▪ Abstract Changes in ploidy occurred early in the diversification of some animal and plant lineages and represent an ongoing phenomenon in others. While the prevalence of polyploid lineages indicates that this phenomenon is a common and successful evolutionary transition, whether polyploidization itself has a significant effect on patterns and rates of diversification remains an open question. Here we review evidence for the creative role of polyploidy in evolution. We present new estimates for the incidence of polyploidy in ferns and flowering plants based on a simple model describing transitions between odd and even base chromosome numbers. These new estimates indicate that ploidy changes may represent from 2 to 4% of speciation events in flowering plants and 7% in ferns. Speciation via polyploidy is likely to be one of the more predominant modes of sympatric speciation in plants, owing to its potentially broad-scale effects on gene regulation and developmental processes, effects that can produce immed...

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Polyploid Incidence and Evolution

Since its discovery in 1907, polyploidy has been recognized as an important phenomenon in vascular plants, and several lines of evidence indicate that most, if not all, plant species ultimately have a polyploid ancestry. However, previous estimates of the frequency of polyploid speciation suggest that the formation and establishment of neopolyploid species is rare. By combining information from the botanical community's vast cytogenetic and phylogenetic databases, we establish that 15% of angiosperm and 31% of fern speciation events are accompanied by ploidy increase. These frequency estimates are higher by a factor of four than earlier estimates and lead to a standing incidence of polyploid species within genera of 35% (n = 1,506). Despite this high incidence, we find no direct evidence that polyploid lines, once established, enjoy greater net species diversification. Thus, the widespread occurrence of polyploid taxa appears to result from the substantial contribution of polyploidy to cladogenesis, but not from subsequent increases in diversification rates of polyploid lines.

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The frequency of polyploid speciation in vascular plants

Numerous studies of morphological and physiological traits (reviewed in 3, 57, 95, 132, 135) as well as the more recent studies of enzyme loci (reviewed in 21, 52, 63) have generally shown the existence of significant amounts of genetic variation both within and between plant populations. These reviews (21, 52, 63) have also demonstrated considerable variation among species in intrapopulation allozyme variation. For instance, Hamrick (63) found that populations of woody plants contained higher levels of genetic variation than did populations of herbaceous species; Gottlieb (52) and Brown (21) demonstrated that predominantly outbreeding species maintain higher levels of intrapopulation genetic variation than predominantly inbreeding species. Nevo (111) found that habitat generalists and animal species with cosmopolitan or tropical distributions were typically more variable than species with specialized habitat preferences or temperate distributions. While these results are interesting and informative, they consider the influence of only a few evolutionarily important characteristics on the main-

https://www.jstor.org/stable/info/2096789

Relationships Between Life History Characteristics and Electrophoretically Detectable Genetic Variation in Plants

Phylogenetic relationships among 88 genera of Rosaceae were investigated using nucleotide sequence data from six nuclear (18S, gbssi1, gbssi2, ITS, pgip, and ppo) and four chloroplast (matK, ndhF, rbcL, and trnL-trnF) regions, separately and in various combinations, with parsimony and likelihood-based Bayesian approaches. The results were used to examine evolution of non-molecular characters and to develop a new phylogenetically based infrafamilial classification. As in previous molecular phylogenetic analyses of the family, we found strong support for monophyly of groups corresponding closely to many previously recognized tribes and subfamilies, but no previous classification was entirely supported, and relationships among the strongly supported clades were weakly resolved and/or conflicted between some data sets. We recognize three subfamilies in Rosaceae: Rosoideae, including Filipendula, Rubus, Rosa, and three tribes; Dryadoideae, comprising the four actinorhizal genera; and Spiraeoideae, comprising Lyonothamnus and seven tribes. All genera previously assigned to Amygdaloideae and Maloideae are included in Spiraeoideae. Three supertribes, one in Rosoideae and two in Spiraeoideae, are recognized.

http://www.bergianska.se/polopoly_fs/1.68351.1325501360!/menu/standard/file/Potter_et_al_2007.pdf

Phylogeny and classification of Rosaceae

SUMMARY Leaves or their functional analogues provide outstanding opportunities for comparative studies. Here, I use leaves to illustrate the crucial role of ecological, biogeographic and phylogenetic comparisons in generating and testing hypotheses regarding the adaptive significance of morphological variation, the relative importance of selective pressures vs phylogenetic constraints, and the rise of adaptations within lineages. The complementary roles of comparative studies and optimality models are stressed throughout. The first section of this paper reviews 23 ecological patterns in leaf form, physiology and arrangement which have been uncovered by comparative studies. Three general sets of energetic trade-offs, involving the economics of gas exchange, support, and biotic interactions, appear likely to influence the evolution of leaves and underlie these trends. The first of these trade-offs is illustrated with an analysis of the adaptive significance of leaf size, in both terrestrial and aquatic plants. The resulting predictions are compared with the actual trends observed, and the relative strengths and limitations of the approach are discussed. The second section addresses the role of selective pressures and phylogenetic constraints in determining features of leaf form and phenology in forest herbs. Ecological comparisons of 74 species from a site in the Virginia Piedmont show that members of each temporal photosynthetic guild display evolutionary convergence in several aspects of leaf form and arrangement. These convergences can each be understood in terms of models that assume that selection favours plants whose form and physiology tend to maximize whole-plant growth. Phylogenetic comparisons indicate that congeners of guild members share the same leaf phenology as the guild members themselves. This remarkable finding suggests that phenology is evolutionarily rather non-labile within genera but that, within guilds, species in several different genera and families converge strongly in other leaf traits. In this case, phylogenetic constraints appear to be important mainly in determining which lineages evolve particular phenologies and leaf adaptations, not whether they arise. The section concludes with a critical discussion of the capacity of t-wo classes of evolutionary models, based primarily on functional considerations or phylogenetic constraints, to produce truly deductive predictions. The third section briefly reviews an analysis of adaptive radiation in leaf shape among violets of eastern North America. Each ecological group of species displays the leaf shape expected on functional grounds and separate lineages (as judged by means of phylogeny independent of leaf shape) show parallel trends. Ecological and phylogenetic comparisons, in combination with optimality models, provide insights into the sequence of habitats invaded and leaf forms evolved. I conclude with comments on the advantages and limitations of comparative studies, and speculate on avenues for future research on leaf form. An integrated approach, involving comparisons at ecological, phylogenetic and biogeographic levels, and complemented by optimality analyses and detailed populational studies involving biomechanics, physiological ecology and ecological genetics, is strongly advocated.

Z. V. Bolkhovskikh

Papers

Chromosome numbers of flowering plants.