Allopolyploidy in bryophytes: Multiple origins of Plagiomnium medium

Abstract

Bryophytes are thought to be unique among land plants in lacking the important evolutionary process of allopolyploidy, which involves interspecific hybridization and chromosome doubling. Electrophoretic data show, however, that the polyploid moss Plagiomnium medium is an aflopolyploid derivative of Plagiomnium eUipticum and Plagiomnium insigne, that P. medium has originated more than once from these progenitors, and that cross-fertilization results in interlocus genetic recombination. Evidence from restriction fragment length polymorphisms in chloroplast DNA implicates P. insigne as the female parent in interspecific hybridizations with P. ellipticum. Contrary to prevailing views, it appears that those evolutionary processes responsible for genetic differentiation and speciation in other land plants occur in the bryophytes as well.It is estimated that 47% of all flowering plants and 95% of all pteridophytes are polyploids and that the majority of these are allopolyploids, which have arisen through doubling of chromosomes in interspecific hybrids (ref. 1, but see ref.2). Among the bryophytes 79% of mosses, 11% of liverworts, and 2% of hornworts are believed to be polyploids (3, 4). In contrast to other land plants, however, all of these have been assumed on the basis of morphology to be autopolyploids (5, 6). Furthermore, hybridization has been documented in only a few isolated cases involving sterile sporophytes from intergeneric crosses (3-6). The absence of hybrid speciation, an important mode of evolution in other land plants, has contributed to the characterization of bryophytes as a group with severely limited evolutionary potential (7,8).Within the moss genus Plagiomnium, section Rosulata includes one polyploid species (Plagiomnium medium; n = 12) and six haploid species (9). On the basis of morphology, Lowry (10) concluded that Plagiomnium ellipticum (n = 6) is the progenitor of autopolyploid P. medium. Koponen (9), however, stressed different characters and argued that Plagiomnium insigne (n = 6) is the only possible progenitor. Because the morphological evidence is ambiguous, we elected to use biochemical evidence to resolve the origin of P. medium. MATERIALS AND METHODSFour gametophytic populations each of P. medium and P. ellipticum were sampled in northern Michigan from many of the same localities sampled in Lowry's (9) original cytological study. Because Lowry's (9) chromosome counts were done on plants collected in Michigan [all vouchers verified by Wyatt (11)] and his and all other counts [reviewed by Koponen (12)] for these species are in agreement, we did not deem it necessary to examine our material cytologically. We also obtained population samples of P. insigne from northern California. From each population, we collected 36 moss clumps (approximately 5 x 5 cm). These were maintained in a growth chamber on a light/dark cycle of 16:8 hr at 15'C and 10'C, respectively. Single healthy shoots were subjected to horizontal starch gel electrophoresis after 1-2 months under these conditions. E...

Low genetic diversity in the Scottish endemicPrimula scoticaHook.

“…In recent years, it has become evident that allopolyploid species may often originate in a multiple fashion involving different pairs of genetically divergent parents, thus generating a certain amount of between plant diversity within the allopolyploid species (Wyatt et al, 1988;Soltis & Soltis, \9mb;Ashton & Abbott, 1992;Brochman, Soltis & Soltis, 1992). Brochman & Elven (1992) have argued that the ability of such allopolyploids to adapt to a wide range of sites, may be due to either; (i) a high level of fixed heterozygosity and consequently biochemical diversity creating a 'general purpose' genotype or; (ii) multiple allopolyploidization giving rise to different fixed heterozygous ' special purpose' genotypes, each of which is adapted to a particular set of conditions.…”

The role of genetic and genomic attributes in the success of polyploids

“…[29][30][31]. Polyphyletic polyploid species have been reported for mosses (32), ferns (33)(34)(35), and many angiosperms (29)(30)(31), and include both autopolyploids [e.g., Heuchera grossulariifolia (36 -38) and Heuchera micrantha (39,40)] and allopolyploids (29)(30)(31). Recurrent formation of a polyploid species has implications for the taxonomy of polyploids, our understanding of the ease with which and rate at which polyploidization can occur, and, most relevant here, the genetic diversity of polyploid "species."…”

CHLOROPLAST‐DNA VARIATION AND MULTIPLE ORIGINS OF AUTOPOLYPLOIDY IN HEUCHERA MICRANTHA (SAXIFRAGACEAE)

“…Multiple origins of allopolyploids have, on rare occasions, been suggested, based on allozyme data (Roose and Gottlieb, 1976;Werth et al, 1985;Wyatt et al, 1988). The fact that autotetraploids in H. micrantha are not only numerous and widespread but are also of multiple origin is significant because, unlike allopolyploidy, autopolyploidy typically has been considered to be rare and of little evolutionary importance (Stebbins, 1950;Lewis, 1980;Levin, 1983;Soltis and Rieseberg, 1986).…”