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Title: Evidence of bottleneck and isolation by distance in an endangered species from the Tropical Andean hotspot

Author
item OLEAS, NORA - Florida International University
item Meerow, Alan
item FRANCISCO-ORTEGA, JAVIER - Florida International University

Submitted to: Journal of Heredity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2012
Publication Date: 5/4/2012
Citation: Oleas, N.H., Meerow, A.W., Francisco-Ortega, J. 2012. Evidence of bottleneck and isolation by distance in an endangered species from the Tropical Andean hotspot. Journal of Heredity. 103(4):557–569.

Interpretive Summary: Although the Tropical Andes is the most diverse of the recognized plant conservation hotspots, there exists scant knowledge about patterns of genetic variation within the species found in the region. Understanding genetic variation is essential to develop successful conservation plans. Phaedranassa tunguraguae is a plant species found only in the Tropical Andes in Ecuador, listed as ‘Endangered’ under IUCN’s criteria based on restricted geographic distribution and habitat alteration. The aim of this study is to estimate the levels of genetic differentiation within and among populations and discuss factors that might influence the genetic structure of this species. The species shows high levels of inbreeding within populations, which are isolated by distance, and forms two genetic clusters, a western group and an eastern, with highly significant differentiation between them. The westernmost population is the most genetically diverse, and the easternmost, the least. Migration rates were in general low, but highest among populations within either of two clusters. Survival of P. tunguraguae may be impacted by the low gene flow between populations. Based on genetic differences inferred by genetic distance and Bayesian analysis, two Management Units are proposed for P. tunguraguae.

Technical Abstract: The Tropical Andes is the most diverse of the recognized plant conservation hotspots. In contrast, there exists scant knowledge about patterns of genetic variation within its constituent species. Understanding genetic variation is essential to develop successful conservation plans. Phaedranassa tunguraguae is a plant species endemic to the Tropical Andes in Ecuador, listed as ‘Endangered’ under IUCN’s criteria based on restricted geographic distribution and habitat alteration. The aim of this study is to estimate the levels of genetic differentiation within and among populations and discuss factors that might influence the genetic structure of this species. We calculate genetic structure across the species’ geographic range for 136 individuals using 12 microsatellite loci. Bayesian methods were used to investigate population structure, migration, and evidence of recent bottlenecks. Genetic distance was also generated to evaluate relationship among populations. The species shows high levels of inbreeding within populations, with an excess of homozygotes. Evidence of recent bottlenecks was found for the majority of populations, which exhibit isolation by distance, and form two genetic clusters, a western group and an eastern, with highly significant differentiation between them. Allele richness decreases from the most diverse westernmost population to the acutely less diverse easternmost population. Migration rates were in general low, but highest among populations within either of two clusters. Both allele reduction and lack of gene flow could have serious implications for survival of P. tunguraguae. The populations exhibit a strong pattern of isolation by distance and evidence of recent bottlenecks, perhaps the consequences of founder effects. These patterns are similar to those characteristic of the only other Tropical Andean species studied with microsatellites, the palm Ceroxylon echinulatum. Based on genetic differences inferred by genetic distance and Bayesian analysis, two Management Units are proposed for P. tunguraguae.