17 Oct 2002 8:55 AR AR173-ES33-21.tex AR173-ES33-21.sgm LaTeX2e(2002/01/18) P1: FHD10.1146/annurev.ecolsys.33.010802.150437Annu. Rev. Ecol. Syst. 2002. 33:589–639doi: 10.1146/annurev.ecolsys.33.010802.150437Copyrightc° 2002 by Annual Reviews. All rights reservedFirst published online as a Review in Advance on August 14, 2002NEOPOLYPLOIDY IN FLOWERING PLANTSJustin Ramsey1,2and Douglas W. Schemske31Department of Botany, Box 355325, University of Washington, Seattle,Washington 98195-5325; email: [email protected] address: Department of Botany, University of Guelph, Guelph,Ontario N1G 2W1, Canada; email: [email protected] of Plant Biology and Kellogg Biological Station, Michigan StateUniversity, East Lansing, Michigan 48824-1312; email: [email protected] Words adaptation, aneuploidy, cytogenetics, polyploidy, speciation■ Abstract Here we review the biology of early generation neopolyploids and dis-cuss the profound changes that accompany their formation. Newly formed auto- andallopolyploids exhibit considerable meiotic complexity, including multivalent pairing,multisomic inheritance, and the production of unbalanced gametes. The cytogeneticbehavior of allopolyploids and autopolyploids differ statistically, but are more similarthan commonly believed. The progeny of neopolyploids include a high frequency ofaneuploids, pseudoeuploids and homeologue-recombinant genotypes that may con-tribute to the phenotypic variability observed in early generation polyploids. We findno evidence to support the traditional view that autopolyploids possess lower fertilitythan allopolyploids, casting doubt on the paradigm that allopolyploids should be morefrequent due to their inherent fertility. The fertility of early generation polyploids in-creases rapidly, owing largely to selection against meiotic configurations that generateunbalanced gametes. Neopolyploids are commonly differentiated from progenitors bya combination of morphological, phenological and life-history characteristics. Furtherprogress toward understanding polyploid evolution will require studies in natural pop-ulations that can evaluate the demographic and larger ecological significance of thecytogenetic and phenotypic character of neopolyploids.INTRODUCTIONPolyploidy, the genome-wide multiplication of chromosome number, is a key fea-ture in plant evolution. It is estimated that between 47 and 70% of flowering plantsare thedescendantsofpolyploid ancestors (Masterson 1994). Differencesin ploidyare commonly observed among closely related plant species and among popula-tions within species (Lewis1980a), and recent molecular studies haverevealed thatpolyploid taxa often have multiple origins (Soltis & Soltis 1993, 1999). These ob-servations demonstrate that polyploidy in plants is a dynamic process. Polyploidsgenerally differ markedly from their progenitors in morphological, ecological,physiological and cytological characteristics (Levin 1983, 2002; Lumaret 1988)0066-4162/02/1215-0589$14.00 589Annu. Rev. Ecol. Syst. 2002.33:589-639. Downloaded from arjournals.annualreviews.orgby University of Wisconsin - Madison on 02/12/07. For personal use only.17 Oct 2002 8:55 AR AR173-ES33-21.tex AR173-ES33-21.sgm LaTeX2e(2002/01/18) P1: FHD590 RAMSEY¥SCHEMSKEthat can contribute both to exploitation of a new niche and to reproductive isola-tion. Thus, polyploidy is a major mechanism of adaptation and speciation in plants(Clausen et al. 1945, Stebbins 1950, Grant 1981, Otto & Whitton 2000, Levin2002).In spite of the importance of polyploidy, the factors contributing to polyploidevolution are poorly understood (Thompson & Lumaret 1992). There are two earlystages of polyploid evolution: formation of new cytotypes and their demographicestablishment. To understand the process of polyploid formation requires informa-tion on the pathways, cytological mechanisms, and rates of polyploid formation.To assess the likelihood that a new polyploid will successfully establish requiresinformation on the viability and fertility of new cytotypes, as well as their pheno-typic characteristics and fitness in different environments. A review of polyploidformation is provided in a companion Annual Review of Ecology and Systemat-ics chapter (Ramsey & Schemske 1998). Here we review the literature regardingnewly formed polyploids to answer the following questions: 1. What are the cyto-genetic characteristics of neopolyploids, and how do these relate to the viability,fertility, and stability of polyploids? 2. What are the phenotypic consequences ofpolyploidy, and by what genetic means are they induced?INFERENCE IN POLYPLOID RESEARCHDespite an enormous literature concerning the biological characteristics of poly-ploids and their progenitors, most investigationscompare naturally occuring estab-lished cytotypes. This approach may confound phenotypic differences attributableto ploidy per se with those that result from evolution since the time of polyploidformation (Bretagnolle & Lumaret 1995, De Kovel & De Jong 2000). For ex-ample, Smith (1946) documented substantial differences in the morphology, size,flowering phenology, and drought tolerance of diploid, tetraploid, and hexaploid“races” of Sedum pulchellum. Without comparative information from closely re-lated homoploid taxa, we haveno way of ascribing the divergenceobserved amongcytotypes to polyploidy versus genic differentiation via natural selection, geneticdrift, interspecific hybridization, or other mechanisms. It is also common prac-tice to compare the geographic distribution of different cytotypes in an effort toidentify the ecological consequences of polyploidy (Lewis 1980b). For example,Mosquin (1966) showed that diploids, tetraploids, and hexaploids of Epilobiumangustifolium occupy very different geographic regions, an observation consistentwith the hypothesis that polyploidy promotes ecological diversification. Yet, inmost plants, profound ecological and geographic differentiation is perhaps just asfrequent without changes in ploidy (Clausen et al. 1940).This chapter is focused on the origins and demographic establishment of poly-ploids, phenomenon dependent on the characteristics of polyploids at the timeof origin. One approach that minimizes the confounding effects of postformationevolution involves the comparison of diploid progenitors with newly formed poly-ploids (neopolyploids). For example, M¨untzing (1951) induced autotetraploids inAnnu. Rev. Ecol. Syst. 2002.33:589-639.
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