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PubMed2000

Osteogenic imprinting upstream of marrow stromal cell differentiation.

Five spontaneously transformed cell lines were established from a population of murine bone marrow stromal cells (BMSCs) and the expression profiles of phenotype-characteristic genes, patterns of in vitro differentiation, and osteogenic capacity after in vivo transplantation were determined for each. All the clones expressed stable levels of cbfa1, the osteogenic "master" gene, whereas the levels of individual phenotypic mRNAs were variable within each, suggestive of both maturational and phenotypic plasticity in vitro. Varying levels of collagen type I and alkaline phosphatase (AP) were expressed in all the clonal lines. The clonal lines with proven in vivo osteogenic potential (3 out of 5) had a high proliferation rate and expressed bone sialoprotein (BSP), whereas the two nonosteogenic clones proliferated more slowly and never expressed BSP. Bone nodules were only observed in 2 out of 3 of the osteogenic lines, and only 1 out of three formed cartilage-like matrix in vitro. There was no evidence of chondrogenesis in the nonosteogenic lines. By contrast, LPL was expressed in two osteogenic and in two nonosteogenic lines. These results demonstrate the presence of multipotential and restricted progenitors in the murine stromal system. cbfa1, collagen type I, and AP expression were common to all, and therefore presumably early, basic traits of stromal cell lines that otherwise significantly differ with respect to growth and differentiation potential. This finding suggests that an osteogenic imprinting lies upstream of diversification, modulation, and restriction of stromal cell differentiation potential.

Alkaline Phosphatase↗
PubMed2006

Phylogenetic relationships and historical biogeography of neotropical parrots (Psittaciformes: Psittacidae: Arini) inferred from mitochondrial and nuclear DNA sequences.

Previous hypotheses of phylogenetic relationships among Neotropical parrots were based on limited taxon sampling and lacked support for most internal nodes. In this study we increased the number of taxa (29 species belonging to 25 of the 30 genera) and gene sequences (6388 base pairs of RAG-1, cyt b, NADH2, ATPase 6, ATPase 8, COIII, 12S rDNA, and 16S rDNA) to obtain a stronger molecular phylogenetic hypothesis for this group of birds. Analyses of the combined gene sequences using maximum likelihood and Bayesian methods resulted in a well-supported phylogeny and indicated that amazons and allies are a sister clade to macaws, conures, and relatives, and these two clades are in turn a sister group to parrotlets. Key morphological and behavioral characters used in previous classifications were mapped on the molecular tree and were phylogenetically uninformative. We estimated divergence times of taxa using the molecular tree and Bayesian and penalized likelihood methods that allow for rate variation in DNA substitutions among sites and taxa. Our estimates suggest that the Neotropical parrots shared a common ancestor with Australian parrots 59 Mya (million of years ago; 95% credibility interval (CrI) 66, 51 Mya), well before Australia separated from Antarctica and South America, implying that ancestral parrots were widespread in Gondwanaland. Thus, the divergence of Australian and Neotropical parrots could be attributed to vicariance. The three major clades of Neotropical parrots originated about 50 Mya (95% CrI 57, 41 Mya), coinciding with periods of higher sea level when both Antarctica and South America were fragmented with transcontinental seaways, and likely isolated the ancestors of modern Neotropical parrots in different regions in these continents. The correspondence between major paleoenvironmental changes in South America and the diversification of genera in the clade of amazons and allies between 46 and 16 Mya suggests they diversified exclusively in South America. Conversely, ancestors of parrotlets and of macaws, conures, and allies may have been isolated in Antarctica and/or the southern cone of South America, and only dispersed out of these southern regions when climate cooled and Antarctica became ice-encrusted about 35 Mya. The subsequent radiation of macaws and their allies in South America beginning about 28 Mya (95% CrI 22, 35 Mya) coincides with the uplift of the Andes and the subsequent formation of dry, open grassland habitats that would have facilitated ecological speciation via niche expansion from forested habitats.

Animals↗
PubMed1999

The Ewing family of tumors and the search for the Achilles' heel.

The ideal cancer therapy would accomodate the specific biology of a tumor and be based upon understanding the mechanisms of malignancy. This vision has been the driving force in cancer research. However, the story of success in clinical cancer management is a story of empirie largely independent from progress in basic research. For the Ewing family of tumors (EFT) comprising Ewing's sarcoma and peripheral primitive neuroectodermal tumor, significant insights into the molecular basis have appeared recently. Some of last year's discoveries may have taken us closer to the identification of the Achilles' heel in this disease. The first clue has been obtained to the mechanism of chromosomal translocation, which constitutes a rate-limiting step in EFT pathogenesis. Also, researchers have progressed in understanding the control of EFT cell proliferation, differentiation, and death. A major role in these processes has been attributed to the EWS-ets gene rearrangement. Specific growth factor circuits appear to be involved in deregulated tumor cell growth. By analogy to heterologous cellular systems, it is possible to postulate an important functional role for CD99(MIC2) as it contributes to the malignant phenotype of EFT. In vitro, as well as the first in vivo, experimental evidence suggests that tumor cell expansion and spread can be counteracted by breaking these physiological pathways. Still, we are far from a tailored biological therapy of EFT. Before this goal may be achieved, we must seek further improvements and diversification of today's standard and intensified treatment regimens.

Animals↗
PubMed2005

Genetic variance and covariance for physiological traits in Lobelia: are there constraints on adaptive evolution?

Physiological traits that control the uptake of carbon dioxide and loss of water are key determinants of plant growth and reproduction. Variation in these traits is often correlated with environmental gradients of water, light, and nutrients, suggesting that natural selection is the primary evolutionary mechanism responsible for physiological diversification. Responses to selection, however, can be constrained by the amount of standing genetic variation for physiological traits and genetic correlations between these traits. To examine the potential for constraint on adaptive evolution, we estimated the quantitative genetic basis of physiological trait variation in one population of each of two closely related species (Lobelia siphilitica and L. cardinalis). Restricted maximum likelihood analyses of greenhouse-grown half-sib families were used to estimate genetic variances and covariances for seven traits associated with carbon and water relations. We detected significant genetic variation for all traits in L. siphilitica, suggesting that carbon-gain and water-use traits could evolve in response to natural selection in this population. In particular, narrow-sense heritabilities for photosynthetic rate (A), stomatal conductance (gs), and water-use efficiency (WUE) in our L. siphilitica population were high relative to previous studies in other species. Although there was significant narrow-sense heritability for A in L. cardinalis, we detected little genetic variation for traits associated with water use (gs and WUE), suggesting that our population of this species may be unable to adapt to drier environments. Despite being tightly linked functionally, the genetic correlation between A and gs was not strong and significant in either population. Therefore, our L. siphilitica population would not be genetically constrained from evolving high A (and thus fixing more carbon for growth and reproduction) while also decreasing gs to limit water loss. However, a significant negative genetic correlation existed between WUE and plant size in L. siphilitica, suggesting that high WUE may be negatively associated with high fecundity. In contrast, our results suggest that any constraints on the evolution of photosynthetic and stomatal traits of L. cardinalis are caused primarily by a lack of genetic variation, rather than by genetic correlations between these functionally related traits.

Adaptation, Physiological↗
PubMed2005

Rapid recent radiation of S-RNase lineages in Witheringia solanacea (Solanaceae).

Strong frequency-dependent selection as found in the self-incompatibility loci of flowering plants maintains allelic lineages for extremely long time scales, such that allelic genealogies can shed insight into long-term demographic patterns of species. Effective mutation rate, as well as demographic change such as population bottlenecks, can influence genealogical structure. In addition, loss of functionality at the self-incompatibility locus is likely to affect radiation rates. Partial sequences for 21 S-RNase alleles of the mid-elevation tropical species Witheringia solanacea were obtained in order to compare their substitution rates and genealogy with those of Witheringia maculata and two species in the closely related genus Physalis. Sequences for W. solanacea fell into the three clades within the Solanaceae already identified for the genus. Terminal branch lengths for W. solanacea, scaled to the total depth of its phylogeny, were intermediate between the unusually short terminal branches of W. maculata and those of the two Physalis species. In contrast to the Physalis species, where interspecific dN/dS for closely related alleles exceeded 1.0 to the same degree as did intraspecific dN/dS, in Witheringia only intraspecific comparisons showed an excess of nonsynonymous substitutions, suggesting postspeciation radiation of alleles. Alleles associated with lowered S-RNase production and self-compatibility showed extremely short terminal branches. In summary, it appears that rapid recent diversification of alleles characterizes the Witheringia lineages. In some cases, this rapid diversification can be attributed to relaxed constraints due to breakdown of self-incompatibility.

Alleles↗
PubMed1998

Genetic evolution of hepatitis G virus in chronically infected individual patients.

Comparative sequence analysis of different isolates of hepatitis G virus (HGV) has demonstrated significant intersubject genetic heterogeneity, but few data on intrasubject genetic evolution have been reported. To further investigate the genetic diversification of the HGV genome, 36 plasma samples from eleven patients chronically infected with HGV serially obtained 2-4 years apart were analysed. We determined the viral nucleotide sequence of the 5' non-coding (NC) and the NS3 regions by directly sequencing the RT-PCR amplified products obtained from the viral RNAs. Intrasubject sequence variation was found to be 1.3-2.4 x 10(-3) base substitutions per genome site per year within the 5' NC region and 1.3-9.4 x 10(-3) base substitutions per genome site per year within the NS3 region. Depending on the genomic region analysed (i.e. 5' NC or NS3 region), pairwise comparisons and phylogenetic reconstructions showed that intersubject genetic distances were 17.5- to 20.8-fold greater than intrasubject ones. Overall, the evolution rate of HGV in the regions analysed is not significantly different from that found in hepatitis C virus.

Chronic Disease↗
PubMed2005

Conserved ontogeny and allometric scaling of resource acquisition and allocation in the Daphniidae.

Life histories vary widely among taxa, but within phylogenetic groups there may be a fundamental framework around which trait variation is organized, perhaps as a consequence of lineage-specific developmental constraints. In organisms with indeterminate growth, there is an ongoing problem of optimally allocating resources between growth and reproduction, and that allocation decision may manifest itself through allometric scaling. Previous work on freshwater zooplankton has shown that the ontogenetic pattern of resource allocation can be described by simple mathematical functions. An important component of understanding how such functions can explain life-history variation is to discover which parameters in these functions are robust, with respect to both resource availability and evolutionary diversification, and which parameters exhibit interspecific allometry. To shed light on these issues, detailed life table experiments were conducted on eight species in the family Daphniidae (Crustacea) at high and low levels of resources. Using data on growth, reproduction, and instar duration, the ontogeny of resource allocation to growth and reproduction could be described as functions that plateau at or shortly after the onset of maturity. To be sure that the results were not an artifact of phylogenetic structure, the parameters were tested in a phylogenetically controlled fashion. The results suggest a simple set of resource allocation rules for daphniids, whereby all species exhibit a similar form of ontogenetic change in allocation, and reach a plateau where approximately 94% of available resources are allocated to reproduction. The asymptotically maximal rate of net resources incorporated in growth and reproduction was positively related to size at maturity, whereas the rates of approach to plateaus (for both net resource assimilation and proportional allocation to reproduction) were negatively related to body size. Per-offspring investment was positively related to the square root of size at maturity. Using this approach, a wide range of interspecific variation in life-history features can be related to a single underlying trait, the size at first reproductive investment.

Adaptation, Physiological↗
PubMed2006

Phenotypic diversification and adaptation of Serratia marcescens MG1 biofilm-derived morphotypes.

We report here the characterization of dispersal variants from microcolony-type biofilms of Serratia marcescens MG1. Biofilm formation proceeds through a reproducible process of attachment, aggregation, microcolony development, hollow colony formation, and dispersal. From the time when hollow colonies were observed in flow cell biofilms after 3 to 4 days, at least six different morphological colony variants were consistently isolated from the biofilm effluent. The timing and pattern of variant formation were found to follow a predictable sequence, where some variants, such as a smooth variant with a sticky colony texture (SSV), could be consistently isolated at the time when mature hollow colonies were observed, whereas a variant that produced copious amounts of capsular polysaccharide (SUMV) was always isolated at late stages of biofilm development and coincided with cell death and biofilm dispersal or sloughing. The morphological variants differed extensively from the wild type in attachment, biofilm formation, and cell ultrastructure properties. For example, SSV formed two- to threefold more biofilm biomass than the wild type in batch biofilm assays, despite having a similar growth rate and attachment capacity. Interestingly, the SUMV, and no other variants, was readily isolated from an established SSV biofilm, indicating that the SUMV is a second-generation genetic variant derived from SSV. Planktonic cultures showed significantly lower frequencies of variant formation than the biofilms (5.05 x 10(-8) versus 4.83 x 10(-6), respectively), suggesting that there is strong, diversifying selection occurring within biofilms and that biofilm dispersal involves phenotypic radiation with divergent phenotypes.

Adaptation, Physiological↗
PubMed2026

Revisiting the genome assembly of Lupinus species reveals differential diploidization after a shared whole-genome duplication.

Accurate genome assemblies are essential for comparative genomics, yet Hi-C-guided scaffolding can introduce structural errors that misrepresent chromosome architecture and bias evolutionary inferences. Here, we identified pervasive scaffolding errors-including artificial fusions, internal inversions, and incomplete contig mounting-in 2 previously published Lupinus genomes (L. cosentinii and L. digitatus) using a segmentation method based on long terminal repeat (LTR) retrotransposon density. We reassembled both genomes, producing chromosome-level references of 472.7 Mb (16 chromosomes) and 427.2 Mb (21 chromosomes), with BUSCO completeness >98.5%. Synteny validation and reapplication of LTR profiling confirmed that all prior errors were resolved. Using these corrected genomes together with 4 additional Lupinus species and 2 outgroup legumes, we investigated postpolyploid evolution. Synonymous substitution rate (Ks) analysis revealed a genus-specific whole-genome duplication (WGD) event (Ks = 0.17) shared by all 6 Lupinus species. The proportion of WGD-derived genes varied markedly, from 60% in L. digitatus to only 36% in L. mutabilis, indicating differential diploidization. While all species retained a core set of WGD duplicates enriched in cytoskeleton organization, ion transport, and defense responses, each exhibited lineage-specific functional trajectories: cell wall modification in L. cosentinii and L. digitatus, nitrogen metabolism in L. albus and L. angustifolius, flower development in L. luteus, and stress/lipid metabolism in L. mutabilis. Our corrected assemblies provide optimal references for Lupinus comparative genomics, and our findings demonstrate that a shared WGD event can lead to both conserved and highly divergent postpolyploid fates, likely underpinning adaptive diversification within the genus.

Lupinus↗
PubMed1996

Diversification of Neu differentiation factor and epidermal growth factor signaling by combinatorial receptor interactions.

The ErbB family includes two receptors, ErbB-1 and ErbB-3, that respectively bind to epidermal growth factor and Neu differentiation factor, and an orphan receptor, ErbB-2. Unlike ErbB-1 and ErbB-2, the intrinsic tyrosine kinase of ErbB-3 is catalytically impaired. By using interleukin-3-dependent cells that ectopically express the three ErbB proteins or their combinations, we found that ErbB-3 is devoid of any biological activity but both ErbB-1 and ErbB-2 can reconstitute its extremely potent mitogenic activity. Transactivation of ErbB-3 correlates with heterodimer formation and is reflected in receptor phosphorylation and the transregulation of ligand affinity. Inter-receptor interactions enable graded proliferative and survival signals: heterodimers are more potent than homodimers, and ErbB-3-containing complexes, especially the ErbB-2/ErbB-3 heterodimer, are more active than ErbB-1 complexes. Nevertheless, ErbB-1 signaling displays dominance over ErbB-3 when the two receptors are coexpressed. Although all receptor combinations activate the mitogen-activated protein kinases ERK and c-Jun kinase, they differ in their rate of endocytosis and in coupling to intervening signaling proteins. It is conceivable that combinatorial receptor interactions diversify signal transduction and confer double regulation, in cis and in trans, of the superior mitogenic activity of the kinase-defective ErbB-3.

Animals↗
PubMedDate not supplied

PENN PASS: a program for graduates of foreign dental schools.

An increasing number of graduates of foreign dental schools who enroll in advanced standing programs to qualify for licensure calls for dental schools to be prepared to handle not only the curricular demands but also the growing cultural diversity among its student population. The "reeducation" of this student group not only meets the need of foreign dentists for an American degree but may also provide health professionals to service various ethnic populations whose language and culture they are able to understand and identify with. A survey of students and graduates of a two-year Program for Advanced Standing Students (PASS) for graduates of foreign dental schools representing 34 countries aimed to arrive at an understanding of this student group through characterization of the foreign dentists and identification of their attitudes and feelings toward various aspects of the program, the school and faculty and their experience of stress. This report includes description of the distinctive features of the program which cater to specific needs and concerns of this non-traditional group of dental students. PASS students are accepted on the basis of their grades in dental school in home country, scores in the National Dental Board Examination Part I, Test of English as Foreign Language (TOEFL), and ratings in personal interviews. They complete an intensive summer program consisting of didactic and laboratory courses which prepares them for integration with four-year students for the last two years of didactic and clinical curriculum. Cultural diversity seminars, a special English class, PASS class meetings and seminars are unique additions to their program and aim to assist them adjust to the educational, social and cultural systems in an American school. Results of the survey show a majority of the PASS students feel that they are part of the school and that there is someone in the school whom they can approach for problems. An understanding of their ethnic and educational background is seen as a significant factor in their second basic dental education. Implications for education of foreign dental graduates amidst increasing diversification of the student body are discussed.

Credentialing↗
PubMed1997

Evolutionary mechanisms and population dynamics of the third variable envelope region of HIV within single hosts.

Clonal diversifications of HIV virus were monitored by periodic samplings on each of the six patients with regard to 183- to 335-bp segments of the env gene, which invariably included the functionally critical V3 region. Subsequently, six individual phylogenetic trees of viral variants were constructed. It was found that at one time or another during the course of disease progression, viral variants were inexplicably released from a strong negative selection against nonsynonymous base substitutions, possibly indicating positive selection. This resulted in concentrated amino acid substitutions at five specific sites within the V3 region. It was noted that these sites were often involved as antigenic determinants that provoked the host immune response and that these sites were also involved in the determination of viral phenotypes as to their cell tropism, syncytium formation capability, and replication rates.

Amino Acid Sequence↗
PubMed2006

Longevity and ageing: appraising the evolutionary consequences of growing old.

Senescence or ageing is an increase in mortality and/or decline in fertility with increasing age. Evolutionary theories predict that ageing or longevity evolves in response to patterns of extrinsic mortality or intrinsic damage. If ageing is viewed as the outcome of the processes of behaviour, growth and reproduction then it should be possible to predict mortality rate. Recent developments have shown that it is now possible to integrate these ecological and physiological processes and predict the shape of mortality trajectories. By drawing on the key exciting developments in the cellular, physiological and ecological process of longevity the evolutionary consequences of ageing are reviewed. In presenting these ideas an evolutionary demographic framework is used to argue how trade-offs in life-history strategies are important in the maintenance of variation in longevity within and between species. Evolutionary processes associated with longevity have an important role in explaining levels of biological diversity and speciation. In particular, the effects of life-history trait trade-offs in maintaining and promoting species diversity are explored. Such trade-offs can alleviate the effects of intense competition between species and promote species coexistence and diversification. These results have important implications for understanding a number of core ecological processes such as how species are divided among niches, how closely related species co-occur and the rules by which species assemble into food-webs. Theoretical work reveals that the proximate physiological processes are as important as the ecological factors in explaining the variation in the evolution of longevity. Possible future research challenges integrating work on the evolution and mechanisms of growing old are briefly discussed.

Aging↗
PubMed2006

Evolutionary history of HIV-1 subtype B and F infections in Brazil.

OBJECTIVE: To reconstruct the onset date of the HIV-1 B and F epidemics in Brazil based on virus diversification over time. DESIGN: We studied HIV-1 env V3 sequences (210 nt) with a known sampling year isolated from HIV-1 positive patients from Brazil between 1989 and 1997: 101 subtype B sequences and 41 subtype F sequences. METHODS: HIV-1 V3 env sequences were grouped by year of collection and the relationship between the sampling years of HIV-1 sequences and their genetic distance to the reconstructed common ancestor (intra-population divergence) or to other sequences from the same year (intra-population diversity) was examined by using linear regression analysis. RESULTS: Regression analysis of nucleotide distances, revealed a highly significant positive correlation between sampling years of subtype B and F V3 sequences and their intra-population divergence (P < 0.001) or diversity (P < 0.0001). In both subtype populations, the divergence and diversity increased at a rate of 0.5 and 0.9% per year, respectively. Considering these evolutionary rates, we estimate the onset of the subtype B and F HIV-1 epidemics in Brazil during early 1970s and early 1980s, respectively. CONCLUSIONS: The consistent correlation between divergence and diversity of the V3 sequences with their sampling years indicates that the molecular clock is operational in the evolution of the HIV-1 in Brazil's epidemic, and show that subtypes B and F are evolving at a similar rate over time. The dating results suggest a discontinuous introduction of these subtypes in the Brazilian population.

Brazil↗
PubMed1998

A stochastic model for the rapid emergence of specific vertebrate immunity incorporating horizontal transfer of systems enabling duplication and combinational diversification.

Recent molecular data indicate that the antigen-specific combinatorial immune response is restricted to jawed vertebrates where it is found in representatives of all class from cartilagenous fishes to mammals. Here, we analyse the relatively rapid emergence of the combinatorial system terms of three stochastic process, with the system reaching essentially full capacity in immunoglobulin recognition elements and diversification and recombination of gene segments in an evolutionary span of time of less than 20 million years. The mechanisms for inducibility were coopted from ancient and widely spread processes in phylogeny for regulation of cell division. The proposed process of formation entailed the evolution of unknown ancestral genes into those specifying bona fide immunoglobulin domains, and the generation of multiple copies of these via a series of events facilitated by horizontal transfer of site-specific recombinases and recombination signal sequences most probably from microbial and fungal sources. The second process is one of rapid "decay" (evolution) which occurred in about 10 million year under stringent selective conditions to generate proper conserved canonical sequences. The third process is that of the long term evolution of these characteristic immunoglobulin domains over the 450 million years since their emergence. As a first approximation the rates of these three processes were computed using first order differential equations. The rate of formation has a magnitude of 10-7 substitutions per site per year, and that of rapid modifications is 10-8 substitutions per site per year. The long term rate of immunoglobulin evolution is comparable to that of other moderately conserved proteins, (1-3) x 10-9 substitutions per site per year). This model is testable by searching for "footprints" of microbial and fungal DNA processing enzymes and recombination mechanisms. The hypothesis raises the general concept that horizontal transfer of genes facilitating rearrangement and duplication can catalyse major steps of macroevolution.

Animals↗
PubMed1999

The diversification of plant cytosolic small heat shock proteins preceded the divergence of mosses.

A cDNA library was constructed with mRNA isolated from heat-stressed cell cultures of Funaria hygrometrica (Bryophyta, Musci, Funariaceae). cDNA clones encoding six cytosolic small heat shock proteins (sHSPs) were identified using differential screening. Phylogenetic analysis of these sHSP sequences with other known sHSPs identified them as members of the previously described higher plant cytosolic class I and II families. Four of the F. hygrometrica sHSPs are members of the cytosolic class I family, and the other two are members of the cytosolic class II family. The presence of members of the cytosolic I and II sHSP families in a bryophyte indicates that these gene families are ancient, and evolved at least 450 MYA. This result also indicates that the plant sHSP gene families duplicated much earlier than did the well-studied phytochrome gene family. Members of the cytosolic I and II sHSP families are developmentally regulated in seeds and flowers in higher plants. Our findings show that the two cytosolic sHSP families evolved before the appearance of these specialized structures. Previous analysis of angiosperm sHSPs had identified class- or family-specific amino acid consensus regions and determined that rate heterogeneity exists among the different sHSP families. The analysis of the F. hygrometrica sHSP sequences reveals patterns and rates of evolution distinct from those seen among angiosperm sHSPs. Some, but not all, of the amino acid consensus regions identified in seed plants are conserved in the F. hygrometrica sHSPs. Taken together, the results of this study illuminate the evolution of the sHSP gene families and illustrate the importance of including representatives of basal land plant lineages in plant molecular evolutionary studies.

Amino Acid Sequence↗
PubMed2001

Molecular insights into the evolution of the family Bovidae: a nuclear DNA perspective.

The evolutionary history of the family Bovidae remains controversial despite past comprehensive morphological and genetic investigations. In an effort to resolve some of the systematic uncertainties within the group, a combined molecular phylogeny was constructed based on four independent nuclear DNA markers (2,573 characters) and three mitochondrial DNA genes (1,690 characters) for 34 bovid taxa representing all seven of the currently recognized bovid subfamilies. The nuclear DNA fragments were analyzed separately and in combination after partition homogeneity tests were performed. There was no significant rate heterogeneity among lineages, and retention index values indicated the general absence of homoplasy in the nuclear DNA data. The conservative nuclear DNA data were remarkably effective in resolving associations among bovid subfamilies, which had a rapid radiation dating back to approximately 23 MYA. All analyses supported the monophyly of the Bovinae (cow, nilgai, and kudu clade) as a sister lineage to the remaining bovid subfamilies, and the data convincingly suggest that the subfamilies Alcelaphinae (hartebeest, tsessebe, and wildebeest group) and Hippotraginae (roan, sable, and gemsbok clade) share a close evolutionary relationship and together form a sister clade to the more primitive Caprinae (represented by sheep, goat, and muskox). The problematic Reduncinae (waterbuck, reedbuck) seem to be the earliest-diverging group of the Caprinae/Alcelaphinae/Hippotraginae clade, whereas the Antilopinae (gazelle and dwarf antelope clade) were always polyphyletic. The sequence data suggest that the initial diversification of the Bovidae took place in Eurasia and that lineages such as the Cephalophinae and other enigmatic taxa (impala, suni, and klipspringer) most likely originated, more or less contemporaneously, in Africa.

Animals↗
PubMed1998

Large-subunit ribosomal RNA systematics of symbiotic dinoflagellates: morphology does not recapitulate phylogeny.

Biochemical, histological, physiological, and genetic evidence indicates that dinoflagellates symbiotic with marine invertebrates are a heterogeneous complex of taxa, representing at least five genera in three orders. Despite a wealth of data regarding morphological, biochemical, and behavioral differences among symbiotic dinoflagellates, knowledge concerning patterns of diversification is limited. I analyzed approximately 900 bp of the 5' end of the large-subunit ribosomal RNA gene from 14 dinoflagellate isolates: six cultured Symbiodinium specimens, two cultured symbiotic Gymnodinium, two algal samples isolated from reef-building corals, an algal sample obtained from cultures of the jellyfish Cassiopea xamachana, and three free-living Gymnodinium isolates. Results show that morphological similarities among the examined symbiotic taxa do not necessarily correspond with molecular phylogeny. The included Symbiodinium taxa represent a paraphyletic assemblage while Gymnodinium is reconstructed as a polyphyletic assemblage. Analysis indicates that all the included symbiotic dinoflagellates descended from a common, symbiotic ancestor (though within the dinoflagellates, symbiosis is a polyphyletic trait). Additionally, two free-living dinoflagellates emerge within the symbiotic clade, suggesting that the symbiotic lifestyle has been lost at least once in this group. It has been hypothesized that rates of evolution within mutualistic endosymbioses should be reduced relative to free-living taxa. However, results indicate that rates of molecular, morphological, biochemical and behavioral change are similar among branches leading to symbiotic and free-living dinoflagellates.

Animals↗