Polyploid evolution and biogeography inChelone(Scrophulariaceae): morphological and isozyme evidence

Abstract

Chelone is a genus of perennial herbs comprising three diploid species (C. cuthbertii, C. glabra, and C. lyonii) and a fourth species (C. obliqua) that occurs as tetraploid and hexaploid races. To assess patterns of isozyme and morphological variation, and to test hypotheses of hybridization and allopolyploidy, we analyzed variation among 16 isozyme loci from 61 populations and 16 morphological characters from 33 populations representing all taxa and ploidy levels. Based on morphological analyses using clustering (unweighted pair group method using an arithmetic average) and ordination (principal components analysis and canonical variance analysis) methods, we recognize three diploid species without infraspecific taxa. Polyploids in the C. obliqua complex were most similar morphologically to diploid populations of C. glabra and C. lyonii. Patterns of isozyme variation among polyploids, which included fixed heterozygosity and recombinant profiles of alleles present in diploids, suggested polytopic origins of tetraploids and hexaploids. Our data indicate independent origins of polyploids in or near the southern Blue Ridge, Interior Highlands and Plains, and Atlantic Coastal Plain regions from progenitors most similar to C. glabra and C. lyonii. Extant tetraploids were not implicated in evolution of hexaploids, and plants similar to C. cuthbertii appeared unlikely as diploid progenitors for polyploids. We propose multiple differentiation and hybridization/polyploidization cycles in different geographic regions to explain the pattern of allopatry and inferred polytopic origins among polyploids.

Life history, diversity and distribution: a study of Japanese pteridophytes

“…For example, many polyploids are either paleopolyploids that might be relicts resulting from prolonged environmental changes in the past or neopolyploids that have had little time to adapt to new environments and spread. Neopolyploidy may result from hybridization, which enables pteridophytes to colonize stressful habitats with smaller distributional ranges to avoid competition with other species (Page 1979a,b , Nelson and Elisens 1999). In this case, polyploidy only permits colonization and adaptation to the new environments but may not necessarily lead to an increase in species’ range, particularly when the hybrid must compete with presumably well adapted parental species (Ehrendorfer 1980, Song et al 1995).…”

Genetic variation in the allotetraploid Dryopteris corleyi (Dryopteridaceae) and its diploid parental species in the Iberian Peninsula

“…Allopolyploids, i.e., interspecifi c hybrids which have undergone a genome duplication, can normally produce balanced, viable gametes ( Manton, 1950 ;Comai, 2000 ). As a result of nonsegregation of homeologous chromosomes during meiosis, they are often reported to have " fi xed heterozygosity " (e.g., Glover and Abbott, 1995;Nelson and Elisens, 1999 ). Genetic diversity of allopolyploid species can increase when multiple origins from different diploid parents take place, with each subsequent origin potentially adding new alleles to the previous pool of the allopolyploid ( Werth et al, 1985 ).…”

Pair-flowered cymes in the Lamiales: structure, distribution and origin

“…S25). This genus, comprising four species (Nelson and Elisens, 1999) is uniform with respect to the inflorescences and flowers. The inflorescences are dense, cone-like terminal aggregates.…”