agaricales/genética , Animais , Copépodes/classificação , Copépodes/genética , Primers do DNA/síntese química , Primers do DNA/química , Gastrópodes/classificação , Gastrópodes/genética , Marcadores Genéticos , Estudo de Associação Genômica Ampla , Genótipo , Sequenciamento de Nucleotídeos em Larga Escala , Iguanas/classificação , Iguanas/genética , Repetições de Microssatélites , Orchidaceae/classificação , Orchidaceae/genética , Stichopus/classificação , Stichopus/genética
11.
PLoS One ; 10(6): e0127575, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-26046351

RESUMO

The worldwide increase of hybridization in different groups is thought to have become more important with the loss of isolating barriers and the introduction of invasive species. This phenomenon could result in the extinction of endemic species. This study aims at investigating the hybridization dynamics between the endemic and threatened Lesser Antillean iguana (Iguana delicatissima) and the invasive common green iguana (Iguana iguana) in the Lesser Antilles, as well as assessing the impact of interspecific hybridization on the decline of I. delicatissima. 59 I. delicatissima (5 localities), 47 I. iguana (12 localities) and 27 hybrids (5 localities), who were all identified based on morphological characters, have been genotyped at 15 microsatellites markers. We also sequenced hybrids using ND4 mitochondrial loci to further investigate mitochondrial introgression. The genetic clustering of species and hybrid genetic assignment were performed using a comparative approach, through the implementation of a Discriminant Analysis of Principal Component (DAPC) based on statistics, as well as genetic clustering approaches based on the genetic models of several populations (Structure, NewHybrids and HIest), in order to get full characterization of hybridization patterns and introgression dynamics across the islands. The iguanas identified as hybrids in the wild, thanks to morphological analysis, were all genetically F1, F2, or backcrosses. A high proportion of individuals were also the result of a longer-term admixture. The absence of reproductive barriers between species leads to hybridization when species are in contact. Yet morphological and behavioral differences between species could explain why males I. iguana may dominate I. delicatissima, thus resulting in short-term species displacement and extinction by hybridization and recurrent introgression from I. iguana toward I. delicatissima. As a consequence, I. delicatissima gets eliminated through introgression, as observed in recent population history over several islands. These results have profound implications for species management of the endangered I. delicatissima and practical conservation recommendations are being discussed in the light of these findings.


Assuntos
Espécies em Perigo de Extinção , Hibridização Genética , Iguanas/genética , Espécies Introduzidas , Animais , Análise por Conglomerados , Análise Discriminante , Variação Genética , Genótipo , Haplótipos , Masculino , Cadeias de Markov , Repetições de Microssatélites/genética , Mitocôndrias/genética , NADH Desidrogenase/genética , Análise de Componente Principal
12.
Proc Biol Sci ; 282(1809): 20150425, 2015 06 22.
Artigo em Inglês | MEDLINE | ID: mdl-26041359

RESUMO

The effects of the direct interaction between hybridization and speciation-two major contrasting evolutionary processes--are poorly understood. We present here the evolutionary history of the Galápagos marine iguana (Amblyrhynchus cristatus) and reveal a case of incipient within--island speciation, which is paralleled by between-island hybridization. In-depth genome-wide analyses suggest that Amblyrhynchus diverged from its sister group, the Galápagos land iguanas, around 4.5 million years ago (Ma), but divergence among extant populations is exceedingly young (less than 50,000 years). Despite Amblyrhynchus appearing as a single long-branch species phylogenetically, we find strong population structure between islands, and one case of incipient speciation of sister lineages within the same island--ostensibly initiated by volcanic events. Hybridization between both lineages is exceedingly rare, yet frequent hybridization with migrants from nearby islands is evident. The contemporary snapshot provided by highly variable markers indicates that speciation events may have occurred throughout the evolutionary history of marine iguanas, though these events are not visible in the deeper phylogenetic trees. We hypothesize that the observed interplay of speciation and hybridization might be a mechanism by which local adaptations, generated by incipient speciation, can be absorbed into a common gene pool, thereby enhancing the evolutionary potential of the species as a whole.


Assuntos
Especiação Genética , Hibridização Genética , Iguanas/genética , Animais , Equador , Dados de Sequência Molecular , Filogenia , Análise de Sequência de DNA
13.
Zootaxa ; 3946(2): 201-20, 2015 Apr 09.
Artigo em Inglês | MEDLINE | ID: mdl-25947685

RESUMO

A new species of the hitherto monotypic genus Chalarodon is described from southern Madagascar and a lectotype (ZMB 4360) is designated for C. madagascariensis Peters, 1854. The new species of terrestrial iguana, Chalarodon steinkampi sp. nov., is defined by several morphological characters and by concordant differentiation in mitochondrial and nuclear DNA with >5% uncorrected pairwise genetic distance in the 16S rRNA gene. It can be most clearly recognized by the presence of smooth (vs. keeled) gular and ventral scales, a spotted pattern extending from flanks onto belly, and an unpigmented throat. The new species is known from only a small area between the villages of Amboasary Sud and Esomony, located west of the Andohahela Massif, while C. madagascariensis appears to be widespread over much of southern and western Madagascar. We highlight the need for further exploration of this unprotected region which might host several other microendemic species.


Assuntos
Iguanas/anatomia & histologia , Iguanas/classificação , Animais , Feminino , Iguanas/genética , Madagáscar , Masculino , RNA Ribossômico 16S , Análise de Sequência de DNA , Especificidade da Espécie
14.
J Hered ; 106(3): 315-21, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-25779972

RESUMO

Iguana delicatissima is an endangered endemic of the Lesser Antilles in the Caribbean. Phylogeographic analyses for many terrestrial vertebrate species in the Caribbean, particularly lizards, suggest ancient divergence times. Often, the closest relatives of species are found on the same island, indicating that colonization rates are so low that speciation on islands is often more likely to generate biodiversity than subsequent colonization events. Mitochondrial sequence analysis of the region spanning ND4 was performed on I. delicatissima individuals from islands across the species' range to estimate genetic divergence among geographically isolated populations. Five unique haplotypes were recovered from 46 individuals. The majority of animals carry a single common haplotype. Two of the haplotypes were only present in individuals classified as hybrids from Îles des Saintes. The final 2 haplotypes, single nucleotide substitutions, were present in animals from Îlet Chancel of Martinique and Saint Barthélemy, respectively. Despite the great distances between islands and habitat heterogeneity within islands, this species is characterized by low haplotype diversity. The low mtDNA variation of I. delicatissima suggests a single colonization coupled with rapid range expansion, potentially hastened by human-mediated dispersal.


Assuntos
Variação Genética , Genética Populacional , Iguanas/genética , Animais , Região do Caribe , Conservação dos Recursos Naturais , DNA Mitocondrial/genética , Espécies em Perigo de Extinção , Evolução Molecular , Haplótipos , Ilhas , Filogeografia , Análise de Sequência de DNA
15.
PLoS One ; 9(9): e106963, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-25229344

RESUMO

Ecological data, the primary source of information on patterns and rates of migration, can be integrated with genetic data to more accurately describe the realized connectivity between geographically isolated demes. In this paper we implement this approach and discuss its implications for managing populations of the endangered Andros Island Rock Iguana, Cyclura cychlura cychlura. This iguana is endemic to Andros, a highly fragmented landmass of large islands and smaller cays. Field observations suggest that geographically isolated demes were panmictic due to high, inferred rates of gene flow. We expand on these observations using 16 polymorphic microsatellites to investigate the genetic structure and rates of gene flow from 188 Andros Iguanas collected across 23 island sites. Bayesian clustering of specimens assigned individuals to three distinct genotypic clusters. An analysis of molecular variance (AMOVA) indicates that allele frequency differences are responsible for a significant portion of the genetic variance across the three defined clusters (Fst =  0.117, p<<0.01). These clusters are associated with larger islands and satellite cays isolated by broad water channels with strong currents. These findings imply that broad water channels present greater obstacles to gene flow than was inferred from field observation alone. Additionally, rates of gene flow were indirectly estimated using BAYESASS 3.0. The proportion of individuals originating from within each identified cluster varied from 94.5 to 98.7%, providing further support for local isolation. Our assessment reveals a major disparity between inferred and realized gene flow. We discuss our results in a conservation perspective for species inhabiting highly fragmented landscapes.


Assuntos
Fluxo Gênico/genética , Iguanas/genética , Animais , Variação Genética , Genética Populacional , Iguanas/classificação
16.
Gen Comp Endocrinol ; 203: 281-95, 2014 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-24769041

RESUMO

Pituitary growth hormone (GH) has been studied in most vertebrate groups; however, only a few studies have been carried out in reptiles. Little is known about pituitary hormones in the order Squamata, to which the green iguana (gi) belongs. In this work, we characterized the hypophysis of Iguana iguana morphologically. The somatotrophs (round cells of 7.6-10 µm containing 250- to 300-nm secretory granules where the giGH is stored) were found, by immunohistochemistry and in situ hybridization, exclusively in the caudal lobe of the pars distalis, whereas the lactotrophs were distributed only in the rostral lobe. A pituitary giGH-like protein was obtained by immuno-affinity chromatography employing a heterologous antibody against chicken GH. giGH showed molecular heterogeneity (22, 44, and 88 kDa by SDS-PAGE/Western blot under non-reducing conditions and at least four charge variants (pIs 6.2, 6.5, 6.9, 7.4) by isoelectric focusing. The pituitary giGH cDNA (1016 bp), amplified by PCR and RACE, encodes a pre-hormone of 218 aa, of which 190 aa correspond to the mature protein and 28 aa to the signal peptide. The giGH receptor cDNA was also partially sequenced. Phylogenetic analyses of the amino acid sequences of giGH and giGHR homologs in vertebrates suggest a parallel evolution and functional relationship between the GH and its receptor.


Assuntos
Hormônio do Crescimento/genética , Hormônio do Crescimento/metabolismo , Iguanas/genética , Iguanas/metabolismo , Receptores da Somatotropina/genética , Receptores da Somatotropina/metabolismo , Sequência de Aminoácidos , Animais , Sequência de Bases , Eletroforese em Gel de Poliacrilamida , Evolução Molecular , Imuno-Histoquímica , Hibridização In Situ , Dados de Sequência Molecular , Filogenia , Hipófise/metabolismo , RNA Mensageiro/metabolismo , Homologia de Sequência de Aminoácidos , Somatotrofos/metabolismo
17.
Biol Lett ; 10(3): 20131093, 2014 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-24598109

RESUMO

Many poikilothermic vertebrate lineages, especially among amphibians and fishes, possess a rapid turnover of sex chromosomes, while in endotherms there is a notable stability of sex chromosomes. Reptiles in general exhibit variability in sex-determining systems; as typical poikilotherms, they might be expected to have a rapid turnover of sex chromosomes. However, molecular data which would enable the testing of the stability of sex chromosomes are lacking in most lineages. Here, we provide molecular evidence that sex chromosomes are highly conserved across iguanas, one of the most species-rich clade of reptiles. We demonstrate that members of the New World families Iguanidae, Tropiduridae, Leiocephalidae, Phrynosomatidae, Dactyloidae and Crotaphytidae, as well as of the family Opluridae which is restricted to Madagascar, all share homologous sex chromosomes. As our sampling represents the majority of the phylogenetic diversity of iguanas, the origin of iguana sex chromosomes can be traced back in history to the basal splitting of this group which occurred during the Cretaceous period. Iguanas thus show a stability of sex chromosomes comparable to mammals and birds and represent the group with the oldest sex chromosomes currently known among amniotic poikilothermic vertebrates.


Assuntos
Evolução Molecular , Iguanas/genética , Cromossomos Sexuais/genética , Animais , Feminino , Masculino , Filogenia , Reação em Cadeia da Polimerase , Processos de Determinação Sexual/genética
18.
Evolution ; 68(7): 2079-85, 2014 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-24433436

RESUMO

Vertebrates possess diverse sex-determining systems, which differ in evolutionary stability among particular groups. It has been suggested that poikilotherms possess more frequent turnovers of sex chromosomes than homoiotherms, whose effective thermoregulation can prevent the emergence of the sex reversals induced by environmental temperature. Squamate reptiles used to be regarded as a group with an extensive variability in sex determination; however, we document how the rather old radiation of lizards from the genus Anolis, known for exceptional ecomorphological variability, was connected with stability in sex chromosomes. We found that 18 tested species, representing most of the phylogenetic diversity of the genus, share the gene content of their X chromosomes. Furthermore, we discovered homologous sex chromosomes in species of two genera (Sceloporus and Petrosaurus) from the family Phrynosomatidae, serving here as an outgroup to Anolis. We can conclude that the origin of sex chromosomes within iguanas largely predates the Anolis radiation and that the sex chromosomes of iguanas remained conserved for a significant part of their evolutionary history. Next to therian mammals and birds, Anolis lizards therefore represent another adaptively radiated amniote clade with conserved sex chromosomes. We argue that the evolutionary stability of sex-determining systems may reflect an advanced stage of differentiation of sex chromosomes rather than thermoregulation strategy.


Assuntos
Evolução Molecular , Especiação Genética , Iguanas/genética , Cromossomos Sexuais/genética , Adaptação Fisiológica/genética , Animais , Feminino , Variação Genética , Iguanas/fisiologia , Masculino , Processos de Determinação Sexual/genética
19.
Syst Biol ; 63(2): 119-33, 2014 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-24262383

RESUMO

Current molecular methods of species delimitation are limited by the types of species delimitation models and scenarios that can be tested. Bayes factors allow for more flexibility in testing non-nested species delimitation models and hypotheses of individual assignment to alternative lineages. Here, we examined the efficacy of Bayes factors in delimiting species through simulations and empirical data from the Sceloporus scalaris species group. Marginal-likelihood scores of competing species delimitation models, from which Bayes factor values were compared, were estimated with four different methods: harmonic mean estimation (HME), smoothed harmonic mean estimation (sHME), path-sampling/thermodynamic integration (PS), and stepping-stone (SS) analysis. We also performed model selection using a posterior simulation-based analog of the Akaike information criterion through Markov chain Monte Carlo analysis (AICM). Bayes factor species delimitation results from the empirical data were then compared with results from the reversible-jump MCMC (rjMCMC) coalescent-based species delimitation method Bayesian Phylogenetics and Phylogeography (BP&P). Simulation results show that HME and sHME perform poorly compared with PS and SS marginal-likelihood estimators when identifying the true species delimitation model. Furthermore, Bayes factor delimitation (BFD) of species showed improved performance when species limits are tested by reassigning individuals between species, as opposed to either lumping or splitting lineages. In the empirical data, BFD through PS and SS analyses, as well as the rjMCMC method, each provide support for the recognition of all scalaris group taxa as independent evolutionary lineages. Bayes factor species delimitation and BP&P also support the recognition of three previously undescribed lineages. In both simulated and empirical data sets, harmonic and smoothed harmonic mean marginal-likelihood estimators provided much higher marginal-likelihood estimates than PS and SS estimators. The AICM displayed poor repeatability in both simulated and empirical data sets, and produced inconsistent model rankings across replicate runs with the empirical data. Our results suggest that species delimitation through the use of Bayes factors with marginal-likelihood estimates via PS or SS analyses provide a useful and complementary alternative to existing species delimitation methods.


Assuntos
Teorema de Bayes , Simulação por Computador , Iguanas/classificação , Filogenia , Animais , Iguanas/anatomia & histologia , Iguanas/genética , Cadeias de Markov , Método de Monte Carlo , Proteínas de Répteis/genética , Especificidade da Espécie
20.
Mol Ecol ; 22(15): 3904-15, 2013 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-23889543

RESUMO

Habitat fragmentation can have profound effects on the distribution of genetic variation within and between populations. Previously, we showed that in the ornate dragon lizard, Ctenophorus ornatus, lizards residing on outcrops that are separated by cleared agricultural land are significantly more isolated and hold less genetic variation than lizards residing on neighbouring outcrops connected by undisturbed native vegetation. Here, we extend the fine-scale study to examine the pattern of genetic variation and population structure across the species' range. Using a landscape genetics approach, we test whether land clearing for agricultural purposes has affected the population structure of the ornate dragon lizard. We found significant genetic differentiation between outcrop populations (FST  = 0.12), as well as isolation by distance within each geographic region. In support of our previous study, land clearing was associated with higher genetic divergences between outcrops and lower genetic variation within outcrops, but only in the region that had been exposed to intense agriculture for the longest period of time. No other landscape features influenced population structure in any geographic region. These results show that the effects of landscape features can vary across species' ranges and suggest there may be a temporal lag in response to contemporary changes in land use. These findings therefore highlight the need for caution when assessing the impact of contemporary land use practices on genetic variation and population structure.


Assuntos
Ecossistema , Fluxo Gênico/genética , Variação Genética , Iguanas/genética , Isolamento Reprodutivo , Animais , Pool Gênico , Deriva Genética , População
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA