Geraldine A. Allen

SEX RATIO VARIATION IN THE DIOECIOUS SHRUB OEMLERIA CERASIFORMIS

Many examples of biased sex ratios are known in natural populations of plants. Proximal causes of these biases are gender diphasy (sex changing), differential mortality between male and female genets, differential rates of clonal growth (numbers of ramets per genet), and differential flowering (differences in flowering frequency or age to maturity). In the western North American shrub Oemleria cerasiformis we determined sex ratios for 60 natural populations and found an excess of males in 56 populations. The male bias was greatest in populations with little recent recruitment. Sampling of young and old plants indicated that males flowered at an earlier age than females, which led to a transient flowering bias in very young plants, and that the genet sex ratio was 1:1 in young mature plants but male biased in old plants, as a result of differential mortality. Examination of dead genets confirmed that mature females have higher mortality rates. Females also have greater reproductive effort and slower growth rates than males. The major cause of biased sex ratios in O. cerasiformis is greater mortality of female plants during their reproductive years, which probably arises directly or indirectly from their greater allocation to reproduction.

Relative reproductive effort in males and females of the dioecious shrub Oemleria cerasiformis

SummaryWe derived an index of reproductive effort (g reproductive tissue per g leaf) from data collected over two seasons on 28 males and 28 females of the dioecious shrub Oemleria cerasiformis. Males produced an average of three times as much flower and flower-stalk tissue as females, but because of their large fruits, females produced four times as much total reproductive biomass. Reproductive effort of both sexes was related to light. Fruit set in females (% carpels producing drupes) averaged 11.2% and was related to spring light levels. Male-biased sex ratios in this species may be related to the greater reproductive effort of females.

Phylogeny and Biogeography of Erythronium (Liliaceae) Inferred from Chloroplast matK and Nuclear rDNA ITS Sequences

Abstract We investigated phylogenetic relationships within Erythronium using DNA sequences from the chloroplast gene matK and the internal transcribed spacer (ITS) of nuclear ribosomal DNA. Erythronium, Amana, and Tulipa form a strongly supported clade that appears to be of Asian origin. Erythronium is widely distributed in the Northern Hemisphere, and consists of three well supported and geographically distinct clades occurring in western North America, eastern North America, and Eurasia. ITS analyses suggest that the Eurasian and eastern North American clades form a monophyletic group that separated into two lineages following divergence from the western North American clade. Although the three clades are each characterized by distinct morphological features, convergence both among and within geographic areas is seen in several characters. The western North American clade exhibits greater morphological and molecular diversity than either of the other two clades, and many of its species hybridize, suggesting both recent and ongoing speciation. The geographic distribution of Erythronium suggests initial diversification in Tertiary mixed mesophytic forest, followed by fragmentation of the range during the late Tertiary or early Pleistocene and subsequent radiation in western North America.

Rapid radiation and dispersal out of the Qinghai-Tibetan Plateau of an alpine plant lineage Rhodiola (Crassulaceae)

Rhodiola L. (Crassulaceae) is a mid-sized plant genus consisting of about 70 species, with most species distributed on the Qinghai-Tibetan Plateau (QTP) and the adjacent areas, and several species in north-east Asia, Europe, and North America. This study explored the origin and diversification history of Rhodiola and tested the biogeographic relationships between the QTP and other regions of the Northern Hemisphere. We sequenced the nuclear ribosomal internal transcribed spacers and eight plastid DNA fragments representing 55 species of Rhodiola, and reconstructed phylogenetic relationships with maximum parsimony, maximum likelihood and Bayesian inference. Several instances of incongruence between the nuclear and the plastid data sets were revealed, which can best be explained by reticulate evolution. Species of Rhodiola and Pseudosedum form a well-supported clade sister to Phedimus. Dating analysis suggested that the origin and diversification times of this group are largely correlated with the extensive uplifts of the Qinghai-Tibetan Plateau. Ancestral state reconstruction supports the hypothesis that Rhodiola originated on the QTP, and then dispersed to other regions of the Northern Hemisphere. Our findings highlight the importance of the uplifts of the Qinghai-Tibetan Plateau in promoting species diversification and the possible role of reticulate evolution in the diversification process. Our results also suggest the biogeographic significance of QTP as the source area in alpine plant evolution in the Northern Hemisphere.

A Comparison of Reproductive Effort in the Dioecious Shrub Oemleria cerasiformis Using Nitrogen, Energy and Biomass as Currencies

-Energy and nitrogen concentration were determined for reproductive structures of the dioecious shrub Oemleria cerasiformis. We compared reproductive effort for 28 plants of each sex, calculated in terms of energy and nitrogen, with previous estimates of reproductive effort using biomass. Energy concentration was very similar among reproductive structures and among individual plants. The concentration of nitrogen was highest in flowers and flower peduncles of both sexes (3.78-5.20%), much lower in fruits (1.77%) and lowest in fruit peduncles (1.03%). In terms of nitrogen, reproductive effort of females was almost twice that of males; in terms of energy or biomass, the difference was approximately fourfold. Using any of these currencies, the difference between the sexes is sufficient to have important life-history implications.

Biomass allocation among reproductive structures in the dioecious shrub Oemleria cerasiformis: a functional interpretation

The allocation of resources among various reproductive structures and functions can suggest the relative importance of past selective pressures in moulding reproductive patterns. To determine how male and female plants of the dioecious shrub Oemleria cerasiformis differ in allocation to reproductive functions, biomass was partitioned among reproductive structures for 20 plants of each sex. Structures contributing to pollinator attraction (petals and hypanthium) were heavier in males than in females. In males, these structures constituted 63% of total reproductive biomass; inflorescence stems and bracts constituted 28%, and the androecium only 9%. In females at flowering, petals and hypanthium constituted 50% of reproductive biomass, inflorescence stems and bracts 37%, and the gynoecium 13% (...)

The impact of Pleistocene climate change on an ancient arctic–alpine plant: multiple lineages of disparate history in Oxyria digyna

The ranges of arctic–alpine species have shifted extensively with Pleistocene climate changes and glaciations. Using sequence data from the trnH-psbA and trnT-trnL chloroplast DNA spacer regions, we investigated the phylogeography of the widespread, ancient (>3 million years) arctic–alpine plant Oxyria digyna (Polygonaceae). We identified 45 haplotypes and six highly divergent major lineages; estimated ages of these lineages (time to most recent common ancestor, TMRCA) ranged from ∼0.5 to 2.5 million years. One lineage is widespread in the arctic, a second is restricted to the southern Rocky Mountains of the western United States, and a third was found only in the Himalayan and Altai regions of Asia. Three other lineages are widespread in western North America, where they overlap extensively. The high genetic diversity and the presence of divergent major cpDNA lineages within Oxyria digyna reflect its age and suggest that it was widespread during much of its history. The distributions of individual lineages indicate repeated spread of Oxyria digyna through North America over multiple glacial cycles. During the Last Glacial Maximum it persisted in multiple refugia in western North America, including Beringia, south of the continental ice, and within the northern limits of the Cordilleran ice sheet. Our data contribute to a growing body of evidence that arctic–alpine species have migrated from different source regions over multiple glacial cycles and that cryptic refugia contributed to persistence through the Last Glacial Maximum.

Morphological and Cytological Variation in the Western North American Aster occidentalis Complex (Asteraceae)

The Aster occidentalis complex is a western North American group of rhizomatous perennials. The group shows considerable morphological variation and includes at least six ploidy levels with chromosome numbers ranging from n = 8 to n = 48. In this study, 283 chromosome counts are reported; most specimens sampled had euploid chromosome numbers based on x = 8, but a few aneuploid plants were also found. The relationship between morphological variation and chromosome number was assessed using a cluster analysis and principal components analysis of up to 35 characters in 172 specimens of known ploidy level. The diploid specimens fell into six morphological groups, corresponding to five of the approximately ten species included in the complex. The polyploids showed greater variability and more extensive intergradation between groups than did the diploids. The geographic distributions of chromosome numbers in the more widely distributed species are also discussed. Aster, taxonomically one of the most difficult of North American genera, has presented sys- tematists with numerous problems in delimit- ing species boundaries and determining rela- tionships. The genus is cytologically variable and contains chromosome numbers based mainly on x = 5, 8, and 9; both aneuploids and polyploids have been reported (Dean 1966; Dean and Chambers 1983; Jones 1980b; Semple

Hybridization studies in the Aster occidentalis (Asteraceae) polyploid complex of Western North America

Hybridization experiments were carried out with 12 of the approximately 15 species in the complex. The crosses involved plants at various ploidy levels from diploid (n=8) to duodecaploid (n=48). Viable F1 progeny were obtained from 26% of the crosses involving diploids, and from 66% of the crosses between polyploids. All but a few of the progeny had a high degree of pollen fertility, and all of those examined had regular pairing of chromosomes at meiosis. Even at the diploid level few reproductive barriers isolate the taxa of this complex, although morphologically distinct entities can be recognized.

Vicariance, long‐distance dispersal, and regional extinction–recolonization dynamics explain the disjunct circumpolar distribution of the arctic‐alpine plant Silene acaulis

PREMISE OF THE STUDY Many arctic-alpine species have vast geographic ranges, but these may encompass substantial gaps whose origins are poorly understood. Here we address the phylogeographic history of Silene acaulis, a perennial cushion plant with a circumpolar distribution except for a large gap in Siberia. METHODS We assessed genetic variation in a range-wide sample of 103 populations using plastid DNA (pDNA) sequences and AFLPs (amplified fragment length polymorphisms). We constructed a haplotype network and performed Bayesian phylogenetic analyses based on plastid sequences. We visualized AFLP patterns using principal coordinate analysis, identified genetic groups using the program structure, and estimated genetic diversity and rarity indices by geographic region. KEY RESULTS The history of the main pDNA lineages was estimated to span several glaciations. AFLP data revealed a distinct division between Beringia/North America and Europe/East Greenland. These two regions shared only one of 17 pDNA haplotypes. Populations on opposite sides of the Siberian range gap (Ural Mountains and Chukotka) were genetically distinct and appear to have resulted from postglacial leading-edge colonizations. We inferred two refugia in North America (Beringia and the southern Rocky Mountains) and two in Europe (central-southern Europe and northern Europe/East Greenland). Patterns in the East Atlantic region suggested transoceanic long-distance dispersal events. CONCLUSIONS Silene acaulis has a highly dynamic history characterized by vicariance, regional extinction, and recolonization, with persistence in at least four refugia. Long-distance dispersal explains patterns across the Atlantic Ocean, but we found no evidence of dispersal across the Siberian range gap.