Adaptive radiation is the rise of a diversity of ecological roles and role-specific adaptations within a lineage. Recently, some researchers have begun to use ‘adaptive radiation’ or ‘radiation’ as ...synonymous with ‘explosive species diversification’. This essay aims to clarify distinctions between these concepts, and the related ideas of geographic speciation, sexual selection, key innovations, key landscapes and ecological keys. Several examples are given to demonstrate that adaptive radiation and explosive diversification are not the same phenomenon, and that focusing on explosive diversification and the analysis of phylogenetic topology ignores much of the rich biology associated with adaptive radiation, and risks generating confusion about the nature of the evolutionary forces driving species diversification. Some ‘radiations’ involve bursts of geographic speciation or sexual selection, rather than adaptive diversification; some adaptive radiations have little or no effect on speciation, or even a negative effect. Many classic examples of ‘adaptive radiation’ appear to involve effects driven partly by geographic speciation, species' dispersal abilities, and the nature of extrinsic dispersal barriers; partly by sexual selection; and partly by adaptive radiation in the classical sense, including the origin of traits and invasion of adaptive zones that result in decreased diversification rates but add to overall diversity.
A new nuclear phylogeny for the large family Brassicaceae opens the way for advanced comparative studies of adaptation, development, coevolution, hybridization, and diversification in this crucial ...group, which is the source for many of the genomic resources now used across the flowering plants.
A new nuclear phylogeny for the large family Brassicaceae opens the way for advanced comparative studies of adaptation, development, coevolution, hybridization, and diversification in this crucial group, which is the source for many of the genomic resources now used across the flowering plants.
Ecology affects each of the three principal processes leading to speciation: genetic differentiation among populations within species, acquisition of reproductive isolation among populations, and the ...rise of ecological differentiation among such populations, allowing them to coexist. Until recently, however, the ties between ecology and speciation in plants have received relatively little attention. This paper reviews some exciting new insights into the role of ecology in speciation, focusing on the angiosperms. I consider five main topics, including (1) the determinants of the spatial scale of genetic differentiation within species; (2) the role and limits of adaptive radiation in increasing net rates of plant diversification; (3) the potential role of ecological speciation; (4) the contributions of hybridization to speciation, adaptive radiation, and the ecological breadth of clades; and (5) the ecological determinants of net diversification rate for individual lineages, and of the species richness for regional floras. Limited dispersal, especially of seeds, favors genetic differentiation at small spatial scales and is likely to foster rapid speciation and narrow endemism. Meta-analyses show that the minimum area required for in situ speciation on islands increases with the spatial scale of gene flow in various organisms. In angiosperms, fleshy fruits dispersed by vertebrates often increase the distance over which seeds are dispersed, but can decrease it in forest understories. Nutrient-poor soils should work against the evolution of fleshy fruits and promote speciation and narrow endemism. Selection for adaptation to different conditions drives adaptive radiation, the rise of a diversity of ecological roles and attendant adaptations within a lineage. On islands, adaptive radiation often leads to woodiness, monocarpy, developmental heterophylly, and sexual dimorphism, as well as differences in habitat, growth form, and floral morphology. Adaptive radiation appears to accelerate speciation in only some plant clades. Extensive radiation in some lineages has been ascribed to early colonization, large amounts of heritable genetic variation, "genetic lines of least resistance" upon which selection could act, absence of potential competitors, and possession of "key innovations" that provide access to novel resources. To these should be added large island area, organismal abundance, saturation of ecological space, and the synergism action of limited dispersal and divergent selection producing parallel radiations in isolated regions. Data for Hawaiian lobeliads suggest that within-island species richness of Cyanea—involving divergence in elevation and flower tube length—saturates within 0.6 and 1.5 Ma. Adaptive radiation in pollinators is an important mechanism of ecological speciation: adaptation to different pollinators leads to pollinator partitioning and reproductive isolation. Selection for longer nectar spurs and pollinator mouth parts led to increased speciation in Aquilegia and other groups. A similar process may work once tubular flowers evolve from cup-shaped blossoms. Selection for floral divergence may be limited in forest understories illuminated by dim, greenish light, which may account for the predominance of small, visually inconspicuous flowers in temperate and tropical understory species. Hybridization can stimulate speciation by forming transgressive phenotypes that exceed the range seen in parental taxa, and by introgressing adaptive gene combinations. The likelihood of transgressive phenotypes increases with the genetic divergence between parental taxa, so speciation via transgressive hybridization may be most likely among taxa with intermediate amounts of divergence. Several large adaptive radiations appear to have occurred after hybridization, suggesting a special role for the extensive amount of genetic variation that can be supplied and refreshed by syngameons. Rates of net species diversification are greater in herbs (especially annuals) vs. woody plants; in animal- vs. wind-pollinated species; in plants with poorly dispersed seeds; in families with a greater diversity of growth forms, pollination and seed dispersal mechanisms, and species distributions; in families at lower latitudes; in families with higher rates of genetic evolution; in hermaphroditic or monoecious vs. dioecious clades; in earlier-maturing woody plants; in plants with bilateral vs. radial flowers; in plants with hummingbird-pollinated flowers; in epiphytic vs. terrestrial bromeliads and orchids; in bromeliads differentiating along geographically extensive cordilleras; and in young vs. old clades. Evidence for the last pattern may, however, be an artifact of (auto)regressing (ln N) / t vs. t. High rates of diversification in epiphytic orchids are tied to small effective population sizes, suggesting a role for intermittent genetic drift alternating with strong selection on floral traits. Across angiosperms, a massive increase in diversification rates was preceded by a major increase in leaf vein density and hydraulic conductance between 140 and 110 Ma ago, leading to higher photosynthetic rates than coexisting ferns and gymnosperms. Based on the economic theory of plant defense, this should have led to lower allocation to anti-herbivore defenses, selecting for low-cost qualitative toxins rather than all-purpose but highly expensive qualitative defenses, triggering an arms' race between angiosperm and their herbivores. Finally, regional plant species richness increases with regional area and proxies for latitude, rainfall, topographic heterogeneity, and vegetation stratification. The Cape Floristic Province has roughly twice as many species as expected from its area and environmental conditions, most likely reflecting the predominance of short-distance dispersal associated with poor soils and myrmecochory in the Cape Province, as well as low rates of regeneration and competitive exclusion following fire.
Can species shift their distributions fast enough to track changes in climate? We used abundance data from the 1950s and the 2000s in Wisconsin to measure shifts in the distribution and abundance of ...78 forest‐understory plant species over the last half‐century and compare these shifts to changes in climate. We estimated temporal shifts in the geographic distribution of each species using vectors to connect abundance‐weighted centroids from the 1950s and 2000s. These shifts in distribution reflect colonization, extirpation, and changes in abundance within sites, separately quantified here. We then applied climate analog analyses to compute vectors representing the climate change that each species experienced. Species shifted mostly to the northwest (mean: 49 ± 29 km) primarily reflecting processes of colonization and changes in local abundance. Analog climates for these species shifted even further to the northwest, however, exceeding species’ shifts by an average of 90 ± 40 km. Most species thus failed to match recent rates of climate change. These lags decline in species that have colonized more sites and those with broader site occupancy, larger seed mass, and higher habitat fidelity. Thus, species’ traits appear to affect their responses to climate change, but relationships are weak. As climate change accelerates, these lags will likely increase, potentially threatening the persistence of species lacking the capacity to disperse to new sites or locally adapt. However, species with greater lags have not yet declined more in abundance. The extent of these threats will likely depend on how other drivers of ecological change and interactions among species affect their responses to climate change.
Carnivorous plants consume animals for mineral nutrients that enhance growth and reproduction in nutrient-poor environments. Here, we report that
(Tofieldiaceae) represents a previously overlooked ...carnivorous lineage that captures insects on sticky inflorescences. Field experiments, isotopic data, and mixing models demonstrate significant N transfer from prey to
, with an estimated 64% of leaf N obtained from prey capture in previous years, comparable to levels inferred for the cooccurring round-leaved sundew, a recognized carnivore. N obtained via carnivory is exported from the inflorescence and developing fruits and may ultimately be transferred to next year's leaves. Glandular hairs on flowering stems secrete phosphatase, as seen in all carnivorous plants that directly digest prey.
is unique among carnivorous plants in capturing prey solely with sticky traps adjacent to its flowers, contrary to theory. However, its glandular hairs capture only small insects, unlike the large bees and butterflies that act as pollinators, which may minimize the conflict between carnivory and pollination.
PREMISE OF THE STUDY:
A recent commentary by Edwards et al. (Am. J. Bot. 103: 975–978) proposed that constraints imposed by the packing of young leaves in buds could explain the positive association ...between non‐entire leaf margins and latitude but did not thoroughly consider alternative explanations.
METHODS:
We review the logic and evidence underlying six major hypotheses for the functional significance of marginal teeth, involving putative effects on (1) leaf cooling, (2) optimal support and supply of the areas served by major veins, (3) enhanced leaf‐margin photosynthesis, (4) hydathodal function, (5) defense against herbivores, and (6) bud packing.
KEY RESULTS:
Theoretical and empirical problems undermine all hypotheses except the support–supply hypothesis, which implies that thinner leaves should have non‐entire margins. Phylogenetically structured analyses across angiosperms, the El Yunque flora, and the genus Viburnum all demonstrate that non‐entire margins are indeed more common in thinner leaves. Across angiosperms, the association of leaf thickness with non‐entire leaf margins is stronger than that of latitude.
CONCLUSION:
We outline a synthetic model showing how biomechanics, hydraulics, vein geometry, rates of leaf expansion, and length of development within resting buds, all tied to leaf thickness, drive patterns in the distribution of entire vs. non‐entire leaf margins. Our model accounts for dominance of entire margins in the tropics, Mediterranean scrub, and tundra, non‐entire margins in cold temperate deciduous forests and tropical vines and early‐successional trees, and entire leaf margins in monocots. Spinose‐toothed leaves should be favored in short‐statured evergreen trees and shrubs, primarily in Mediterranean scrub and related semiarid habitats.
A New World of plants Givnish, Thomas J.
Science (American Association for the Advancement of Science),
12/2017, Letnik:
358, Številka:
6370
Journal Article
Recenzirano
A searchable database collates information on all known vascular plants in the Americas
On page 1614 of this issue, Ulloa Ulloa
et al.
(
1
) provide the first comprehensive overview of vascular plant ...diversity in the New World. The study, which includes a 2600-page online checklist and a continuously updated, searchable database Vascular Plants of the Americas, see (
2
) is a monumental achievement that will be of enormous interest to conservation biologists, ecologists, evolutionary biologists, biogeographers, land managers, and governmental officials around the world.
•We trace 97 million years of bromeliad adaptation, biogeography, and species diversification.•We use these data to test an integrative model for bromeliad evolution.•Patterns of correlated and ...contingent evolution are consistent with this model.•Diversification rates are significantly higher in epiphytic, tank-forming, bird-pollinated, and montane lineages.•86% Of bromeliad species richness reflects six major adaptive radiations in different areas.
We present an integrative model predicting associations among epiphytism, the tank habit, entangling seeds, C3 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 (Dcrown=1.05My−1), associated primarily with the Serra do Mar and nearby ranges of coastal Brazil, and in the core tillandsioids (Dcrown=0.67My−1), 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.
The endemic Hawaiian lobeliads are exceptionally species rich and exhibit striking diversity in habitat, growth form, pollination biology and seed dispersal, but their origins and pattern of ...diversification remain shrouded in mystery. Up to five independent colonizations have been proposed based on morphological differences among extant taxa. We present a molecular phylogeny showing that the Hawaiian lobeliads are the product of one immigration event; that they are the largest plant clade on any single oceanic island or archipelago; that their ancestor arrived roughly 13 Myr ago; and that this ancestor was most likely woody, wind-dispersed, bird-pollinated, and adapted to open habitats at mid-elevations. Invasion of closed tropical forests is associated with evolution of fleshy fruits. Limited dispersal of such fruits in wet-forest understoreys appears to have accelerated speciation and led to a series of parallel adaptive radiations in Cyanea, with most species restricted to single islands. Consistency of Cyanea diversity across all tall islands except Hawai i suggests that diversification of Cyanea saturates in less than 1.5 Myr. Lobeliad diversity appears to reflect a hierarchical adaptive radiation in habitat, then elevation and flower-tube length, and provides important insights into the pattern and tempo of diversification in a species-rich clade of tropical plants.
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