Hawaiian Silversword Research Articles

Biogeomorphological influence of the Hawaiian silversword ( Argyroxiphium sandwicense DC.) on soil erosion in Haleakala (Maui, Hawai'i)

Soils were examined at 2505 m elevation in Haleakala's crater (Maui, Hawaiʻi) beneath 50 adult Hawaiian silversword plants ( Argyroxiphium sandwicense DC.); mean canopy diameter was 42.0 cm. Exposed volcanic Inceptisols (Andic Humitropepts) seem significantly eroded beyond the dense rosette crowns, but remain unaffected below plants. Rosettes are perched on isolated basal soil mounds or pedestals 27–121 mm high (mean: 77.5 mm). Geomorphic field response of soils below rosettes and adjacent (∼ 100 cm apart) bare soils differs. Infiltration rates are higher under plants (mean: 158.7 mm/min) than in exposed control soils (60.0 mm/min). Soils below silverswords also show greater shear strength (146.1 g/cm 2) and compressibility (2.795 kg/cm 2) than unprotected soils (36.1 g/cm 2, and 0.108 kg/cm 2, respectively). Soil in the plant mounds contains more organic matter; this has influenced other pedological properties, which also differ substantially between sampling positions. Substrate under plants has a porosity ∼ 53% higher than exposed soil, while bulk density is 62% higher in soil outside the plant crown. The observed microtopographic differences are ascribed to greater soil erosion by rainsplash and runoff outside the silversword canopy. The dense rosette crown effectively intercepts raindrops; soils beneath plants also have a high surface cohesiveness provided by a dense network of fine plant rootlets and partially decomposed organic material. Higher runoff rates occur on the less permeable substrate beyond rosettes, which is affected by soil crusting.

ECOLOGICAL SPECIATION IN THE EAST MAUI-ENDEMIC DUBAUTIA (ASTERACEAE) SPECIES

Adaptive diversification can be viewed as a balance between the conservative force of interpopulation gene flow and selection for differential environments. In this paper, we examine ecological, morphological, and genetic differentiation in a small clade consisting of four East Maui-endemic species of Dubautia: D. menziesii, D. platyphylla, D. reticulata, and D. waianapanapaensis, in the Hawaiian silversword alliance (Asteraceae). The East Maui clade is apparently recently derived (less than 1 million years ago) and is geographically restricted yet displays significant ecological and morphological differences. We used geographic data from historical herbarium specimens, measurements of plant architecture and leaf morphometrics, and measures of genetic differentiation in both microsatellite and nuclear coding loci to examine the correlation of different forms of divergence in this small species flock. We found overlap in large-scale geographic distributions, significant differentiation in most habitat factors, significant microsatellite differentiation, and many shared alleles at nuclear coding loci suggesting on-going lineage sorting. Despite the presence of apparent hybrids in some populations, microsatellite variation is consistent with isolation among species. Using Mantel tests, we compared the direction and extent of diversification among different datasets, to determine whether ecological/morphological divergence was correlated with genetic divergence. Correlations among different datasets showed that habitat was strongly correlated with plant architecture but not leaf morphology. Taken together, these results indicate that ecological and morphological diversification has driven genetic divergence at rapidly evolving microsatellite loci, whereas there is continuing lineage sorting at neutral sites in nuclear coding loci.

CONTRASTING PATTERNS AND PROCESSES OF EVOLUTIONARY CHANGE IN THE TARWEED–SILVERSWORD LINEAGE: REVISITING CLAUSEN, KECK, AND HIESEY'S FINDINGS1

Abstract Jens C. Clausen, David D. Keck, and William M. Hiesey's biosystematic research on continental tarweeds (Madiinae; Compositae) provided diverse examples of evolutionary change for Clausen's synthesis, Stages in the Evolution of Plant Species. Subsequent anatomical work by Sherwin Carlquist demonstrated that the tarweed lineage also includes a spectacular example of adaptive radiation, the Hawaiian silversword alliance. Molecular phylogenetic data and evidence from genetic and hybridization studies have allowed additional perspectives on Clausen et al.'s and Carlquist's hypotheses of tarweed–silversword evolution. In Californian Layia, Clausen et al.'s evidence for gradual allopatric diversification for the n = 7 taxa accords with patterns of molecular divergence and decay of interfertility across lineages inferred from a rate-constant rDNA tree. In contrast, recent evidence on patterns and timing of diversification in an n = 8 Layia clade indicates multiple examples of accelerated phenotypic evolu...

ECOLOGICAL SPECIATION IN THE EAST MAUI–ENDEMIC DUBAUTIA (ASTERACEAE) SPECIES

Adaptive diversification can be viewed as a balance between the conservative force of interpopulation gene flow and selection for differential environments. In this paper, we examine ecological, morphological, and genetic differentiation in a small clade consisting of four East Maui–endemic species of Dubautia D. menziesii, D. platyphylla, D. reticulata, and D. waianapanapaensis, in the Hawaiian silversword alliance (Asteraceae). The East Maui clade is apparently recently derived (less than 1 million years ago) and is geographically restricted yet displays significant ecological and morphological differences. We used geographic data from historical herbarium specimens, measurements of plant architecture and leaf morphometrics, and measures of genetic differentiation in both microsatellite and nuclear coding loci to examine the correlation of different forms of divergence in this small species flock. We found overlap in large-scale geographic distributions, significant differentiation in most habitat factors, significant microsatellite differentiation, and many shared alleles at nuclear coding loci suggesting on-going lineage sorting. Despite the presence of apparent hybrids in some populations, microsatellite variation is consistent with isolation among species. Using Mantel tests, we compared the direction and extent of diversification among different datasets, to determine whether ecological/morphological divergence was correlated with genetic divergence. Correlations among different datasets showed that habitat was strongly correlated with plant architecture but not leaf morphology. Taken together, these results indicate that ecological and morphological diversification has driven genetic divergence at rapidly evolving microsatellite loci, whereas there is continuing lineage sorting at neutral sites in nuclear coding loci.

ORIGIN AND RAPID DIVERSIFICATION OF A TROPICAL MOSS

Molecular sequences rarely evolve at a constant rate. Yet, even in instances where a clock can be assumed or approximated for a particular set of sequences, fossils or clear patterns of vicariance are rarely available to calibrate the clock. Thus, obtaining absolute timing for diversification of natural lineages can prove difficult. Unfortunately, without absolute time we cannot develop a complete understanding of important evolutionary processes, including adaptive radiations and key innovations. In the present study, the coding sequence of the nuclear gene, glyceraldehyde 3-phosphate dehydrogenase (gpd), extracted from the paleotropical moss, Mitthyridium, was found to exhibit clocklike behavior and used to reconstruct the history of 80 distinct molecular lineages that cover the full geographic range of Mitthyridium. Two separate clades endemic to two geographically distinct oceanic archipelagos were revealed by this phylogenetic analysis. This allowed the use of island age (as derived from potassium-argon dating) as a maximum age of origin of each monophyletic group, providing two independent time anchors for the clock found in gpd, the final piece needed to study absolute time. Based on results from both maximum age calibrations, which separately yielded highly consistent estimates, the ancestor of this moss group arose approximately 8 million years ago, and then diversified at the rapid rate of 0.56 +/- 0.004 new lineages per million years. Such a rate is on par with the highest diversification rates reported in the literature including rapidly radiating insular groups like the Hawaiian silversword alliance, a classic example of an adaptive radiation. Using independent sources of data, it was found that neither the age nor diversification estimates were affected by the use of molecular lineages rather than species as the operational taxonomic units. Identifying the cause for this rapid diversification requires further testing, but it appears to be related to a general shift in reproductive strategy from sexual to asexual, which may be a key innovation for this young group.

Biogeographic Interpretation of Splits Graphs: Least Squares Optimization of Branch Lengths

Although most often used to represent phylogenetic uncertainty, network methods are also potentially useful for describing the phylogenetic complexity expected to characterize recent species radiations. One network method with particular advantages in this context is split decomposition. However, in its standard implementation this approach is limited by a conservative criterion for branch length estimation. Here we extend the utility of split decomposition by introducing a least squares optimization technique for correcting branch lengths that may be underestimated by the standard implementation. This optimization of branch lengths is generally expected to improve divergence time estimates calculated from splits graphs. We illustrate the effect of least squares optimization on such estimates using the Australasian Myosotis and the Hawaiian silversword alliance as examples. We also discuss the biogeographic interpretation and limitations of splits graphs.

ORIGIN AND RAPID DIVERSIFICATION OF A TROPICAL MOSS

Molecular sequences rarely evolve at a constant rate. Yet, even in instances where a clock can be assumed or approximated for a particular set of sequences, fossils or clear patterns of vicariance are rarely available to calibrate the clock. Thus, obtaining absolute timing for diversification of natural lineages can prove difficult. Unfortunately, without absolute time we cannot develop a complete understanding of important evolutionary processes, including adaptive radiations and key innovations. In the present study, the coding sequence of the nuclear gene, glyceraldehyde 3-phosphate dehydrogenase (gpd), extracted from the paleotropical moss, Mitthyridium, was found to exhibit clocklike behavior and used to reconstruct the history of 80 distinct molecular lineages that cover the full geographic range of Mitthyridium. Two separate clades endemic to two geographically distinct oceanic archipelagos were revealed by this phylogenetic analysis. This allowed the use of island age (as derived from potassium-argon dating) as a maximum age of origin of each monophyletic group, providing two independent time anchors for the clock found in gpd, the final piece needed to study absolute time. Based on results from both maximum age calibrations, which separately yielded highly consistent estimates, the ancestor of this moss group arose approximately 8 million years ago, and then diversified at the rapid rate of 0.56 ± 0.004 new lineages per million years. Such a rate is on par with the highest diversification rates reported in the literature including rapidly radiating insular groups like the Hawaiian silversword alliance, a classic example of an adaptive radiation. Using independent sources of data, it was found that neither the age nor diversification estimates were affected by the use of molecular lineages rather than species as the operational taxonomic units. Identifying the cause for this rapid diversification requires further testing, but it appears to be related to a general shift in reproductive strategy from sexual to asexual, which may be a key innovation for this young group.

RAPID ALLOPATRIC SPECIATION IN LOGPERCH DARTERS (PERCIDAE: PERCINA)

Theory predicts that clades diversifying via sympatric speciation will exhibit high diversification rates. However, the expected rate of diversification in clades characterized by allopatric speciation is less clear. Previous studies have documented significantly higher speciation rates in freshwater fish clades diversifying via sympatric versus allopatric modes, leading to suggestions that the geographic pattern of speciation can be inferred solely from knowledge of the diversification rate. We tested this prediction using an example from darters, a clade of approximately 200 species of freshwater fishes endemic to eastern North America. A resolved phylogeny was generated using mitochondrial DNA gene sequences for logperches, a monophyletic group of darters composed of 10 recognized species. Divergence times among logperch species were estimated using a fossil calibrated molecular clock in centrarchid fishes, and diversification rates in logperches were estimated using several methods. Speciation events in logperches are recent, extending from 4.20 +/- 1.06 million years ago (mya) to 0.42 +/- 0.22 mya, with most speciation events occurring in the Pleistocene. Diversification rates are high in logperches, at some nodes exceeding rates reported for well-studied adaptive radiations such as Hawaiian silverswords. The geographic pattern of speciation in logperches was investigated by examining the relationship between degree of sympatry and the absolute age of the contrast, with the result that diversification in logperches appears allopatric. The very high diversification rate observed in the logperch phylogeny is more similar to freshwater fish clades thought to represent examples of sympatric speciation than to clades representing allopatric speciation. These results demonstrate that the geographic mode of speciation for a clade cannot be inferred from the diversification rate. The empirical observation of high diversification rates in logperches demonstrates that allopatric speciation can occur rapidly.

RAPID ALLOPATRIC SPECIATION IN LOGPERCH DARTERS (PERCIDAE: PERCINA)

Theory predicts that clades diversifying via sympatric speciation will exhibit high diversification rates. However, the expected rate of diversification in clades characterized by allopatric speciation is less clear. Previous studies have documented significantly higher speciation rates in freshwater fish clades diversifying via sympatric versus allopatric modes, leading to suggestions that the geographic pattern of speciation can be inferred solely from knowledge of the diversification rate. We tested this prediction using an example from darters, a clade of approximately 200 species of freshwater fishes endemic to eastern North America. A resolved phylogeny was generated using mitochondrial DNA gene sequences for logperches, a monophyletic group of darters composed of 10 recognized species. Divergence times among logperch species were estimated using a fossil calibrated molecular clock in centrarchid fishes, and diversification rates in logperches were estimated using several methods. Speciation events in logperches are recent, extending from 4.20 ± 1.06 million years ago (mya) to 0.42 ± 0.22 mya, with most speciation events occurring in the Pleistocene. Diversification rates are high in logperches, at some nodes exceeding rates reported for well-studied adaptive radiations such as Hawaiian silverswords. The geographic pattern of speciation in logperches was investigated by examining the relationship between degree of sympatry and the absolute age of the contrast, with the result that diversification in logperches appears allopatric. The very high diversification rate observed in the logperch phylogeny is more similar to freshwater fish clades thought to represent examples of sympatric speciation than to clades representing allopatric speciation. These results demonstrate that the geographic mode of speciation for a clade cannot be inferred from the diversification rate. The empirical observation of high diversification rates in logperches demonstrates that allopatric speciation can occur rapidly.

Influence of substrate on the distribution of the Hawaiian Silversword ( Argyroxiphium sandwicense DC.) in Haleakala (Maui, HI)

The spatial patterns of the Hawaiian silversword ( Argyroxiphium sandwicense DC.) were studied in Haleakala (Maui, HI). The silversword is a “giant” rosette plant nearly brought to extinction by human impact and goat browsing during the 1920s, but stern protection has resulted in the resurgence of plant populations. Silversword regeneration is occurring vigorously in soils with surficial layers of volcaniclastic fragments. Ten sites with sizable silversword populations and the associated substrates were examined in Haleakala's crater between 2175 and 2755 m. At each site, the population structure of 100 plants was determined along wandering-quarter transects, which limit sampling bias. Substrates where rosettes were rooted and the size of the biggest stone fragments upslope and downslope from the plant's base were determined. Volcaniclastic substrates were examined with photographs along 12-m-long transverse transects. Fine-debris samples (gravel and pebbles) were analyzed by mechanical sifting of surficial fragments gathered from 15×15 cm miniplots. Volcaniclastic fragments in silversword areas have different sources. (i) Most were ejected during eruptions yielding pyroclastic materials (ash to blocks) that built cinder cones on Haleakala's crater. (ii) On steep slopes, weathering of (olivine alkali) basalt outcrops and subsequent mass wasting of rock fragments contributed a mantle of clasts to slopes below. (iii) On some cinder cones, welded spatter was produced during late eruptive stages; this coalesced into ruff-like agglutinate layers around crater rims, called Pohaku-o-Hanalei (“wreath of stones”). Agglutinate deposits weather gradually, supplying clasts that roll downhill and accumulate on cone flanks. (iv) On weathered aa lava flows, stone fragments and rocky crags abound along eroding lava-flow ridges, associated with vegetation; but the intervening troughs, covered with fine ash and cinder, remain bare. Silversword population structures indicate healthy regeneration. All populations display a typical pattern of decreasing silversword numbers with increasing size (=age). Nearly 65% of the rosettes are rooted near cobbles (5–10 cm long) or pebbles (2.5–5 cm), and ∼23% grow at the base of blocks (>10 cm) or outcrops; 9% of the plants are on gravel (<2.5 cm), but only 1% have germinated on sandy soil without granules or stones; 2% of the silverswords grow on organic litter of dead rosettes. Plants on six sites showed noticeable differences in clast size between their upslope and downslope sides; particles are significantly larger upslope from rosettes. This suggests that successful seedlings germinate below clasts, which deflect finer downslope-moving sediment, thus protecting young plants from burial by descending debris. Statistical tests indicate a few blocks above plants may have been stopped by adult rosettes. Such a relationship underscores the dynamic nature of steep cinder and rubble (talus) slopes, regularly affected by dry debris slides, frost creep, and other mass-wasting processes. Slope instability is also evinced by (i) common bending and deformation of silversword roots—particularly in seedlings—which trail upslope; (ii) pronounced downhill tilting and asymmetry of tall rosettes on steep gradients; (iii) presence of accumulated fine-debris steps (9.9–13.8 cm thick) upslope from plants and blocks; (iv) ubiquitous fine-earth flags exposed below embedded blocks, which intercept descending debris and deflect it laterally; (v) widespread miniature sorted stripes.

GAI homologues in the Hawaiian silversword alliance (Asteraceae-Madiinae): molecular evolution of growth regulators in a rapidly diversifying plant lineage.

Accelerated evolution of regulatory genes has been proposed as an explanation for decoupled rates of morphological and molecular evolution. The Hawaiian silversword alliance (Asteraceae-Madiinae) has evolved drastic differences in growth form, including rosette plants, cushion plants, shrubs, and trees, since its origin approximately 6 MYA. We have isolated genes in the DELLA subfamily of putative growth regulators from 13 taxa of Hawaiian and North American Madiinae. The Hawaiian taxa contain two copies of DaGAI that form separate clades within the Madiinae, consistent with an allotetraploid origin for the silversword alliance. DaGAI retains conserved features that have previously been identified in DELLA genes. Selective constraint in the Hawaiian DaGAI copies remains strong in spite of rapid growth form divergence in the silversword alliance, although the constraint was somewhat relaxed in the Hawaiian copies relative to the North American lineages. We failed to detect evidence for positive selection on individual codons. Notably, selective constraint remained especially strong in the gibberellin-responsive DELLA region for which the gene subfamily is named, which is truncated or deleted in all identified dwarf mutants in GAI homologues in different angiosperm species. In contrast with the coding region, however, approximately 900 bp of the upstream flanking region shows variable rates and patterns of evolution, which might reflect positive selection on regulatory regions.

Accelerated regulatory gene evolution in an adaptive radiation.

The disparity between rates of morphological and molecular evolution remains a key paradox in evolutionary genetics. A proposed resolution to this paradox has been the conjecture that morphological evolution proceeds via diversification in regulatory loci, and that phenotypic evolution may correlate better with regulatory gene divergence. This conjecture can be tested by examining rates of regulatory gene evolution in species that display rapid morphological diversification within adaptive radiations. We have isolated homologues to the Arabidopsis APETALA3 (ASAP3/TM6) and APETALA1 (ASAP1) floral regulatory genes and the CHLOROPHYLL A/B BINDING PROTEIN9 (ASCAB9) photosynthetic structural gene from species in the Hawaiian silversword alliance, a premier example of plant adaptive radiation. We have compared rates of regulatory and structural gene evolution in the Hawaiian species to those in related species of North American tarweeds. Molecular evolutionary analyses indicate significant increases in nonsynonymous relative to synonymous nucleotide substitution rates in the ASAP3/TM6 and ASAP1 regulatory genes in the rapidly evolving Hawaiian species. By contrast, no general increase is evident in neutral mutation rates for these loci in the Hawaiian species. An increase in nonsynonymous relative to synonymous nucleotide substitution rate is also evident in the ASCAB9 structural gene in the Hawaiian species, but not to the extent displayed in the regulatory loci. The significantly accelerated rates of regulatory gene evolution in the Hawaiian species may reflect the influence of allopolyploidy or of selection and adaptive divergence. The analyses suggest that accelerated rates of regulatory gene evolution may accompany rapid morphological diversification in adaptive radiations.

The influence of surface volcaniclastic layers from Haleakala (Maui, Hawaii) on soil water conservation

This study focuses on the soils and surficial volcaniclastic layers of Haleakala's crater (Maui, Hawaii). The main objective is to assess the effects of covers with fragments of various sizes (ash, cinder, lapilli) on soil water conservation. Soil and gravel samples were collected in Haleakala National Park from a site at 2505 m where the Hawaiian silversword, a giant rosette-plant, grows densely on pyroclastic materials. An evaporation experiment lasting 22 days showed a gradual drop in seven pairs of soil samples initially at field capacity. One set of samples was left bare, the other was covered by gravel mulches (GM); these resulted in lengthening of T 100% (total desiccation time) by a factor of 2.3–5.2. Bare soils dried after 70–140 h, but drying time under gravel was 246–509 h. Mean grain size ( M z) and sorting ( φ σ ) had the greatest influence on evaporation rates. Coarse lapilli ( M z: 13.8 mm) were less effective than fine ash ( M z: 2.9–3.8 mm) in preventing water losses, while medium-grained cinder ( M z: 4–5.2 mm) produced the greatest water savings. Lapilli (mean φ σ : 0.48) and ash ( φ σ : 0.6) were moderately- to well-sorted; cinders, with a broader grain-size range ( φ σ : 1.13), were poorly sorted. This allowed infilling of large interstices between coarse fragments by smaller grains, effectively reducing pore size and therefore evaporation rates. A second experiment determined water storage and rates of water loss by mulches. Wetting occurred swiftly, within 3–4 min. All gravel types were dry within 26 h. This drying process is important for water conservation, as it effectively prevents further water loss from the mulch surface. Larger fragments stored less water. This is related to their `surface area/weight' ratio, which increases for smaller particles. Thus, fine ash or cinder grains, with a high total area, intercept more water than larger lapilli. A 5-cm thick layer of ash intercepted an average of ∼6.8 mm of rain, slightly more than the same depth of cinder (6.3 mm), but lapilli retained only 4.7 mm. Therefore, light rainfall events are more likely to contribute water to soil under lapilli than below finer pyroclastic material. Volcaniclastic covers serve an important ecological role in Haleakala by prolonging periods of water availability to plants, thus allowing Hawaiian silverswords to grow for longer time spans.

Interspecific hybrid ancestry of a plant adaptive radiation: allopolyploidy of the Hawaiian silversword alliance (Asteraceae) inferred from floral homeotic gene duplications

The polyploid Hawaiian silversword alliance (Asteraceae), a spectacular example of adaptive radiation in plants, was shown previously to have descended from North American tarweeds of the Madia/Raillardiopsis group, a primarily diploid assemblage. The origin of the polyploid condition in the silversword alliance was not resolved in earlier biosystematic, cytogenetic, and molecular studies, apart from the determination that polyploidy in modern species of Madia/Raillardiopsis arose independent of that of the Hawaiian group. We determined that two floral homeotic genes, ASAP3/TM6 and ASAP1, are found in duplicate copies within members of the Hawaiian silversword alliance and appear to have arisen as a result of interspecific hybridization between two North American tarweed species. Our molecular phylogenetic analyses of the ASAP3/TM6 loci suggest that the interspecific hybridization event in the ancestry of the Hawaiian silversword alliance involved members of lineages that include Raillardiopsis muirii (and perhaps Madia nutans) and Raillardiopsis scabrida. The ASAP1 analysis also indicates that the two species of Raillardiopsis are among the closest North American relatives of the Hawaiian silversword alliance. Previous biosystematic evidence demonstrates the potential for allopolyploid formation between members of the two North American tarweed lineages; a vigorous hybrid between R. muirii and R. scabrida has been produced that formed viable, mostly tetraporate (diploid) pollen, in keeping with observed meiotic failure. Various genetic consequences of allopolyploidy may help to explain the phenomenal evolutionary diversification of the silversword alliance.

New Combinations and New Genera in the North American Tarweeds (Compositae-Madiinae)

New combinations and new genera for species in Hemizonia DC., Molina, and Raillardiopsis Rydberg allow for a revised, practical taxonomy of Madiinae that better reflects phylogenetic relationships. Reinstatement of Anisocarpus Nuttall, Centromadia Greene, Deinandra Greene, and Hemizonella A. Gray, abandonment of Raillardiopsis Rydberg, and recognition of four new genera (Carlquistia, Harmonia, Jensia, Kyhosia) for tarweed lineages without available generic names result from changes in circumscription based on monophyletic groups. Results of phylogenetic, biosystematic, and cytogenetic studies in Madiinae (Kyhos et al., 1990; Baldwin et al., 1991; Baldwin, 1992, 1993, 1996, unpublished; Carr et al., 1996) indicate that Hemizonia DC. sensu Keck (1959), Molina sensu Keck (1959), and Raillardiopsis Rydberg are not monophyletic. Hemizonia sensu Keck (1959) comprises a minimum of three monophyletic groups that correspond to section Centromadia (Greene) D. D. Keck, section Hemizonia, and section Madiomeris Nuttall sensu Tanowitz (1982) plus the informal Fruticosae or Zonamra (cf. Clausen, 1951; Keck, 1959). sensu Keck (1959), Raillardiopsis, and the monophyletic Hawaiian silversword alliance (Argyroxiphium DC., Dubautia Gaudichaud-Beauprd, Wilkesia A. Gray; see Carr, 1985) constitute a clade lacking a formal name (the Madia lineage in Baldwin, 1996) that is extremely heterogeneous and difficult to diagnose morphologically. The Hawaiian group comprises trees, shrubs, subshrubs, large rosette plants, mat plants, cushion plants, and vines that are strikingly divergent in morphological and ecological characteristics from the primarily Californian herbs in sensu Keck (1959) and Raillardiopsis (see Carr, 1985; Baldwin & Robichaux, 1995; Baldwin, 1997). In addition to the distinctive Hawaiian lineage, a minimum of seven monophyletic groups can be reliably diagnosed from morphological and molecular data within the clade comprising sensu Keck (1959), Raillardiopsis, and the silversword alliance. Recognition at the generic level of each of the three lineages in Hemizonia sensu Keck (1959) and each of the seven lineages in the paraphyletic group comprising sensu Keck (1959) plus Raillardiopsis in the traditional (only) sense results in a practical taxonomy that conforms to the criterion of monophyly (= holophyly) of taxa. The revision of sensu Keck (1959) plus Raillardiopsis (hereafter, MADRAIL) also allows for continued generic distinction of the unusual Hawaiian species in the silversword alliance without maintaining non-monophyletic California tarweed genera. I realize that additional nomenclatural changes in the silversword alliance are necessary to achieve a taxonomy of the Hawaiian species that includes only monophyletic genera. The new combinations herein focus only on genera relevant to treatments in preparation for the Flora of North America North of Mexico.

Reappraising adaptive radiation

Reappraising adaptive radiation

Age and rate of diversification of the Hawaiian silversword alliance (Compositae).

Comparisons between insular and continental radiations have been hindered by a lack of reliable estimates of absolute diversification rates in island lineages. We took advantage of rate-constant rDNA sequence evolution and an "external" calibration using paleoclimatic and fossil data to determine the maximum age and minimum diversification rate of the Hawaiian silversword alliance (Compositae), a textbook example of insular adaptive radiation in plants. Our maximum-age estimate of 5.2 +/- 0.8 million years ago for the most recent common ancestor of the silversword alliance is much younger than ages calculated by other means for the Hawaiian drosophilids, lobelioids, and honeycreepers and falls approximately within the history of the modern high islands (</=5.1 +/- 0.2 million years ago). By using a statistically efficient estimator that reduces error variance by incorporating clock-based estimates of divergence times, a minimum diversification rate for the silversword alliance was estimated to be 0.56 +/- 0.17 species per million years. This exceeds average rates of more ancient continental radiations and is comparable to peak rates in taxa with sufficiently rich fossil records that changes in diversification rate can be reconstructed.

Molecular Evolution and Adaptive Radiation.

Preface List of Contributors Part I. Introduction: 1. Adaptive radiation and molecular evolution: concepts and research issues Thomas J. Givnish 2. Homoplasy in molecular vs. morphological data: the likelihood of correct phylogenetic inference Thomas J. Givnish, and Kenneth J. Sytsma Part II. Integrative Studies: 3. Adaptive radiation of the Hawaiian silversword alliance: congruence and conflict of phylogenetic evidence from molecular and non-molecular investigations Bruce G. Baldwin 4. The chronicle of marsupial evolution Mark S. Springer, John A. W. Kirsch, and Judd A. Chase 5. Evolutionary origins of phenotypic diversity in Daphnia John K. Colbourne, Paul D. N. Hebert, and Derek J. Taylor 6. Evolutionary trends in the ecology of New World monkeys inferred from a combined phylogenetic analysis of nuclear, mitochondrial, and morphological data Ines Horovitz, and Axel Meye 7. Adaptive radiation in the aquatic plant family Pontederiaceae: insights from phylogenetic analysis Spencer C. H. Barrett, and Sean W. Graham 8. Molecular evolution and adaptive radiation in Brocchinia (Bromeliaceae: Pitcairnioideae) atop tepuis of the Guayana Shield Thomas J. Givnish, Kenneth J. Sytsma, James F. Smith, William J. Hahn, David H. Benzing, and Elizabeth M. Burkhardt Part III. Convergence: 9. You aren't always what you eat: evolution of nectar-feeding among Old World fruitbats (Megachiroptera: Pteropodidae) John A. W. Kirsch, and Francois-Joseph Lapointe 10. Chloroplast DNA restriction sites and floral versus non-floral characters in the obligate twig epiphytes in subtribe Oncidiinae (Orchidaceae) Mark W. Chase, and Jeffrey D. Palmer 11. Adaptation, cladogenesis, and the evolution of habitat association in North American tiger beetles: a phylogenetic perspective Alfried P. Vogler Part IV. Rapid Radiations: 12. Molecular phylogenetic tests of sympatric speciation models in Lake Malawi cichlid fishes Peter N. Reinthal, and Axel Mey 13. A rapid adaptive radiation due to a key innovation in Aquilegia Scott Hodges 14. Origin and evolution of Argyranthemum (Asteraceae: Anthemideae) in Macaronesia Javier Francisco-Ortega, Daniel J. Crawford, Arnoldo Santos-Guerra, and Robert K. Jansen Part V. Reproductive Strategies: 15. Floral diversification, pollination biology, and molecular evolution in Platanthera (Orchidaceae) Jeffrey R. Hapeman, and Kenneth Inoue 16. Phylogenetic perspectives on the evolution of dioecy: adaptive radiation in the endemic Hawaiian genera Schiedea and Alsinodendron (Caryophyllaceae: Alsinoideae) Ann K. Sakai, Stephen G. Weller, Warren L. Wagner, and Pamela S. Soltis 17. Ecological and reproductive shifts in the diversification of the endemic Hawaiian Drosophila Michael P. Kambysellis, and Elysse M. Craddock Part VI. Character Divergence and Community Assembly: 18. History of ecological selection in sticklebacks - uniting experimental and phylogenetic approaches Eric B. Taylor, James D. McPhail, and Dalph Schluter 19. Phylogenetic studies of convergent adaptive radiations in Caribbean Anolis lizards Todd Jackman, Jonathan B. Losos, Allan Larson, and Kevin de Queiros Part VII. Macroevolutionary Patterns: 20. Molecular and morphological evolution during the post-Palaeozoic diversification of echinoids Andrew B. Smith, and D. T. J. Littlewood 21. How fast is speciation: molecular, geological and phylogenetic evidences from adaptive radiations of fish Amy R. McCune Index.

Nuclear ribosomal DNA evidence for a western North American origin of Hawaiian and South American species of Sanicula (Apiaceae).

Results from phylogenetic analysis of nuclear rDNA internal transcribed spacer (ITS) sequences from a worldwide sample of Sanicula indicate that Hawaiian sanicles (Sanicula sect. Sandwicenses) constitute a monophyletic group that descended from a western North American ancestor in Sanicula sect. Sanicoria, a paraphyletic assemblage of mostly Californian species. A monophyletic group comprising representatives of all 15 species of S. sect. Sanicoria and the three sampled species of S. sect. Sandwicenses was resolved in all maximally parsimonious trees, rooted with sequences from species of Astrantia and Eryngium. All sequences sampled from eastern North American, European, and Asian species of Sanicula fell outside the ITS clade comprising S. sect. Sanicoria and S. sect. Sandwicenses. A lineage comprising the Hawaiian taxa and three species endemic to coastal or near-coastal habitats in western North America (Sanicula arctopoides, Sanicula arguta, and Sanicula laciniata) is diagnosed by nucleotide substitutions and a 24-bp deletion in ITS2. The hooked fruits in Sanicula lead us to conclude that the ancestor of Hawaiian sanicles arrived from North America by external bird dispersal; similar transport has been hypothesized for the North American tarweed ancestor of the Hawaiian silversword alliance (Asteraceae). Two additional long-distance dispersal events involving members of S. sect. Sanicoria can be concluded from the ITS phylogeny: dispersal of Sanicula crassicaulis and Sanicula graveolens from western North America to southern South America.

Biodiversity of planthoppers (Hemiptera: Delphacidae) on the Hawaiian silversword alliance: effects of host plant phylogeny and hybridization

Biodiversity of planthoppers (Hemiptera: Delphacidae) on the Hawaiian silversword alliance: effects of host plant phylogeny and hybridization