17 Oct 2002 8 55 AR AR173 ES33 21 tex AR173 ES33 21 sgm LaTeX2e 2002 01 18 P1 FHD 10 1146 annurev ecolsys 33 010802 150437 Annu Rev Ecol Syst 2002 33 589 639 doi 10 1146 annurev ecolsys 33 010802 150437 c 2002 by Annual Reviews All rights reserved Copyright First published online as a Review in Advance on August 14 2002 NEOPOLYPLOIDY IN FLOWERING PLANTS Justin Ramsey1 2 and Douglas W Schemske3 Annu Rev Ecol Syst 2002 33 589 639 Downloaded from arjournals annualreviews org by University of Wisconsin Madison on 02 12 07 For personal use only 1 Department of Botany Box 355325 University of Washington Seattle Washington 98195 5325 email jramsey u washington edu 2 Present address Department of Botany University of Guelph Guelph Ontario N1G 2W1 Canada email jramsey uoguelph ca 3 Department of Plant Biology and Kellogg Biological Station Michigan State University East Lansing Michigan 48824 1312 email schem msu edu Key Words adaptation aneuploidy cytogenetics polyploidy speciation Abstract Here we review the biology of early generation neopolyploids and discuss the profound changes that accompany their formation Newly formed auto and allopolyploids exhibit considerable meiotic complexity including multivalent pairing multisomic inheritance and the production of unbalanced gametes The cytogenetic behavior of allopolyploids and autopolyploids differ statistically but are more similar than commonly believed The progeny of neopolyploids include a high frequency of aneuploids pseudoeuploids and homeologue recombinant genotypes that may contribute to the phenotypic variability observed in early generation polyploids We find no evidence to support the traditional view that autopolyploids possess lower fertility than allopolyploids casting doubt on the paradigm that allopolyploids should be more frequent due to their inherent fertility The fertility of early generation polyploids increases rapidly owing largely to selection against meiotic configurations that generate unbalanced gametes Neopolyploids are commonly differentiated from progenitors by a combination of morphological phenological and life history characteristics Further progress toward understanding polyploid evolution will require studies in natural populations that can evaluate the demographic and larger ecological significance of the cytogenetic and phenotypic character of neopolyploids INTRODUCTION Polyploidy the genome wide multiplication of chromosome number is a key feature in plant evolution It is estimated that between 47 and 70 of flowering plants are the descendants of polyploid ancestors Masterson 1994 Differences in ploidy are commonly observed among closely related plant species and among populations within species Lewis 1980a and recent molecular studies have revealed that polyploid taxa often have multiple origins Soltis Soltis 1993 1999 These observations demonstrate that polyploidy in plants is a dynamic process Polyploids generally differ markedly from their progenitors in morphological ecological physiological and cytological characteristics Levin 1983 2002 Lumaret 1988 0066 4162 02 1215 0589 14 00 589 17 Oct 2002 8 55 Annu Rev Ecol Syst 2002 33 589 639 Downloaded from arjournals annualreviews org by University of Wisconsin Madison on 02 12 07 For personal use only 590 AR AR173 ES33 21 tex RAMSEY AR173 ES33 21 sgm LaTeX2e 2002 01 18 P1 FHD SCHEMSKE that can contribute both to exploitation of a new niche and to reproductive isolation Thus polyploidy is a major mechanism of adaptation and speciation in plants Clausen et al 1945 Stebbins 1950 Grant 1981 Otto Whitton 2000 Levin 2002 In spite of the importance of polyploidy the factors contributing to polyploid evolution are poorly understood Thompson Lumaret 1992 There are two early stages of polyploid evolution formation of new cytotypes and their demographic establishment To understand the process of polyploid formation requires information on the pathways cytological mechanisms and rates of polyploid formation To assess the likelihood that a new polyploid will successfully establish requires information on the viability and fertility of new cytotypes as well as their phenotypic characteristics and fitness in different environments A review of polyploid formation is provided in a companion Annual Review of Ecology and Systematics chapter Ramsey Schemske 1998 Here we review the literature regarding newly formed polyploids to answer the following questions 1 What are the cytogenetic characteristics of neopolyploids and how do these relate to the viability fertility and stability of polyploids 2 What are the phenotypic consequences of polyploidy and by what genetic means are they induced INFERENCE IN POLYPLOID RESEARCH Despite an enormous literature concerning the biological characteristics of polyploids and their progenitors most investigations compare naturally occuring established cytotypes This approach may confound phenotypic differences attributable to ploidy per se with those that result from evolution since the time of polyploid formation Bretagnolle Lumaret 1995 De Kovel De Jong 2000 For example 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 related homoploid taxa we have no way of ascribing the divergence observed among cytotypes to polyploidy versus genic differentiation via natural selection genetic drift interspecific hybridization or other mechanisms It is also common practice to compare the geographic distribution of different cytotypes in an effort to identify the ecological consequences of polyploidy Lewis 1980b For example Mosquin 1966 showed that diploids tetraploids and hexaploids of Epilobium angustifolium occupy very different geographic regions an observation consistent with the hypothesis that polyploidy promotes ecological diversification Yet in most plants profound ecological and geographic differentiation is perhaps just as frequent without changes in ploidy Clausen et al 1940 This chapter is focused on the origins and demographic establishment of polyploids phenomenon dependent on the characteristics of polyploids at the time of origin One approach that minimizes the confounding effects of postformation evolution involves the comparison of diploid progenitors with newly formed polyploids neopolyploids For example Mu ntzing 1951 induced autotetraploids in 17 Oct 2002 8 55
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