Rapid allopatric speciation in logperch darters (Percidae: Percina)

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

Phylogeny and historical biogeography of true morels (Morchella) reveals an early Cretaceous origin and high continental endemism and provincialism in the Holarctic

True morels (Morchella, Ascomycota) are arguably the most highly-prized of the estimated 1.5 million fungi that inhabit our planet. Field guides treat these epicurean macrofungi as belonging to a few species with cosmopolitan distributions, but this hypothesis has not been tested. Prompted by the results of a growing number of molecular studies, which have shown many microbes exhibit strong biogeographic structure and cryptic speciation, we constructed a 4-gene dataset for 177 members of the Morchellaceae to elucidate their origin, evolutionary diversification and historical biogeography. Diversification time estimates place the origin of the Morchellaceae in the middle Triassic 243.63 (95% highest posterior density [HPD] interval: 169.35-319.89) million years ago (Mya) and the divergence of Morchella from its closest relatives in the early Cretaceous 129.61 (95% HPD interval: 90.26-173.16) Mya, both within western North America. Phylogenetic analyses identified three lineages within Morchella: a basal monotypic lineage represented by Morchella rufobrunnea, and two sister clades comprising the black morels (Elata Clade, 26 species) and yellow morels (Esculenta Clade, 16 species). Morchella possesses a Laurasian distribution with 37/41 species restricted to the Holarctic. All 33 Holarctic species represented by multiple collections exhibited continental endemism. Moreover, 16/18 North American and 13/15 Eurasian species appeared to exhibit provincialism. Although morel fruit bodies produce thousands of explosively discharged spores that are well suited to aerial dispersal, our results suggest that they are poorly adapted at invading novel niches. Morels also appear to have retained the ancestral fruit body plan, which has remained remarkably static since the Cretaceous.     

Phylogenetic assessment and biogeographic analyses of tribe <Emphasis Type="Italic">Peracarpeae</Emphasis> (Campanulaceae)

Peracarpeae is a small tribe consisting of three genera: Homocodon, Heterocodon and Peracarpa, with a disjunct distribution between eastern Asia and western North America. Homocodon is endemic to southwestern China and was previously placed in the western North American genus Heterocodon. Our phylogenetic analysis using four plastid markers (matK, atpB, rbcL and trnL-F) suggests the polyphyly of Peracarpeae. Homocodon is sister to a clade consisting of the eastern Asian Adenophora, Hanabusaya and species of Campanula from the Mediterranean region and North America, rather than forming a clade with Heterocodon. Homocodon and its Eurasia relatives are estimated to have diverged in the early Miocene (16.84 mya, 95% HPD 13.35–21.45 mya). The eastern Asian Peracarpa constitutes a clade with the North American Heterocodon, Githopsis and three species of Campanula, supporting a disjunction between eastern Asia and North America in Campanulaceae. The Asian-North American disjunct lineages diverged in the early Miocene (16.17 mya, 95% HPD 13.12–20.9 mya). The biogeographic analyses suggest that Homocodon may be a relict of an early radiation in eastern Asia, and that Peracarpa and its closest North American relatives most likely originated from a Eurasian ancestor.     

A young clade repeating an old pattern: diversity in Nothonotus darters (Teleostei: Percidae) endemic to the Cumberland River

Hypotheses of diversification in eastern North American freshwater fishes have focused primarily on allopatric distributions of species between disjunct highland areas and major river systems. However, these hypotheses do not fully explain the rich diversity of species within highland regions and river systems. Relatively old diversification events at small geographic scales have been observed in the Barcheek Darter subclade that occurs in the Cumberland River drainage (CRD) in Kentucky and Tennessee, United States of America, but it is unknown if this pattern is consistent in other darter subclades. We explored phylogeographic diversity in two species of Nothonotus darters, N. microlepidus and N. sanguifluus, endemic to the CRD to compare phylogenetic patterns between Barcheek Darters and species of Nothonotus. We collected sequence data for a mitochondrial gene (cytb) and three nuclear genes (MLL, S7 and RAG1) from 19 N. microlepidus and 35 N. sanguifluus specimens. Gene trees were estimated using maximum likelihood and Bayesian methods, and a 'species tree' was inferred using a Bayesian method. These trees indicate that species diversity in Nothonotus is underestimated. Five distinct lineages were evident, despite retained ancestral polymorphism and unsampled extirpated populations. Comparison of chronograms for Barcheek Darters and Nothonotus revealed that microendemism resulting from species diversification at small geographic scales in the CRD is a consistent pattern in both old and young darter subclades. Our analyses reveal that geographic isolating mechanisms that result in similar phylogeographic patterns in the CRD are persistent through long expanses of evolutionary time.     

Phylogeny and biogeography of the carnivorous plant family Sarraceniaceae

The carnivorous plant family Sarraceniaceae comprises three genera of wetland-inhabiting pitcher plants: Darlingtonia in the northwestern United States, Sarracenia in eastern North America, and Heliamphora in northern South America. Hypotheses concerning the biogeographic history leading to this unusual disjunct distribution are controversial, in part because genus- and species-level phylogenies have not been clearly resolved. Here, we present a robust, species-rich phylogeny of Sarraceniaceae based on seven mitochondrial, nuclear, and plastid loci, which we use to illuminate this family's phylogenetic and biogeographic history. The family and genera are monophyletic: Darlingtonia is sister to a clade consisting of Heliamphora+Sarracenia. Within Sarracenia, two clades were strongly supported: one consisting of S. purpurea, its subspecies, and S. rosea; the other consisting of nine species endemic to the southeastern United States. Divergence time estimates revealed that stem group Sarraceniaceae likely originated in South America 44-53 million years ago (Mya) (highest posterior density [HPD] estimate = 47 Mya). By 25-44 (HPD = 35) Mya, crown-group Sarraceniaceae appears to have been widespread across North and South America, and Darlingtonia (western North America) had diverged from Heliamphora+Sarracenia (eastern North America+South America). This disjunction and apparent range contraction is consistent with late Eocene cooling and aridification, which may have severed the continuity of Sarraceniaceae across much of North America. Sarracenia and Heliamphora subsequently diverged in the late Oligocene, 14-32 (HPD = 23) Mya, perhaps when direct overland continuity between North and South America became reduced. Initial diversification of South American Heliamphora began at least 8 Mya, but diversification of Sarracenia was more recent (2-7, HPD = 4 Mya); the bulk of southeastern United States Sarracenia originated co-incident with Pleistocene glaciation, <3 Mya. Overall, these results suggest climatic change at different temporal and spatial scales in part shaped the distribution and diversity of this carnivorous plant clade.     

Molecular phylogeny and biogeography of Linanthus (Polemoniaceae)

To better understand the evolutionary history of Linanthus (Polemoniaceae) and its relatives, molecular phylogenies based on DNA sequence data from the internal transcribed spacer (ITS) region of nrDNA and the chloroplast gene matK were estimated using several methods. Our data suggest two separate and well-supported lineages of Linanthus in close association with two other genera-Leptodactylon and Phlox. These results agree with previous molecular systematic work on the Polemoniaceae, but do not support the traditional classification of the genus as a natural group, nor do they support the sectional classification within the genus. With a distribution centered primarily in western North America and a high degree of endemism in the California Floristic Province, it has been suggested by Raven and Axelrod that the origin and diversification of Linanthus and its relatives were tied to the development of a summer-dry climate in western North America, which began around 13-15 million years ago (mya). Increased drying during the Pliocene (1.2-5 mya) has also been hypothesized by Axelrod to have led to an increase in plant speciation in California and adjacent areas. Divergence times within the Linanthus lineages were estimated from the ITS and matK gene trees. A log-likelihood ratio test could not reject clock-like evolution for the matK data; however, the clock was strongly rejected for the ITS data set. Although ITS molecular evolution was not clock-like, the estimated times of divergence were similar to those of the matK data set. Within both lineages of Linanthus there seems to have been considerable diversification that has occurred since the Pliocene.     

Monophyly of Kelloggia Torrey ex Benth. (Rubiaceae) and evolution of its intercontinental disjunction between western North America and eastern Asia

Kelloggia Torrey ex Bentham (Rubiaceae) consists of two species disjunctly distributed in western North America (K. galioides Torrey) and the western part of eastern Asia (K. chinensis Franch.). The two species exhibit a high level of morphological divergence. To test its monophyly and to infer its biogeographic history, we estimated the phylogeny of Kelloggia and its relatives from sequences of three chloroplast DNA regions (rbcL gene, atpB-rbcL spacer, and rps16 intron). The monophyly of Kelloggia was strongly supported, and it forms a sister relationship with the tribe Rubieae. The divergence time between the two disjunct species of Kelloggia was estimated to be 5.42 ± 2.32 million years ago (mya) using the penalized likelihood method based on rbcL sequence data with fossil calibration. Our result does not support the Madrean-Tethyan hypothesis, which assumes an earlier divergence time of 20-25 mya. Ancestral area analysis, as well as dispersal-vicariance (DIVA) analysis, suggests the Asian origin of Kelloggia and the importance of Eurasia in the diversification of its close relatives in the Rubieae-Theligoneae-Paederieae group. The intercontinental disjunction in Kelloggia is suggested to have evolved via long-distance dispersal from Asia into western North America.     

The influence of life‐history strategy on genetic differentiation and lineage divergence in darters (Percidae: Etheostomatinae)

Recent studies determined that darters with specialized breeding strategies can exhibit deep lineage divergence over fine geographic scales without apparent physical barriers to gene flow. However, the extent to which intrinsic characteristics interact with extrinsic factors to influence population divergence and lineage diversification in darters is not well understood. This study employed comparative phylogeographic and population genetic methods to investigate the influence of life history on gene flow, dispersal ability, and lineage divergence in two sympatric sister darters with differing breeding strategies. Our results revealed highly disparate phylogeographic histories, patterns of genetic structure, and dispersal abilities between the two species suggesting that life history may contribute to lineage diversification in darters, especially by limiting dispersal among large river courses. Both species also showed striking differences in demographic history, indicating that extrinsic factors differentially affected each species during the Pleistocene. Collectively, our results indicate that intrinsic and extrinsic factors have influenced levels of gene flow among populations within both species examined. However, we suggest that life‐history strategy may play a more important role in lineage diversification in darters than previously appreciated, a finding that has potentially important implications for understanding diversification of the rich North American freshwater fish fauna.     

Phylogeography of the Northern Alligator Lizard (Squamata,Anguidae): Hidden diversity in a western endemic

Western North America includes the California Floristic Province and the Pacific Northwest, biologically diverse regions highlighted by a complex topography, geology, climate and history. A number of animals span these regions and show distinctive patterns of dispersal, vicariance and lineage diversification. Examining phylogeographic patterns in the fauna of this area aids in our understanding of the forces that have contributed to the generation and maintenance of regional biodiversity. Here, we investigate the biogeography and population structure of the Northern Alligator Lizard (Elgaria coerulea), a wide‐ranging anguid endemic to western North America. We sequenced two mtDNA fragments (ND2 and ND4) for 181 individuals across the range of the species and analysed these data with phylogenetic approaches to infer population and biogeographic history, and date major divergences within the taxon. We further used Bayesian clustering methods to assess major patterns of population structure and performed ecological niche modelling (ENM) to aid in our interpretation of geographic structure and diversification of E. coerulea lineages. Our phylogeographic examination of E. coerulea uncovered surprising diversity and structure, recovering 10 major lineages, each with substantial geographic substructure. While some divergences within the species are relatively old (Pliocene, 5.3–2.6 mya), most intraspecific variation appears to be of more recent origin (Pleistocene, 2.6 mya‐11,700 ya). Current diversity appears to have arisen in the Sierra Nevada Mountains and spread west and north since the Pliocene. Finally, our ENMs suggest that much of the Coast Ranges in California provided ideal habitat during the Last Glacial Maxima (LGM) that has since contracted dramatically and shifted northwards, whereas significant portions of the Sierra Nevada were unsuitable during the LGM and have since become more suitable. Interestingly, E. coerulea shares a number of genetic boundaries with other sympatric taxa, suggesting common historical events and geomorphological features have shaped the biota of this region.     

Phylogenetics and biogeography of eastern Asian-North American disjunct genus Pachysandra （Buxaceae） inferred from nucleotide sequences

Pachysandra is an eastern Asian-North American disjtunct genus with three species, two in eastern Asia （Pachysandra axillaris and Pachysandra terminalis） and one in eastern North America （Pachysandra procurnbens）. Although morphological and cytological studies suggest a close affinity of Pprocumbens with P axillaris, molecular data from nuclear and chloroplast DNA regions have provided conflicting signals. In this study, we tested previous phylogenetic hypotheses using sequences of nuclear ribosomal DNA internal transcribed spacers and chloroplast ndhF gene from multiple individuals of each of the three species. We also estimated the time of divergence between eastem Asia and eastern North America. Our results support the morphological and cytological conclusion that P procumbens is more closely related to P axillaris than to P terminalis. The estimated time of divergence of P axillaris and P procumbens was 14.6±5.5 mya, consistent with estimates from many other eastern Asian-North American disjunct genera. The migration of Pachysandra populations from eastern Asia to North America might have occurred by way of the North Atlantic land bridge.     

Demographic and phylogeographic histories of two venomous North American snakes of the genus Agkistrodon

Many studies have revealed that lineages currently inhabiting formerly glaciated areas were pushed into southern glacial refugia and have expanded into their modern range since the last glacial maximum. There have been few studies that compare the effects of glacial cycles on lineage diversification and historical demography in closely related species with overlapping ranges. In this study we compare phylogeographic structure, historical demography, and approximate lineage age in two closely related and broadly co-occurring venomous snakes in eastern North America, the cottonmouth (Agkistrodon piscivorus) and copperhead (A. contortrix) using sequences from the mtDNA gene cytochrome b. We inferred three geographic lineages of A. contortrix and two of A. piscivorus with no common geographic or temporal pattern of lineage diversification identified for these species. Lineage diversification occurred in the Late Pliocene for A. piscivorus (2.5 mya) and in the Early Pleistocene for A. contortrix (1.5 mya). Demographic estimates revealed population expansion following the last glacial maximum (20,000 years ago) in two lineages of A. contortrix (the Central clade and Eastern clade) and one lineage of A. piscivorus (the Continental clade). The Florida clade of A. piscivorus is the only lineage for which constant population size through time was inferred, possibly due to stable populations persisting in areas unaffected by glacial advances. Our data suggest that unique habitat preferences may have shaped both the phylogeographic and demographic histories of each species.     

Phylogeny of Acridocarpus-Brachylophon (Malpighiaceae): implications for tertiary tropical floras and Afroasian biogeography

Abstract.— A major tenet of African Tertiary biogeography posits that lowland rainforest dominated much of Africa in the late Cretaceous and was replaced by xeric vegetation as a response to continental uplift and consequent widespread aridification beginning in the late Paleogene. The aridification of Africa is thought to have been a major factor in the extinction of many African humid-tropical lineages, and in the present-day disparity of species diversity between Africa and other tropical regions. This primarily geologically based model can be tested with independent phylogenetic evidence from widespread African plant groups containing both humid- and xeric-adapted species. We estimated the phylogeny and lineage divergence times within one such angiosperm group, the acridocarpoid clade (Malpighiaceae), with combined ITS, ndhF , and trnL-F data from 15 species that encompass the range of morphological and geographic variation within the group. Dispersal-vicariance analysis and divergence-time estimates suggest that the basal acridocarpoid divergence occurred between African and Southeast Asian lineages approximately 50 million years ago (mya), perhaps after a southward ancestral retreat from high-latitude tropical forests in response to intermittent Eocene cooling. Dispersion of Acridocarpus from Africa to Madagascar is inferred between approximately 50 and 35 mya, when lowland humid tropical forest was nearly continuous between these landmasses. A single dispersal event within Acridocarpus is inferred from western Africa to eastern Africa between approximately 23 and 17 mya, coincident with the widespread replacement of humid forests by savannas in eastern Africa. Although the spread of xeric environments resulted in the extinction of many African plant groups, our data suggest that for others it provided an opportunity for further diversification.     

Historical biogeography, divergence times, and diversification patterns of bumble bees (Hymenoptera: Apidae: Bombus)

Bumble bees (Bombus) are a cold-adapted, largely alpine group that can elucidate patterns of Holarctic historical biogeography, particularly in comparison to the alpine plants with which they likely coevolved. A recently published molecular phylogeny of bumble bees provides uniquely comprehensive species sampling for exploring historical patterns of distribution and diversification. Using this phylogeny and detailed data on extant distributions, I reconstruct the historical distribution of bumble bees in a temporal framework, estimating divergence times using fossil data and molecular rates derived from the literature. The nearly comprehensive phylogeny allows assessment of the tempo of diversification within the bumble bees using lineage-through-time plots and diversification statistics, which have been performed with special consideration to confidence intervals. These analyses reveal movements of Bombus concordant with geographic and climatic events of the late Cenozoic. The initial diversification of extant bumble bee lineages was estimated at around 25 to 40 Ma, near the Eocene-Oligocene boundary 34 Ma, a period of dramatic global cooling. Dispersal-vicariance analysis (DIVA) predicted an Old World Bombus ancestor, with early diversification events largely restricted to the eastern Old World. The numerous intercontinental dispersal events occurred mostly in the direction of Old World to New World and North America to South America. Early movements from the Palearctic into the Nearctic most likely took place after 20 Ma and may have coincided with a period of Miocene cooling that gave rise to taiga habitat across Beringia. Subsequent dispersal between these regions is estimated to have occurred among boreal and tundra-adapted species mostly in the last 5 million years. Radiations are estimated in both Nearctic and Neotropical regions at approximately 6 to 8 Ma and after 3.5 Ma, concordant with the opening of land corridors between the continents.     

A biogeographical analysis of Muhlenbergia (Poaceae: Chloridoideae: Cynodonteae: Muhlenbergiinae)

A phylogeny based on the analysis of six DNA sequence markers (ITS, ndhA intron, rpl32-trnL, rps3, rps16 intron, and rps16-trnK) is used to infer ancestral areas and divergence times, and reconstruct the biogeographical history and evolution of 150 of the 183 (82%) species of Muhlenbergia. Our results suggest that the genus originated 9.3 mya in the Sierra Madre (Occidental and Oriental) in Mexico, splitting into six lineages: M. ramulosa diverging 8.2 mya, M. subg. Muhlenbergia at 5.9 mya, M. subg. Pseudosporobolus at 5.9 mya, M. subg. Clomena at 5.4 mya, M. subg. Bealia at 4.3 mya, and M. subg. Trichochloa at 1 mya, each of these with a high probability of Sierra Madrean origin. Our results further suggest that founder-event speciation from Sierra Madre to South America occurred independently multiple times in all five subgenera during the Pleistocene and late Pliocene. One long-distance dispersal event most likely originating from Central or Eastern North America to East and Central Asia occurred 1.6–1 mya in M. subg. Muhlenbergia. In our cladogram, members of M. subg. Trichochloa show little genetic resolution, suggesting very low levels of divergence among the species, and this may be a consequence of rapid radiation.     

Nuclear and mitochondrial phylogeography of the Atlantic forest endemic Xiphorhynchus fuscus (Aves: Dendrocolaptidae): biogeography and systematics implications

We studied the intraspecific evolutionary history of the South American Atlantic forest endemic Xiphorhynchusfuscus (Aves: Dendrocolaptidae) to address questions such as: Was the diversification of this bird's populations associated to areas of avian endemism? Which models of speciation (i.e., refuges, river as barriers or geotectonism) explain the diversification within X. fuscus? Does the genetic data support subspecies as independent evolutionary units (species)? We used mitochondrial (n=34) and nuclear (n=68) DNA sequences of X. fuscus to study temporal and spatial relationships within and between populations. We described four main monophyletic lineages that diverged during the Pleistocene. The subspecies taxonomy did not match all the evolutionary lineages; subspecies atlanticus was the only one that represented a monophyletic and isolated lineage. The distribution of these lineages coincided with some areas of endemism for passerines, suggesting that those areas could be regions of biotic differentiation. The ancestor of X. fuscus diverged approximately 3 million years ago from Amazonian taxa and the phylogeographic pattern suggested that X. fuscus radiated from northeastern Brazil. Neither the riverine nor the geotectonic vicariance models are supported as the primary cause for diversification of geographic lineages, but rainforest contractions and expansions (ecological vicariance) can explain most of the spatial divergence observed in this species. Finally, analyses of gene flow and divergence time estimates suggest that the endangered subspecies atlanticus (from northeastern Brazil) can be considered a full species under the general lineage species concept.     

Temporal diversification of Mesoamerican cichlid fishes across a major biogeographic boundary

The Mexican Neovolcanic Plateau sharply divides the vertebrate fauna of Mesoamerica where the climate of both the neotropics and temperate North America gradually blend. Only a few vertebrate groups such as the Heroine cichlids, distributed from South America to the Rio Grande in North America, are found both north and south of the Neovolcanic Plateau. To better understand the geography and temporal diversification of cichlids at this geologic boundary, we used mitochondrial DNA sequences of the cytochrome b (cyt b) gene to reconstruct the relationships of 52 of the approximately 80 species of Heroine cichlids in Mesoamerica. Our analysis suggests several cichlids in South America should be considered as part of the Mesoamerican Heroine clade because they and the cichlids north of the Isthmus of Panama are clearly supported as monophyletic with respect to all other Neotropical cichlids. We also recovered a group containing species in Paratheraps+Paraneetroplus+Vieja as the sister clade to Herichthys. Herichthys is the only cichlid clade north of the Mexican Plateau and it is monophyletic. Non-parametric rate smoothing of cichlid cyt b sequence resulted in an estimated divergence time of approximately 6 million years for Herichthys. This temporal diversification is concordant with divergence times estimated for anurans in the genus Bufo, a group that exhibits a similar geographic distribution. Our results indicate the 5-million-year-old extension of the Mexican Neovolcanic Plateau to the Gulf Coast of Mexico has strongly influenced the current transition between the vertebrate faunas of the Neotropics and Nearctic.     

Speciation in the White-breasted Nuthatch (Sitta carolinensis): a multilocus perspective

Inferring the evolutionary and ecological processes that have shaped contemporary species distributions using the geographic distribution of gene lineages is the principal goal of phylogeographic research. Researchers in the field have recognized that inferences made from a single gene, often mitochondrial, can be informative regarding the pattern of diversification but lack conclusive information regarding the evolutionary mechanisms that led to the observed patterns. Here, we use a multilocus (20 loci) data set to explore the evolutionary history of the White‐breasted Nuthatch (Sitta carolinensis). A previous single‐locus study found S. carolinensis is comprised of four reciprocally monophyletic clades geographically restricted to the pine and oak forests of: (i) eastern North America, (ii) southern Rocky Mountain and Mexican Mountain ranges, (iii) Eastern Sierra Nevada and Northern Rocky Mountains and (iv) Pacific slope of North America. The diversification of the clades was attributed to the fragmentation of North American pine and oak woodlands in the Pliocene with subsequent divergences owing to the Pleistocene glacial cycles. Principal component, clustering and species tree analyses of the multilocus data resolved the same four groups or lineages found in the single‐locus study. Coalescent analyses and hypothesis testing of nested isolation and migration models indicate that isolation and not gene flow has been the major evolutionary mechanism responsible for shaping genetic variation, and all the divergence events within S. carolinensis have occurred in response to the Pleistocene glacial cycles.     

Integrated Fossil and Molecular Data Reveal the Biogeographic Diversification of the Eastern Asian-Eastern North American Disjunct Hickory Genus (Carya Nutt.)

The hickory genus (Carya) contains ca. 17 species distributed in subtropical and tropical regions of eastern Asia and subtropical to temperate regions of eastern North America. Previously, the phylogenetic relationships between eastern Asian and eastern North American species of Carya were not fully confirmed even with an extensive sampling, biogeographic and diversification patterns had thus never been investigated in a phylogenetic context. We sampled 17 species of Carya and 15 species representing all other genera of the Juglandaceae as outgroups, with eight nuclear and plastid loci to reconstruct the phylogeny of Carya. The phylogenetic positions of seven extinct genera of the Juglandaceae were inferred using morphological characters and the molecular phylogeny as a backbone constraint. Divergence times within Carya were estimated with relaxed Bayesian dating. Biogeographic analyses were performed in DIVA and LAGRANGE. Diversification rates were inferred by LASER and APE packages. Our results support two major clades within Carya, corresponding to the lineages of eastern Asia and eastern North America. The split between the two disjunct clades is estimated to be 21.58 (95% HPD 11.07-35.51) Ma. Genus-level DIVA and LAGRANGE analyses incorporating both extant and extinct genera of the Juglandaceae suggested that Carya originated in North America, and migrated to Eurasia during the early Tertiary via the North Atlantic land bridge. Fragmentation of the distribution caused by global cooling in the late Tertiary resulted in the current disjunction. The diversification rate of hickories in eastern North America appeared to be higher than that in eastern Asia, which is ascribed to greater ecological opportunities, key morphological innovations, and polyploidy.     

Intercontinental biogeography of subfamily Orontioideae (Symplocarpus, Lysichiton, and Orontium) of Araceae in Eastern Asia and North America

Symplocarpus, Lysichiton, and Orontium (Orontioideae) are three of the few north temperate genera of the primarily tropical Araceae. Symplocarpus is disjunctly distributed in eastern Asia (3 spp.) and eastern North America (1 sp.); Lysichiton has an intercontinental discontinuous distribution in eastern Asia (1 sp.) and northwestern North America (1 sp.); and the monotypic Orontium is restricted to eastern North America. Phylogenetic analysis of the trnL-F and ndhF sequences supports (1) the monophyly of both Symplocarpus and Lysichiton, (2) the sister-group relationship of Symplocarpus and Lysichiton, and (3) the clade of Orontium, Symplocarpus, and Lysichiton. Although Symplocarpus shows a much wider disjunction than Lysichiton, the estimated divergence time of the former [4.49+/-1.69 or 6.88+/-4.18 million years ago (mya)] was similar to that of the latter (4.02+/-1.60 or 7.18+/-4.33 mya) based on the penalized likelihood and the Bayesian dating methods, respectively. Eastern Asia was suggested to be the ancestral area of the Symplocarpus-Lysichiton clade based on the dispersal-vicariance analysis. Our biogeographic results support independent migrations of Symplocarpus and Lysichiton across the Bering land bridge in the late Tertiary (Pliocene/late Miocene). Fossil evidence suggests Orontioideae dated back to the late Cretaceous in the temperate Northern Hemisphere (72 mya). The relative rate test shows similar substitution rates of the trnL-F sequences between the proto and the true aroids, although the latter has substantially higher species diversity. The proto Araceae perhaps suffered from a higher rate of extinction in the temperate zone associated with periods of climatic cooling in the Tertiary.