DIRECT AND INDIRECT ESTIMATES OF SEED VERSUS POLLEN MOVEMENT WITHIN A POPULATION OF PONDEROSA PINE.

Area of Science:

• Population Genetics
• Forest Ecology
• Plant Reproduction

Background:

• Understanding plant population structure is crucial for conservation and management.
• Maternally and paternally inherited DNA markers reveal different aspects of gene flow.
• Ponderosa pine (Pinus ponderosa Laws) is a key species in Western North American forests.

Purpose of the Study:

• To investigate the spatial genetic structure of ponderosa pine using mitochondrial DNA (mtDNA) and chloroplast DNA (cpDNA).
• To differentiate the roles of seed and pollen dispersal in shaping genetic patterns.
• To assess the extent of gene flow via both maternal and paternal lineages.

Main Methods:

• Analysis of spatial distribution of maternally inherited mtDNA and paternally inherited cpDNA polymorphisms.
• Identification of haplotype structures and genetic relatedness using allozyme genotypes.
• Direct measurement of pollen movement using unique allozyme alleles.

Main Results:

• Mitochondrial DNA (mtDNA) haplotypes exhibited significant patch structure, indicating limited seed dispersal and the formation of matrilineal clusters.
• Individuals within mtDNA patches were related as half-sibs.
• Chloroplast DNA (cpDNA) polymorphisms showed no patch structure, suggesting extensive pollen dispersal.
• Pollen movement was found to be nearly unlimited, with marked pollen dispersing widely.

Conclusions:

• Seed dispersal is a major limiting factor for genetic structuring in ponderosa pine populations.
• Pollen dispersal facilitates broad gene flow, counteracting the effects of limited seed dispersal.
• Distinct spatial genetic structures arise from the differential dispersal mechanisms of seed and pollen.