Northwestern Venezuela Research Articles

A new species of Piaroa (Schizomida: Hubbardiidae) from Venezuela, with taxonomic notes on the genus.

A new species belonging to the schizomid genus Piaroa Villarreal, Giupponi and Tourinho, 2008 is described from north-western Venezuela. A complementary description of Piaroa guipongai Villarreal and Garcia, 2012 is provided including SEM pictures of relevant structures of both sexes. A key for males of Piaroa and Colombiazomus Armas and Delgado-Santa, 2012 is included. The presence of Dm3 setae on Hubbardiidae is discussed.

Re-establishment of Pithecellobium subglobosum in Colombia and Venezuela (Leguminosae, Mimosoideae, tribe Ingeae)

Pithecellobium subglobosum is re-established as a species and P. concinnum and P. larense are referred to its synonymy. A critical analysis of type specimens of Pithecellobium section Pithecellobium from the Neotropic as well as many other herbarium collections shows that P. subglobosum is a morphologically distinct species related to P. roseum. Pithecellobium subglobosum is found in northeastern Colombia and northwestern Venezuela. An amended description, including information on pollen, foliar anatomy, ecology, distribution and conservation assessment are included.

Palaeontological Evidence for the Last Temporal Occurrence of the Ancient Western Amazonian River Outflow into the Caribbean

Fossil catfishes from fluvio-lacustrine facies of late Miocene Urumaco, early Pliocene Castilletes and late Pliocene San Gregorio formations provide evidence of a hydrographic connection in what is today desert regions of northern Colombia and Venezuela. New discoveries and reevaluation of existing materials leads to the recognition of two new records of the pimelodid Brachyplatystoma cf. vaillantii, and of three distinct doradid taxa: Doraops sp., Rhinodoras sp., and an unidentified third form. The presence of fossil goliath long-whiskered catfishes and thorny catfishes are indicative of the persistence of a fluvial drainage system inflow into the South Caribbean during the Pliocene/Pleistocene boundary, complementary to the previous western Amazonian hydrographic system described from the Middle Miocene Villavieja Formation in central Colombia and Late Miocene Urumaco Formation in northwestern Venezuela. The Pliocene Castilletes and San Gregorio formations potentially represent the last lithostratigraphic units related with an ancient western Amazonian fish fauna and that drainage system in the Caribbean. Alternatively, it may preserve faunas from a smaller, peripheral river basin that was cut off earlier from the Amazon-Orinoco, today found in the Maracaibo basin and the Magdalena Rivers.

Timing of the last deglaciation in the Sierra Nevada of the Mérida Andes, Venezuela

In the tropical Mérida Andes (northwestern Venezuela), glacial landforms were found at altitudes between 2600 and 5000m, corresponding to 600km2 of ice cover during the maximum glacial extension. However, the lack of sufficient absolute age data prevents detailed reconstruction of the timing of the last deglaciation. On the northwestern flank of the Mucuñuque Massif, successive moraines and striated eroded basement surfaces were sampled for cosmogenic 10Be investigation. Their compilation with published data allows the establishment of a detailed chronology of the post-LGM glacier history. The oldest moraines (18.1 and 16.8ka) correspond to the Oldest Dryas. Successive moraine ridges indicate stops in the overall retreat between the LGM and the Younger Dryas. The cold and short Older Dryas stadial has been identified. Results indicate that most of the ice withdrew during the Pleistocene. The dataset supports an intensification of the vertical retreat rate from ~25m/ka during the late Pleistocene to ~310m/ka during the Pleistocene/Holocene. Afterwards, the glacier was confined and located in the higher altitude zones. The altitude difference of the Younger Dryas moraines in the Mucubají, La Victoria and Los Zerpa valleys indicates a strong effect of valley orientation on the altitude of moraine development.

Diet of the freshwater crab Bottiella niceforei (Schmitt & Pretzmann, 1968) (Decapoda: Trichodactylidae) and its relationship with organic matter processing in an intermittent stream of northwestern Venezuela

In order to study the role of the freshwater crab Bottiella niceforei in processing the organic matter in an intermittent stream of northwestern of Venezuela, we studied its natural diet by analyzing the gut contents during the period between June 2009 and February 2010. The abundance was determined based upon the proportion of individuals captured by traps throughout all the sampling period and on each pool. The highest crab densities occurred in September (2.7 ind trap-1), followed by June (2.3 ind trap-1) and July (2.1 ind trap-1); while the lowest were obtained in November and February, possibly due to the erosive effect of the current during the rainy season. No significant differences in the abundance and diet between pools were found. During the period from June to November it was found that the most abundant item in the crab diet was the plant detritus, with an average of 68%, followed by animal matter (fish remains), 50% on the average, and amorphous vegetal detritus with 14%. These results demonstrate the important participation of B. niceforei on the leaf litter processing in the pools of cano Carichuano.

Ariid sea catfishes from the coeval Pirabas (Northeastern Brazil), Cantaure, Castillo (Northwestern Venezuela), and Castilletes (North Colombia) formations (early Miocene), with description of three new species

Ariidae catfish are described from the early Miocene Pirabas Formation in northeastern Brazil, Cantaure and Castillo formations in northwestern Venezuela, and Castilletes Formation in North Colombia. A skull from the Pirabas Formation is described as Cathorops goeldii, n. sp. and an otolith is identified as Cathorops sp. The otoliths from Cantaure, Castillo and Castilletes formations are described as Cantarius nolfi n. sp. and Bagre protocaribbeanus n. sp. These coeval lithostratigraphic units reflect the Proto-Caribbean conditions and the shallow water tropical palaeoenvironment during the Miocene, particularly associated with marine coastal lagoon and estuarine influence.

Dietary variation in the crab Aratus pisonii (H. Milne Edwards, 1837) (Decapoda, Sesarmidae) in a mangrove gradient in northwestern Venezuela

In order to investigate if the variety of resources consumed by Aratus pisonii (H. Milne Edwards, 1837) changes along a structural mangrove gradient, the natural diet of this crab species was studied in five mangrove forests. Mangrove forests with different degrees of structural development (arboreal, arbustive, scrub) and located in different environments (estuarine, marine, hypersaline) on the northwest coast of Venezuela were considered, during the rainy and dry seasons. Rhizophora mangle Linnaeus, 1753 was the predominant mangrove species. The gut contents of 313 individuals were analysed, yielding a total of 12 prey categories. The diet of A. pisonii was based on mangrove fragments (leaves and bark). The index of relative importance (IRI) of mangrove fragments varied between 58% and 96%. Other items supplemented the diet: seagrass, algae, insects and crustaceans. The variety of resources consumed by A. pisonii was related to the mangrove structure and varied with the season. During the rainy period food diversity in the gut content increased, as mangrove heterogeneity and complexity increased, but during the dry season the trend was reversed. Aratus pisonii appears to enhance an opportunistic feeding behaviour when leaf quality decreases, which occurs during the dry season mainly in the hypersaline mangroves with less structural development (arbustive and scrub). During the drought the IRI of the items of animal origin increased in all the localities; this could be a response to the nutritional needs of the crabs during this season. In this work, we report the first documented egg consumption of its conspecifics, which supports the idea of cannibalistic behaviour associated mainly with crabs that live in the hypersaline and scrub mangrove with the lowest structural development and leaf quality.

Description of a new shrew of the genus Cryptotis (Mammalia: Soricomorpha: Soricidae) from the Sierra de Aroa, an isolated mountain range in northwestern Venezuela, with remarks on biogeography and conservation

Description of a new shrew of the genus Cryptotis (Mammalia: Soricomorpha: Soricidae) from the Sierra de Aroa, an isolated mountain range in northwestern Venezuela, with remarks on biogeography and conservation

Squamata reptiles of a fragment of tropical dry forest in northwestern Venezuela (Lake Maracaibo region)

We present a commented taxonomic list of the reptiles found during herpetological surveys carried out in an isolated fragment of tropical dry forest located in the municipality of San Francisco, Zulia state, northwestern Venezuela between January-December 2011. We report a total of 24 species belonging to the order Squamata, distributed in 12 families and 21 genera. Colubridae is the most diverse family with six species, followed by Dipsadidae (four species), Boidae, Gymnophthalmidae, Phyllodactylidae and Teiidae with two species each, and finally Dactyloidae, Iguanidae, Elapidae, Gekkonidae, Sphaerodactylidae and Viperidae with a single species each. The species composition at this site matches what would be expected in a tropical dry forest in the region. Our study suggests that this isolated tropical dry forest fragment is the last refuge of the herpetofauna that once occupied much of the dry forests of the northern Maracaibo basin and should therefore be considered for conservation purposes.

Description of a new shrew of the genus Cryptotis (Mammalia: Soricomorpha: Soricidae) from the Sierra de Aroa, an isolated mountain range in northwestern Venezuela, with remarks on biogeography and conservation

In South America, shrews of the genus Cryptotis have a primarily Andean distribution. Based on specimens from the non-Andean Sierra de Aroa in Venezuela, we name Cryptotis aroensis sp. nov., which we assign to the C. thomasi group of thegenus owing to its possession of characters that include a relatively large body size, luxuriant fur, moderately enlargedforefeet with elongated and narrow claws, unicuspid teeth relatively narrow and concave on the posteroventral margin,ectoloph of first upper molar with the anterior element reduced relatively to the posterior element, and mandible with thearticular process not robust, high, and broad, and with the coronoid process joining the ramus at a low angle. The newspecies can be differentiated from other members of the C. thomasi group on the basis of its possession of a uniquecombination of characters, that include a rich grayish brown pelage, a narrow palate at the level of the second upper molars(no overlap in this measurement observed with 146 specimens of 10 other species of the group), nasal cavity and ethmo-turbinals partially visible in occlusal view of palate, lacrimal foramina wide and deep, tympanic process of petromastoidsshowing a minute foramen, unicuspid teeth with posterolingual cuspules, fourth unicuspid tooth labially placed, thirdupper molar complex and nearly as wide as the second upper molar, and bicuspulate lower incisors. The new species isknown from only 3 specimens obtained at the type locality, which is in a pristine patch of cloud forest at elevation 1730m, and represents the first mammalian taxon known to be endemic to the Sierra de Aroa, a small and isolated mountainrange that was previously reported to possess numerous biotic elements that are either exclusive, or shared with the muchlarger Cordillera de la Costa to the east. The clear morphological differentiation of the new species with respect to itsAndean relatives suggests that its ancestors colonized the Sierra de Aroa several glacial maxima ago, when montanevegetation belts were lower than today. The presumably optimal habitat of the new species (cloud forests of the Sierra deAroa above 1500 m) covers less than 40 km2 , and is threatened by deforestation and global climate change. Therefore, thenew species can be categorized as endangered by application of criteria B2a and E of the current “Red List Categories and Criteria” of the International Union for Conservation of Nature.

New records and distribution extensions of centrolenid frogs for Venezuela

We report the first record of Centrolene notostictum for Venezuela, the first records of Centrolene venezuelense and Hyalinobatrachium pallidum for Zulia state, and extend the distribution of Hyalinobatrachium tatayoi and Espadarana andina based on specimens coming from the eastern versant of the Sierra de Perijá in northwestern Venezuela. The altitudinal ranges of all species are extended, and comments and notes on natural history provided.

Chemical Composition of the Substances from Dorsal Patches of Males of the CuraÇAoan Long-Nosed Bat,Leptonycteris curasoae(Phyllostomidae: Glossophaginae)

In the absence of visual cues, chemical signals are especially important for nocturnal mammals such as bats, because they facilitate individual recognition, communication, and mate selection. In a recent study, it was reported that adult males of the Curaçaoan long-nosed bat, Leptonycteris curasoae, develop an odoriferous dorsal patch during the short mating season. It was postulated that dorsal patches signal health condition to females, and that females are preferentially attracted to the odor of males with dorsal patches. The chemical characterization of the dorsal patch is key to understanding its implications in chemical communication in a sexual context. In the present study, organic compounds collected from dorsal patches of males of L. curasoae from northwestern Venezuela were extracted using solid-phase micro-extraction (SPME) techniques and tentatively identified using GC-MS (Gas Chromatography-Mass Spectrometry). Nineteen compounds were present in 75% or more of the patches examined: 3-methyl-2-buten-1-thiol, acetic acid, 2′-aminoacetophenone, diacetyl, 2-pentanone, 2,3-dimethylpyrazine, 2-nonanone, acetamide, 2-undecanone, piperidinone, 4-methylquinazoline, 2,4-dimethylquinazoline, 3-methyl-2,5-pyrrolidinedione, 2-butanone, 2-methylfuran, 3-methyl-2-butenal, δ-valerolactone, 3-methyl-2-butenoic acid, and 2-methyl-2-butenoic acid. Although some of these compounds have been reported as important in female attraction among other male mammals during their respective breeding seasons, the actual function of these chemicals in L. curasoae remains to be determined. Some of these compounds have also been identified as natural insecticides, and this may be associated with lower ectoparasite loads reported on males with dorsal patches. These results, when considered along with previous observations, suggest that the dorsal patch in males of L. curasoae promotes the attraction of females during the mating season, and/or provides protection against ectoparasites.

Aspistor verumquadriscutis, a new fossil species of sea catfishes (Siluriformes; Ariidae) from the upper Miocene of Venezuela

The Late Miocene Urumaco Formation, Northwestern Venezuela, one of the most fossiliferous units in the Neogene of tropical America, represents a shallow, marginal marine to deltaic wetland and fluvial system. A new extinct species of sea catfishes is described from the Urumaco Formation. Aspistor verumquadriscutis n. sp. is placed in the genera Aspistor based on five synapomorphies shared with modern congeners: epioccipital dorsally exposed, parieto-supraoccipital posterior margin convex, nuchal plates forming a large butterfly-shaped or moon-shaped structure, anterior margin of nuchal plate slightly concave, and nuchal plate overlapping parieto-supraoccipital. The new fossil species is distinguished from its modern congeners by having a shorter parieto-supraoccipital process, and a larger and longer nuchal plate, nuchal plate length 0.9–1.0 in parieto-supraoccipital process length (vs. 1.1–1.7 in A. luniscutis), and nuchal-plate width at medial area 0.9–1.0 in parieto-supraoccipital process length (vs. 1.1–1.5 in A. luniscutis); nuchal plate granulose over its entire surface (vs. with half lateral surface smooth in A. quadriscutis), nuchal plate subquadrangular shaped, almost as long as wide (vs. nuchal plate subtrapezoidal or butterfly shaped, anterior portion always narrower than the posterior portion in A. quadriscutis), and lateral margin of the nuchal plate straight (vs. with a constriction at the medial portion in A. quadriscutis).

Caracterización geomorfológica de las dunas longitudinales del Istmo de Médanos, estado Falcón, Venezuela

El trabajo analiza la geomorfología de dunas costeras longitudinales del Istmo de Médanos, costa noroccidental de Venezuela. La metodología consistió en consultas bibliográficas, cartográficas, fotogramétricas y satelitales, trabajos de campo y análisis sedimentológico. Los resultados indican que estas dunas están compuestas por arenas de grano fino en un 84.6%, muy bien seleccionadas en más del 60%, principalmente subangulares, con asimetría negativa predominante, distribución leptocurtica, y bajo contenido de carbonato de calcio cercano al 10%. Los datos sugieren que los sedimentos son de origen terrígeno y escasa distancia de transporte hasta el lugar de acumulación. Los vientos predominantes actuales son del noreste, con componentes direccionales secundarios que retrabajan los sedimentos generando dunas transversales, barcanas y longitudinales; las dunas longitudinales son paralelas a la dirección del viento y se presentan colonizadas por vegetación xerofítica favorecida por la inactividad de las mismas. Estas dunas se originaron probablemente por una conjunción de factores como: disponibilidad de sedimentos en una amplia llanura costera relacionada con un nivel marino regresivo, vientos fuertes y persistentes, orientación oblicua de la costa respecto a la dirección del viento, una topografía continental favorable adyacente a la playa, bajo condiciones climáticas distintas a las actuales.

Taxonomic revision of the geckos of the Gonatodes concinnatus complex (Squamata: Sphaerodactylidae), with description of two new species

The Gonatodes concinnatus complex, as here considered, consists of Gonatodes species characterized by a white suprahumeral spot with black margins; vermiculations or not on back; and transversely enlarged scales under the tail, showing the sequence 1’1’1”, and in some specimens 1’1’2” on the anterior portion. Two species are presently recognized in this Amazonian complex: G. concinnatus and G. tapajonicus. New material collected in eastern Amazonia (states of Pará and Amapá, Brazil) made it necessary to review these species. We analyzed several populations within this complex, from Colombia, Ecuador, Peru, Venezuela and Brazil, including these new records. Specimens were separated in groups defined on basis of color pattern. Stepwise discriminant function analyses were then performed to compare the external morphology (measurements and scale counts) in these groups. Results support recognition of five taxa, corresponding to G. concinnatus from western Amazonia, in Ecuador and northern Peru; G. ligiae from northwestern Venezuela (east of the Andes); G. tapajonicus, from the Tapajós river basin, in Pará, Brazil; and two new species, one from eastern Amazonia, in the states of Pará (north and south of the Amazon river) and Amapá, Brazil, and another from central Colombia, east of the Andes. Diagnoses and descriptions of all species are presented.

Mantle flow beneath northwestern Venezuela: Seismic evidence for a deep origin of the Mérida Andes

We measured shear wave splitting from SKS data recorded by the national seismic network of Venezuela and a linear broadband PASSCAL/Rice seismic array across the Mérida Andes. The linear array was installed in the second phase of the passive seismic component of the BOLIVAR project to better understand the complicated regional tectonics in western Venezuela. Using the method proposed by Wolfe and Silver (1998), SKS waveforms from 2 to 36 earthquakes, mostly from the Tonga subduction zone, were selected for each of the 23 stations in the region in order to do splitting analysis. The fast polarization directions can be divided into 3 zones, all in agreement with local GPS data: The first zone comprises the stations north of the dextral strike–slip Oca–Ancon fault. These stations show the largest split times (1.6–3.2s), oriented in a roughly EW direction, and are similar to splitting observations made further to the east along the strike slip plate boundary (Growdon et al., 2009). We attribute this to trench-parallel mantle flow that passes around the northwest corner of the subducting Caribbean plate and along the northern edge of South America as proposed by Russo and Silver (1994), forming an eastward flow beneath the southern Caribbean plate. Zone two is the Mérida Andes, with the right lateral Bocono fault in the center, where split orientations are at ~N45°E, suggesting that the observed seismic anisotropy is likely caused by lithospheric deformation parallel to the Bocono fault. Zone three is east of the Bocono fault inside the Barinas–Apure Basin, where the measured split times are smaller (~0.8s) with an EW fast direction that is consistent with those observed at the Guarico Basin, Maturin Basin and the Guayana Shield in the east, and are interpreted as orientation with the motion of the continent.

Population Genetics of Agave cocui: Evidence for Low Genetic Diversity at the Southern Geographic Limit of Genus Agave

The Agave genus embraces many species with outstanding ecological and economic importance in the arid regions of the Americas. Even though this genus covers a broad geographic distribution, our knowledge on the population genetics of species is concentrated in taxa located in North America. Recently, it has been demonstrated that plant domestication decreases levels of genetic diversity in managed populations and increases population structure with respect to wild populations. We examined levels of allozyme diversity (N = 17 loci) and population structure of Agave cocui, the species at the southern limit of distribution of the genus. We sampled 7 wild populations (N = 30-35 individuals per population) representative of the geographic distribution of the species in Venezuela. Among the agaves studied, A. cocui has some of the lowest estimates of genetic diversity (H(e)[species] = 0.059, H(e)[population] = 0.054) reported until present. We propose that this condition is probably linked to the recent origin of this species in arid and semiarid regions of Colombia and Venezuela, probably through one or a few founder events. The lowest estimates of genetic diversity were associated with small populations in very restricted arid patches; but also with overexploitation of rosettes for production of fermented drinks and fibers. Santa Cruz de Pecaya, one of the 2 centers of economic use of agaves in northwestern Venezuela presented one of the lowest values of genetic variability, a sign suggesting that human impact represents a significant threat to the available genetic pool that this species possesses in the region.

A new species of Hydroscapha LeConte from northwestern Venezuela (Coleoptera: Myxophaga: Hydroscaphidae)

A new species of Hydroscapha LeConte from northwestern Venezuela (Coleoptera: Myxophaga: Hydroscaphidae)

Evidence for a cosmogenic origin of fired glaciofluvial beds in the northwestern Andes: Correlation with experimentally heated quartz and feldspar

Fired sediment, considered equivalent to the ‘Black Mat’ impact of 12.9 ka, has been located and analyzed in the Andes of northwestern Venezuela. The ‘Black Mat’ refers to possible fallout from the Encke Comet airburst presumed to have occurred over the Laurentide Ice Sheet, the impact spreading ejecta over large portions of North America and Europe, making it an interhemispheric event of considerable magnitude. These possible equivalent beds in the northern Andes, first considered to result from a lightning-induced conflagration adjacent to the retreating Late Wisconsinan (Mérida Glaciation) ice, are now known to have undergone intense heating upon impact to a temperature much higher than what would occur in a wet, first-stage, successional tundra. Analyses carried out by SEM and FESEM, in SE and BSE modes, show massive micro-disruption on grain surfaces, fractures diminishing with depth toward grain interiors and C welded onto quartz and plagioclase minerals. Bubbles on some grains, possibly the result of exclusion of water-of-crystallization, are seen on some samples, principally quartz. The presence of copious monazite in the carbonaceous coatings is considered part of the incoming ejecta, as it is not a common indicator mineral in the local lithology. Analysis by SEM and FESEM of quartz and plagioclase subjected experimentally to temperatures ranging from 500 to 900 °C shows that intense heating affects resident mineralogies to differing extents, with grain disruption more prevalent along cleavage planes deep into grain interiors. The intergrowth of carbonaceous “black mat” material with thermally disrupted and fragmented quartz and feldspar, a “welded” patina of 100–400 nm thickness could only occur with temperatures in excess of 900 °C, the event interpreted here to be of cosmogenic origin.

Changes Associated with Field-Scale Demonstration in a Steam-Stimulated Crude Oil from the Lagunillas Oilfield (Lake Maracaibo, Venezuela)

Cyclic steam injection with alkali is currently very commonly used to improve heavy-crude oil production in Venezuela. This work is an analysis of oil-associated water and crude samples from LL-2670 well in the Lagunillas oilfield at Lake Maracaibo (northwestern Venezuela). The aim of this research is to analyze the organic acids thus generated and evaluate chemistry changes in the saturated and aromatic fractions of crude oil during the first cycle of steam stimulation by cyclic injection with alkali. It was noted that the percentages of sulfur and saturates, aromatics, resins, and asphaltenes (SARA) and the American Petroleum Institute (API) gravity varied little in the analyzed crude. In contrast, there were significant variations in the biomarker distribution, particularly in the mono- and triaromatic steranes, benzothiophenes, phenanthrenes, and alkyl-naphthalenes of the crude.