The Caribbean islands provide an ideal setting for studying biodiversity, given their complex geological and environmental history, and their historical and current geographical proximity to the American mainland. Magnolia, a flagship tree genus that has 15 endemic and threatened taxa (12 species and 3 subspecies) on the Caribbean islands, offers an excellent case study to empirically test Caribbean biogeographical hypotheses. We constructed phylogenetic hypotheses to: (1) reveal their evolutionary history, (2) test the current largely morphology-based classification and assess species limits, and (3) investigate major biogeographic hypotheses proposed for the region. Nuclear and chloroplast DNA sequence data of all 15 Caribbean Magnolia taxa are included, supplemented by a selection of American mainland species, and species representing most major clades of the Magnoliaceae family. We constructed phylogenetic hypotheses in a time-calibrated Bayesian framework, supplemented with haplotype network analyses and ancestral range estimations. Genetic synapomorphies in the studied markers confirm the species limits of 14 out of 15 morphologically recognizable Caribbean Magnolia taxa. There is evidence for four colonization events of Magnolia into the Caribbean from the American mainland, which most likely occurred by overwater dispersal, given age estimates of maximum 16 mya for their presence on the Caribbean islands.
Genetic data on threatened plant populations can facilitate the development of adequate conservation strategies to reduce extinction risk. Such data are particularly important for species affected by habitat fragmentation such as Magnolia cubensis subsp. acunae, a Critically Endangered magnolia subspecies endemic to Cuba. Using genetic data from 67 individuals, we aimed to evaluate the effect of habitat fragmentation on two subpopulations in the Guamuhaya mountain range, in Topes de Collantes Protected Natural Landscape and Lomas de Banao Ecological Reserve. We characterize the structure and genetic diversity of these subpopulations, with the objective of managing their conservation more effectively. We used Landsat satellite images to determine land-cover types at the two locations and calculated indices of habitat fragmentation. For genetic analyses, we extracted DNA from the leaf tissue of individuals from the two subpopulations and used 11 microsatellite markers to genotype them. We calculated heterozygosity, allelic richness and the F-statistics, to evaluate genetic variability. The montane rainforest in Topes de Collantes was most affected by habitat fragmentation, with smaller patches of more irregular shapes, compared to submontane forest at this location and both montane and submontane forests in Lomas de Banao. Genetic diversity was higher in Topes de Collantes, but we found no genetic differentiation between subpopulations. Our findings suggest the two subpopulations can be considered a single evolutionary unit and conservation entity. We propose to use individuals from both subpopulations for reinforcement to increase the overall genetic diversity of the subspecies.
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Antecedentes: En Cuba, los estudios sobre Portulaca carecen de un consenso de los taxones presentes. Las especies se encuentran pobremente representadas en colecciones de herbario y para ellas se infieren distribuciones geográficas más amplias. Esta situación dificulta la evaluación de su riesgo de extinción y, por tanto, la implementación de acciones de conservación. Preguntas: ¿Cómo se distribuyen las Portulaca nativas y naturalizadas en Cuba? ¿Cuál es el estado de conservación de las especies nativas? Sitio y años de estudio: Cuba, 1902-2020. Métodos: Se georreferenciaron los registros de presencia de las especies y de cada una se determinó la distribución geográfica, ecológica y fitogeográfica. El estado de conservación de las especies nativas se evaluó según las categorías y criterios de IUCN. Resultados: Portulaca en Cuba incluye 11 especies nativas (una endémica) y una naturalizada, distribuidas en todo el país, mayormente en complejos de vegetación de costa y matorrales xeromorfos. Tres especies se encuentran En Peligro Crítico, cinco En Peligro, una Casi Amenazada y dos en Preocupación Menor. Las principales amenazas son la ganadería y los incendios. En la mayoría de las especies, menos de la mitad del área de ocupación se encuentra en áreas protegidas. Conclusiones: Se actualizó la distribución Portulaca en Cuba y se presenta la primera evaluación completa del estado de conservación del género en el país. Entre las especies no pueden identificarse patrones de disyunción o vicarianza, geográfica o ecológica. La mayoría de las especies están amenazadas de extinción, aunque el género está ampliamente representado en áreas protegidas.
Landscape features impact gene ow and the spatial patterns of genetic variation between populations of a species. Because many Magnoliaceae species occur in fragmented and highly disturbed landscapes, the family is an excellent model for landscape genetic studies. This research focuses on the subspecies and localities of Magnolia cubensis and aims to: (1) compare the genetic diversity, (2) search for genetic patterns, (3) describe the functional connectivity and (4) access the structural connectivity of the landscape. This study employs 21 microsatellite markers on two subspecies, complemented with landscape characteristics of the Guamuhaya and Sierra Maestra massifs in Cuba. Magnolia cubensis subsp. acunae does not have a well-de ned spatial genetic pattern: there is no evidence of isolation by distance or spatial autocorrelation and the little genetic differentiation between the two localities does not re ect the characteristics of the landscape that separates them or the cost values to cross it. Magnolia cubensis subsp. cubensis presents evidence of isolation by distance and the autocorrelation analyses indicate that the approximate scale of the genetic neighborhood is between 35 and 40 km. There is a marked genetic structure with probability values that indicate the existence of three genetic groups. Large genetic differentiation was only found between Gran Piedra and the other localities, which re ects low gene ow. Our results support the recognition of these subspecies at the species level. We de ne one evolutionary signi cant unit in Magnolia cubensis subsp. acunae and two evolutionary signi cant units in Magnolia cubensis subsp. cubensis. These results must be combined with ecological, social and distribution data, in order to obtain a more accurate and realistic perspective of the conservation management strategies for these taxa.
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