Evolutionary Time for Dispersal Limits the Extent but Not the Occupancy of Species’ Potential Ranges in the Tropical Plant Genus Psychotria (Rubiaceae) (original) (raw)
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American journal of botany, 2014
Premise of the study: Tropical forests are the most species-rich terrestrial communities on Earth, and understory trees and shrubs comprise a large fraction of their plant species diversity, especially at high rainfalls. The mechanisms responsible for generating such high levels of diversity remain unknown. One hypothesis is that fl eshy-fruited understory species should have limited seed dispersal due to the sedentary nature of their avian dispersers, resulting in restricted gene fl ow, population differentiation at small spatial scales, and ultimately, high rates of allopatric speciation.
Frontiers in Genetics
Species diversity is unequally distributed across the globe, with the greatest concentration occurring in the tropics. Even within the tropics, there are significant differences in the numbers of taxa found in each continental region. Manilkara is a pantropical genus of trees in the Sapotaceae comprising c. 78 species. Its distribution allows for biogeographic investigation and testing of whether rates of diversification differ amongst tropical regions. The age and geographical origin of Manilkara are inferred to determine whether Gondwanan break-up, boreotropical migration or long distance dispersal have shaped its current disjunct distribution. Diversification rates through time are also analyzed to determine whether the timing and tempo of speciation on each continent coincides with geoclimatic events. Bayesian analyses of nuclear (ITS) and plastid (rpl32-trnL, rps16-trnK , and trnS-trnFM) sequences were used to reconstruct a species level phylogeny of Manilkara and related genera in the tribe Mimusopeae. Analyses of the nuclear data using a fossil-calibrated relaxed molecular clock indicate that Manilkara evolved 32-29 million years ago (Mya) in Africa. Lineages within the genus dispersed to the Neotropics 26-18 Mya and to Asia 28-15 Mya. Higher speciation rates are found in the Neotropical Manilkara clade than in either African or Asian clades. Dating of regional diversification correlates with known palaeoclimatic events. In South America, the divergence between Atlantic coastal forest and Amazonian clades coincides with the formation of drier Cerrado and Caatinga habitats between them. In Africa diversification coincides with Tertiary cycles of aridification and uplift of the east African plateaux. In Southeast Asia dispersal may have been limited by the relatively recent emergence of land in New Guinea and islands further east c. 10 Mya.
2010
Aim When hypotheses of historical biogeography are evaluated, age estimates of individual nodes in a phylogeny often have a direct impact on what explanation is concluded to be most likely. Confidence intervals of estimated divergence times obtained in molecular dating analyses are usually very large, but the uncertainty is rarely incorporated in biogeographical analyses. The aim of this study is to use the group Urophylleae, which has a disjunct pantropical distribution, to explore how the uncertainty in estimated divergence times affects conclusions in biogeographical analysis. Two hypotheses are evaluated:
Journal of Ecology, 2005
1 Eidothea hardeniana (Proteaceae) is a narrow endemic representative of an ancient lineage restricted to a single site in northern New South Wales (Australia). This study aims to identify the life-history traits most likely to have influenced the current distribution pattern of this rain forest tree. 2 Using ecological and molecular analyses we found that its range is limited by the absence of efficient dispersal mechanisms rather than by habitat availability, or as a result of a recent bottleneck or of reproductive failure. 3 Resprouts can take over the position of senesced plants, even in the absence of disturbance, allowing local persistence and the maintenance of genetic diversity. Longterm persistence and preferential outcrossing further favour relatively high levels of diversity (H E = 0.542) despite a small effective population size (N e = 21.6). 4 We used eight life-history traits to assess if the E. hardeniana findings were valid across 258 local taxa. Current distribution patterns of rain forest species within a species-rich community were accounted for by linking two important components of community assembly theory: dispersal and niche assembly. 5 The interaction of the seed-based dispersal dimension and resprouting potential best explains the current distribution of rare local taxa. Major dimensions of life-history trait variation were identified among local plant species, suggesting that a range of interacting traits contribute to a species' response to environmental variables and mitigate the influence of potentially adverse circumstances. 6 The benefits of merging ecological and genetic approaches to interpret species distribution and population structure are applicable across a broader range of studies. Our findings highlight how currently constrained palaeo-endemic species with small populations in refugial habitats may retain the capacity to both persist and expand in response to changing circumstances and opportunities. This has important implications for species conservation, habitat management and reserve design.
Molecular Phylogenetics and Evolution, 2014
In this study we explore what historical biogeographic events are responsible for the wide and disjunct distribution of extant species in Lasiantheae, a pantropical group of trees and shrubs in the coffee family. Three of the genera in the group, Lasianthus, Saldinia, and Trichostachys, are found to be monophyletic, while there are indications that the fourth, Ronabea, is paraphyletic. We also address how the uncertainty in topology and divergence times affects the level of confidence in the biogeographic reconstruction. A data set consisting of chloroplast and nuclear ribosomal DNA data was analyzed using a Bayesian relaxed molecular clock approach to estimate phylogenetic relationships and divergence times, and the dispersal-extinction-cladogenesis (DEC) method to reconstruct geographic range evolution. Our results show that the Lasiantheae stem lineage originated in the neotropics, and the group expanded its range to the palaeotropics during the Eocene, either by continental migration through the boreotropics or by transatlantic long-distance dispersal. Two cases of Oligocene/Miocene over water-dispersal were also inferred, once from the paleotropics to the neotropics within Lasianthus, and once to Madagascar, concurrent with the origin of Saldinia. A lot of the diversification within Lasianthus took place during the Miocene and may have been influenced by climatic factors such as a period of markedly warm and moist climate in Asia and the aridification of the interior of the African continent. When biogeographic reconstructions were averaged over a random sample of 1000 dated phylogenies, the confidence in the biogeographic reconstruction decreased for most nodes, compared to when a single topology was used. A good understanding of phylogenetic relationships is necessary to understand the biogeographic history of a group, bit since the phylogeny is rarely completely known it is important to include phylogenetic uncertainty in biogeographic analysis. For nodes where the resolution is uncertain, the use of a single ''best'' topology as a basis for biogeographic analysis will result in inflated confidence in a biogeographic reconstruction which may be just one of several possible reconstructions.
The Complex Biogeographic History of a Widespread Tropical Tree Species
Evolution, 2008
some species were established millions of years ago. Here we relate biogeographic history to patterns of population differentiation, mutational and demographic processes in the widespread rainforest tree Symphonia globulifera using ribosomal (ITS) and chloroplast DNA sequences and nuclear microsatellite (nSSR) loci. Fossil records document sweepstakes dispersal origins of Neotropical S. globulifera populations from Africa during the Miocene. Despite historical long-distance gene flow, nSSR differentiation across 13 populations from Costa Rica, Panama, Ecuador (east and west of Andes) and French Guiana was pronounced (F ST = 0.14, R ST = 0.39, P < 0.001) and allele-size mutations contributed significantly (R ST > F ST ) to the divergences between cis-and trans-Andean populations. Both DNA sequence and nSSR data reflect contrasting demographic histories in lower Mesoamerica and Amazonia. Amazon populations show weak phylogeographic structure and deviation from drift-mutation equilibrium indicating recent population expansion. In Mesoamerica, genetic drift was strong and contributed to marked differentiation among populations. The genetic structure of S. globulifera contains fingerprints of drift-dispersal processes and phylogeographic footprints of geological uplifts and sweepstakes dispersal.
Global Ecology and Biogeography, 2010
Aims To better understand how demographic processes shape the range dynamics of woody plants (in this case, Proteaceae), we introduce a likelihood framework for fitting process-based models of range dynamics to spatial abundance data.Location The fire-prone Fynbos biome (Cape Floristic Region, South Africa).Methods Our process-based models have a spatially explicit demographic submodel (describing dispersal, reproduction, mortality and local extinction) as well as an observation submodel (describing imperfect detection of individuals), and are constrained by species-specific predictions of habitat distribution models and process-based models for seed dispersal by wind. Free model parameters were varied to find parameter sets with the highest likelihood. After testing this approach with simulated data, we applied it to eight Proteaceae species that differ in breeding system (monoecy versus dioecy) and adult fire survival. We assess the importance of Allee effects and negative density dependence for range dynamics, by using the Akaike information criterion to select between alternative models fitted for the same species.Results The best model for all dioecious study species included Allee effects, whereas this was true for only one of four monoecious species. As expected, sprouters (in which adults survive fire) were estimated to have lower rates of reproduction and catastrophic population extinction than related non-sprouters. Overcompensatory population dynamics seem important for three of four non-sprouters. We also found good quantitative agreement between independent data and most estimates of reproduction, carrying capacity and extinction probability.Main conclusions This study shows that process-based models can quantitatively describe how large-scale abundance distributions arise from the movement and interaction of individuals. It stresses links between the life history, demography and range dynamics of Proteaceae: dioecious species seem more susceptible to Allee effects which reduce migration ability and increase local extinction risk, and sprouters seem to have high persistence of established populations, but their low reproduction limits habitat colonization and migration.
Systematic Biology, 2003
Systematic and biogeographical relationships within the Hawaiian clade of the pantropical understory shrub genus Psychotria (Rubiaceae) were investigated using phylogenetic analysis of 18S-26S ribosomal DNA internal (ITS) and external (ETS) transcribed spacers. Phylogenetic analyses strongly suggest that the Hawaiian Psychotria are monophyletic and the result of a single introduction to the Hawaiian Islands. The results of phylogenetic analyses of ITS and ETS partitions alone give slightly different topologies among basal lineages of the Hawaiian clade; however, such differences are not well supported. Relationships in the section Straussia clade in particular are not well resolved because of few nucleotide changes on internal branches, suggesting extremely rapid radiation in the lineage. Parsimony and likelihood reconstructions of ancestral geographical distributions using the topologies inferred from both parsimony and likelihood analysis of combined data and using different combinations of models and branch lengths gave highly congruent results. However, for one internal node (corresponding to the majority of the "greenwelliae" clade), parsimony reconstructions were unable to distinguish between three possible island states, whereas likelihood reconstructions resulted in clear ordering of possible states, with the island of O`ahu slightly more probable than other islands under all but one model and branch length combination considered (the Jukes-Cantor-like model with branch lengths inferred under parsimony, under which conditions Maui Nui is more probable). A pattern of colonization from oldest to youngest islands was inferred from the phylogeny, using maximum parsimony and maximum likelihood. Additionally, a much higher incidence of intraisland versus interisland speciation was inferred.