Abstract Detail



Population Genetics/Genomics

Trapnell, Dorset [1], Ishibashi, Caitlin [2], Kartzinel, Tyler [3], Hamrick, James [4], Quigley, Charlotte [5].

Phylogeography of the Neotropical epiphytic orchid, Brassavola nodosa: evidence for a secondary contact zone.

PREMISE OF THE STUDY:  Contemporary spatial patterns of genetic variation of separate genomes are valuable for inferring historical processes and can reveal cryptic evolutionary and landscape processes.  In northwestern Costa Rica, a puzzling and approximately concordant genetic discontinuity occurs among populations of several plant species.  We conducted phylogeographic analyses of the dry forest, epiphytic orchid, Brassavola nodosa whose wind-borne seeds have the potential for long-distance dispersal, to test for a genetic discontinuity and to explore underlying causes.  
METHODS:  We genotyped 1237 individuals from 18 populations distributed throughout northwestern Costa Rica with 19 nuclear loci and two non-coding chloroplast sequence regions.  We estimated levels of genetic diversity and structure, relative importance of pollen and seed dispersal (mp/ms), and divergence time to learn how diversity was partitioned across the landscape.  
KEY RESULTS:  Nuclear genetic diversity was high with little structure among populations (GSTn = 0.078).  Chloroplast haplotypes, however, were highly structured revealing a sharp discontinuity between northwestern and southeastern regions of B. nodosa occurrence in Costa Rica.  Haplotype differences suggest two formerly isolated lineages that diverged approximately 10,000-100,000 YBP.  Haplotype mixing and greater diversity occur at a secondary contact zone where lineages meet.  Pollen contributed significantly more than seeds to overall gene flow among sites (mp/ms = 13.7) and substantially more (181.4) between the two regions.   
CONCLUSIONS:  Sharply contrasting patterns in the two genomes reflect the relative effectiveness of biotic versus abiotic dispersers of pollen and seeds respectively. Isolation of the two lineages likely resulted from the complex environmental and geophysical history of the region.  Our results suggest a recent cryptic seed dispersal barrier and/or zone of secondary contact.  We hypothesize that powerful northeasterly trade winds channeled between the Guanacaste and Tilarán Cordilleras hinder movement of wind-borne seeds between the two regions.


1 - University of Georgia, Plant Biology, 2502 Miller Plant Sciences, 120 Carlton St., Athens, GA, 30602, USA
2 - University of Georgia, Plant Biology Dept., 2502 Miller Plant Sciences Bldg, Athens, Georgia, 30602, United States
3 - Brown Univeristy, Ecology and Evolutionary Biology, Institute at Brown for Environment and Society, 85 Waterman Street, Providence, RI, 02912, USA
4 - University Of Georgia, Department Of Plant Biology, Miller Plant Sciences Building, Athens, GA, 30602, United States
5 - University of Maine, School of Marine Sciences, 3, Orono, Maine, 04469, United States

Keywords:
none specified

Presentation Type: Oral Paper
Number: 0010
Abstract ID:159
Candidate for Awards:None


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