Asparagales are a diverse monophyletic order that has numerous species (ca. 50% of monocots) incl... more Asparagales are a diverse monophyletic order that has numerous species (ca. 50% of monocots) including important crop plants such as Allium, Asparagus, and Vanilla, and a host of ornamentals such as irises, hyacinths, and orchids. Historically, Asparagales have been of interest partly because of their fascinating chromosomal evolution. We examine the evolutionary dynamics of Asparagales genomes in an updated phylogenetic framework that combines analyses of seven gene regions (atpl, atpB, matK, ndhF, rbcL, trnL intron, and trnL-F intergenic spacer) for 79 taxa of Asparagales and outgroups. Asparagales genomes are evolutionarily labile for many characters, including chromosome number and genome size. The history and causes of variation in chromosome number and genome size remain unclear, primarily because of the lack of data in small clades in the phylogenetic tree and the lack of comparative genetic maps, apart from Allium and Asparagus. Genomic tools such as bacterial artificial chromosome (BAC) libraries should be developed, as both molecular cytogenetic markers and a source of nuclear genes that can be widely used by evolutionary biologists and plant breeders alike to decipher mechanisms of chromosomal evolution.
We used ndhF sequence variation to reconstruct relationships across 282 taxa representing 78 mono... more We used ndhF sequence variation to reconstruct relationships across 282 taxa representing 78 monocot families and all 12 orders. The resulting tree is highly resolved and places commelinids sister to Asparagales, with both sister to Liliales-Pandanales in the strict consensus; Pandanales are sister to Dioscoreales in the bootstrap majority-rule tree, just above Petrosaviales. Acorales are sister to all other monocots, with Alismatales sister to all but Acorales. Relationships among the four major clades of commelinids remain unresolved. Relationships within orders are consistent with those based on rbcL, alone or in combination with atpB and 18S nrDNA, and generally better supported: ndhF contributes more than twice as many informative characters as rbcL, and nearly as many as rbcL, atpB, and 18S nrDNA combined. Based on functional arguments, we hypothesized that net venation and fleshy fruits should both evolve-and thus undergo concerted convergence-in shaded habitats, and revert to parallel venation and dry, passively dispersed fruits in open, sunny habitats. Our data show that net venation arose at least 26 times and disappeared 9 times, whereas fleshy fruits arose 22 times and disappeared 11 times. Both traits arose together at least 15 times and disappeared together 5 times. They thus show a highly significant pattern of concerted convergence (P < I0-9) and are each even more strongly associated with shaded habitats (P < I0-10 to I0-23); net venation is also associated, as predicted, with broad-leaved aquatic plants. Exceptions to this pattern illustrate the importance of other selective constraints and phylogenetic inertia.
Data deposition: Alignments, trees, and analyses for this project have been deposited at Dryad un... more Data deposition: Alignments, trees, and analyses for this project have been deposited at Dryad under the accession doi:10.5061/dryad.305s0. DNA sequences have been deposited at GenBank under the accession PRJNA313089.
Phylogenetic analyses based on mo¬ lecular data indicate that the species of Rollandia are embedd... more Phylogenetic analyses based on mo¬ lecular data indicate that the species of Rollandia are embedded within the genus Cyanea and that together these genera form a inonophyletic group. Cyanea and Rollandia are therefore merged under the former name. A revised key to the baccate genera of Hawaiian Fobelioideae and an expanded description of the genus are provided; eight new' combinations and one new name are proposed; and lectotypes are selected for Rollandia humboldtiana and R. longi flora var. angustifolia. This expanded circumscription makes Cyanea the largest genus in the Hawaiian flora, with 64 species and 10 heteronymic subspecies.
We present an integrative model predicting associations among epiphytism, the tank habit, entangl... more We present an integrative model predicting associations among epiphytism, the tank habit, entangling seeds, C 3 vs. CAM photosynthesis, avian pollinators, life in fertile, moist montane habitats, and net rates of species diversification in the monocot family Bromeliaceae. We test these predictions by relating evolutionary shifts in form, physiology, and ecology to time and ancestral distributions, quantifying patterns of correlated and contingent evolution among pairs of traits and analyzing the apparent impact of individual traits on rates of net species diversification and geographic expansion beyond the ancestral Guayana Shield. All predicted patterns of correlated evolution were significant, and the temporal and spatial associations of phenotypic shifts with orogenies generally accorded with predictions. Net rates of species diversification were most closely coupled to life in fertile, moist, geographically extensive cordilleras, with additional significant ties to epiphytism, avian pollination, and the tank habit. The highest rates of net diversification were seen in the bromelioid tank-epiphytic clade (D crown = 1.05 My À1), associated primarily with the Serra do Mar and nearby ranges of coastal Brazil, and in the core tillandsioids (D crown = 0.67 My À1), associated primarily with the Andes and Central America. Six large-scale adaptive radiations and accompanying pulses of speciation account for 86% of total species richness in the family. This study is among the first to test a priori hypotheses about the relationships among phylogeny, phenotypic evolution, geographic spread, and net species diversification, and to argue for causality to flow from functional diversity to spatial expansion to species diversity.
Rapateaceae and Bromeliaceae each have a center of diversity in South America and a single specie... more Rapateaceae and Bromeliaceae each have a center of diversity in South America and a single species native to a sandstone area in west Africa that abutted the Guayana Shield in northern South America before the Atlantic rifted. They thus provide ideal material for examining the potential role of vicariance versus long-distance dispersal in creating amphiatlantic disjunctions. Analyses based on ndhF sequence variation indicate that Rapateaceae and Bromeliaceae are each monophyletic and underwent crown radiation around 41 and 23 Ma, respectively. Both exhibit clocklike sequence evolution, with bromeliads evolving roughly one-third more slowly than rapateads. Among rapateads, the divergence of west African Maschalocephalus dinklagei from its closest South American relatives implies that Maschalocephalus resulted via long-distance dispersal 7 Ma, not ancient continental drift; only its sandstone habitat is vicariant. Rapateads arose first at low elevations in the Guayana Shield; the earliest divergent genera are widespread along riverine corridors there and, to a lesser extent, in Amazonia and the Brazilian Shield. Speciation at small spatial scales accelerated 15 Ma with the invasion of high-elevation, insular habitats atop tepuis. Among bromeliads, Pitcairnia feliciana diverges little from its congeners and appears to be the product of long-distance dispersal ca. 12 Ma. Brocchinia/Ayensua and then Lindmania are sister to all other bromeliads, indicating that the Guayana Shield was also the cradle of the bromeliads. Three lineages form an unresolved trichotomy representing all other bromeliads: (1) Tillandsioideae, (2) Hechtia, and (3) a large clade including remaining genera of Pitcairnioideae and all Bromelioideae. The last includes a clade of pitcairnioid genera endemic to the Guayana and Brazilian Shields; a xeric group (Abromeitiella/Deuterocohnia/Dyckia/Encholirium/Fosterella) from southern South America and the southern Andes, sister to Pitcairnia; and Andean Puya, sister to Bromelioideae, with many of the latter native to the Brazilian Shield. Both Rapateaceae and Bromeliaceae appear to have arisen at low elevations in the Guayana Shield, experienced accelerated speciation after invading dissected mountainous terrain, and undergone long-distance dispersal to west Africa recently. Bromeliad acquisition of key adaptations to drought (e.g., CAM photosynthesis, tank habit, tillandsioid leaf trichomes) 17 Ma appears to have coincided with and help cause the centripetal invasion of drier, more seasonal regions beyond the Guayana Shield, resulting in a wider familial range and dominance of the epiphytic adaptive zone. Geology, past and present climate, and proximity to South America help account for both families occurring in nearly the same area of Africa. We present a new classification for Rapateaceae, including a new tribe Stegolepideae, a new subfamily Monotremoideae, and revisions to tribe Saxofridericieae and subfamily Rapateoideae.
Cladistic analysis of ndhF sequences identifies eight major bromeliad clades arranged in ladderli... more Cladistic analysis of ndhF sequences identifies eight major bromeliad clades arranged in ladderlike fashion. The traditional subfamilies Tillandsioideae and Bromelioideae are monophyletic, but Pitcairnioideae are paraphyletic, requiring the description of four new subfamilies, recircumscription of Pitcairnioideae and Navioideae, the sinking of Ayensua, and description of the new genus Sequencia. Brocchinioideae are basalmost, followed by Lindmanioideae, both restricted to the Guayana Shield. Next is an unresolved trichotomy involving Hechtioideae from Central America, Tillandsioideae, and the remaining bromeliads in subfamilies Navioideae, Pitcairnioideae, Puyoideae, and Bromelioideae. Bromeliads arose as C 3 terrestrial plants on moist infertile sites in the Guayana Shield roughly 70 Mya, spread centripetally in the New World, and reached tropical West Africa (Pitcairnia feliciana) via long-distance dispersal about 10 Mya. Modern lineages began to diverge from each other 19 Mya and invaded drier areas in Central and South America beginning 15 Mya, coincident with a major adaptive radiation involving the repeated evolution of epiphytism, CAM photosynthesis, impounding leaves, several features of leaf/trichome anatomy, and accelerated diversification at the generic level. This ''bromeliad revolution'' occurred after the uplift of the northern Andes and shift of the Amazon to its present course. Epiphytism may have accelerated speciation by increasing ability to colonize along the length of the Andes, while favoring the occupation of a cloud-forest landscape frequently dissected by drier valleys. Avian pollination (mainly by hummingbirds) evolved at least twice ca. 13 Mya; entomophily was ancestral. Hechtia, Abromeitiella-Deuterocohnia-Dyckia-Encholirium, and Puya exhibit a remarkable pattern of concerted convergence in six anatomical and physiological leaf traits adapted to drought.
Molecular data provide several key insights into the origin and diversification of the Hawaiian l... more Molecular data provide several key insights into the origin and diversification of the Hawaiian lobeliads, which comprise one-ninth of the flora of the most isolated archipelago on earth. Soon after colonizing the Hawaiian chain from elsewhere in the Southern hemisphere, this group radiated into four major clades, adapted to bogs and other open, wet high-elevation habitats, to inland outcrops and rock walls, to sea cliffs and dry forest, and to rain-and cloud-forest edges and interiors. Woodiness and bird pollination arose long before the lobeliads arrived in Hawaii; fleshy fruits evolved autochthonously in moist to wet forests, and were lost on sea cliffs. Limited seed dispersal (associated with fleshy fruits in forest-interior plants) appears to have triggered substantial speciation in the genus Cyanea, and helped generate convergent radiations in flower length, elevational distribution, and plant height on each of the four major islands. Some of the processes that accelerated speciation in Cyaneasuch ~s limited seed dispersal, narrow ranges, and highly specialized flowers-also appear to have increased the I ikelihood of extinction. The roles of adaptive radiation visa -vis limited dispersal and sexual selection in promoting speciation in other groups (African rift-lake cichlids, coral reef fish, lilies and their relatives) are also discussed, with special reference to the phenomena of convergent adaptive radiations and of visual selection. Natural enemies may exert stronger density-dependent mortality on their hosts under rainier, more humid, warmer, and less seasonal conditions, and help create strong ecological gradients in plant species diversity within the tropics. Adaptive radiation may thus have interacted synergistically with several processes to generate the taxonomic richness and ecological diversity of the largest clade in the Hawaiian flora.
Previous studies based on DNA restriction-site and sequence variation have shown that the Hawaiia... more Previous studies based on DNA restriction-site and sequence variation have shown that the Hawaiian lobeliads are monophyletic and that the two largest genera, Cyanea and Clermontia, diverged from each other ca. 9.7 Mya. Sequence divergence among species of Clermontia is quite limited, however, and extensive hybridization is suspected, which has interfered with production of a well-resolved molecular phylogeny for the genus. Clermontia is of considerable interest because several species posses petal-like sepals, raising the question of whether such a homeotic mutation has arisen once or several times. In addition, morphological and molecular studies have implied different patterns of inter-island dispersal within the genus. Here we use nuclear ISSRs (inter-simple sequence repeat polymorphisms) and five plastid non-coding sequences to derive biparental and maternal phylogenies for Clermontia. Our findings imply that (1) Clermontia is not monophyletic, with Cl. pyrularia nested within Cyanea and apparently an intergeneric hybrid; (2) the earliest divergent clades within Clermontia are native to Kauài, then Ò ahu, then Maui, supporting the progression rule of dispersal down the chain toward progressively younger islands, although that rule is violated in later-evolving taxa in the ISSR tree; (3) almost no sequence divergence among several Clermontia species in 4.5 kb of rapidly evolving plastid DNA; (4) several apparent cases of hybridization/introgression or incomplete lineage sorting (i.e., Cl. oblongifolia, peleana, persicifolia, pyrularia, samuelii, tuberculata), based on extensive conflict between the ISSR and plastid phylogenies; and (5) two origins and two losses of petaloid sepals, or-perhaps more plausibly-a single origin and two losses of this homeotic mutation, with its introgression into Cl. persicifolia. Our phylogenies are better resolved and geographically more informative than others based on ITS and 5S-NTS sequences and nuclear SNPs, but agree with them in supporting Clermontia's origin on Kauài or some older island and dispersal down the chain subsequently.
show that tree diversity increases with tree height in North America and argue it reflects habita... more show that tree diversity increases with tree height in North America and argue it reflects habitat 'suitability'. This finding conflicts with classical results, lacks controls for covariates of tree height, and can be explained alternatively using the modified Janzen-Connell effect and regional variance in habitats.
We used ndhF sequence variation to reconstruct relationships across 282 taxa representing 78 mono... more We used ndhF sequence variation to reconstruct relationships across 282 taxa representing 78 mono-cot families and all 12 orders. The resulting tree is highly resolved and places commelinids sister to Asparagales, with both sister to Liliales–Pandanales in the strict consensus; Pandanales are sister to Dioscoreales in the bootstrap majority-rule tree, just above Petrosaviales. Acorales are sister to all other monocots, with Alismatales sister to all but Acorales. Relationships among the four major clades of commelinids remain unresolved. Relationships within orders are consistent with those based on rbcL, alone or in combination with atpB and 18S nrDNA, and generally better supported: ndhF contributes more than twice as many informative characters as rbcL, and nearly as many as rbcL, atpB, and 18S nrDNA combined. Based on functional arguments, we hypothesized that net venation and fleshy fruits should both evolve—and thus undergo concerted convergence—in shaded habitats, and revert to parallel venation and dry, passively dispersed fruits in open, sunny habitats. Our data show that net venation arose at least 26 times and disappeared 9 times, whereas fleshy fruits arose 22 times and disappeared 11 times. Both traits arose together at least 15 times and disappeared together 5 times. They thus show a highly significant pattern of concerted convergence (P 10 9) and are each even more strongly associated with shaded habitats (P 10 10 to 10 23); net venation is also associated, as predicted, with broad-leaved aquatic plants. Exceptions to this pattern illustrate the importance of other selective constraints and phylogenetic inertia.
Asparagales are a diverse monophyletic order that has numerous species (ca. 50% of monocots) incl... more Asparagales are a diverse monophyletic order that has numerous species (ca. 50% of monocots) including important crop plants such as Allium, Asparagus, and Vanilla, and a host of ornamentals such as irises, hyacinths, and orchids. Historically, Asparagales have been of interest partly because of their fascinating chromosomal evolution. We examine the evolutionary dynamics of Asparagales genomes in an updated phylogenetic framework that combines analyses of seven gene regions (atp1, atpB, matK, ndhF, rbcL, trnL intron, and trnL–F intergenic spacer) for 79 taxa of Asparagales and outgroups. Asparagales genomes are evolutionarily labile for many characters, including chromosome number and genome size. The history and causes of variation in chromosome number and genome size remain unclear, primarily because of the lack of data in small clades in the phylogenetic tree and the lack of comparative genetic maps, apart from Allium and Asparagus. Genomic tools such as bacterial artificial chromosome (BAC) libraries should be developed, as both molecular cytogenetic markers and a source of nuclear genes that can be widely used by evolutionary biologists and plant breeders alike to decipher mechanisms of chromosomal evolution.
Ecologists have long classified Midwestern prairies based on compositional variation assumed to r... more Ecologists have long classified Midwestern prairies based on compositional variation assumed to reflect local gradients in moisture availability. The best known classification is based on Curtis' continuum index (CI), calculated using the presence of indicator species thought centered on different portions of an underlying moisture gradient. Direct evidence of the extent to which CI reflects differences in moisture availability has been lacking, however. Many factors that increase moisture availability (e.g., soil depth, silt content) also increase nutrient supply and decrease soil mechanical impedance; the ecological effects of the last have rarely been considered in any ecosystem. Decreased soil mechanical impedance should increase the availability of soil moisture and nutrients by reducing the root costs of retrieving both. Here we assess the relative importance of soil moisture, nutrient supply, and mechanical impedance in determining prairie composition and structure. We us...
... other dark-reaction enzymes, measured per unit leaf mass, than do leaves of species grown und... more ... other dark-reaction enzymes, measured per unit leaf mass, than do leaves of species grown under shadier conditions (Bjbrkman, 1981); the adap-tive value of greater investment in leaf nitrogen content in sunnier conditions has been analysed at length by Mooney & Gulmon ...
Asparagales are a diverse monophyletic order that has numerous species (ca. 50% of monocots) incl... more Asparagales are a diverse monophyletic order that has numerous species (ca. 50% of monocots) including important crop plants such as Allium, Asparagus, and Vanilla, and a host of ornamentals such as irises, hyacinths, and orchids. Historically, Asparagales have been of interest partly because of their fascinating chromosomal evolution. We examine the evolutionary dynamics of Asparagales genomes in an updated phylogenetic framework that combines analyses of seven gene regions (atpl, atpB, matK, ndhF, rbcL, trnL intron, and trnL-F intergenic spacer) for 79 taxa of Asparagales and outgroups. Asparagales genomes are evolutionarily labile for many characters, including chromosome number and genome size. The history and causes of variation in chromosome number and genome size remain unclear, primarily because of the lack of data in small clades in the phylogenetic tree and the lack of comparative genetic maps, apart from Allium and Asparagus. Genomic tools such as bacterial artificial chromosome (BAC) libraries should be developed, as both molecular cytogenetic markers and a source of nuclear genes that can be widely used by evolutionary biologists and plant breeders alike to decipher mechanisms of chromosomal evolution.
We used ndhF sequence variation to reconstruct relationships across 282 taxa representing 78 mono... more We used ndhF sequence variation to reconstruct relationships across 282 taxa representing 78 monocot families and all 12 orders. The resulting tree is highly resolved and places commelinids sister to Asparagales, with both sister to Liliales-Pandanales in the strict consensus; Pandanales are sister to Dioscoreales in the bootstrap majority-rule tree, just above Petrosaviales. Acorales are sister to all other monocots, with Alismatales sister to all but Acorales. Relationships among the four major clades of commelinids remain unresolved. Relationships within orders are consistent with those based on rbcL, alone or in combination with atpB and 18S nrDNA, and generally better supported: ndhF contributes more than twice as many informative characters as rbcL, and nearly as many as rbcL, atpB, and 18S nrDNA combined. Based on functional arguments, we hypothesized that net venation and fleshy fruits should both evolve-and thus undergo concerted convergence-in shaded habitats, and revert to parallel venation and dry, passively dispersed fruits in open, sunny habitats. Our data show that net venation arose at least 26 times and disappeared 9 times, whereas fleshy fruits arose 22 times and disappeared 11 times. Both traits arose together at least 15 times and disappeared together 5 times. They thus show a highly significant pattern of concerted convergence (P < I0-9) and are each even more strongly associated with shaded habitats (P < I0-10 to I0-23); net venation is also associated, as predicted, with broad-leaved aquatic plants. Exceptions to this pattern illustrate the importance of other selective constraints and phylogenetic inertia.
Data deposition: Alignments, trees, and analyses for this project have been deposited at Dryad un... more Data deposition: Alignments, trees, and analyses for this project have been deposited at Dryad under the accession doi:10.5061/dryad.305s0. DNA sequences have been deposited at GenBank under the accession PRJNA313089.
Phylogenetic analyses based on mo¬ lecular data indicate that the species of Rollandia are embedd... more Phylogenetic analyses based on mo¬ lecular data indicate that the species of Rollandia are embedded within the genus Cyanea and that together these genera form a inonophyletic group. Cyanea and Rollandia are therefore merged under the former name. A revised key to the baccate genera of Hawaiian Fobelioideae and an expanded description of the genus are provided; eight new' combinations and one new name are proposed; and lectotypes are selected for Rollandia humboldtiana and R. longi flora var. angustifolia. This expanded circumscription makes Cyanea the largest genus in the Hawaiian flora, with 64 species and 10 heteronymic subspecies.
We present an integrative model predicting associations among epiphytism, the tank habit, entangl... more We present an integrative model predicting associations among epiphytism, the tank habit, entangling seeds, C 3 vs. CAM photosynthesis, avian pollinators, life in fertile, moist montane habitats, and net rates of species diversification in the monocot family Bromeliaceae. We test these predictions by relating evolutionary shifts in form, physiology, and ecology to time and ancestral distributions, quantifying patterns of correlated and contingent evolution among pairs of traits and analyzing the apparent impact of individual traits on rates of net species diversification and geographic expansion beyond the ancestral Guayana Shield. All predicted patterns of correlated evolution were significant, and the temporal and spatial associations of phenotypic shifts with orogenies generally accorded with predictions. Net rates of species diversification were most closely coupled to life in fertile, moist, geographically extensive cordilleras, with additional significant ties to epiphytism, avian pollination, and the tank habit. The highest rates of net diversification were seen in the bromelioid tank-epiphytic clade (D crown = 1.05 My À1), associated primarily with the Serra do Mar and nearby ranges of coastal Brazil, and in the core tillandsioids (D crown = 0.67 My À1), associated primarily with the Andes and Central America. Six large-scale adaptive radiations and accompanying pulses of speciation account for 86% of total species richness in the family. This study is among the first to test a priori hypotheses about the relationships among phylogeny, phenotypic evolution, geographic spread, and net species diversification, and to argue for causality to flow from functional diversity to spatial expansion to species diversity.
Rapateaceae and Bromeliaceae each have a center of diversity in South America and a single specie... more Rapateaceae and Bromeliaceae each have a center of diversity in South America and a single species native to a sandstone area in west Africa that abutted the Guayana Shield in northern South America before the Atlantic rifted. They thus provide ideal material for examining the potential role of vicariance versus long-distance dispersal in creating amphiatlantic disjunctions. Analyses based on ndhF sequence variation indicate that Rapateaceae and Bromeliaceae are each monophyletic and underwent crown radiation around 41 and 23 Ma, respectively. Both exhibit clocklike sequence evolution, with bromeliads evolving roughly one-third more slowly than rapateads. Among rapateads, the divergence of west African Maschalocephalus dinklagei from its closest South American relatives implies that Maschalocephalus resulted via long-distance dispersal 7 Ma, not ancient continental drift; only its sandstone habitat is vicariant. Rapateads arose first at low elevations in the Guayana Shield; the earliest divergent genera are widespread along riverine corridors there and, to a lesser extent, in Amazonia and the Brazilian Shield. Speciation at small spatial scales accelerated 15 Ma with the invasion of high-elevation, insular habitats atop tepuis. Among bromeliads, Pitcairnia feliciana diverges little from its congeners and appears to be the product of long-distance dispersal ca. 12 Ma. Brocchinia/Ayensua and then Lindmania are sister to all other bromeliads, indicating that the Guayana Shield was also the cradle of the bromeliads. Three lineages form an unresolved trichotomy representing all other bromeliads: (1) Tillandsioideae, (2) Hechtia, and (3) a large clade including remaining genera of Pitcairnioideae and all Bromelioideae. The last includes a clade of pitcairnioid genera endemic to the Guayana and Brazilian Shields; a xeric group (Abromeitiella/Deuterocohnia/Dyckia/Encholirium/Fosterella) from southern South America and the southern Andes, sister to Pitcairnia; and Andean Puya, sister to Bromelioideae, with many of the latter native to the Brazilian Shield. Both Rapateaceae and Bromeliaceae appear to have arisen at low elevations in the Guayana Shield, experienced accelerated speciation after invading dissected mountainous terrain, and undergone long-distance dispersal to west Africa recently. Bromeliad acquisition of key adaptations to drought (e.g., CAM photosynthesis, tank habit, tillandsioid leaf trichomes) 17 Ma appears to have coincided with and help cause the centripetal invasion of drier, more seasonal regions beyond the Guayana Shield, resulting in a wider familial range and dominance of the epiphytic adaptive zone. Geology, past and present climate, and proximity to South America help account for both families occurring in nearly the same area of Africa. We present a new classification for Rapateaceae, including a new tribe Stegolepideae, a new subfamily Monotremoideae, and revisions to tribe Saxofridericieae and subfamily Rapateoideae.
Cladistic analysis of ndhF sequences identifies eight major bromeliad clades arranged in ladderli... more Cladistic analysis of ndhF sequences identifies eight major bromeliad clades arranged in ladderlike fashion. The traditional subfamilies Tillandsioideae and Bromelioideae are monophyletic, but Pitcairnioideae are paraphyletic, requiring the description of four new subfamilies, recircumscription of Pitcairnioideae and Navioideae, the sinking of Ayensua, and description of the new genus Sequencia. Brocchinioideae are basalmost, followed by Lindmanioideae, both restricted to the Guayana Shield. Next is an unresolved trichotomy involving Hechtioideae from Central America, Tillandsioideae, and the remaining bromeliads in subfamilies Navioideae, Pitcairnioideae, Puyoideae, and Bromelioideae. Bromeliads arose as C 3 terrestrial plants on moist infertile sites in the Guayana Shield roughly 70 Mya, spread centripetally in the New World, and reached tropical West Africa (Pitcairnia feliciana) via long-distance dispersal about 10 Mya. Modern lineages began to diverge from each other 19 Mya and invaded drier areas in Central and South America beginning 15 Mya, coincident with a major adaptive radiation involving the repeated evolution of epiphytism, CAM photosynthesis, impounding leaves, several features of leaf/trichome anatomy, and accelerated diversification at the generic level. This ''bromeliad revolution'' occurred after the uplift of the northern Andes and shift of the Amazon to its present course. Epiphytism may have accelerated speciation by increasing ability to colonize along the length of the Andes, while favoring the occupation of a cloud-forest landscape frequently dissected by drier valleys. Avian pollination (mainly by hummingbirds) evolved at least twice ca. 13 Mya; entomophily was ancestral. Hechtia, Abromeitiella-Deuterocohnia-Dyckia-Encholirium, and Puya exhibit a remarkable pattern of concerted convergence in six anatomical and physiological leaf traits adapted to drought.
Molecular data provide several key insights into the origin and diversification of the Hawaiian l... more Molecular data provide several key insights into the origin and diversification of the Hawaiian lobeliads, which comprise one-ninth of the flora of the most isolated archipelago on earth. Soon after colonizing the Hawaiian chain from elsewhere in the Southern hemisphere, this group radiated into four major clades, adapted to bogs and other open, wet high-elevation habitats, to inland outcrops and rock walls, to sea cliffs and dry forest, and to rain-and cloud-forest edges and interiors. Woodiness and bird pollination arose long before the lobeliads arrived in Hawaii; fleshy fruits evolved autochthonously in moist to wet forests, and were lost on sea cliffs. Limited seed dispersal (associated with fleshy fruits in forest-interior plants) appears to have triggered substantial speciation in the genus Cyanea, and helped generate convergent radiations in flower length, elevational distribution, and plant height on each of the four major islands. Some of the processes that accelerated speciation in Cyaneasuch ~s limited seed dispersal, narrow ranges, and highly specialized flowers-also appear to have increased the I ikelihood of extinction. The roles of adaptive radiation visa -vis limited dispersal and sexual selection in promoting speciation in other groups (African rift-lake cichlids, coral reef fish, lilies and their relatives) are also discussed, with special reference to the phenomena of convergent adaptive radiations and of visual selection. Natural enemies may exert stronger density-dependent mortality on their hosts under rainier, more humid, warmer, and less seasonal conditions, and help create strong ecological gradients in plant species diversity within the tropics. Adaptive radiation may thus have interacted synergistically with several processes to generate the taxonomic richness and ecological diversity of the largest clade in the Hawaiian flora.
Previous studies based on DNA restriction-site and sequence variation have shown that the Hawaiia... more Previous studies based on DNA restriction-site and sequence variation have shown that the Hawaiian lobeliads are monophyletic and that the two largest genera, Cyanea and Clermontia, diverged from each other ca. 9.7 Mya. Sequence divergence among species of Clermontia is quite limited, however, and extensive hybridization is suspected, which has interfered with production of a well-resolved molecular phylogeny for the genus. Clermontia is of considerable interest because several species posses petal-like sepals, raising the question of whether such a homeotic mutation has arisen once or several times. In addition, morphological and molecular studies have implied different patterns of inter-island dispersal within the genus. Here we use nuclear ISSRs (inter-simple sequence repeat polymorphisms) and five plastid non-coding sequences to derive biparental and maternal phylogenies for Clermontia. Our findings imply that (1) Clermontia is not monophyletic, with Cl. pyrularia nested within Cyanea and apparently an intergeneric hybrid; (2) the earliest divergent clades within Clermontia are native to Kauài, then Ò ahu, then Maui, supporting the progression rule of dispersal down the chain toward progressively younger islands, although that rule is violated in later-evolving taxa in the ISSR tree; (3) almost no sequence divergence among several Clermontia species in 4.5 kb of rapidly evolving plastid DNA; (4) several apparent cases of hybridization/introgression or incomplete lineage sorting (i.e., Cl. oblongifolia, peleana, persicifolia, pyrularia, samuelii, tuberculata), based on extensive conflict between the ISSR and plastid phylogenies; and (5) two origins and two losses of petaloid sepals, or-perhaps more plausibly-a single origin and two losses of this homeotic mutation, with its introgression into Cl. persicifolia. Our phylogenies are better resolved and geographically more informative than others based on ITS and 5S-NTS sequences and nuclear SNPs, but agree with them in supporting Clermontia's origin on Kauài or some older island and dispersal down the chain subsequently.
show that tree diversity increases with tree height in North America and argue it reflects habita... more show that tree diversity increases with tree height in North America and argue it reflects habitat 'suitability'. This finding conflicts with classical results, lacks controls for covariates of tree height, and can be explained alternatively using the modified Janzen-Connell effect and regional variance in habitats.
We used ndhF sequence variation to reconstruct relationships across 282 taxa representing 78 mono... more We used ndhF sequence variation to reconstruct relationships across 282 taxa representing 78 mono-cot families and all 12 orders. The resulting tree is highly resolved and places commelinids sister to Asparagales, with both sister to Liliales–Pandanales in the strict consensus; Pandanales are sister to Dioscoreales in the bootstrap majority-rule tree, just above Petrosaviales. Acorales are sister to all other monocots, with Alismatales sister to all but Acorales. Relationships among the four major clades of commelinids remain unresolved. Relationships within orders are consistent with those based on rbcL, alone or in combination with atpB and 18S nrDNA, and generally better supported: ndhF contributes more than twice as many informative characters as rbcL, and nearly as many as rbcL, atpB, and 18S nrDNA combined. Based on functional arguments, we hypothesized that net venation and fleshy fruits should both evolve—and thus undergo concerted convergence—in shaded habitats, and revert to parallel venation and dry, passively dispersed fruits in open, sunny habitats. Our data show that net venation arose at least 26 times and disappeared 9 times, whereas fleshy fruits arose 22 times and disappeared 11 times. Both traits arose together at least 15 times and disappeared together 5 times. They thus show a highly significant pattern of concerted convergence (P 10 9) and are each even more strongly associated with shaded habitats (P 10 10 to 10 23); net venation is also associated, as predicted, with broad-leaved aquatic plants. Exceptions to this pattern illustrate the importance of other selective constraints and phylogenetic inertia.
Asparagales are a diverse monophyletic order that has numerous species (ca. 50% of monocots) incl... more Asparagales are a diverse monophyletic order that has numerous species (ca. 50% of monocots) including important crop plants such as Allium, Asparagus, and Vanilla, and a host of ornamentals such as irises, hyacinths, and orchids. Historically, Asparagales have been of interest partly because of their fascinating chromosomal evolution. We examine the evolutionary dynamics of Asparagales genomes in an updated phylogenetic framework that combines analyses of seven gene regions (atp1, atpB, matK, ndhF, rbcL, trnL intron, and trnL–F intergenic spacer) for 79 taxa of Asparagales and outgroups. Asparagales genomes are evolutionarily labile for many characters, including chromosome number and genome size. The history and causes of variation in chromosome number and genome size remain unclear, primarily because of the lack of data in small clades in the phylogenetic tree and the lack of comparative genetic maps, apart from Allium and Asparagus. Genomic tools such as bacterial artificial chromosome (BAC) libraries should be developed, as both molecular cytogenetic markers and a source of nuclear genes that can be widely used by evolutionary biologists and plant breeders alike to decipher mechanisms of chromosomal evolution.
Ecologists have long classified Midwestern prairies based on compositional variation assumed to r... more Ecologists have long classified Midwestern prairies based on compositional variation assumed to reflect local gradients in moisture availability. The best known classification is based on Curtis' continuum index (CI), calculated using the presence of indicator species thought centered on different portions of an underlying moisture gradient. Direct evidence of the extent to which CI reflects differences in moisture availability has been lacking, however. Many factors that increase moisture availability (e.g., soil depth, silt content) also increase nutrient supply and decrease soil mechanical impedance; the ecological effects of the last have rarely been considered in any ecosystem. Decreased soil mechanical impedance should increase the availability of soil moisture and nutrients by reducing the root costs of retrieving both. Here we assess the relative importance of soil moisture, nutrient supply, and mechanical impedance in determining prairie composition and structure. We us...
... other dark-reaction enzymes, measured per unit leaf mass, than do leaves of species grown und... more ... other dark-reaction enzymes, measured per unit leaf mass, than do leaves of species grown under shadier conditions (Bjbrkman, 1981); the adap-tive value of greater investment in leaf nitrogen content in sunnier conditions has been analysed at length by Mooney & Gulmon ...
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Papers by Thomas Givnish