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Rodney L. Robichaud
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Pollen gene dispersal in black walnut across a heterogeneous landscape in Central IndianaRodney L. Robichaud
The purpose of the present study was to investigate levels of gene flow among populations of black walnut (Juglans nigra L.) located within a heterogeneous landscape of Central Indiana. Black walnut is a monoecious, wind-pollinated, shade-intolerant deciduous hardwood with considerable economic value. Loss of habitat, intensive harvesting, and, in some populations, little to no regeneration has led some to believe that isolated populations of black walnut located within remnant patches of forest may be experiencing negative genetic effects (promotion of genetic drift and increased inbreeding). Migration (i.e. gene flow) counteracts genetic drift and may increase the overall level of genetic diversity within a population. Therefore, in order to better understand gene flow within and among populations of black walnut, a number of studies were conducted to estimate either directly or indirectly the extent of seed dispersal and pollen gene flow in this species. To this end, a set of twelve nuclear microsatellite markers were utilized to measure genetic diversity and to genetically fingerprint individual black walnut trees and seeds. Within four populations, two in continuous forest stands and two in isolated remnant patches, every individual black walnut tree was sampled, representing a complete census. In addition, seeds were sampled from six maternal trees from the two remnants and from one of the continuous stands. Investigations into the genetic consequences of simulated harvest practices within a mature second growth stand of black walnut (Chapter 2), paternity analyses of collected seed to measure potential gene flow (Chapter 3), and parentage analyses of all sampled trees to measure realized gene flow (Chapter 4) were conducted. Overall, the estimated levels of pollen gene dispersal were sufficient to counteract the possible negative effects of population isolation due to fragmentation.
Biological sciences; Black walnut; Continuous forest; Fragmentation; Gene dispersal; Juglans nigra; Potential gene flow; Realized gene flow; Selection; Genetics; Forestry; 0478:Forestry; 0369:Genetics
K. R. Woeste, Olin E., Jr.
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