Intraspecific variation in Podostemum ceratophyllum (Podostemaceae): evidence of refugia and colonization since the last glacial maximum.
OBJECTIVE
Intraspecific variation among 20 populations of Podostemum ceratophyllum Michx. was investigated to test the hypothesis of range expansion from southern refugia since the last glacial maximum.


METHODS
Six noncoding regions of chloroplast DNA were sequenced in 60 individuals. Populations were divided into two groups, north and south of the glacial boundary, in addition to isolated populations in Arkansas and Honduras. Variation in populations north of the boundary was compared with variation in populations to the south and in the isolated populations.


RESULTS
Nucleotide diversity was an order of magnitude lower in populations north of the glacial boundary than in those to the south. The Arkansas and Honduras populations showed no variation. The predominant haplotype in northern populations was also found in a Virginia population.


CONCLUSIONS
Reduced variation north of the glacial boundary suggests a founder event associated with range expansion since the last glacial maximum. Colonization probably occurred from populations in refugia located several hundred kilometers south of the glacial boundary. The results provide insight into the effects of past and current climate change on patterns of geographic distribution and genetic variation in aquatic plants.
Department of Biological and Environmental Sciences, Western Connecticut State University, Danbury, Connecticut 06810, USA.
Susie
S
Fehrmann
C Thomas
CT
Philbrick
Richard
R
Halliburton
D001483:Base Sequence; D057231:Climate Change; D018742:DNA, Chloroplast / Q000737:chemistry / Q000235:genetics; D021901:DNA, Intergenic / Q000737:chemistry / Q000235:genetics; D018744:DNA, Plant / Q000737:chemistry / Q000235:genetics; D014644:Genetic Variation; D005828:Genetics, Population; D005843:Geography; D006239:Haplotypes; D006721:Honduras; D046448:Ice Cover; D019684:Magnoliopsida / Q000235:genetics*; D008969:Molecular Sequence Data; D017422:Sequence Analysis, DNA; D014481:United States
D018742:DNA, Chloroplast; D021901:DNA, Intergenic; D018744:DNA, Plant