Embryonic development of the neotropical pit viper Bothrops atrox (Serpentes: Viperidae: Crotalinae), with emphasis on pit organ morphogenesis and its evolution in snakes.

BACKGROUND: Bothrops atrox is a pit viper with a loreal pit organ, and its embryological development remains undescribed. Here, we provide a comprehensive description of the embryology of B. atrox, focusing on the loreal pit organ and cephalic scales. RESULTS: We characterized 13 developmental stages of B. atrox based on external features consistent with the embryogenesis of previously described snake species. The loreal pit organ originates from the circumorbital region and migrates to its final position. In Crotalinae, the pit organ first becomes visible at stage 28, whereas in Pythonidae labial, pit organs appear at Stage 35. Pit organs evolved independently three times in Serpentes, encompassing Boidae, Pythonidae, and Crotalinae. Boidae lacks embryological information for pit organs. Furthermore, we observed that head scalation onset occurs at Stage 33 in B. atrox, with fusion of scales surrounding the loreal pit organ. CONCLUSIONS: The embryology of pit organs in Pythonidae and Boidae species remains poorly understood. Our detailed embryological descriptions are critical for proposing developmental scenarios for pit organs and guiding future research on these structures.

Genome-wide SNPs clarify lineage diversity confused by coloration in coralsnakes of the Micrurus diastema species complex (Serpentes: Elapidae).

New world coralsnakes of the genus Micrurus are a diverse radiation of highly venomous and brightly colored snakes that range from North Carolina to Argentina. Species in this group have played central roles in developing and testing hypotheses about the evolution of mimicry and aposematism. Despite their diversity and prominence as model systems, surprisingly little is known about species boundaries and phylogenetic relationships within Micrurus, which has substantially hindered meaningful analyses of their evolutionary history. Here we use mitochondrial genes together with thousands of nuclear genomic loci obtained via ddRADseq to study the phylogenetic relationships and population genomics of a subclade of the genus Micrurus: The M. diastema species complex. Our results indicate that prior species and species-group inferences based on morphology and color pattern have grossly misguided taxonomy, and that the M. diastema complex is not monophyletic. Based on our analyses of molecular data, we infer the phylogenetic relationships among species and populations, and provide a revised taxonomy for the group. Two non-sister species-complexes with similar color patterns are recognized, the M. distans and the M. diastema complexes, the first being basal to the monadal Micrurus and the second encompassing most North American monadal taxa. We examined all 13 species, and their respective subspecies, for a total of 24 recognized taxa in the M. diastema species complex. Our analyses suggest a reduction to 10 species, with no subspecific designations warranted, to be a more likely estimate of species diversity, namely, M. apiatus, M. browni, M. diastema, M. distans, M. ephippifer, M. fulvius, M. michoacanensis, M. oliveri, M. tener, and one undescribed species.

Phylogenetic relationships of the enigmatic longtailed rattlesnakes (Crotalus ericsmithi, C. lannomi, and C. stejnegeri).

The longtailed rattlesnakes of western Mexico represent an enigmatic group of poorly known venomous snake species: Crotalus ericsmithi, C. lannomi, and C. stejnegeri. In the 120 years since their discovery, fewer than twenty individuals have been deposited in natural history collections worldwide. These three species share similar morphological traits, including a particularly long tail that has been interpreted as either an ancestral condition among rattlesnakes or as derived within the longtailed group. An understanding of the phylogenetic distinctiveness and relationships among the longtailed rattlesnakes, and their relationships to other rattlesnake groups, has previously been hampered by a dearth of comparative material and tissues for collection of DNA sequence data. Facilitated by the recent availability of tissue samples from multiple individuals of each species, we estimate the phylogenetic relationships among the longtailed rattlesnakes and their placement among other rattlesnake groups, using DNA sequence data from three mitochondrial and three nuclear gene fragments. We explore phylogenetic signal in our data using Bayesian and maximum likelihood methods, species tree analyses and hypothesis testing. Our results strongly support the monophyly of longtailed rattlesnakes and suggest the three species diverged from each other during the mid to late Pliocene or early Pleistocene (~1.5-5.6 mya). Contrary to prevailing hypotheses, we find no evidence for an early or basal divergence of the longtailed clade within the rattlesnake tree, and instead estimate that it diverged relatively recently (~6.8 mya) from its sister lineage, composed of the diamondback rattlesnakes (C. atrox group) and the prairie rattlesnakes (C. viridis group). With our added sampling of lineages and identification of previously used problematic sequences, we provide a revised hypothesis for relationships among Crotalus species, yet underscore the need for future studies and new data to deliver a well-supported robust estimate of rattlesnake relationships.

Diversidade das metaloproteinases presentes no veneno de Bothrops neuwiedi: identificação de SVMPs que induzem alterações na hemostasia / Diversity of metalloproteinases present in the Bothrops neuwiedi venom: identification of SVMPs that cause alterations on hemostasis

The snake venom metalloproteinases (SVMPs) are abundant enzymes in the venoms of viper snakes and responsible for most of the symptoms of envenoming. Their actions are related to the hydrolysis of extracellular matrix components, plasma proteins and hydrolysis or binding to cell surface proteins resulting in the activation or inhibition of their activity. In previous studies we recently found a diversity of SVMPs transcripts produced after stimulation of Bothrops neuwiedi venom gland. In this work, our aim was to characterize the different metalloproteinases in the Bothrops neuwiedi venom affecting hemostasis. Initially, the presence of distinct SVMPs in the venom was accessed by twodimensional electrophoresis and reverse phase chromatography. To obtain fractions enriched with SVMPs and characterize their functional activities, the venom was fractionated into molecular exclusion column, associated with anion exchange column and the resulting pools tested for enzymatic, hemorrhagic and fibrinolytic activities, blood clotting, reactivity with anti-SVMPs antibodies and mass spectrometry. This approach allowed the identification of six SVMPs, four class P-III and two class P-I. The SVMPs class P-III had gelatinolytic and hemorrhagic activities, of these, two had yet fibrinolytic activity. The two P-I were only fibrinolytic. Regarding coagulation activity, at least one P-III was characterized as prothrombin activator and one P-III as factor X activator. We conclude that there is a high variety of SVMPs in Bothrops neuwiedi snake venom, which disturb different hemostatic mechanisms and contribute to symptoms caused by this snake envenoming.

As metaloproteinases de venenos de serpentes (SVMPs) são enzimas abundantes em venenos de espécies da família Viperidae e responsáveis por grande parte dos sintomas do envenenamento. Sua ação está relacionada com a proteólise dos componentes da matriz extracelular, proteínas plasmáticas e também com hidrólise ou ligação a proteínas de superfície celular induzindo a ativação ou inibição da atividade das mesmas. Em estudos com serpentes do “Complexo Bothrops neuwiedi”, verificamos recentemente a diversidade dos transcritos de SVMPs produzidos após estímulo da glândula de veneno. Neste trabalho, o principal objetivo foi caracterizar as diferentes metaloproteinases presentes no veneno de Bothrops neuwiedi com ações na hemostasia. Inicialmente, confirmamos a presença de distintas SVMPs no veneno através de eletroforese bidimensional e cromatografia em coluna de fase reversa. Para a obtenção de frações enriquecidas com SVMPs e caracterização de suas atividades funcionais, o veneno foi fracionado em coluna de exclusão molecular, associado à coluna de troca aniônica e os pools resultantes testados quanto às atividades enzimática, hemorrágica, fibrinolítica, coagulante, reatividade com anticorpos anti-SVMPs e espectrometria de massas. Dessa forma, foi possível a identificação de seis pools contendo SVMPs, sendo quatro da classe P-III e dois da classe P-I. As SVMPs de classe P-III apresentaram atividades gelatinolítica e hemorrágica, destas, duas ainda apresentaram atividade fibrinolítica. As duas P-I foram apenas fibrinolíticas. Com relação à atividade coagulante, foram caracterizadas ao menos uma P-III ativadora de protrombina e uma P-III ativadora de fator X. Com isso concluímos que há grande variedade de SVMPs no veneno de Bothrops neuwiedi, as quais agem em diferentes mecanismos hemostáticos e contribuem para os sintomas causados nos envenenamentos por essa serpente.