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PubMed2004

Novel conserved domains in proteins with predicted roles in eukaryotic cell-cycle regulation, decapping and RNA stability.

BACKGROUND: The emergence of eukaryotes was characterized by the expansion and diversification of several ancient RNA-binding domains and the apparent de novo innovation of new RNA-binding domains. The identification of these RNA-binding domains may throw light on the emergence of eukaryote-specific systems of RNA metabolism. RESULTS: Using sensitive sequence profile searches, homology-based fold recognition and sequence-structure superpositions, we identified novel, divergent versions of the Sm domain in the Scd6p family of proteins. This family of Sm-related domains shares certain features of conventional Sm domains, which are required for binding RNA, in addition to possessing some unique conserved features. We also show that these proteins contain a second previously uncharacterized C-terminal domain, termed the FDF domain (after a conserved sequence motif in this domain). The FDF domain is also found in the fungal Dcp3p-like and the animal FLJ22128-like proteins, where it fused to a C-terminal domain of the YjeF-N domain family. In addition to the FDF domains, the FLJ22128-like proteins contain yet another divergent version of the Sm domain at their extreme N-terminus. We show that the YjeF-N domains represent a novel version of the Rossmann fold that has acquired a set of catalytic residues and structural features that distinguish them from the conventional dehydrogenases. CONCLUSIONS: Several lines of contextual information suggest that the Scd6p family and the Dcp3p-like proteins are conserved components of the eukaryotic RNA metabolism system. We propose that the novel domains reported here, namely the divergent versions of the Sm domain and the FDF domain may mediate specific RNA-protein and protein-protein interactions in cytoplasmic ribonucleoprotein complexes. More specifically, the protein complexes containing Sm-like domains of the Scd6p family are predicted to regulate the stability of mRNA encoding proteins involved in cell cycle progression and vesicular assembly. The Dcp3p and FLJ22128 proteins may localize to the cytoplasmic processing bodies and possibly catalyze a specific processing step in the decapping pathway. The explosive diversification of Sm domains appears to have played a role in the emergence of several uniquely eukaryotic ribonucleoprotein complexes, including those involved in decapping and mRNA stability.

Amino Acid Sequence↗

PubMed2006

Comprehensive comparative analysis of kinesins in photosynthetic eukaryotes.

BACKGROUND: Kinesins, a superfamily of molecular motors, use microtubules as tracks and transport diverse cellular cargoes. All kinesins contain a highly conserved approximately 350 amino acid motor domain. Previous analysis of the completed genome sequence of one flowering plant (Arabidopsis) has resulted in identification of 61 kinesins. The recent completion of genome sequencing of several photosynthetic and non-photosynthetic eukaryotes that belong to divergent lineages offers a unique opportunity to conduct a comprehensive comparative analysis of kinesins in plant and non-plant systems and infer their evolutionary relationships. RESULTS: We used the kinesin motor domain to identify kinesins in the completed genome sequences of 19 species, including 13 newly sequenced genomes. Among the newly analyzed genomes, six represent photosynthetic eukaryotes. A total of 529 kinesins was used to perform comprehensive analysis of kinesins and to construct gene trees using the Bayesian and parsimony approaches. The previously recognized 14 families of kinesins are resolved as distinct lineages in our inferred gene tree. At least three of the 14 kinesin families are not represented in flowering plants. Chlamydomonas, a green alga that is part of the lineage that includes land plants, has at least nine of the 14 known kinesin families. Seven of ten families present in flowering plants are represented in Chlamydomonas, indicating that these families were retained in both the flowering-plant and green algae lineages. CONCLUSION: The increase in the number of kinesins in flowering plants is due to vast expansion of the Kinesin-14 and Kinesin-7 families. The Kinesin-14 family, which typically contains a C-terminal motor, has many plant kinesins that have the motor domain at the N terminus, in the middle, or the C terminus. Several domains in kinesins are present exclusively either in plant or animal lineages. Addition of novel domains to kinesins in lineage-specific groups contributed to the functional diversification of kinesins. Results from our gene-tree analyses indicate that there was tremendous lineage-specific duplication and diversification of kinesins in eukaryotes. Since the functions of only a few plant kinesins are reported in the literature, this comprehensive comparative analysis will be useful in designing functional studies with photosynthetic eukaryotes.

Algal Proteins↗

PubMed2006

The orthology of HLA-E and H2-Qa1 is hidden by their concerted evolution with other MHC class I molecules.

BACKGROUND: Whether MHC molecules undergo concerted evolution or not has been the subject of a long-standing debate. RESULTS: By comparing sequences of eight functional homologues of HLA-E from primates and rodents with those of MHC class Ia molecules from the same eight species, we find that different portions of MHC class I molecules undergo different patterns of evolution. By focusing our analyses sequentially on these various portions, we have obtained clear evidence for concerted evolution of MHC class I molecules, suggesting the occurrence of extensive interallelic and intergenic exchanges. Intra-species homogenisation of sequences is particularly noticeable at the level of exon 4, which codes for the alpha3 domain, but our results suggest that homogenisation also concerns certain residues of the alpha1-alpha2 codomain that lie outside the antigen recognition site. CONCLUSION: A model is presented in which Darwinian selective pressures due to pathogens could, at the same time, favour diversification of MHC class Ia molecules and promote concerted evolution of separate loci by spreading advantageous motifs arising by mutations in individual MHC molecules to other alleles and to other loci of the MHC region. This would also allow MHC molecules to co-evolve with the proteins with which they interact to fulfil their functions of antigen presentation and regulation of NK cell activity. One of the raisons d'être of the MHC may therefore be to favour at the same time both diversification of MHC class Ia molecules and homogenisation of the whole pool of MHC class I molecules (Ia and Ib) involved in antigen presentation. REVIEWERS: This article was reviewed by Stephan Beck, Lutz Walter and Pierre Pontarotti.

Journal Article↗

PubMed2002

Phylogenetic analysis of the human basic helix-loop-helix proteins.

BACKGROUND: The basic helix-loop-helix (bHLH) proteins are a large and complex multigene family of transcription factors with important roles in animal development, including that of fruitflies, nematodes and vertebrates. The identification of orthologous relationships among the bHLH genes from these widely divergent taxa allows reconstruction of the putative complement of bHLH genes present in the genome of their last common ancestor. RESULTS: We identified 39 different bHLH genes in the worm Caenorhabditis elegans, 58 in the fly Drosophila melanogaster and 125 in human (Homo sapiens). We defined 44 orthologous families that include most of these bHLH genes. Of these, 43 include both human and fly and/or worm genes, indicating that genes from these families were already present in the last common ancestor of worm, fly and human. Only two families contain both yeast and animal genes, and no family contains both plant and animal bHLH genes. We suggest that the diversification of bHLH genes is directly linked to the acquisition of multicellularity, and that important diversification of the bHLH repertoire occurred independently in animals and plants. CONCLUSIONS: As the last common ancestor of worm, fly and human is also that of all bilaterian animals, our analysis indicates that this ancient ancestor must have possessed at least 43 different types of bHLH, highlighting its genomic complexity.

Animals↗

PubMed2025

Genome-wide phylogeny reshapes our understanding of the evolution of deep-sea dragonfishes, bristlemouths, viperfishes, and allies (Stomiiformes).

BACKGROUND: The evolutionary relationships within Stomiiformes, a diverse order of deep-sea fishes dominating the mesopelagic and bathypelagic zones, remain contentious due to conflicting morphological and molecular evidence. These fishes, comprising 464 species across four traditionally recognized families (Gonostomatidae, Sternoptychidae, Phosichthyidae, and Stomiidae), exhibit remarkable adaptations such as bioluminescence, ultra-black pigmentation, and extreme jaw morphologies. Their global abundance and ecological significance, including contributions to the biological carbon pump, underscores the need to resolve their phylogeny amid escalating threats from climate change and human activities. RESULTS: We conducted the most comprehensive phylogenomic analysis of Stomiiformes to date, integrating 936 nuclear loci from 60 species and an expanded dataset of 135 species with mitochondrial sequences from publicly available repositories such as the Barcode of Life Data Systems (BOLD) database. We used maximum likelihood and coalescent-based approaches to assess family monophyly and relationships, including extensive quality control to address contamination in public databases. Our analyses reveal unstable tree topologies and complex evolutionary histories that challenge traditional classifications, while our quality control analyses identified 29% of BOLD sequences as misidentified or contaminated, emphasizing rigorous curation for deep-sea taxa. Congruent with a recent taxonomic treatment of Stomiiformes, the families Phosichthyidae and Gonostomatidae exhibit polyphyly and paraphyly, respectively, while subfamilies within Stomiidae are extensively non-monophyletic, leading us to recommend their abandonment. We propose the recognition of eight monophyletic families: Vinciguerriidae, Diplophidae, Gonostomatidae, Yarrellidae, Ichthyococcidae, Phosichthyidae, Sternoptychidae, and Stomiidae, supported by robust molecular and morphological evidence. CONCLUSIONS: This revised classification reflects the morphological and ecological diversity of Stomiiformes, aligning with their evolutionary diversification in the deep sea. Our phylogenomic framework resolves longstanding systematic uncertainties and highlights the power of genome-wide data in tackling taxonomically challenging clades. These findings provide a foundation for understanding deep-sea fish diversification and assessing the potential ecological drivers for their evolutionary diversity.

Animals↗

PubMed2026

Comprehensive genomic and computational insights into Brucella suis: pan-genome analysis, evolutionary perspectives, and in-silico vaccine design.

BACKGROUND: Brucella suis is a zoonotic intracellular pathogen responsible for brucellosis, mainly in swine and humans. Although numerous genome sequences are publicly available, an integrative genomic analysis combining pan-genome architecture, structural organization, evolutionary relationships, and vaccine-associated targets remains limited. RESULTS: In this study, we analyzed 91 publicly available B.suis genomes to characterize their pan-genome composition and genomic structure. The pan-genome exhibited an open configuration, indicating continued genomic diversification. A total of 2,146 core genes were identified, representing conserved functions essential for species maintenance, while the accessory genome reflected strain-level variability. Phylogenetic reconstruction based on single-copy orthologs revealed distinct evolutionary clades among the strains. A complementary phylogenetic analysis of pan-genome gene presence-absence patterns further supported clade differentiation and highlighted variation in accessory gene repertoires. Comparative synteny and genome structural analyses demonstrated largely conserved chromosomal organization with localized rearrangements across strains. Screening of the core proteome identified 64 putative antigenic proteins with predicted surface localization and immunogenic properties. Additionally, resistance-associated determinants related to tetracycline and doxycycline were detected in one genome within the dataset. CONCLUSIONS: This comprehensive genomic analysis defines the pan-genome structure, evolutionary relationships, and genome organization of B.suis. The integration of core and pan-genome-based phylogenies provides complementary insights into strain diversification, while the identified conserved antigenic candidates offer a foundation for future experimental validation and rational vaccine development strategies.

Genome, Bacterial↗

PubMed2026

Hide and seek: de novo identification in sugar beet reveals impact of non-autonomous LTR retrotransposons.

Plant genomes are filled with retrotransposons and their derivatives, constantly undergoing sequence diversification and structural rearrangement. Among them, short, non-autonomous retrotransposons lack full coding capacity and often form subfamilies. As a result, non-autonomous retrotransposons are incompletely identified in most to all genome assemblies.Here, we capitalize on our comprehensive understanding of the transposable element (TE) landscape in sugar beet (Beta vulgaris) to assess the extent of the blind spot for non-autonomous long terminal repeat (LTR) retrotransposons. This use case serves to answer if all of these sequences are derivatives of easier-to-identify full-length elements or if there is more variability that is currently overlooked.For this we applied a semi-automated structural discovery workflow followed by in-depth manual verification to characterize non-autonomous LTR retrotransposons in sugar beet. We retrieve more than 100 non-autonomous LTR retrotransposon families that lack complete autonomous coding capacity, including canonical terminal-repeat retrotransposons in miniature (TRIMs), elongated non-coding derivatives and families retaining fragmented coding remnants. The identified families span a broad range, including elements exceeding 15,000 bp in length and display evidence for reshuffling and modular evolution. Only a subset of families could be confidently linked to autonomous retrotransposons, showing sequence diversification within the non-autonomous LTR retrotransposon fraction beyond the autonomous genomic templates.We highlight that a large fraction of non-autonomous LTR retrotransposons is incompletely recovered with the current TE identification workflows, even if the output is well-curated and condensed into TE libraries and suggest procedures to remedy this gap. This study gives a genome-wide view into the non-autonomous LTR retrotransposon landscape of a single plant genome and highlights the importance of structure-based approaches for their identification and classification.

LTR retrotransposons↗

PubMed2006

Comparative analysis of Hox downstream genes in Drosophila.

Functional diversification of body parts is dependent on the formation of specialized structures along the various body axes. In animals, region-specific morphogenesis along the anteroposterior axis is controlled by a group of conserved transcription factors encoded by the Hox genes. Although it has long been assumed that Hox proteins carry out their function by regulating distinct sets of downstream genes, only a small number of such genes have been found, with very few having direct roles in controlling cellular behavior. We have quantitatively identified hundreds of Hox downstream genes in Drosophila by microarray analysis, and validated many of them by in situ hybridizations on loss- and gain-of-function mutants. One important finding is that Hox proteins, despite their similar DNA-binding properties in vitro, have highly specific effects on the transcriptome in vivo, because expression of many downstream genes respond primarily to a single Hox protein. In addition, a large fraction of downstream genes encodes realizator functions, which directly affect morphogenetic processes, such as orientation and rate of cell divisions, cell-cell adhesion and communication, cell shape and migration, or cell death. Focusing on these realizators, we provide a framework for the morphogenesis of the maxillary segment. As the genomic organization of Hox genes and the interaction of Hox proteins with specific co-factors are conserved in vertebrates and invertebrates, and similar classes of downstream genes are regulated by Hox proteins across the metazoan phylogeny, our findings represent a first step toward a mechanistic understanding of morphological diversification within a species as well as between species.

Animals↗

PubMed2001

Proximodistal domain specification and interactions in developing Drosophila appendages.

The morphological diversification of appendages represents a crucial aspect of animal body plan evolution. The arthropod antenna and leg are homologous appendages, thought to have arisen via duplication and divergence of an ancestral structure (Snodgrass, R. (1935) Book Principles of Insect Morphology. New York: McGraw-Hill). To gain insight into how variations between the antenna and the leg may have arisen, we have compared the epistatic relationships among three major proximodistal patterning genes, Distal-less, dachshund and homothorax, in the antenna and leg of the insect arthropod Drosophila melanogaster. We find that Drosophila appendages are subdivided into different proximodistal domains specified by specific genes, and that limb-specific interactions between genes and the functions of these genes are crucial for antenna-leg differences. In particular, in the leg, but not in the antenna, mutually antagonistic interactions exist between the proximal and medial domains, as well as between medial and distal domains. The lack of such antagonism in the antenna leads to extensive coexpression of Distal-less and homothorax, which in turn is essential for differentiation of antennal morphology. Furthermore, we report that a fundamental difference between the two appendages is the presence in the leg and absence in the antenna of a functional medial domain specified by dachshund. Our results lead us to propose that the acquisition of particular proximodistal subdomains and the evolution of their interactions has been essential for the diversification of limb morphology.

Animals↗

PubMed2006

Time-domain signal divergence and discrimination without receptor modification in sympatric morphs of electric fishes.

Polymorphism in an animal communication channel provides a framework for studying proximate rules of signal design as well as ultimate mechanisms of signal diversification. Reproductively isolated mormyrid fishes from Gabon's Brienomyrus species flock emit distinctive electric organ discharges (EODs) thought to function in species and sex recognition. Species boundaries and EODs appear congruent in these fishes, with the notable exception of three morphs designated types I, II and III. Within the species flock, these morphs compose a monophyletic group that has recently been called the magnostipes complex. Co-occurring morphs of this complex express distinctive EODs, yet they appear genetically indistinguishable at several nuclear loci. In this study, we investigated EOD discrimination by these morphs using both behavioral and physiological experiments. During the breeding season, wild-caught type I and type II males showed evidence that they can discriminate their own morph's EOD waveform from that of a sympatric and genetically distinct reference species. However, we found that type I and type II males exhibited an asymmetry in unconditioned responses to paired playback of EODs recorded from type I versus type II females. Males of the type II morph responded preferentially to EODs of type II females, whereas type I males did not appear to discriminate homotypic and heterotypic EODs in our experimental paradigm. Part of this behavioral asymmetry may have resulted from a previously undetected difference in adult size, which may have enhanced apparent discrimination by the smaller morph (type II) due to a relatively higher risk of injury from the larger morph (type I). Knollenorgan receptors, which mediate electrical communication in mormyrids, showed similar spectral tuning in type I and type II. These electroreceptors coded temporal features of any single magnostipes-complex EOD with similar patterns of time-locked spikes in both morphs. By contrast, Knollenorgans exhibited distinctive responses to different EOD waveforms. These results suggest that discrete EOD variation in this rapidly diversifying complex is functional in terms of morph-specific advertisement and recognition. Time-domain signal divergence has outpaced frequency-domain divergence between sympatric morphs, requiring little to no change in receptor response properties. We discuss our findings in light of a model for EOD time-coding by the Knollenorgan pathway, as well as evolutionary hypotheses concerning sympatric signal diversification in the magnostipes complex.

Animal Communication↗

PubMed2025

The modern expansion of Dscam1 isoform diversity in Drosophila is linked to fitness and immunity.

Drosophila melanogaster Down Syndrome cell adhesion molecule 1 (Dscam1) gene encodes 38,016 diverse cell surface receptor proteins via alternative splicing, which have both nervous and immune functions. However, it remains elusive why organisms have evolved such an astonishing diversity of isoforms. Here, we show that fitness and immunity properties have driven the modern evolution of Dscam1 isoform diversity. We assess multiple aspects of fly fitness in deletion mutants harboring exon 4, 6, or 9 clusters, respectively, reducing ectodomain isoform diversity stepwise from 18,612 to 396. All fitness-related traits generally improved as the potential number of isoforms increased; however, the magnitude of the changes varied remarkably in a variable cluster-specific manner. Correlation analysis revealed that fitness-related traits were much more sensitive to reductions in Dscam1 diversity compared to canonical neuronal self/non-self discrimination. We conclude that the role of Dscam1 isoforms in canonical neuronal self-avoidance and self/non-self discrimination is mediated by a small fraction of all isoforms (<1/10), whereas a separate role essential for other developmental contexts and resistances, likely in fitness and immunity, requires almost full isoform diversity. Thus, fitness and immunity properties, rather than canonical neuronal functions, are the dominant drivers during the modern diversification of the Dscam1 isoform. Our findings suggest that Dscam1 diversity is closely linked to adaptation and species diversification in arthropods.

Animals↗

PubMed2026

Life in sediments fosters 'sexual' speciation in the Shewanella baltica complex.

Understanding how intra- and interspecific differentiation arises in natural microbial populations is central to explaining the processes that drive bacterial evolution. Motivated by the co-occurrence of multiple putative genospecies closely related to Shewanella baltica in Baltic Sea sediments, we investigated the genomic structure of this species complex across fine spatial scales. We analyzed 112 genome sequences from strains collected across several sediment cores and depths (0-6 cm) at Vaxön (Stockholm archipelago, Sweden) as well as earlier isolates from this site and allopatric strains from surrounding locations obtained from both sediments and the water column. Using a reverse-ecology population genomics approach, we found unprecedented genomic diversification among sediment-associated strains, which form a species complex resolving into three cohesive evolutionary groups (G1, G2, and G3) with distinct signatures of metabolic specialization including sulfite respiration. While G1 consists predominantly of a single species (S. baltica) with high gene turnover, G2 and G3 comprise an array of divergent putative genospecies and previously reported species consistently recovered from sediments. Patterns of homologous recombination indicate that diversification of the lineages within G2 and G3 is primarily recombination-driven ('sexual') and is associated with specialization in sulfite reduction and utilization of certain carbon sources. The extent of diversity uncovered here far exceeds that reported for S. baltica from other environments, suggesting that a sediment-associated lifestyle promotes the emergence of novel genotypes. These findings expand the known limits of sympatric speciation in prokaryotes beyond subspecific ecotypes, demonstrating that bacterial species can diverge and persist as distinct lineages in the absence of spatial segregation and at microgeographic scales. Furthermore, our results suggest that collective interactions and ecological differentiation can structure sediment-associated bacterial populations strongly enough to drive divergence at the species level.

Journal Article↗

PubMed2005

Angiosperm divergence times: the effect of genes, codon positions, and time constraints.

An understanding of the evolution of modern terrestrial ecosystems requires an understanding of the dynamics associated with angiosperm evolution, including the timing of their origin and diversification into their extraordinary present-day diversity. Molecular estimates of angiosperm age have varied widely, and many substantially predate the Early Cretaceous fossil appearance of the group. In this study, the effect of different genes, codon positions, and chronological constraints on node ages are examined on divergence time estimates across seed plants, with a special focus on angiosperms. Penalized likelihood was used to estimate divergence times on a phylogenetic hypothesis for seed plants derived from Bayesian analysis, with branch lengths estimated with maximum likelihood. The plastid genes atpB, psaA, psbB, and rbcL were used individually and in combination, using first and second, third, and the three codon positions, including and excluding age constraints on 20 nodes derived from a critical examination of the land-plant fossil record. The optimal level of rate smoothing according to each unconstrained and constrained dataset was obtained with penalized likelihood. Tests for a molecular clock revealed significantly unclocklike rates in all datasets. Addition of fossil constraints resulted in even greater departures from constancy. Consistently with significant deviations from a clock, estimated optimal smoothing values were low, but a strict correlation between rate heterogeneity and optimal smoothing value was not found. Age estimates for nodes across the phylogeny varied, sometimes substantially, with gene and codon position. Nevertheless, estimates based on the four concatenated genes are very similar to the mean of the four individual gene estimates. For any given node, unconstrained age estimates are more variable than constrained estimates and are frequently younger than well-substantiated fossil members of the clade. Constrained estimates of ages of clades are older than unconstrained estimates and oldest fossil representatives, sometimes substantially so. Angiosperm age estimates decreased as rate smoothing increased. Whereas the range of unconstrained angiosperm age estimates spans the fossil age of the clade, the range of constrained estimates is narrower (and older) than the earliest angiosperm fossils. Results unambiguously indicate the relevance of constraints in reducing the variability of ages derived from different partitions of the data and diminishing the effect of the smoothing parameter. Constrained optimizations of divergence times and substitution rates across the phylogeny suggest appreciably different evolutionary dynamics for angiosperms and for gymnosperms. Whereas the gymnosperm crown group originated shortly after the origin of seed plants, a long time elapsed before the origin of crown group angiosperms. Although absolute age estimates of angiosperms and angiosperm clades are older than their earliest fossils, the estimated pace of phylogenetic diversification largely agrees with the rapid appearance of angiosperm lineages in stratigraphic sequences.

Base Sequence↗

PubMed2006

Phylogenetic autocorrelation and evolutionary interpretation of the higher-taxon approach for biodiversity analyses.

Although in most recent broad-scale analyses, diversity is measured by counting the number of species in a given area or spatial unity (species richness), a 'top-down' approach has been used sometimes, counting higher-taxon (genera, family) instead of species with some advantages. However, this higher-taxon approach is quite empirical and the cut-off level is usually arbitrarily defined. In this work, we show that the higher-taxon approach could be theoretically linked with models of phenotypic diversification by means of phylogenetic autocorrelation analysis in such a way that the taxonomic (or phylogenetic) rank to be used could not be necessarily arbitrary. This rank expresses past time in which taxa became independent for a given phenotypic trait or for the evolution of average phenotypes across different traits. We illustrated the approach by evaluating phylogenetic patches for 23 morphological, ecological and behavioural characters in New World terrestrial Carnivora. The higher-taxon counts at 18.8 mya (S(L)) defined by phylogenetic correlograms are highly correlated with species richness (r = 0.899; P < 0.001 with ca. 13 degrees of freedom by taking spatial autocorrelation into account). However, S(L) in North America is usually larger than in South America. Thus, although there are more species in South and Central America, the fast recent diversification that occurred in this region generated species that are "redundant" in relation to lineages that were present at 18.8 my. BP. Therefore, the number of lineages can be comparatively used as a measure of evolutionary diversity under a given model of phenotypic divergence among lower taxonomic units.

Animals↗

PubMed2005

Coevolution and biogeography among Nematodirinae (Nematoda: Trichostrongylina) Lagomorpha and Artiodactyla (Mammalia): exploring determinants of history and structure for the northern fauna across the holarctic.

Nematodes of the subfamily Nematodirinae are characteristic components of a Holarctic fauna. The topology of a generic-level phylogenetic hypothesis, patterns of diversity, and geographic distributions for respective nematode taxa in conjunction with data for host occurrence are consistent with primary distributions determined across Beringia for species of Murielus, Rauschia, Nematodirus, and Nematodirella. Ancestral hosts are represented by Lagomorpha, with evidence for a minimum of 1 host-switching-event and subsequent radiation in the Artiodactyla. Diversification may reflect vicariance of respective faunas along with episodic or cyclical range expansion and isolation across Beringia during the late Tertiary and Quaternary. Secondarily, species of Nematodirus attained a distribution in the Neotropical region with minimal diversification of an endemic fauna represented by Nematodirus molini among tayassuids, Nematodirus lamae among camelids and Nematodirus urichi in cervids during the Pleistocene. Nematodirines are a core component of an Arctic-Boreal fauna of zooparasitic nematodes (defined by latitude and altitude) adapted to transmission in extreme environments characterized by seasonally low temperatures and varying degrees of desiccation. The history and distribution of this fauna is examined in the context of biotic and abiotic determinants for geographic colonization and host switching with an exploration of predicted responses of complex host-parasite systems to ecological perturbation under a regime of global climate change.

Animals↗

PubMed1996

Calibrating the Ordovician Radiation of marine life: implications for Phanerozoic diversity trends.

It has long been suspected that trends in global marine biodiversity calibrated for the Phanerozoic may be affected by sampling problems. However, this possibility has not been evaluated definitively, and raw diversity trends are generally accepted at face value in macroevolutionary investigations. Here, we analyze a global-scale sample of fossil occurrences that allows us to determine directly the effects of sample size on the calibration of what is generally thought to be among the most significant global biodiversity increases in the history of life: the Ordovician Radiation. Utilizing a composite database that includes trilobites, brachiopods, and three classes of molluscs, we conduct rarefaction analyses to demonstrate that the diversification trajectory for the Radiation was considerably different than suggested by raw diversity time-series. Our analyses suggest that a substantial portion of the increase recognized in raw diversity depictions for the last three Ordovician epochs (the Llandeilian, Caradocian, and Ashgillian) is a consequence of increased sample size of the preserved and catalogued fossil record. We also use biometric data for a global sample of Ordovician trilobites, along with methods of measuring morphological diversity that are not biased by sample size, to show that morphological diversification in this major clade had leveled off by the Llanvirnian. The discordance between raw diversity depictions and more robust taxonomic and morphological diversity metrics suggests that sampling effects may strongly influence our perception of biodiversity trends throughout the Phanerozoic.

Animals↗

PubMed2002

The underrepresentation of Hispanics/Latinos in nursing education: a deafening silence.

While our national population is growing more ethnically and racially diverse, the nursing workforce and faculty remains predominantly White (non-Hispanic). Ethnic/racial minorities are seriously underrepresented in nursing and, as such, are a factor in the nursing workforce shortage. The nursing literature has addressed the need for ethnic/racial diversity for several decades, most often citing diversification as a means of providing culturally competent care. However the fact remains that the nursing population continues to be underrepresented by people of color. The diversification of the nursing profession will require culturally sensitive research and theory development regarding the recruitment and education of ethnic/racial minorities. While there is a growing body of knowledge regarding the educational needs and experiences of minorities in nursing education, much of this data generalize minorities as if they were a homogeneous group. There is a striking paucity of research regarding the underepresentation of Hispanics in nursing and the unique issues of recruitment and retention of this group in nursing education. This paper provides a review of the mostly anecdotal literature regarding the experiences of Hispanics in nursing education. It explores the underrepresentation and paucity of culturally specific knowledge regarding the recruitment, retention, and graduation of Hispanics/Latinos in nursing. The homogeneity of nursing and its consequences specifically in relation to Hispanics is discussed. The research implications are highlighted throughout.

Cultural Diversity↗

PubMed2006

Imidazoline receptors, novel agents and therapeutic potential.

The initial realization that agents containing an imidazoline structure may interact with a distinct class of receptors, has led to a major class of cardiovascular agents, which now has the potential to enter a third generation. There is now general acceptance that there are three main imidazoline receptor classes, the I(1) imidazoline receptor which mediates the sympatho-inhibitory actions to lower blood pressure, the I(2) receptor which is an important allosteric binding site of monoamine oxidase and the I(3) receptor which regulates insulin secretion from pancreatic beta cells. Thus all three represent important targets for cardiovascular research. Interestingly, an I(1)- receptor candidate has been cloned (IRAS, imidazoline receptor antisera selected) which is a homologue of the mouse cell adhesion integrin binding protein Nischarin. There has been range of new agonists and antagonists with very high selectivity for I(1), I(2) and I(3) receptors developed. Three different endogenous ligands have been characterized including agmatine (decarboxylated arginine), a range of beta-carbolines including harman and harmane, and more recently imidazoleacetic acid-ribotide. The imidazoline field has recently seen an enormous diversification with discoveries that I(1) and I(2) receptors also play a role in cell proliferation, regulation of body fat, neuroprotection, inflammation and some psychiatric disorders such as depression. This diversification has continued with the addition of effective agents with imidazoline affinity in the fields of cancer, pain and opioid addiction, stress, cell adhesion, epilepsy and appetite. The imidazoline field has maturated considerably with a range of highly selective leader molecules, candidate receptors and endogenous ligands. We are therefore only at the threshold of an exciting new era as we begin to understand the diverse and complex nature of their function.

Animals↗