Using fossils and molecular data to reveal the origins of the Cape proteas (subfamily Proteoideae)

High rates of evolution preceded shifts to sex-biased gene expression in Leucadendron, the most sexually dimorphic angiosperms

Differences between males and females are usually more subtle in dioecious plants than animals, but strong sexual dimorphism has evolved convergently in the South African Cape plant genus Leucadendron. Such sexual dimorphism in leaf size is expected largely to be due to differential gene expression between the sexes. We compared patterns of gene expression in leaves among 10 Leucadendron species across the genus. Surprisingly, we found no positive association between sexual dimorphism in morphology and the number or the percentage of sex-biased genes (SBGs). Sex bias in most SBGs evolved recently and was species specific. We compared rates of evolutionary change in expression for genes that were sex biased in one species but unbiased in others and found that SBGs evolved faster in expression than unbiased genes. This greater rate of expression evolution of SBGs, also documented in animals, might suggest the possible role of sexual selection in the evolution of gene expression. However, our comparative analysis clearly indicates that the more rapid rate of expression evolution of SBGs predated the origin of bias, and shifts towards bias were depleted in signatures of adaptation. Our results are thus more consistent with the view that sex bias is simply freer to evolve in genes less subject to constraints in expression level.

Evolutionary stability, landscape heterogeneity, and human land-usage shape population genetic connectivity in the Cape Floristic Region biodiversity hotspot

As human-induced change eliminates natural habitats, it impacts genetic diversity and population connectivity for local biodiversity. The South African Cape Floristic Region (CFR) is the most diverse extratropical area for plant biodiversity, and much of its habitat is protected as a UNESCO World Heritage site. There has long been great interest in explaining the underlying factors driving this unique diversity, especially as much of the CFR is endangered by urbanization and other anthropogenic activity. Here, we use a population and landscape genetic analysis of SNP data from the CFR endemic plant Leucadendron salignum or "common sunshine conebush" as a model to address the evolutionary and environmental factors shaping the vast CFR diversity. We found that high population structure, along with relatively deeper and older genealogies, is characteristic of the southwestern CFR, whereas low population structure and more recent lineage coalescence depict the eastern CFR. Population network analyses show genetic connectivity is facilitated in areas of lower elevation and higher seasonal precipitation. These population genetic signatures corroborate CFR species-level patterns consistent with high Pleistocene biome stability and landscape heterogeneity in the southwest, but with coincident instability in the east. Finally, we also find evidence of human land-usage as a significant gene flow barrier, especially in severely threatened lowlands where genetic connectivity has been historically the highest. These results help identify areas where conservation plans can prioritize protecting high genetic diversity threatened by contemporary human activities within this unique cultural UNESCO site.

Phylotranscriptomics reveals the complex evolutionary and biogeographic history of the genus Tsuga with an East Asian-North American disjunct distribution

The disjunct distribution between East Asia and North America is one of the best established biogeographic patterns. A robust phylogeny is fundamental for understanding the biogeographic histories of taxa with this distribution pattern. Tsuga (hemlock) is a genus of Pinaceae with a typical intercontinental disjunct distribution in East Asia and eastern and western North America, and its phylogeny has not been completely reconstructed in previous studies. In this study, we reconstructed a highly resolved phylogeny of Tsuga using 881 nuclear genes, 60 chloroplast genes and 23 mitochondrial genes and explored its biogeographic and reticulate evolutionary history. The results of phylogenetic analysis, molecular dating and ancestral area reconstruction indicate that Tsuga very likely originated from North America in the late Oligocene and dispersed from America to East Asia via the Bering Land Bridge during the middle Miocene. In particular, we found complex reticulate evolutionary pattern among the East Asian hemlock species. T. sieboldii possibly originated from hybridization with the ancestor of T. chinensis from mainland China and T. forrestii as the paternal donor and the ancestor of T. diversifolia and T. ulleungensis as the maternal donor. T. chinensis (Taiwan) could have originated by hybridization together with T. sieboldii and then evolved independently after dispersal to the Taiwan Island, subsequently experiencing mitochondrial DNA introgression with T. chinensis from mainland China. Moreover, our study found that T. chinensis from western China is more closely related to T. forrestii than to T. chinensis from eastern China. The nonmonophyletic T. chinensis needs taxonomic reconsideration.

Identification of copy number variation and population analysis of the sacred lotus (Nelumbo nucifera)

The sacred lotus (Nelumbo nucifera) is widely cultured in East Asia for its horticultural, agricultural, and medicinal values. Although many molecular markers had been used to extrapolate population genetics of the sacred lotus, a study of large variations, such as copy number variation (CNV), are absent up to now. In this study, we applied whole-genome re-sequencing to 24 lotus accessions, and use read depth information to genotype and filter original CNV call. Totally 448 duplications and 4,267 deletions were identified in the final CNV set. Further analysis of population structure revealed that the population structure patterns revealed by CNV and SNP are largely consistent with each other. Our result indicated that deep sequencing followed by genotyping is a quick and straightforward way to mine out CNV from the population, and the CNV along with SNP could enable us to better comprehend the biology of the plant.

Microscale trait-environment associations in two closely-related South African shrubs

PREMISE OF THE STUDY

Plant traits are often associated with the environments in which they occur, but these associations often differ across spatial and phylogenetic scales. Here we study the relationship between microenvironment, microgeographical location, and traits within populations using co-occurring populations of two closely related evergreen shrubs in the genus Protea.

METHODS

We measured a suite of functional traits on 147 plants along a single steep mountainside where both species occur, and we used data-loggers and soil analyses to characterize the environment at 10 microsites spanning the elevational gradient. We used Bayesian path analyses to detect trait-environment relationships in the field for each species. We used complementary data from greenhouse grown seedlings derived from wild collected seed to determine whether associations detected in the field are the result of genetic differentiation.

KEY RESULTS

Microenvironmental variables differed substantially across our study site. We found strong evidence for six trait-environment associations, although these differed between species. We were unable to detect similar associations in greenhouse-grown seedlings.

CONCLUSIONS

Several leaf traits were associated with temperature and soil variation in the field, but the inability to detect these in the greenhouse suggests that differences in the field are not the result of genetic differentiation.

Estimating divergence times and ancestral breeding systems in Ficus and Moraceae

Background and Aims

Although dioecy, which characterizes only 6 % of angiosperm species, has been considered an evolutionary dead end, recent studies have demonstrated that this is not necessarily the case. Moraceae (40 genera, 1100 spp., including Ficus, 750 spp.) are particularly diverse in breeding systems (including monoecy, gynodioecy, androdioecy and dioecy) and thus represent a model clade to study macroevolution of dioecy.

Methods

Ancestral breeding systems of Ficus and Moraceae were inferred. To do so, a new dated phylogenetic tree of Ficus and Moraceae was first reconstructed by combining a revised 12-fossil calibration set and a densely sampled molecular data set of eight markers and 320 species. Breeding system evolution was then reconstructed using both parsimony and model-based (maximum likelihood and Bayesian) approaches with this new time scale.

Key Results

The crown group ages of Ficus and Moraceae were estimated in the Eocene (40.6-55.9 Ma) and Late Cretaceous (73.2-84.7 Ma), respectively. Strong support was found for ancestral dioecy in Moraceae. Although the ancestral state of Ficus remained particularly sensitive to model selection, the results show that monoecy and gynodioecy evolved from dioecy in Moraceae, and suggest that gynodioecy probably evolved from monoecy in Ficus.

Conclusions

Dioecy was found not to be an evolutionary dead end in Moraceae. This study provides a new time scale for the phylogeny and a new framework of breeding system evolution in Ficus and Moraceae.

Correlated evolution between climate and suites of traits along a fast-slow continuum in the radiation of Protea

Evolutionary radiations are responsible for much of Earth's diversity, yet the causes of these radiations are often elusive. Determining the relative roles of adaptation and geographic isolation in diversification is vital to understanding the causes of any radiation, and whether a radiation may be labeled as "adaptive" or not. Across many groups of plants, trait-climate relationships suggest that traits are an important indicator of how plants adapt to different climates. In particular, analyses of plant functional traits in global databases suggest that there is an "economics spectrum" along which combinations of functional traits covary along a fast-slow continuum. We examine evolutionary associations among traits and between trait and climate variables on a strongly supported phylogeny in the iconic plant genus Protea to identify correlated evolution of functional traits and the climatic-niches that species occupy. Results indicate that trait diversification in Protea has climate associations along two axes of variation: correlated evolution of plant size with temperature and leaf investment with rainfall. Evidence suggests that traits and climatic-niches evolve in similar ways, although some of these associations are inconsistent with global patterns on a broader phylogenetic scale. When combined with previous experimental work suggesting that trait-climate associations are adaptive in Protea, the results presented here suggest that trait diversification in this radiation is adaptive.

Life-History Traits Evolved Jointly with Climatic Niche and Disturbance Regime in the Genus Leucadendron (Proteaceae)

Organisms have evolved a diversity of life-history strategies to cope with variation in their environment. Persistence as adults and/or seeds across recruitment events allows species to dampen the effects of environmental fluctuations. The evolution of life cycles with overlapping generations should thus permit the colonization of environments with uncertain recruitment. We tested this hypothesis in Leucadendron (Proteaceae), a genus with high functional diversity native to fire-prone habitats in the South African fynbos. We analyzed the joint evolution of life-history traits (adult survival and seed-bank strategies) and ecological niches (climate and fire regime), using comparative methods and accounting for various sources of uncertainty. In the fynbos, species with canopy seed banks that are unable to survive fire as adults display nonoverlapping generations. In contrast, resprouters with an underground seed bank may be less threatened by extreme climatic events and fire intervals, given their iteroparity and long-lasting seed bank. Life cycles with nonoverlapping generations indeed jointly evolved with niches with less exposure to frost but not with those with less exposure to drought. Canopy seed banks jointly evolved with niches with more predictable fire return, compared to underground seed banks. The evolution of extraordinary functional diversity among fynbos plants thus reflects, at least in part, the diversity of both climates and fire regimes in this region.

Isolation by distance and isolation by environment contribute to population differentiation in Protea repens (Proteaceae L.), a widespread South African species

PREMISE OF THE STUDY

The Cape Floristic Region (CFR) of South Africa is renowned for its botanical diversity, but the evolutionary origins of this diversity remain controversial. Both neutral and adaptive processes have been implicated in driving diversification, but population-level studies of plants in the CFR are rare. Here, we investigate the limits to gene flow and potential environmental drivers of selection in Protea repens L. (Proteaceae L.), a widespread CFR species.

METHODS

We sampled 19 populations across the range of P. repens and used genotyping by sequencing to identify 2066 polymorphic loci in 663 individuals. We used a Bayesian F_ST outlier analysis to identify single-nucleotide polymorphisms (SNPs) marking genomic regions that may be under selection; we used those SNPs to identify potential drivers of selection and excluded them from analyses of gene flow and genetic structure.

RESULTS

A pattern of isolation by distance suggested limited gene flow between nearby populations. The populations of P. repens fell naturally into two or three groupings, which corresponded to an east-west split. Differences in rainfall seasonality contributed to diversification in highly divergent loci, as do barriers to gene flow that have been identified in other species.

CONCLUSIONS

The strong pattern of isolation by distance is in contrast to the findings in the only other widespread species in the CFR that has been similarly studied, while the effects of rainfall seasonality are consistent with well-known patterns. Assessing the generality of these results will require investigations of other CFR species.

Characterization of CYCLOIDEA-like genes in Proteaceae, a basal eudicot family with multiple shifts in floral symmetry

BACKGROUND AND AIMS

The basal eudicot family Proteaceae (approx. 1700 species) shows considerable variation in floral symmetry but has received little attention in studies of evolutionary development at the genetic level. A framework for understanding the shifts in floral symmetry in Proteaceae is provided by reconstructing ancestral states on an upated phylogeny of the family, and homologues of CYCLOIDEA (CYC), a key gene for the control of floral symmetry in both monocots and eudicots, are characterized.

METHODS

Perianth symmetry transitions were reconstructed on a new species-level tree using parsimony and maximum likelihood. CYC-like genes in 35 species (31 genera) of Proteaceae were sequenced and their phylogeny was reconstructed. Shifts in selection pressure following gene duplication were investigated using nested branch-site models of sequence evolution. Expression patterns of CYC homologues were characterized in three species of Grevillea with different types of floral symmetry.

KEY RESULTS

Zygomorphy has evolved 10-18 times independently in Proteaceae from actinomorphic ancestors, with at least four reversals to actinomorphy. A single duplication of CYC-like genes occurred prior to the diversification of Proteaceae, with putative loss or divergence of the ProtCYC1 paralogue in more than half of the species sampled. No shifts in selection pressure were detected in the branches subtending the two ProtCYC paralogues. However, the amino acid sequence preceding the TCP domain is strongly divergent in Grevillea ProtCYC1 compared with other species. ProtCYC genes were expressed in developing flowers of both actinomorphic and zygomorphic Grevillea species, with late asymmetric expression in the perianth of the latter.

CONCLUSION

Proteaceae is a remarkable family in terms of the number of transitions in floral symmetry. Furthermore, although CYC-like genes in Grevillea have unusual sequence characteristics, they display patterns of expression that make them good candidates for playing a role in the establishment of floral symmetry.

Anchored phylogenomics improves the resolution of evolutionary relationships in the rapid radiation of Protea L

PREMISE OF THE STUDY

Estimating phylogenetic relationships in relatively recent evolutionary radiations is challenging, especially if short branches associated with recent divergence result in multiple gene tree histories. We combine anchored enrichment next-generation sequencing with species tree analyses to produce a robust estimate of phylogenetic relationships in the genus Protea (Proteaceae), an iconic radiation in South Africa.

METHODS

We sampled multiple individuals within 59 out of 112 species of Protea and 6 outgroup species for a total of 163 individuals, and obtained sequences for 498 low-copy, orthologous nuclear loci using anchored phylogenomics. We compare several approaches for building species trees, and explore gene tree-species tree discrepancies to determine whether poor phylogenetic resolution reflects a lack of informative sites, incomplete lineage sorting, or hybridization.

KEY RESULTS

Phylogenetic estimates from species tree approaches are similar to one another and recover previously well-supported clades within Protea, in addition to providing well-supported phylogenetic hypotheses for previously poorly resolved intrageneric relationships. Individual gene trees are markedly different from one another and from species trees. Nonetheless, analyses indicate that differences among gene trees occur primarily concerning clades supported by short branches.

CONCLUSIONS

Species tree methods using hundreds of nuclear loci provided strong support for many previously unresolved relationships in the radiation of the genus Protea. In cases where support for particular relationships remains low, these appear to arise from few informative sites and lack of information rather than strongly supported disagreement among gene trees.

Species-rich and polyploid-poor: Insights into the evolutionary role of whole-genome duplication from the Cape flora biodiversity hotspot

PREMISE OF THE STUDY

Whole-genome duplication (WGD) in angiosperms has been hypothesized to be advantageous in unstable environments and/or to increase diversification rates, leading to radiations. Under the first hypothesis, floras in stable environments are predicted to have lower proportions of polyploids than highly, recently disturbed floras, whereas species-rich floras would be expected to have higher than expected proportions of polyploids under the second. The South African Cape flora is used to discriminate between these two hypotheses because it features a hyperdiverse flora predominantly generated by a limited number of radiations (Cape clades), against a backdrop of climatic and geological stability.

METHODS

We compiled all known chromosome counts for species in 21 clades present in the Cape (1653 species, including 24 Cape clades), inferred ploidy levels for these species by inspection or derived from the primary literature, and compared Cape to non-Cape ploidy levels in these clades (17,520 species) using G tests.

KEY RESULTS

The Cape flora has anomalously low proportions of polyploids compared with global levels. This pattern is consistently observed across nearly half the clades and across global latitudinal gradients, although individual lineages seem to be following different paths to low levels of WGD and to differing degrees.

CONCLUSIONS

This pattern shows that the diversity of the Cape flora is the outcome of primarily diploid radiations and supports the hypothesis that WGD may be rare in stable environments.

Fossil evidence for open, Proteaceae-dominated heathlands and fire in the Late Cretaceous of Australia

PREMISE OF THE STUDY

The origin of biomes is of great interest globally. Molecular phylogenetic and pollen evidence suggest that several plant lineages that now characterize open, burnt habitats of the sclerophyll biome, became established during the Late Cretaceous of Australia. However, whether this biome itself dates to that time is problematic, fundamentally because of the near-absence of relevant, appropriately aged, terrestrial plant macro- or mesofossils.

METHODS

We recovered, identified, and interpreted the ecological significance of fossil pollen, foliar and other remains from a section of core drilled in central Australia, which we dated as Late Campanian-Maastrichtian.

KEY RESULTS

The sediments contain plant fossils that indicate nutrient-limited, open, sclerophyllous vegetation and abundant charcoal as evidence of fire. Most interestingly, >30 pollen taxa and at least 12 foliage taxa are attributable to the important Gondwanan family Proteaceae, including several minute, amphistomatic, and sclerophyllous foliage forms consistent with subfamily Proteoideae. Microfossils, including an abundance of Sphagnales and other wetland taxa, provided strong evidence of a fenland setting. The local vegetation also included diverse Ericaceae and Liliales, as well as a range of ferns and gymnosperms.

CONCLUSIONS

The fossils provide strong evidence in support of hypotheses of great antiquity for fire and open vegetation in Australia, point to extraordinary persistence of Proteaceae that are now emblematic of the Mediterranean-type climate southwestern Australian biodiversity hotspot and raise the profile of open habitats as centers of ancient lineages.

Dated Plant Phylogenies Resolve Neogene Climate and Landscape Evolution in the Cape Floristic Region

In the context of molecularly-dated phylogenies, inferences informed by ancestral habitat reconstruction can yield valuable insights into the origins of biomes, palaeoenvironments and landforms. In this paper, we use dated phylogenies of 12 plant clades from the Cape Floristic Region (CFR) in southern Africa to test hypotheses of Neogene climatic and geomorphic evolution. Our combined dataset for the CFR strengthens and refines previous palaeoenvironmental reconstructions based on a sparse, mostly offshore fossil record. Our reconstructions show remarkable consistency across all 12 clades with regard to both the types of environments identified as ancestral, and the timing of shifts to alternative conditions. They reveal that Early Miocene land surfaces of the CFR were wetter than at present and were dominated by quartzitic substrata. These conditions continue to characterize the higher-elevation settings of the Cape Fold Belt, where they have fostered the persistence of ancient fynbos lineages. The Middle Miocene (13-17 Ma) saw the development of perennial to weakly-seasonal arid conditions, with the strongly seasonal rainfall regime of the west coast arising ~6.5-8 Ma. Although the Late Miocene may have seen some exposure of the underlying shale substrata, the present-day substrate diversity of the CFR lowlands was shaped by Pliocene-Pleistocene events. Particularly important was renewed erosion, following the post-African II uplift episode, and the reworking of sediments on the coastal platform as a consequence of marine transgressions and tectonic uplift. These changes facilitated adaptive radiations in some, but not all, lineages studied.

What has molecular systematics contributed to our knowledge of the plant family Proteaceae?

Molecular systematics has revolutionized our understanding of the evolution of the Proteaceae. Phylogenetic relationships have been reconstructed down to generic level and below from alignments of chloroplast and nuclear DNA sequences. These trees have enabled the monophyly of all subfamilies, tribes, and subtribes to be rigorously tested and the construction of a new classification of the family at these ranks. Molecular data have also played a major part in testing the monophyly of genera and infrageneric taxa, some of which have been recircumscribed as a result. Molecular trees and chronograms have been used to test numerous previously postulated biogeographic and evolutionary hypotheses, some of which have been modified or abandoned as a result. Hypotheses that have been supported by molecular phylogenetic trees and chronograms include the following: that the proteaceous pattern of repeated disjunct distributions across the southern hemisphere is partly the result of long-distance dispersal; that high proteaceous diversity in south-western Australia and the Cape Floristic Region of South Africa is due to high diversification rates in some clades but is not an evolutionary response to Mediterranean climates; that the sclerophyllous leaves of many shrubby members of the family are not adaptations to dry environments but for protecting mesophyll in brightly illuminated habitats; that deeply encrypted foliar stomata are adaptations for minimizing water loss in dry environments; and that Protea originated in the Cape Floristic Region of South Africa and that one of its subclades has greatly expanded its distribution into tropical savannas. Reconstructing phylogeny down to species level is now the main goal of molecular systematists of the Proteaceae. The biggest challenge in achieving this task will be resolving species trees from numerous gene trees in complexes of closely related species.

Developing nuclear DNA phylogenetic markers in the angiosperm genus Leucadendron (Proteaceae): a next-generation sequencing transcriptomic approach

Despite the recent advances in generating molecular data, reconstructing species-level phylogenies for non-models groups remains a challenge. The use of a number of independent genes is required to resolve phylogenetic relationships, especially for groups displaying low polymorphism. In such cases, low-copy nuclear exons and non-coding regions, such as 3' untranslated regions (3'-UTRs) or introns, constitute a potentially interesting source of nuclear DNA variation. Here, we present a methodology meant to identify new nuclear orthologous markers using both public-nucleotide databases and transcriptomic data generated for the group of interest by using next generation sequencing technology. To identify PCR primers for a non-model group, the genus Leucadendron (Proteaceae), we adopted a framework aimed at minimizing the probability of paralogy and maximizing polymorphism. We anchored when possible the right-hand primer into the 3'-UTR and the left-hand primer into the coding region. Seven new nuclear markers emerged from this search strategy, three of those included 3'-UTRs. We further compared the phylogenetic potential between our new markers and the ribosomal internal transcribed spacer region (ITS). The sequenced 3'-UTRs yielded higher polymorphism rates than the ITS region did. We did not find strong incongruences with the phylogenetic signal contained in the ITS region and the seven new designed markers but they strongly improved the phylogeny of the genus Leucadendron. Overall, this methodology is efficient in isolating orthologous loci and is valid for any non-model group given the availability of transcriptomic data.

Age estimates for the buckwheat family Polygonaceae based on sequence data calibrated by fossils and with a focus on the amphi-Pacific Muehlenbeckia

The buckwheat family Polygonaceae is a diverse group of plants and is a good model for investigating biogeography, breeding systems, coevolution with symbionts such as ants and fungi, functional trait evolution, hybridization, invasiveness, morphological plasticity, pollen morphology and wood anatomy. The main goal of this study was to obtain age estimates for Polygonaceae by calibrating a Bayesian phylogenetic analysis, using a relaxed molecular clock with fossil data. Based on the age estimates, we also develop hypotheses about the historical biogeography of the Southern Hemisphere group Muehlenbeckia. We are interested in addressing whether vicariance or dispersal could account for the diversification of Muehlenbeckia, which has a "Gondwanan" distribution. Eighty-one species of Polygonaceae were analysed with MrBayes to infer species relationships. One nuclear (nrITS) and three chloroplast markers (the trnL-trnF spacer region, matK and ndhF genes) were used. The molecular data were also analysed with Beast to estimate divergence times. Seven calibration points including fossil pollen and a leaf fossil of Muehlenbeckia were used to infer node ages. Results of the Beast analyses indicate an age of 110.9 (exponential/lognormal priors)/118.7 (uniform priors) million years (Myr) with an uncertainty interval of (90.7-125.0) Myr for the stem age of Polygonaceae. This age is older than previously thought (Maastrichtian, approximately 65.5-70.6 Myr). The estimated divergence time for Muehlenbeckia is 41.0/41.6 (39.6-47.8) Myr and its crown clade is 20.5/22.3 (14.2-33.5) Myr old. Because the breakup of Gondwana occurred from 95-30 Myr ago, diversification of Muehlenbeckia is best explained by oceanic long-distance and maybe stepping-stone dispersal rather than vicariance. This study is the first to give age estimates for clades of Polygonaceae and functions as a jumping-off point for future studies on the historical biogeography of the family.

Estimating the age of fire in the Cape flora of South Africa from an orchid phylogeny

Fire may have been a crucial component in the evolution of the Cape flora of South Africa, a region characterized by outstanding levels of species richness and endemism. However, there is, to date, no critical assessment of the age of the modern fire regime in this biome. Here, we exploit the presence of two obligate post-fire flowering clades in the orchid genus Disa, in conjunction with a robust, well-sampled and dated molecular phylogeny, to estimate the age by which fire must have been present. Our results indicate that summer drought (winter rainfall), the fire regime and the fynbos vegetation are several million years older than currently suggested. Summer drought and the fynbos vegetation are estimated to date back to at least the Early Miocene (ca 19.5 Ma). The current fire regime may have been established during a period of global cooling that followed the mid-Miocene Climatic Optimum (ca 15 Ma), which led to the expansion of open habitats and increased aridification. The first appearance of Disa species in the grassland biome, as well as in the subalpine habitat, is in striking agreement with reliable geological and palaeontological evidence of the age of these ecosystems, thus corroborating the efficacy of our methods. These results change our understanding of the historical mechanisms underlying botanical evolution in southern Africa, and confirm the potential of using molecular phylogenies to date events for which other information is lacking or inconclusive.