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Cytological studies have shown many newly formed allopolyploids (neoallopolyploids) exhibit chromosomal variation as a result of meiotic irregularities, but few naturally occurring neoallopolyploids have been examined. Little is known about how long chromosomal variation may persist and how it might influence the establishment and evolution of allopolyploids in nature. In this study we assess chromosomal composition in a natural neoallotetraploid, Tragopogon mirus, and compare it with T. miscellus, which is an allotetraploid of similar age (~40 generations old). We also assess whether parental gene losses in T. mirus correlate with entire or partial chromosome losses. of 37 T. mirus individuals that were karyotyped, 23 (62%) were chromosomally additive of the parents, whereas the remaining 14 individuals (38%) had aneuploid compositions. The proportion of additive versus aneuploid individuals differed from that found previously in T. miscellus, in which aneuploidy was more common (69%; Fisher's exact test, P= 0.0033). Deviations from parental chromosome additivity within T. mirus individuals also did not reach the levels observed in T. miscellus, but similar compensated changes were observed. The loss of T. dubius-derived genes in two T. mirus individuals did not correlate with any chromosomal changes, indicating a role for smaller-scale genetic alterations. Overall, these data for T. mirus provide a second example of prolonged chromosomal instability in natural neoallopolyploid populations. [ABSTRACT FROM AUTHOR]

Hybridization and/or incomplete sorting of ancestral polymorphism are commonly implicated to explain discordant phylogenetic analyses of closely related species complexes. One genus in which these phenomena have been suggested to have played major roles based on phylogenetic data is Conradina, a genus of mints (Lamiaceae) endemic to the southeastern USA containing several endangered species. The goals of this study were to use microsatellite data to better understand patterns of genetic structure in Conradina, to test hypotheses of recent or ancient hybridization and incomplete lineage sorting, and to clarify species boundaries. Individuals from 55 populations representing all Conradina species were genotyped using 10 microsatellite loci. Analyses of the patterns of genetic structure in Conradina revealed a clear differentiation of populations following recognized species boundaries, indicating that species have diverged from one another genetically and interspecific hybridization has not occurred recently. Neither ancient hybridization nor incomplete lineage sorting is supported as the sole cause of species nonmonophyly, suggesting that both may have contributed to patterns found in phylogenetic trees; however, analyses of other types of data may be more appropriate to distinguish between these two hypotheses. Because all described species appear to be valid entities, the current listing status of most endangered species of Conradina is appropriate; however, populations of Conradina canescens are genetically differentiated into three groups, each of which may merit species status, and several recently discovered populations of Conradina in Dunn's Creek State Park in Florida are highly differentiated genetically and also appear to represent a new species. [ABSTRACT FROM AUTHOR]

Heliconia bihai is a highly polymorphic species. Populations of the species are distributed throughout the Lesser Antilles and northern South America; the most obvious sign of polymorphism is manifested through differences in bract color. This variation has been attributed to pollinator-mediated selection, but other processes are also plausible. To test the potential contribution of drift in the evolution of phenotypic variation in this system, we examined the distribution of morphological and genetic variation within and between populations of H. bihai in the Caribbean islands of St. Vincent and St. Lucia. Morphological characterization was limited to flower and inflorescence characteristics, including bract color. AFLPs were used to investigate levels of genetic diversity within and between populations. Genetic similarity among individuals was equivalent to that expected for conspecific individuals. Levels of AFLP and population subdivision were high and were comparable to those of outcrossing species in one island, but they were low and comparable with selfing or clonal species in the other, indicating that genetic variation between islands may be under different evolutionary regimes. There was a significant geographical structure in morphological variation, but this was considerably less pronounced than that found at the genetic level except for bract color patterns, which were different for different islands. We found no correlation between genetic similarity and geographic distance or between genetic similarity and morphological similarity. Observed patterns of genetic and morphological variation in H. bihai suggest that genetic drift is likely to have had a minor role in their development. Instead, these patterns are consistent with phenomena such as selection, inbreeding, and habitat fragmentation that may be operating independently at different spatial scales. [ABSTRACT FROM AUTHOR]

We investigated concerted evolution of rRNA genes in multiple populations of Tragopogon mirus and T. miscellus, two allotetraploids that formed recurrently within the last 80 years following the introduction of three diploids (T. dubius, T. pratensis, and T. porrifolius) from Europe to North America. Using the earliest herbarium specimens of the allotetraploids (1949 and 1953) to represent the genomic condition near the time of polyploidization, we found that the parental rDNA repeats were inherited in roughly equal numbers. In contrast, in most present-day populations of both tetraploids, the rDNA of T. dubius origin is reduced and may occupy as little as 5% of total rDNA in some individuals. However, in two populations of T. mirus the repeats of T. dubius origin outnumber the repeats of the second diploid parent (T. porrifolius), indicating bidirectional concerted evolution within a single species. In plants of T. miscellus having a low rDNA contribution from T. dubius, the rDNA of T. dubius was nonetheless expressed. We have apparently caught homogenization of rDNA repeats (concerted evolution) in the act, although it has not proceeded to completion in any allopolyploid population yet examined. [ABSTRACT FROM AUTHOR]