Earlier Phylogenetic Analyses Research Articles

Phylogenetic study of the New Caledonian endemic genus Adenodaphne (Lauraceae) confirms its synonymy with Litsea

ABSTRACT The genus Adenodaphne is currently considered endemic to New Caledonia, but its distinction from Litsea is questionable based on morphological similarity. An earlier phylogenetic analysis (ITS) including one species of Adenodaphne and two Asian species of Litsea did support their close relationship but did not permit resolution of their generic boundary. We sampled the four species of Adenodaphne currently recognized (11 accessions) and 11 of the 13 endemic species of Litsea currently recognized, plus one undescribed species (24 accessions in total). Based on our extensive herbarium studies, fieldwork, and especially our molecular phylogenetic analyses (ITS), we conclude that Adenodaphne is not distinct from Litsea and that all species of Adenodaphne should be recognized within Litsea, thereby necessitating the creation of two new species synonymies and one nomen novum. In addition, Litsea paoueensis is here synonymized with L. deplanchei. Finally, our phylogenetic analysis suggests that the sole species of Litsea from New Zealand, which is endemic, results from a rarely documented long-distance dispersal event from New Caledonia.

Multigene phylogeny of the family Cordycipitaceae (Hypocreales): new taxa and the new systematic position of the Chinese cordycipitoid fungus Paecilomyces hepiali

The phylogeny and systematics of cordycipitoid fungi have been extensively studied in the last two decades. However, systematic positions of some taxa in the family Cordycipitaceae have not yet been thoroughly resolved. In this study, a new phylogenetic framework of Cordycipitaceae is reconstructed using multigene (nrSSU, nrLSU, tef-1α, rpb1 and rpb2) sequence data with large-scale taxon sampling. In addition, ITS sequence data of species belonging to the Lecanicillium lineage in the family Cordycipitaceae are used to further determine their phylogenetic placements. Based on molecular phylogenetic data together with morphological evidence, two new genera (Flavocillium and Liangia), 16 new species and four new combinations are introduced. In the new genus Flavocillium, one new species F. bifurcatum and three new combinations previously described as Lecanicillium, namely F. acerosium, F. primulinium and F. subprimulinium, are proposed. The genus Liangia is built by the new species Lia. sinensis with Lecanicillium-like asexual morph, isolated from an entomopathogenic fungus Beauveria yunnanensis. Due to the absence of Paecilomyces hepiali, an economically and medically significant fungus, in the earlier phylogenetic analyses, its systematic position has been puzzling in both business and academic communities for a long time. Here, P. hepiali is recharacterized using the holotype material along with seven additional samples. It is assigned to the genus Samsoniella (Cordycipitaceae, Hypocreales) possessing Cordyceps-like sexual morph and Isaria-like asexual morph, and thus a new combination, namely S. hepiali is proposed. An additional nine new species in Samsoniella are described: S. alpina, S. antleroides, S. cardinalis, S. cristata, S. lanmaoa, S. kunmingensis, S. ramosa, S. tortricidae and S. yunnanensis. Four new species in Cordyceps are described: C. chaetoclavata, C. cocoonihabita, C. shuifuensis and C. subtenuipes. Simplicillium yunnanense, isolated from synnemata of Akanthomyces waltergamsii, is described as a new species.

Detection of Concordance between Transcriptional Levels of GPCRs and Receptor-Activity-Modifying Proteins

SummaryA recent phylogenetic analysis showed global co-evolution of G protein-coupled receptors (GPCRs) and receptor-activity-modifying proteins (RAMPs) suggesting global interactions between these two protein families. Experimental validation of these findings is challenging because in humans whereas there are only three genes encoding RAMPs, there are about 800 genes encoding GPCRs. Here, we report an experimental approach to evaluate GPCR-RAMP interactions. As a proof-of-concept experiment, we over-expressed RAMP2 in HEK293T cells and evaluated the effect on the transcriptional levels of 14 representative GPCRs that were selected based on the earlier phylogenetic analysis. We utilized a multiplexed error-correcting fluorescence in situ hybridization (MERFISH) method to detect message levels for individual GPCRs in single cells. The MERFISH results showed changes in GPCR message levels with RAMP2 over-expression in a concordant pattern that was predicted by the earlier phylogenetic analysis. These results provide additional evidence that GPCR-RAMP interactions are more widespread than previously appreciated and that these interactions have functional consequences.

Revaluation of the taxonomic characters and distribution of Omalonyx geayi (Gastropoda, Succineidae)

ABSTRACT Omalonyx geayi Tillier, 1980 was originally described on the basis of specimens from Kaw swamp, French Guiana. This species distinguished from other of Omalonyx d'Orbigny, 1837: (i) by hermaphrodite duct twice as long and sacculate, without radial ducts but a funnel-shaped insertion on the ovariotestis, and (ii) by longitudinal wrinkled folds on the phallus inner wall. Two recent collections - from Trinidad and Carauari (Amazonas, Brazil) included specimens with ovariotestis and hermaphrodite duct morphologies similar to that originally described for O. geayi, but with phallus morphology not consistent with identification as O. geayi. A further eight lots, from Suriname, Ecuador, Brazil (Amazonas and Alagoas States), Bolivia and Cayenne-Kourou Road in French Guiana comprised specimens with phallus morphology analogous to O. geayi and ovariotestis and hermaphrodite duct similar to that of other Omalonyx species. Based on histological examination, and earlier phylogenetic analyses of morphological characters, we conclude that the ovariotestis and hermaphrodite duct conditions previously described for O. geayi were based on parasitized specimens. Accordingly, O. geayi is redescribed, and new information presented on the species' wide distribution in South America.

Protein Clustering and RNA Phylogenetic Reconstruction of the Influenza a Virus NS1 Protein Allow an Update in Classification and Identification of Motif Conservation

The non-structural protein 1 (NS1) of influenza A virus (IAV), coded by its third most diverse gene, interacts with multiple molecules within infected cells. NS1 is involved in host immune response regulation and is a potential contributor to the virus host range. Early phylogenetic analyses using 50 sequences led to the classification of NS1 gene variants into groups (alleles) A and B. We reanalyzed NS1 diversity using 14,716 complete NS IAV sequences, downloaded from public databases, without host bias. Removal of sequence redundancy and further structured clustering at 96.8% amino acid similarity produced 415 clusters that enhanced our capability to detect distinct subgroups and lineages, which were assigned a numerical nomenclature. Maximum likelihood phylogenetic reconstruction using RNA sequences indicated the previously identified deep branching separating group A from group B, with five distinct subgroups within A as well as two and five lineages within the A4 and A5 subgroups, respectively. Our classification model proposes that sequence patterns in thirteen amino acid positions are sufficient to fit >99.9% of all currently available NS1 sequences into the A subgroups/lineages or the B group. This classification reduces host and virus bias through the prioritization of NS1 RNA phylogenetics over host or virus phenetics. We found significant sequence conservation within the subgroups and lineages with characteristic patterns of functional motifs, such as the differential binding of CPSF30 and crk/crkL or the availability of a C-terminal PDZ-binding motif. To understand selection pressures and evolution acting on NS1, it is necessary to organize the available data. This updated classification may help to clarify and organize the study of NS1 interactions and pathogenic differences and allow the drawing of further functional inferences on sequences in each group, subgroup and lineage rather than on a strain-by-strain basis.

Two species ofHesslandona(Phosphatocopida, Crustacea) from the Upper Cambrian of western Hunan, South China and the phylogeny of Phosphatocopida

The phosphatocopidsHesslandona necopinaMüller, 1964 andHesslandona longispinosa(Kozur, 1974) new combination, recovered from the Upper Cambrian in western Hunan, South China, are described. The ontogenetic stages ofH. necopinaare revised, with newly defined second and third ontogenetic stages. The second stage is characterized by a bipartite mandibular limb stem consisting of separate coxa and basipod. The third stage is characterized by the partial fusion of the mandibular coxa and basipod. These two parts may become completely fused possibly in a later ontogenetic stage.Vestrogothia longispinosaKozur, 1974 is reassigned toHesslandonabecause of the presence of an interdorsum and a relatively narrow doublure. The new data reported here, plus earlier reports of phosphatocopids from the same section and horizon in western Hunan since 2005, are included in an updated phylogenetic analysis of the Phosphatocopida. Autapomorphies that define several monophyletic groups (e.g., the Crustacea sensu lato, Labrophora, Eucrustacea, Phosphatocopida, Euphosphatocopida, Vestrogothiina, Hesslandonina, and Dorsospinata) are discussed. The present analysis confirms results from earlier phylogenetic analyses in showing the Phosphatocopida-Eucrustacea sister-taxon relationship, but differs from them in supporting the paraphyly of the Hesslandonidae and the monophyly of the Vestrogothiidae.

The "false Eucoila" finally named; Striatovertex a new genus of Eucoilinae (Hymenoptera, Cynipoidea, Figitidae)

The new genus Striatovertex is described to accomodate a distinct group of eucoiline wasps (Hymenoptera: Cynipoidea: Figitidae) currently included in the nominate genus Eucoila Westwood, but known among specialists to not belong there for decades. They are characteristically large wasps with reduced wing pubescence, parasitizing dung-breeding Diptera, and are common in North and South America, but also present in Australia and Hawaii. Their diagnostic characters place them in what is currently Ganaspini rather than very close to Eucoila in Eucoilini, and this has been confirmed by earlier phylogenetic analyses. Diagnostic and other distinctive characters are reviewed, and thirteen new combinations are made for species belonging to this group.

Variation in potential effector genes distinguishing Australian and non‐Australian isolates of the cotton wilt pathogen Fusarium oxysporum f.sp. vasinfectum

This study identified genes that distinguish Australian Fusarium oxysporum f.sp. vasinfectum (Fov) isolates from related co‐localized non‐pathogenic F. oxysporum isolates and from non‐Australian Fov isolates. One gene is a homologue of the F. oxysporum f.sp. lycopersici (Fol) effector gene SIX6, encoding a 215‐residue cysteine‐rich secreted protein. The Six6 proteins from Fol and Fov contained eight conserved cysteine residues, five of which occurred in the highly diverged 48‐amino‐acid region where FovSix6 differs from FolSix6 at 32 residues. Two other potential effector genes, PEP1 and PEP2, were identified in a cDNA library of Fov genes expressed during infection of cotton. The presence of FovSIX6 and other differences in DNA fingerprints clearly distinguished Australian Fov isolates from non‐Australian Fov isolates and these differences further support the hypothesis based on earlier phylogenetic analysis that Australian Fov is different from Fov in other cotton‐growing areas. A specific diagnostic for Fov based on FovSIX6 is described.

HLA Class I Restriction as a Possible Driving Force for Chikungunya Evolution

After two decades of quiescence, epidemic resurgence of Chikungunya fever (CHIKF) was reported in Africa, several islands in the Indian Ocean, South-East Asia and the Pacific causing unprecedented morbidity with some cases of fatality. Early phylogenetic analyses based on partial sequences of Chikungunya virus (CHIKV) have led to speculation that the virus behind recent epidemics may result in greater pathogenicity. To understand the reasons for these new epidemics, we first performed extensive analyses of existing CHIKV sequences from its introduction in 1952 to 2009. Our results revealed the existence of a continuous genotypic lineage, suggesting selective pressure is active in CHIKV evolution. We further showed that CHIKV is undergoing mild positive selection, and that site-specific mutations may be driven by cell-mediated immune pressure, with occasional changes that resulted in the loss of human leukocyte antigen (HLA) class I-restricting elements. These findings provide a basis to understand Chikungunya virus evolution and reveal the power of post-genomic analyses to understand CHIKV and other viral epidemiology. Such an approach is useful for studying the impact of host immunity on pathogen evolution, and may help identify appropriate antigens suitable for subunit vaccine formulations.

Molecular genetic comparison of Onchocerca sp. infecting dogs in Europe with other spirurid nematodes including Onchocerca lienalis

In the past 15 years, subconjunctival onchocercosis has been reported from 63 dogs in south-western United States (Arizona, California, Utah) and Southern and Central Europe (Germany, Greece, Hungary, Portugal, Switzerland). To reveal the taxonomic status of the parasite responsible for these infections, fragments of the mitochondrial cytochrome oxidase subunit I (COI) and NADH dehydrogenase subunit 5 (ND5) genes of three European strains of canine Onchocerca sp. and the 16S ribosomal RNA (16S rRNA) gene of their Wolbachia endosymbionts were sequenced and compared to the homologous sequences of other spirurid nematodes. The evolutionary divergence between COI and ND5 gene sequences of Greek, Hungarian and Portuguese strains of canine Onchocerca sp. were similar in magnitude to that seen within Thelazia callipaeda or Onchocerca lienalis. The evolutionary divergence between the sequences of canine Onchocerca sp. and other Onchocerca spp. including O. lienalis were similar or higher in magnitude to that seen between other Onchocerca spp. The results of the current and earlier phylogenetic analyses indicate that canine Onchocerca sp. separated from other Onchocerca spp. early in the evolution. Based on the similar clinical pictures, the identical morphology of nematodes and the sequence analyses of COI and ND5 genes of the worms and 16S rRNA gene of their wolbachiae, the Onchocerca worms isolated from European dogs appear to belong to the same species. The results support the earlier biological and morphological arguments that a distinct species, most likely O. lupi originally described from the subconjunctival tissues of a Caucasian wolf is responsible for canine ocular onchocercosis in Europe.

Computer modeling of binding of diverse weak toxins to nicotinic acetylcholine receptors

Weak toxins are the “three-fingered” snake venoms toxins grouped together by having an additional disulfide in the N-terminal loop I. In general, weak toxins have low toxicity, and biological targets have been identified for some of them only, recently by detecting the effects on the nicotinic acetylcholine receptors (nAChR). Here the methods of docking and molecular dynamics simulations are used for comparative modeling of the complexes between four weak toxins of known spatial structure (WTX, candoxin, bucandin, γ-bungarotoxin) and nAChRs. WTX and candoxin are those toxins whose blocking of the neuronal α7- and muscle-type nAChR has been earlier shown in binding assays and electrophysiological experiments, while for the other two toxins no such activity has been reported. Only candoxin and WTX are found here to give stable solutions for the toxin-nAChR complexes. These toxins appear to approach the binding site similarly to short α-neurotoxins, but their final position resembles that of α-cobratoxin, a long α-neurotoxin, in the complex with the acetylcholine-binding protein. The final spatial structures of candoxin and WTX complexes with the α7 neuronal or muscle-type nAChR are very similar and do not provide immediate answer why candoxin has a much higher affinity than WTX, but both of them share a virtually irreversible mode of binding to one or both these nAChR subtypes. Possible explanation comes from docking and MD simulations which predict fast kinetics of candoxin association with nAChR, no gross changes in the toxin conformation (with smaller toxin flexibility on α7 nAChR), while slow WTX binding to nAChR is associated with slow irreversible rearrangement both of the tip of the toxin loop II and of the binding pocket residues locking finally the toxin molecule. Computer modeling showed that the additional disulfide in the loop I is not directly involved in receptor binding of WTX and candoxin, but it stabilizes the structure of loop I which plays an important role in toxin delivery to the binding site. In summary, computer modeling visualized possible modes of binding for those weak toxins which interact with the nAChR, provided no solutions for those weak toxins whose targets are not the nAChRs, and demonstrated that the additional disulfide in loop I cannot be a sound criteria for joining all weak toxins into one group; the conclusion about the diversity of weak toxins made from computer modeling is in accord with the earlier phylogenetic analysis.

PHYLOGENETIC ANALYSES OF THE BRYOPSIDALES (ULVOPHYCEAE, CHLOROPHYTA) BASED ON RUBISCO LARGE SUBUNIT GENE SEQUENCES1

Current taxonomy of the Bryopsidales recognizes eight families; most of which are further categorized into two suborders, the Bryopsidineae and Halimedineae. This concept was supported by early molecular phylogenetic analyses based on rRNA sequence data, but subsequent cladistic analyses of morphological characters inferred monophyly in only the Halimedineae. These conflicting results prompted the current analysis of 32 taxa from this diverse group of green algae based on plastid‐encoded RUBISCO large subunit (rbcL) gene sequences. Results of these analyses suggested that the Halimedineae and Bryopsidineae are distinct monophyletic lineages. The families Bryopsidaceae, Caulerpaceae, Codiaceae, Derbesiaceae, and Halimediaceae were inferred as monophyletic, however the Udoteaceae was inferred as non‐monophyletic. The phylogenetic position of two taxa with uncertain subordinal affinity, Dichotomosiphon tuberosus Lawson and Pseudocodium floridanum Dawes & Mathieson, were also inferred. Pseudocodium was consistently placed within the halimedinean clade suggesting its inclusion into this suborder, however familial affinity was not resolved. D. tuberosus was the inferred sister taxon of the Halimedineae based on analyses of rbcL sequence data and thus a possible member of this suborder.

Phylogeny and taxonomy of the North American clade of the Ceratocystis fimbriata complex

Ceratocystis fimbriata is a widely distributed, plant pathogenic fungus that causes wilts and cankers on many woody hosts. Earlier phylogenetic analyses of DNA sequences revealed three geographic clades within the C. fimbriata complex that are centered respectively in North America, Latin America and Asia. This study looked for cryptic species within the North American clade. The internal transcribed spacer regions (ITS) of the rDNA were sequenced, and phylogenetic analysis indicated that most isolates from the North American clade group into four host-associated lineages, referred to as the aspen, hickory, oak and cherry lineages, which were isolated primarily from wounds or diseased trees of Populus, Carya, Quercus and Prunus, respectively. A single isolate collected from P. serotina in Wisconsin had a unique ITS sequence. Allozyme electromorphs also were highly polymorphic within the North American clade, and the inferred phylogenies from these data were congruent with the ITS-rDNA analyses. In pairing experiments isolates from the aspen, hickory, oak and cherry lineages were interfertile only with other isolates from their respective lineages. Inoculation experiments with isolates of the four host-associated groupings showed strong host specialization by isolates from the aspen and hickory lineages on Populus tremuloides and Carya illinoensis, respectively, but isolates from the oak and cherry lineages did not consistently reveal host specialization. Morphological features distinguish isolates in the North American clade from those of the Latin American clade (including C. fimbriata sensu stricto). Based on the phylogenetic evidence, interfertility, host specialization and morphology, the oak and cherry lineages are recognized as the earlier described C. variospora, the poplar lineage as C. populicola sp. nov., and the hickory lineage as C. caryae sp. nov. A new species associated with the bark beetle Scolytus quadrispinosus on Carya is closely related to C. caryae and is described as C. smalleyi.

Nuclear receptors are markers of animal genome evolution.

Nuclear hormone receptors form one evolutionary related super-family of proteins, which mediate the interaction between hormones (or other ligands) and gene expression in animals. Early phylogenetic analyses showed two main periods of gene duplication which gave rise to present-day diversity in most animals: one at the origin of the family, and another specifically in vertebrates. Moreover this second period is composed itself by, probably, two rounds of duplication, as proposed by Susumu Ohno at the origin of vertebrates. There are indeed often two, three or four vertebrate orthologs of each invertebrate nuclear receptor, in accordance with this theory. The complete genome of Drosophila melanogaster contains 21 nuclear receptors, compared to 49 in the human genome. In addition, many nuclear receptors have more paralogs in the zebrafish than in mammals, and a genome duplication has been proposed at the origin of ray-finned fishes. Nuclear receptors are a very good model to investigate the dating and functional role of these duplications, since they are dispersed in the genome, allow robust phylogenetic reconstruction, and are functionnaly well characterized, with different adaptations for different paralogs. We illustrate this with examples from differents nuclear receptors and different groups of species.

Organic-walled microfossils of possible dinoflagellate affinity from the Lower Permian of Sonora (northwest Mexico)

Shallow-water carbonates from the Lower Permian of Sonora, northwest Mexico, have yielded small organic-walled microfossils that show several features characteristic of dinoflagellates. The oldest unequivocal dinoflagellate fossils, however, presently known come from the Middle Triassic. Earlier reports of microfossils with possible dinoflagellate affinity from the Paleozoic and Neoproterozoic, together with dinoflagellate-specific biomarkers found in Early Cambrian rocks and molecular phylogenetic analyses, suggest the presence of an intermediate stage of evolution, or protodinoflagellate group in pre-Mesozoic times.

A new phylogeny and phylogenetic classification for the Canthyloscelidae (Diptera: Psychodomorpha)

A new phylogeny and phylogenetic classification for the Canthyloscelidae (Diptera: Psychodomorpha) is presented. A phylogenetic analysis of the Scatopsoidea is performed. A sister-group relationship between the Canthyloscelidae and Scatopsidae is accepted and the monophyly of the Canthyloscelidae is corroborated, including the genera Exiliscelis, Synneuron, Hyperoscelis, and Canthyloscelis. An earlier phylogenetic analysis of the group is considered, in which Synneuron was accepted as the sister-group of the Scatopsidae and Exiliscelis was considered the sister-group of Synneuron + Scatopsidae. Some apomorphic similarities between the larvae of all genera of Canthyloscelidae, especially the reduction of the head capsule, are considered true synapomorphies. Exiliscelis is considered the sister-group of the rest of the family and is placed in a new subfamily, Exiliscelinae. In the Canthyloscelinae, Synneuron is the sister-group of Hyperoscelis + Canthyloscelis. A phylogenetic classification of the group is proposed. Prohyperoscelis rohdendorfi Kovalev, 1985, from the Middle Jurassic in Russia, is accepted as the sister-group of Canthyloscelis.

Differential regulation of six novel MYB-domain genes defines two distinct expression patterns in allotetraploid cotton (Gossypium hirsutum L.).

A PCR-based strategy was employed to identify myb-related genes potentially involved in the differentiation and development of cotton seed trichomes. cDNA clones representing six newly identified cotton myb-domain genes (GhMYB) of the R2R3-MYB family were characterized in the allotetraploid species Gossypium hirsutum L. (2n = 4x = 52; AADD). Several interesting motifs and domains in the transregulatory region (TRR) were identified as potential candidates for modulating GhMYB activity. One such structural feature is a basic 40-amino acid stretch (TRR1) located immediately downstream of the DNA-binding domain (DBD) in five of the GhMYBs. Furthermore, the conserved motif GIDxxH identified in a subset of plant MYBs is also present in the same position in the TRR1 domains of GhMYB1 and GhMYB6, exactly 12 amino acid residues downstream of the last tryptophan in the R3 repeat of the DBD. At least two of the GhMYBs (GhMYB4 and GhMYB5) contain unidentified ORFS in the 5' leader sequence (5'-uORFs) that may serve to regulate the synthesis of these particular GhMYB proteins at the translational level. Multiple alignment of DBD sequences indicated that GhMYBs show structural similarity to plant R2R3-MYB factors implicated in phenylpropanoid biosynthesis. GhMYB5 is the most distantly related cotton R2R3-MYB and is found in an isolated cluster that includes the drought-inducible AtMYB2. Sequence comparisons of DBD and TRR domains from GhMYBs, MIXTA (AmMYBMx) and G11 (AtMYBG11) did not reveal any striking similarity beyond conserved motifs. However, based on earlier phylogenetic analysis, GhMYB2, GhMYB3, and GHMYB4 are members of a cluster that contains GLABROUS1, while GhMYB1 and GhMYB6 belong to a closely related cluster. Semi-quantitative RT-PCR analysis revealed two discrete patterns of GhMYB gene expression. Type I cotton MYB (GhMYB-1, -2, and -3) transcripts were found in all tissue-types examined and were relatively more abundant than those derived from type II GhMYB genes (GhMYB-4, -5, and -6), which showed distinct, tissue-specific expression patterns. The developmental regulation of GhMYBs is consistent with a role for these DNA-binding factors in the differentiation and expansion of cotton seed trichomes.

Phylogeny and Historical Biogeography of Steamer-Ducks (Anatidae: Tachyeres)

-An earlier phylogenetic analysis of morphological characters (Livezey, 1986a) indicates that Tachyeres is a member of a specialized clade of Southern Hemisphere shelducks (Tadorninae). Within Tachyeres, the three flightless species appear to be monophyletic, with the two Atlantic species-T. leucocephalus and T. brachypterus-being closest relatives. This phylogenetic hypothesis mirrors the pattern of morphometric similarities among the four species. Speciation in the genus is explainable by the isolation caused by two major glaciations in southern South America and related fluctuations in sea level, and intervening dispersals. The biogeographic model is compared to a morphometric assessment of populations of T. patachonicus and electrophoretic analyses of the four species of Tachyeres. [Anatidae; flightlessness; glaciation; historical biogeography; Patagonia; phylogenetics; Pleistocene; South America; steamer-ducks; Tachyeres.J 'Ihe importance of knowledge of phylogenetic relationships is appreciated widely, not only for the construction of natural classifications of organisms (Cracraft, 1974; Farris, 1976; Wiley, 1981), but also as a basis for an understanding of historical constraints on morphology (Alberch, 1981; Lauder, 1981, 1982; Felsenstein, 1985) and biogeography (Wiley, 1981). Historical constraints are especially important in closely related species-groups in which some members share a strong, derived morphological trend (Grehan and Ainsworth, 1985). Four species of steamer-duck are recognized (Humphrey and Thompson, 1981): (1) flying steamer-duck (Tachyeres patachonicus) of freshwater and marine habitats throughout southern Argentina, Chile, and the Falkland Islands; (2) Magellanic flightless steamer-duck (T. pteneres) of coastal habitats of southern Chile and Tierra del Fuego; (3) white-headed flightless steamer-duck (T. leucocephalus) of coastal Chubut, Argentina; and (4) Falkland flightless steamer-duck (T. brachypterus) of the marine shores of the Falkland Islands. I review previous evaluations of the relationships of Tachyeres to other waterfowl and present a morphologically based phylogenetic analysis of the four species of steamer-ducks. The resultant phylogenetic hypothesis is related to the current knowledge of the geological history of the region, especially the role of glaciations as vicariance events in the marine littoral of southernmost South America. A speciation model then is compared to morphometric analyses and electrophoretic studies of the genus. OPINIONS REGARDING RELATIONSHIPS