Antecedentes y Objetivos: Guarianthe skinneri es una orquídea nativa de Chiapas, México, con distribución centroamericana, objeto de extracción y comercio ilícito; por esta razón, está catalogada como amenazada en la Norma Mexicana NOM-059-SEMARNAT-2010. En la región del Soconusco (Chiapas, México) y Guatemala, se le denomina “Candelaria”, debido a que su época de floración coincide con las fechas de la homónima virgen. En la ciudad de Tapachula (Chiapas, México), es común encontrar individuos de esta especie en los patios de domicilios particulares. El objetivo de este trabajo fue estimar la diversidad y estructura genética de G. skinneri a partir de muestras obtenidas de una población urbana de Tapachula y de su comparación con cinco poblaciones silvestres de Guatemala, para determinar el potencial de la población urbana como fuente de propágulos y averiguar si la distancia genética entre poblaciones se relaciona con la distancia geográfica que las separa.Métodos: Como marcador genético se utilizó la variación nucleotídica en secuencias de dos regiones de ADN nuclear ribosomal (ITS 1-2 y ITS 3-4). Se concatenaron las secuencias y se obtuvieron los parámetros convencionales de diversidad y estructura genética.Resultados clave: Se observaron poblaciones desde bajos hasta altos niveles de diversidad genética. Se registró un total de 38 haplotipos cuyo número entre poblaciones osciló entre 1 y 15. La diversidad haplotípica (Hd) estuvo entre 0 y 1, el número promedio de sitios polimórficos entre 0 y 165. La diversidad nucleotídica (π) y el número promedio de diferencias nucleotídicas muestran que Tapachula tuvo la mayor diversidad, seguida por poblaciones de Guatemala. La estructura genética fue moderada (Fst=0.083) y la distancia genética no se asoció con la distancia geográfica de las poblaciones.Conclusiones: Los patrones de diversidad y estructura genética entre poblaciones se atribuyen a factores antropogénicos derivados de su uso ornamental, especialmente en la ciudad de Tapachula.
Knowledge of the genetic diversity of species in a biological community is useful for assessing the ecological and evolutionary processes that define the structure and dynamics of that community. We investigated the potential relationship between the trans-specific genetic diversity (or genetic diversity across tree species) and the diversity of tree species in a tropical subdeciduous forest. The nucleotide variation of the concatenated regions ITS 1 and ITS 3 (ITS1-3) was used to determine the trans-specific genetic diversity of 19 species of trees in five local communities at El Ocote Biosphere Reserve (REBISO), Chiapas, Mexico. Tree diversity was obtained by counting individual trees within 0.1 ha circular plots in each locality. The relationship between trans-specific genetic diversity and species diversity was established through simple linear regressions between genetic diversity parameters and community diversity. A correlation matrix was built with genetic distances (Kimura’s two-parameter model) and differences in species diversity between communities. A significant relationship was observed between nucleotide diversity (π) and species richness ( Sp), and a negative association between haplotype diversity and gamma diversity (γ). Our results show species-rich and genetically diverse tree communities and a weak association between trans-specific genetic variation and species diversity in tree communities at REBISO. This research suggests a possible ecological and genetic relationship within each community. Genetic diversity values may provide an important degree of variation upon which environmental selection pressures could operate, which may be helpful to face the current environmental modifications associated with climatic change.
Two rivers in the hot desert of northwestern México have been considered as filter barriers in the distribution of mammals: Río Conchos in Chihuahua and Río Nazas in Durango. Between both rivers, the black-tailed jackrabbit, Lepus californicus, shows significant differences in external morphological traits. We investigated if these differences are supported by phylogenetical signals and compared them with populations living at similar latitudes in the Baja California Peninsula to determine the importance of the genetic variation caused by the rivers. An external mophology, and a cranial geometric morphometric analysis were performed using the dorsal, ventral, and lateral views of the skull; and a genetic analysis of cytochrome b gene. Measurements and fur color patterns of specimens from two continental groups, north of Río Conchos (NRC) and south of Río Nazas (SRN), were compared to four groups (A-D) inhabiting different latitudes of the Baja California Peninsula (BCP). The parietal region, zygomatic arch, and auditory bullae were identified as the main cranial structures related to skull shape; however, no differences were observed in size and shape between groups. The phylogenetic reconstruction of L. californicus showed that it is a monophyletic species, with high branch support values (100). It is represented by two polyphyletic subclades, one with haplotypes of the SRN and NRC populations and the other with haplotypes of the BCP populations. The average genetic distance (p-distance) and genetic differentiation (FST) between SRN and NRC were low (0.8 % and 0.09, respectively), with higher mean values between the BCP groups (1.23 % and 0.30, respectively). The statistical parsimony network of Cyt b did not identify a clear geographic genetic structure between haplotypes of SRN and NRC and they did not share haplotypes with the BCP populations. There are neither cranial geometric morphometric nor genetic differences between L. californicus populations related to either the rios Conchos or Nazas; thus, these rivers cannot be considered geographic barriers. However, there are morphological differences between the populations in Chihuahua and Durango and the populations inhabiting Baja California Peninsula, which may be associated with evolutionary distance and local habitat characteristics.
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