Sierra Madre Occidental Research Articles

Chusquea septentrionalis sp. nov. (Poaceae: Bambusoideae) from the Madrean region in Durango, Mexico

Chusquea is a monophyletic genus divided into five subgenera. Chusquea subg. Swallenochloa is recognized based on the combination of a more or less shrubby and clumping habit, often relatively short internodes, and the usual presence of intravaginal branching. It is distributed from Mexico to Chile, with species also in the mountains of eastern and southeastern Brazil, commonly occupying high elevation grasslands, although a few species inhabit montane forests. Based on the review of herbarium specimens and fieldtrips to the Sierra Madre Occidental in the state of Durango, Mexico, we here describe and illustrate Chusquea septentrionalis, the newest species to be classified within subgen. Swallenochloa. This novelty is compared with the rare, high elevation Mexican endemics C. matlatzinca and C. perotensis, from which it can be separated by its thick‐walled, hollow culms, intravaginal branching pattern, central bud slightly larger than the subsidiary buds, subsidiary buds axillary and arranged linearly, and the long inner ligule of the foliage leaves. Chusquea septentrionalis is referred to Chusquea subgen. Swallenochloa sect. Swallenochloa, because of the morphological characters that it shares with the rest of the species in this section, especially the branching pattern. With the description of this new species, the diversity of native Chusquea and woody bamboos overall in Mexico increases to 22 and 52 species, respectively. Due to the reduced distribution of this new species, we propose to include it in the Norma Oficial Mexicana (NOM‐059‐SEMARNAT‐2010) and IUCN red list for its protection. A morphological key to the species of C. sect. Swallenochloa known from Mexico is provided.

One black bear (Ursus americanus) connects the great sierras: Genetic evidence

The black bear has inhabited North America for three million years. Two clades diverged during this period: coastal and continental; the continental clade includes two subclasses (western and eastern). The contact between both is a recent event. Because there is a high genetic differentiation between subclasses, the genetic flow of populations between Sierra Madre Oriental and Sierra Madre Occidental is considered as restricted to nonexistent; also, desert environments and human settlements act as a barrier. There are no recent records of black bears in Durango, so the capture of an individual from there presents the opportunity to test whether there is a possible connection between the populations of Sierra Madre Occidental and Sierra Madre Oriental. Our objective was to determine the geographic origin of this individual and validate whether there is a likely connection between populations from both mountain ranges. A black bear specimen was captured in Felipe Carrillo Puerto, municipality of Guadalupe Victoria, Durango. This specimen was sedated. Tissue samples from ear, hair and excrement were collected; samples of mtDNA were extracted and amplified, and two 418-bp sequences were obtained. The haplotype was characterized by a neutrality test of the control region. To determine the origin of the specimen, GenBank was searched for matches with haplotypes previously described and geographically characterized. Six 418-bp sequences were successfully amplified. The neutrality test yielded a single haplotype, with a 99.32 % agreement with haplotype C. Haplotype C has been previously described for the Trans-Pecos region in Texas; accordingly, this haplotype belongs to the eastern subclade. The origin of the black bear specimen captured was Sierra Madre Oriental, based on the presence of haplotype C. This bear traveled at least 250 km to reach the municipality of Guadalupe Victoria. This displacement event indicates that connectivity between black bear populations from both Sierras Madres has been maintained. This distance is similar to displacements previously reported in fragmented environments where a suitable habitat is surrounded by arid zones. However, this displacement took place between two large mountain ranges, rather than within a single mountain range. Genetic diversity, frequency of displacement events between the Sierras, time and distance between displacements, dispersal routes and presence of patches of suitable habitat, are all factors that should be evaluated in order to understand the current dispersal and genetic-flow patterns between the subspecies of bears in Mexico.

The Current Status of the Distribution Range of the Western Pine Beetle, Dendroctonus brevicomis (Curculionidae: Solytinae) in Northern Mexico.

The distribution range of the western pine beetle Dendroctonus brevicomis LeConte (Coleoptera: Curculionidae) is supported only by scattered records in the northern parts of Mexico, suggesting that its populations may be marginal and rare in this region. In this study, we review the geographical distribution of D. brevicomis in northern Mexico and perform a geometric morphometric analysis of seminal rod shape to evaluate its reliability for identifying this species with respect to other members of the Dendroctonus frontalis Zimmermann (Coleoptera: Curculionidae) complex. Our results provide 30 new records, with 26 distributed in the Sierra Madre Occidental and 4 in the Sierra Madre Oriental. These records extend the known distribution range of D. brevicomis to Durango and Tamaulipas states in northern Mexico. Furthermore, we find high geographic variation in size and shape of the seminal rod, with conspicous differences among individuals from different geographical regions, namely west and east of the Great Basin and between mountain systems in Mexico.

The Role of Climatic Variables for Estimating Probability of Abundance of Tree Species

ABSTRACT We analyzed the influence of climatic variables on the abundance of native tree species in 1,490 sampling plots systematically distributed in the Sierra Madre Occidental (state of Durango, Northwestern Mexico, 26°50′ and 22°17′N and 107°09′ and 102°30′W). We used the Weibull distribution and the finite Gaussian mixture model to study the climatic limits of 15 tree species in relation to seven variables thought to affect species abundance. We found that although they may occur in the same geographical region, some species display a wider range of ecological tolerance than others. Of the 15 species under study, only two (Quercus magnoliifolia and Q. arizonica) can be considered generalists in relation to some climatic variables, while the other 13 species behaved as specialists, implying a narrower range of distribution. The analytical techniques used enabled us to demarcate the zones in which the probability of abundance of each species is highest in relation to the climate variables considered. T...

Clinical benefits of neoadjuvant chemoradiotherapy for borderline resectable pancreatic head adenocarcinoma: An observational study using inverse probability of treatment weighting

We present a multiproxy record from magnetic susceptibility, loss on ignition and chemical analysis of a sediment core collected from “Ciénega Las Taunas”, a peatland in the northwest of the Sierra Madre Occidental in Mexico. The oldest sediments were dated to 12,850 cal yr BP. The relatively cool and wet Younger Dryas (YD) shows higher concentrations of TiO2 and Chemical Index of Alteration (CIA), suggesting higher runoff into the cienega. The transition from the YD to the early Holocene is marked by a decrease in susceptibility, pointing to weakened erosional processes during a period of closed forest vegetation, suggesting a predominantly winter rainfall regime. A change in seasonality likely occurred after ca. 9200 cal yr BP, as shown by: 1) an increase in most major elements, suggesting increased dust fallout from distant sources, and 2) more pollen assemblages from temperate vegetation (pine-oak forest). We related these changes to increased summer rains and monsoons in NW Mexico. A possible hiatus or a very slow sedimentation period occurred during the middle Holocene at this site. Finally, high-frequency changes in sediment properties were especially observed in the Late Holocene, suggesting contrasting sediment inputs controlled by an unstable water table and/or related to ENSO.

Strong genetic structure and signs of population bottlenecks in the land snailHumboldtiana durangoensisin the Sierra Madre Occidental of Western Mexico

Phylogeographic studies of different montane biological groups in Mexico have revealed complex patterns in a broad scale but an absence of genetic structure within local mountain systems such as the Sierra Madre Occidental. In this study, we estimate the genetic structure and demographic history of the endemic land snail Humboldtiana durangoensis within this mountain range. Nine polymorphic microsatellite loci in 178 individuals from 16 localities throughout the complete geographic distribution were analyzed. Strong deviations from Hardy–Weinberg equilibrium and low levels of heterozygosity were detected in the seven genetic clusters. The gene flow between two of the main geographic regions (North and South) was symmetric (≈4 individuals). In addition, the analysis detected changes in the effective population size indicating that both geographic regions experienced a drastic reduction in their effective population size probably associated with the Pleistocene climatic changes.

Mexican biogeographic provinces: Map and shapefiles.

We provide a map of the 14 biogeographic provinces of Mexico based on the ecoregions recognized for the country, which combine climatic, geological and biotic criteria. These provinces belong to the Nearctic region (Californian, Baja Californian, Sonoran, Chihuahuan Desert and Tamaulipas provinces), Neotropical region (Pacific Lowlands, Balsas Basin, Veracruzan and Yucatán Peninsula provinces) and the Mexican transition zone (Sierra Madre Occidental, Sierra Madre Oriental, Transmexican Volcanic Belt, Sierra Madre del Sur and Chiapas Highlands provinces). In order to facilitate future biogeographic analyses, we provide a file of the biogeographical regionalisation of Mexico by converting the map into a polygon shapefile and a raster file with all provinces. We also separately provide each of the provinces in vector and raster format. All the maps are in geographical and Lambert Conformal Conic projections.

Lithosphere thickness in the Gulf of California region

The Gulf of California has a long tectonic history. Before the subduction of the Guadalupe and Magdalena plates ceased, extension of the Gulf began to the east, at the Basin and Range province. Later, it was focused west of the Sierra Madre Occidental and the opening of the Gulf started. Currently, the Gulf rifting has different characteristics to the north than to the south. In this study, we analyze the lithosphere thickness in the Gulf of California region by means of P-wave and S-wave receiver functions. We grouped our lithosphere-thickness estimates into five froups: 1) North of the Gulf, with a thin lithosphere (~50km) related to the extension observed in the Salton Through region; 2) the northwestern part of Baja California, with a thicker lithosphere (~80km), thinning towards the Gulf due to the extension and opening processes (~65km); 3) central Baja California, with no converted phase corresponding to the lithosphere-asthenosphere boundary but evidence of the presence of a slab remnant; 4) the southern Baja California peninsula, showing a shallow lithosphere-astenosphere boundary (LAB) (<55km) and a lithosphere thinning towards the Gulf; and 5) the eastern Gulf margin with lithosphere thinning towards the south. These groups can be further assembled into three regions: A) The northernmost Gulf, where both margins of the Gulf show a relatively constant lithosphere thickness, consistent with an old basement in Sonora and the presence of the Peninsular Ranges batholith in northern Baja California, thinning up towards the axis of the rift in the northernmost Gulf. B) Central and southern Gulf, where the lithosphere thickness in this region ranges from 40 to 55km, which is consistent with the presence of a younger crust. C) Central Baja California peninsula, where LAB is not detected; but there is evidence of a slab remnant.

Discrimination of Picea chihuahuana Martinez populations on the basis of climatic, edaphic, dendrometric, genetic and population traits.

BackgroundPicea chihuahuana, which is endemic to Mexico, is currently listed as “Endangered” on the Red List. Chihuahua spruce is only found in the Sierra Madre Occidental (SMO), Mexico. About 42,600 individuals are distributed in forty populations. These populations are fragmented and can be classified into three geographically distinct clusters in the SMO. The total area covered by P. chihuahuana populations is less than 300 ha. A recent study suggested assisted migration as an alternative to the ex situ conservation of P. chihuahuana, taking into consideration the genetic structure and diversity of the populations and the predictions regarding the future climate of the habitat. However, detailed background information is required to enable development of plans for protecting and conserving species and for successful assisted migration. Thus, it is important to identify differences between populations in relation to environmental conditions. The genetic diversity of populations, which affect vigor, evolution and adaptability of the species, must also be considered. In this study, we examined 14 populations of P. chihuahuana, with the overall aim of discriminating the populations and form clusters of this species.MethodsEach population was represented by one 50 × 50 m plot established in the center of its respective location. Climate, soil, dasometric, density variables and genetic and species diversities were assessed in these plots for further analyses. The putatively neutral and adaptive AFLP markers were used to calculate genetic diversity. Affinity Propagation (AP) clustering technique and k-means clustering algorithm were used to classify the populations in the optimal number of clusters. Later stepwise binomial logistic regression was applied to test for significant differences in variables of the southern and northern P. chihuahuana populations. Spearman’s correlation test was used to analyze the relationships among all variables studied.ResultsThe binomial logistic regression analysis revealed that seven climate variables, the geographical longitude and sand proportion in the soil separated the southern from northern populations. The northern populations grow in more arid and continental conditions and on soils with lower sand proportion. The mean genetic diversity using all AFLP studied of P. chihuahuana was significantly correlated with the mean temperature in the warmest month, where warmer temperatures are associated to larger genetic diversity. Genetic diversity of P. chihuahuana calculated with putatively adaptive AFLP was not statistically significantly correlated with any environmental factor.DiscussionFuture reforestation programs should take into account that at least two different groups (the northern and southern cluster) of P. chihuahuana exist, as local adaptation takes place because of different environmental conditions.

Potential distribution of endangered Mexican golden trout (Oncorhynchus chrysogaster) in the Rio Sinaloa and Rio Culiacan basins (Sierra Madre Occidental) based on landscape characterization and species distribution models

The Mexican Golden Trout (Oncorhynchus chrysogaster) is a threatened native species inhabiting three river basins in the Sierra Madre Occidental. Despite some efforts from science groups to obtain information about this trout, the Rio Sinaloa and Rio Culiacan basins, to the south, remain the least studied area, compared to the Rio Fuerte basin. To overcome this gap, a survey (2014 to 2015) was undertaken to obtain new records and confirm the presence for historic records in both watersheds. After filtering records for this species, eighteen locations were used to model potential distribution, using the GARP and MaxEnt, including landscape characterization based on hydrologic analysis and satellite imagery classification. Coincidence between models was >85% for a potential distribution area of 4300 km2, defined by six bioclimatic and physiographic variables, with the hydrologic network covering 3000 km. To avoid overestimation, the final distribution area included only the 100 m fringe surrounding the drainage network and its associated landscape features. Jackknife resampling was used to validate both the models, successfully predicting more than 80% of the locations (p 2000 m, high water quality (transparent, dissolved oxygen >5 mg L-1; temperature < 26 °C), and was part of a matrix of undisturbed forests. This study provides new findings about this endangered species and new elements for designing appropriate monitoring programs supporting trout conservation and management.

Abundancia y densidad de jaguar (panthera onca) en el apff meseta de Cacaxtla, Sinaloa, México

Existe poca información acerca de las poblaciones del jaguar en Sinaloa, México, ya que sólo se cuenta con registros anecdóticos y entrevistas acerca de la presencia de este félido. El objetivo de este estudio fue generar información acerca de la abundancia y densidad del jaguar en el área natural protegida Meseta de Cacaxtla. Para detectar al jaguar se usaron trampas cámara. La densidad obtenida fue de 1.59 ind./100 km2 y 15 jaguares para el área natural protegida. Consideramos que el área natural protegida es una región importante para las poblaciones del jaguar de la Sierra Madre Occidental, ya que esta área puede representar un eslabón entre Sahuaripa y la costa de Jalisco.

Tectono-stratigraphic evolution of the Comondú Group from Bahía de La Paz to Loreto, Baja California Sur, Mexico

The late Oligocene to mid-Miocene volcanic and volcaniclastic rocks of the Comondú Group are well exposed along the Main Rift Escarpment of Baja California Sur from the Bahía de La Paz region to Bahía Concepción. New mapping and stratigraphic analysis of the Comondú Group from Bahía de La Paz to Loreto reveal facies trends and correlations that form the foundation for a continuous stratigraphic framework for the Comondú Group along a 300km-long transect on the eastern coast of the Baja California peninsula. Broad but distinct lithostratigraphic trends, alluvial fan facies, and volcanic and volcaniclastic facies record an overall coarsening-upwards package that includes ignimbrite deposits within increasingly proximal alluvial fan deposits, both derived from the east. Geochronology of the unit, including 32 isotope ages and 12 previously unpublished 40Ar/39Ar ages, provide the timing of four main increasingly proximal depositional events. Non-marine sandstone, defining the base of the Comondú Group, was first deposited between ~26Ma and ~24Ma. Emplacement of rhyolitic ignimbrites initiated between ~24Ma and ~23Ma and marked a westward expansion of volcanic activity affiliated with the Sierra Madre Occidental ignimbrite sequences in southern Sinaloa, western Durango, and northern Nayarit. A change in volcanism occurred at ~19Ma to ~18Ma with more ignimbrites, increased intermediate compositions, and the appearance of local vents and proximal volcanic facies. A final localized change of volcanism occurred from ~14 to ~12Ma in the Loreto area with an increase of proximal alluvial fan deposits and local volcanoes in the Upper Comondú Group. The bulk of the Upper Comondú Group is absent south of the Loreto area and has either been removed by erosion as a source for the Magdalena Fan in the Pacific Ocean, or was focused primarily in the Loreto area and northward. We use a pre-rift tectonic reconstruction of the Gulf of California to align broad stratigraphic trends along the peninsula, the Gulf conjugate margins, and within the Gulf. The Cascadia arc of Oregon and northern California may be a modern analog for the Comondú Group with a linear volcanic arc formed above shrinking subducting microplates, and a broad backarc region of moderate extension and scattered volcanism.

The bird species diversity in the wintering season is negatively associated with precipitation, tree species diversity and stand density in the Sierra Madre Occidental, Durango, Mexico

Bird migration constitutes a redistribution of bird diversity that radically changes the composition of the bird community worldwide. It comprises about 19% of the world’s bird species. Several studies have indicated that changes in avian community structure and differences in bird richness in different seasons are mainly driven by seasonality and by winter harshness, and that the associated costs increase with the distance involved. Western Mexico is an important wintering area for most passerines that breed in western North America, and that travel long on the long-distance Central and Pacific migration routes. In this study, we examined bird species richness and diversity during the breeding and wintering seasons in the Central Sierra Madre Occidental (SMO), North Durango (Mexico) in relation to i) tree species diversity, ii) tree dimension, iii) forest stand density and site quality, iv) density and dimension of snag trees, and v) various climate variables. The overall aim of the study was to determine how the observed associations between bird species diversity and variables i-v are affected by the season considered (breeding or wintering). The diversity of bird species in the breeding season was not affected by any of the climate and forest stand variables considered. In contrast, bird species diversity in the wintering season was significantly and weakly to moderately associated with climate variables, tree species diversity and stand density, although not with density or dimension of snag trees. Bird species diversity was higher at lower elevations and in drier and warmer locations of the SMO. The association detected is therefore mainly a local migratory phenomenon.

Laramide to Miocene syn-extensional plutonism in the Puerta del Sol area, central Sonora, Mexico

Plutonic rocks of the Puerta del Sol area, in central Sonora, represent the extension to the south of the El Jaralito batholith, and are part of the footwall of the Sierra Mazatán metamorphic core complex, whose low-angle detachment fault bounds the outcrops of plutonic rocks to the west. Plutons in the area record the magmatic evolution of the Laramide arc and the Oligo-Miocene syn-extensional plutonism in Sonora. The basement of the area is composed by the ca. 1.68 Ga El Palofierral orthogneiss that is part of the Caborca block. The Laramide plutons include the El Gato diorite (71.29 ± 0.45 Ma, U-Pb), the El Pajarito granite (67.9 ± 0.43 Ma, U-Pb), and the Puerta del Sol granodiorite (49.1 ± 0.46 Ma, U-Pb). The younger El Oquimonis granite (41.78 ± 0.32 Ma, U-Pb) is considered part of the scarce magmatism that in Sonora records a transition to the Sierra Madre Occidental magmatic event. The syn-extensional plutons are the El Garambullo gabbro (19.83 ± 0.18 Ma, U-Pb) and the Las Mayitas granodiorite (19.2 ± 1.2 Ma, K-Ar). A migmatitic event that affected the El Palofierral orthogneiss, El Gato diorite, and El Pajarito granite between ca. 68 and 59 Ma might be related to the emplacement of the El Pajarito granite. The plutons are metaluminous to slightly peraluminous, with the exception of El Oquimonis granite, which is a peraluminous two-mica, garnet-bearing granite. They are mostly high-K calc-alkaline with nearly uniform chondrite-normalized REE and primitive-mantle normalized multielemental patterns that are characteristic of continental margin arcs and resemble patterns reported for other Laramide granites of Sonora. The Laramide and syn-extensional plutons also have Sr, Nd and Pb isotopic ratios that plot within the fields reported for Laramide granites emplaced in the Caborca terrane in northwestern and central Sonora. Nevertheless, and despite their geochemical affinity to continental magmatic arcs, the El Garambullo gabbro and Las Mayitas granodiorite are syn-extensional plutons that were emplaced at ca. 20 Ma during development of the Sierra Mazatán metamorphic core complex. The 40Ar/39Ar and K-Ar ages obtained for the El Palofierral orthogneiss, the Puerta del Sol granodiorite, the El Oquimonis granite, and the El Garambullo gabbro range from 26.3 ± 0.6 to 17.4 ± 1.0 Ma and are considered cooling ages associated with the exhumation of the metamorphic core complex.

The morphological phylogeny of the family Protoschizomidae revisited (Arachnida: Schizomida): setal characters, fossil and paraphyletic genera

Abstract The schizomid family Protoschizomidae, endemic to North America, is represented by two genera and 15 species. While most of the species are distributed in caves in the Sierra Madre Oriental system in Mexico; other species are found in caves in the Sierra Madre Occidental system. Recently, a new species of this family was described from a cave in the Mexican Trans-Volcanic Belt, representing the linking bridge between both Sierras. In the present contribution, we propose a new nomenclature of the pedipalp setae of the protoschizomids. We revise the phylogenetic status of Protoschizomidae using 137 morphological characters (including the proposed pedipalp setae) and 7 outgroup taxa using parsimony criteria. Based on our results, Protoschizomidae was recovered as monophyletic, but the monophyly of Protoschizomus Rowland, 1975 was not recovered because of the inclusion of Agastoschizomus Rowland, 1971 and the fossil Onychothelphynous bonneri Pierce, 1951. Therefore, we transfer the genus Onychothelyp...

Clarifying historical range to aid recovery of the Mexican wolf

ABSTRACTWe assessed historical, morphological, and genetic information on the range of the Mexican wolf (Canis lupus baileyi) to plan the recovery of this endangered subspecies. Early accounts of its range included the Sierra Madre Occidental, Mexico, and southeastern Arizona, southwestern New Mexico, and sometimes western Texas, USA. Such accounts are supported by ecological, physiographic, and morphological data. Recent suggestions to depict a more extensive northern periphery have been based primarily on a fragmented geographic sampling of genetic markers assumed to be diagnostic at subspecies level. Some of these genetic markers, found in extant Mexican wolves, reportedly also occur in a few individuals far to the north of the range defined in early accounts. Extending the historical range northward would necessitate drawing that line far north of transitions in wolf phenotype, breaks in vegetation associations, barriers to gene flow, and differences in prey base. We review morphologic, genetic, and ecological information to illustrate why such historical range extensions are not supported. The historical distribution of the Mexican wolf likely does not correspond to the detected distribution of certain molecular markers. The historical range of the Mexican wolf should not be altered through the identification of similar habitat in other locations, the distribution of inadequately sampled molecular markers, or by theoretical arguments about movement capacity. Rather, it should respect the original descriptions that were made when the animal was still present on the landscape, and which are concordant with ecological relationships, physiography, morphology, and the principles of population genetics. Clarifying the historical range of the Mexican wolf accurately will be foundational to developing a scientifically defensible recovery plan. © 2017 The Wildlife Society.

Ruling out genetic erosion in Picea chihuahuana Martínez

Genetic erosion has been variously defined as the loss of particular alleles, the reduction in richness of the total number of alleles, and the reduction in evenness of the frequencies of alleles in a given place within populations or across species. Picea chihuahuana Martinez is an endangered endemic species known to occur in at least 40 locations along the Sierra Madre Occidental, in the states of Durango and Chihuahua (Mexico), but covering a total area of no more than 300 ha. The total number of individuals has been estimated to be around 42,600, and the number of mature individuals may be <2500. The populations (including mature trees, saplings and seedlings) vary in size from 21 to 5546 individuals. It has been suggested that small populations may be more susceptible to loss of genetic variability via genetic erosion caused by genetic drift, endogamy depression and strong unidirectional selection. The predicted reduction and eventual disappearance of a suitable habitat for P. chihuahuana due to climatic change imposes an additional risk of extinction. The principal aim of this study was therefore to estimate genetic erosion in 14 populations of P. chihuahuana Martinez by comparing genetic diversity across diameter at breast height classes (as a proxy for age classes) by using AFLP markers and four indices of genetic diversity that are commonly applied in combination with dominant genetic markers. No evidence of genetic erosion was found in the 14 P. chihuahuana populations analyzed.

Sistematización bioclimática de la Sierra Madre Occidental (México) y su relación con los pisos de vegetación

Based on bioclimatic diagnosis of 377 meteorological stations throughout the physiographic province of Sierra Madre Occidental (SMO) and the floristic and vegetation information collected, have been identified bioclimatic territorial units, of which his geobotanical characterization is performed. The area is included in the Tropical Macrobioclima, where Tropical Desert, Tropical Xeric and Tropical Pluviseasonal bioclimates are presented. To each one, their bioclimatic belts have been identified (19 in total) of which corresponding geobotanical diagnosis is made through the identification of their respective vegetation belts, emphasizing the structure of the potential natural vegetation, its main floristic markers and its catenal distribution. These results are completed with maps of bioclimates, thermotypes and ombrotypes, and three vegetation transects made at different latitudes.

Números cromosómicos para tres especies de Cosmos sección Discopoda (Asteraceae, Coreopsideae), con notas citogeográficas

Antecedentes y Objetivos: Cosmos secc. Discopoda (Asteraceae, Coreopsideae) es un modelo de estudio sobre poliploidía y aneuploidía. La sección es monofilética, agrupa 24 especies herbáceas perennes y existen especies poliploides y aneuploides. Sin embargo, no se conocen los números cromosómicos para todas las especies y su citogeografía no ha sido estudiada. El propósito de la presente comunicación es dar a conocer conteos cromosómicos para tres especies y discutir sobre el nivel de ploidía ancestral y patrones de distribución geográfica de los niveles de ploidía en la sección.Métodos: Se realizó una recopilación de los registros cromosómicos y se realizaron conteos cromosómicos para tres especies a partir de la preparación de estructuras vegetativas. Mediante un sistema de información geográfica y una base de datos geográficos con 810 registros, se analizó la distribución geográfica de niveles de ploidía asignando un nivel de ploidía a cada registro por especie. Además, se realizó una reconstrucción del nivel de ploidía ancestral mediante análisis empleando un modelo de máxima verosimilitud.Resultados clave: Cosmos nitidus y C. ramirezianus son diploides (2n=2x=24) y C. pseudoperfoliatus es tetraploide (2n=4x=48). En Cosmos secc. Discopoda actualmente se conoce el número cromosómico de 20 especies, 12 son diploides (2n=2x), seis taxa son exclusivamente poliploides (2n=4x, 6x, 8x), cuatro son diploides y poliploides y existen dos eventos independientes de aneuploidía. La reconstrucción del nivel de ploidía ancestral permite reconocer que x=12 es el número cromosómico básico en la sección.Conclusiones: Las especies de Cosmos secc. Discopoda no muestran una correlación entre los niveles de ploidía y sus rangos de distribución geográfica. En contraste, existe un aumento del nivel de ploidía de sur a norte, con una concentración de poliploides en el norte de la Sierra Madre Occidental.

Spatial modeling of forest fires in Mexico: an integration of two data sources

Forest fires are a cause of global concern, which requires generating knowledge on their spatial behavior. By hypothesizing that the spatial pattern of forest fires across Mexico is randomly distributed, this study aimed at making an analysis of the distribution of forest fires (2005-2015) using remote sensing information and field data collected by CONAFOR (National Forest Commission) and MODIS (Moderate-Resolution Imaging Spectroradiometer). The study compared both sources of information through the G-statistic test that identified clustering patterns. The “hot spots” analysis identified clustered areas with significant values in both data sources. These zones were extended through Sierra Madre Occidental, Peninsula de Yucatan, northern Sierra Madre Oriental and Peninsula de Baja California. The highly coincidental clusters were found in the central-western region along the Eje Neovolcanico, as well as in a small part of Sierra Madre del Sur. The analysis of spatial correlation determined that both sources of information complement each other, enhancing their scope. It is concluded that forest fires in Mexico follow a spatial clustering trend.