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PubMedDate not supplied

Marital assortment and phenotypic convergence: longitudinal evidence.

This study provides a direct test of whether the observed similarity of spouses is due to initial assortment rather than to convergence of phenotypes. With data from three well-known longitudinal studies, phenotypic convergence is examined using both variable- and person-centered analyses. The longitudinal evidence does not support the hypothesis that couples increasingly resemble each other with time. Spouse correlations most likely reflect initial assortment at marriage and not the convergence of phenotypes.

Adult↗

PubMed2004

Convergence, divergence, and homogenization in the ecological structure of emydid turtle communities: the effects of phylogeny and dispersal.

Studies that have explored the origins of patterns of community structure from a phylogenetic perspective have generally found either convergence (similarity) in community structure between regions through adaptive evolution or lack of convergence (dissimilarity) due to phylogenetic conservatism in the divergent ecological characteristics of lineages inhabiting different regions. We used a phylogenetic approach to document a third pattern in the structure of emydid turtle communities. Emydid communities in southeastern North America tend to have a higher proportion of aquatic species than those in the northeast. This pattern reflects phylogenetic conservatism in the ecology and biogeography of two basal emydid clades, limiting convergence in community structure between these regions. However, differences in community structure between northeastern and southeastern North America have also been homogenized considerably by the dispersal of species with phylogenetically conserved ecological characteristics between regions. This pattern of ecologically conservative dispersal may be important in many continental and oceanic systems.

Animals↗

PubMed1987

Convergence of the maximum likelihood reconstruction algorithm for emission computed tomography.

Convergence properties of the maximum likelihood estimator (MLE) for emission computed tomographic (ECT) image reconstruction are evaluated as a function of Poisson noise, precision of the assumed system resolution model and iteration number up to 10,000 iterations. In the ECT reconstruction problem, the photon-emitting source distribution is to be estimated from measurements of projections of the emitted photon flux. The MLE algorithm seeks a source distribution which will maximise the maximum likelihood function relating the estimated and the measured projections. A Monte Carlo model of the system transfer function of a single photon emission computed tomographic (SPECT) system allowed realistic projection data to be simulated from a known source distribution. Poisson noise was added to the Monte Carlo simulations. By using projection data from a known source distribution generated through a known system transfer function, we were able to simultaneously evaluate the convergence of both the projection estimations as well as the source distribution estimations. As predicted by theory, the estimates of the projections did continue to improve (or remain the same) for all combinations of Poisson noise (up to 10% RMS) and system resolution (+/- 10% of true value) tested. Convergence of source distribution estimates to the true value was found for up to 10,000 iterations only for low noise (0.1% RMS) with the correct resolution function. For all other combinations, there was some optimum iteration (between 30 and 400) after which the source estimate was degraded even though the estimate of the projections was improved.

Algorithms↗

PubMed1992

Review of convergent beam tomography in single photon emission computed tomography.

Investigation of convergent-beam single photon emission computed tomography (SPECT) is actively being pursued to evaluate its clinical potentials. Fan-beam, cone-beam, pin-hole and astigmatic collimators are being used with rotating gamma cameras having large crystal areas, to increase the sensitivity for emission and transmission computed tomography of small organs such as the thyroid, brain or heart. With new multi-detector SPECT systems, convergent-beam geometry offers the ability to simultaneously obtain emission and transmission data necessary to quantify uptake of radiopharmaceutical distributions in the heart. The development of convergent-beam geometry in SPECT requires the integration of hardware and software. In considering hardware, the optimum detector system for cone-beam tomography is a system that satisfies the data sufficiency condition for which the scanning trajectory intersects any plane passing through the reconstructed region of interest. However, the major development of algorithms has been for the data insufficient case of single planar orbit acquisitions. The development of these algorithms have made possible the preliminary evaluation of this technology and the imaging of brain and heart are showing significant potential for the clinical application of cone-beam tomography. Presently, significant research activity is pursuing the development of algorithms for data acquisitions that satisfy the data sufficiency condition and that can be implemented easily and inexpensively on clinical SPECT systems.

Brain↗

PubMed2000

A slice-by-slice blurring model and kernel evaluation using the Klein-Nishina formula for 3D scatter compensation in parallel and converging beam SPECT.

Converging collimation increases the geometric efficiency for imaging small organs, such as the heart, but also increases the difficulty of correcting for the physical effects of attenuation, geometric response and scatter in SPECT. In this paper, 3D first-order Compton scatter in non-uniform scattering media is modelled by using an efficient slice by-slice incremental blurring technique in both parallel and converging beam SPECT. The scatter projections are generated by first forming an effective scatter source image (ESSI), then forward-projecting the ESSI. The Compton scatter cross section described by the Klein-Nishina formula is used to obtain spatial scatter response functions (SSRFs) of scattering slices which are parallel to the detector surface. Two SSRFs of neighbouring scattering slices are used to compute two small orthogonal 1D blurring kernels used for the incremental blurring from the slice which is further from the detector surface to the slice which is closer to the detector surface. First-order Compton scatter point response functions (SPRFs) obtained using the proposed model agree well with those of Monte Carlo (MC) simulations for both parallel and fan beam SPECT. Image reconstruction in fan beam SPECT MC simulation studies shows increased left ventricle myocardium-to-chamber contrast (LV contrast) and slightly improved image resolution when performing scatter compensation using the proposed model. Physical torso phantom fan beam SPECT experiments show increased myocardial uniformity and image resolution as well as increased LV contrast. The proposed method efficiently models the 3D first-order Compton scatter effect in parallel and converging beam SPECT.

Biophysical Phenomena↗

PubMed2004

Convergent evolution of domain architectures (is rare).

MOTIVATION: In this paper, we shall examine the evolution of domain architectures across 62 genomes of known phylogeny including all kingdoms of life. We look in particular at the possibility of convergent evolution, with a view to determining the extent to which the architectures observed in the genomes are due to functional necessity or evolutionary descent. We used domains of known structure, because from this and other information we know their evolutionary relationships. We use a range of methods including phylogenetic grouping, sequence similarity/alignment, mutation rates and comparative genomics to approach this difficult problem from several angles. RESULTS: Although we do not claim an exhaustive analysis, we conclude that between 0.4 and 4% of sequences are involved in convergent evolution of domain architectures, and expect the actual number to be close to the lower bound. We also made two incidental observations, albeit on a small sample: the events leading to convergent evolution appear to be random with no functional or structural preferences, and changes in the number of tandem repeat domains occur more readily than changes which alter the domain composition. CONCLUSION: The principal conclusion is that the observed domain architectures of the sequences in the genomes are driven by evolutionary descent rather than functional necessity. CONTACT: gough@supfam.org.

Conserved Sequence↗

PubMedDate not supplied

Interhemispheric integration: II. Symmetry and convergence of the corticostriatal projections of the left and the right principal sulcus (PS) and the left and the right supplementary motor area (SMA) of the rhesus monkey.

The relationship between the termination zones of projections from paired homotopic areas of the frontal lobes was examined in the caudate nucleus and the putamen of the macaque monkey. Injections of WGA-HRP and tritiated amino acids were made in topographically matched regions of the principal sulcus (PS) or of the supplementary motor area (SMA) in each hemisphere, such that the projections from the same area on each side were differentially labeled in the same animal. Adjacent sections through the neostriatum were processed for the respective tracers, permitting the relationship between the converging projections to be defined. The topographic distribution and strength of ipsilateral corticostriatal projections observed for separately labeled left and right hemispheres were strikingly similar. Projections from the left and the right PS terminated preferentially in central parts of the left and right neostriata, respectively, while projections of the left and right SMAs terminated preferentially in dorsolateral parts of respective left and right neostriata. Therefore, little evidence for asymmetry of corticostriatal projections was found. The projections of the left and the right PS to the same neostriatum were also compared. Remarkably, whether in the left or right hemisphere, projections from the left and the right PS were in precise register in topographically specific territories of the caudate and putamen. Likewise, projections of the left and right SMAs converged in both the left and right neostriata. Such convergence allows for a remarkable degree of interhemispheric integration in the descending corticostriatal networks.

Animals↗

PubMedDate not supplied

Some temporal and parietal cortical connections converge in CA1 of the primate hippocampus.

Large sectors of polymodal cortex project to the hippocampal formation via convergent input to the entorhinal cortex. The present study reports an additional access route, whereby several cortical areas project directly to CA1. These are parietal areas 7a and 7b, area TF medial to the occipitotemporal sulcus (OTS), and a restricted area in the lateral bank of the OTS that may be part of ventromedial area TE. These particular cortical areas are implicated in visuospatial processes; and their projection to and convergence within CA1 may be significant for the elaboration of 'view fields', for the postulated role of the hippocampal formation in topographic learning and memory, or for the snapshot identification of objects in the setting of complex visuospatial relationships. Convergence of vestibular and visual inputs (from areas 7b and 7a respectively) would support previous physiological findings that hippocampal neurons respond to combinations of whole-body motion and a view of the environment. The direct corticohippocampal connections are widely divergent, especially those from the temporal areas, which extend over much of the anteroposterior axis of the hippocampal main body. Divergent connections potentially influence large populations of CA1 pyramidal neurons, consistent with the suggestion that these neurons are involved in conjunctive coding. The same region of ventromedial TE, besides the direct connections to CA1, also gives rise to direct projections to area V1, and may correspond to a functionally specialized subdivision, perhaps part of VTF.

Animals↗

PubMed2001

JNK functions in the non-canonical Wnt pathway to regulate convergent extension movements in vertebrates.

Recent genetic studies in Drosophila identified a novel non-canonical Wnt pathway, the planar cell polarity (PCP) pathway, that signals via JNK to control epithelial cell polarity in Drosophila. Most recently, a pathway regulating convergent extension movements during gastrulation in vertebrate embryos has been shown to be a vertebrate equivalent of the PCP pathway. However, it is not known whether the JNK pathway functions in this non-canonical Wnt pathway to regulate convergent extension movements in vertebrates. In addition, it is not known whether JNK is in fact activated by Wnt stimulation. Here we show that Wnt5a is capable of activating JNK in cultured cells, and present evidence that the JNK pathway mediates the action of Wnt5a to regulate convergent extension movements in Xenopus. Our results thus demonstrate that the non-canonical Wnt/JNK pathway is conserved in both vertebrate and invertebrate and define that JNK has an activity to regulate morphogenetic cell movements.

Amino Acid Sequence↗

PubMed2002

The planar polarity gene strabismus regulates convergent extension movements in Xenopus.

The signaling mechanisms that specify, guide and coordinate cell behavior during embryonic morphogenesis are poorly understood. We report that a Xenopus homolog of the Drosophila planar cell polarity gene strabismus (stbm) participates in the regulation of convergent extension, a critical morphogenetic process required for the elongation of dorsal structures in vertebrate embryos. Overexpression of Xstbm, which is expressed broadly in early development and subsequently in the nervous system, causes severely shortened trunk structures; a similar phenotype results from inhibiting Xstbm translation using a morpholino antisense oligo. Experiments with Keller explants further demonstrate that Xstbm can regulate convergent extension in both dorsal mesoderm and neural tissue. The specification of dorsal tissues is not affected. The Xstbm phenotype resembles those obtained with several other molecules with roles in planar polarity signaling, including Dishevelled and Frizzled-7 and -8. Unlike these proteins, however, Stbm has little effect on conventional Wnt/beta-catenin signaling in either frog or fly assays. Thus our results strongly support the emerging hypothesis that a vertebrate analog of the planar polarity pathway governs convergent extension movements.

Adaptor Proteins, Signal Transducing↗

PubMed2002

Molecular basis of adaptive convergence in experimental populations of RNA viruses.

Characterizing the molecular basis of adaptation is one of the most important goals in modern evolutionary genetics. Here, we report a full-genome sequence analysis of 21 independent populations of vesicular stomatitis ribovirus evolved on the same cell type but under different demographic regimes. Each demographic regime differed in the effective viral population size. Evolutionary convergences are widespread both at synonymous and nonsynonymous replacements as well as in an intergenic region. We also found evidence for epistasis among sites of the same and different loci. We explain convergences as the consequence of four factors: (1) environmental homogeneity that supposes an identical challenge for each population, (2) structural constraints within the genome, (3) epistatic interactions among sites that create the observed pattern of covariation, and (4) the phenomenon of clonal interference among competing genotypes carrying different beneficial mutations. Using these convergences, we have been able to estimate the fitness contribution of the identified mutations and epistatic groups. Keeping in mind statistical uncertainties, these estimates suggest that along with several beneficial mutations of major effect, many other mutations got fixed as part of a group of epistatic mutations.

Epistasis, Genetic↗

PubMed1988

Convergence of immigrant suicide rates to those in the destination country.

Factors influencing the 1969-1973 suicide rate in 25 immigrant groups in Canada were investigated. Standardized mortality ratios (SMRs) were calculated for each group relative to the suicide rates in the origin country populations. Compared with their origin countries, immigrant females exhibited a significant increase in suicide rates (SMR = 1.11, p less than 0.01), whereas immigrant males did not (SMR = 0.98). Another set of standardized mortality ratios were then calculated for both origin and immigrant populations using the Canadian native-born rates as the standard. For the majority of immigrant groups, the standardized mortality ratios were significantly different from the ratios of their corresponding origin country populations, with 60% of the female immigrant groups and 41% of the male immigrant groups exhibiting higher ratios. Considerable variation was observed in the immigrant standardized mortality ratios, with a significant proportion of this variability being associated with the suicide rates in the origin countries (males r = 0.60, p less than 0.01; females r = 0.47, p less than 0.05). Using the standardized mortality ratios based on the Canadian native-born rates, the degree of "convergence" of immigrant suicide rates to the Canadian native-born rates was examined. Overall, significant convergence occurred for both sexes (p less than 0.01), with the immigrant suicide rates converging 40% of the initial difference between the standardized mortality ratios for the origin country and the Canadian native-born.

Adolescent↗

PubMed1998

Convergence of nociceptive and non-nociceptive input onto the medullary dorsal horn in man.

Referred pain arising in orofacial pain states is probably due to convergence of different somatosensory input onto the medullary dorsal horn (MDH). To examine convergence between nociceptive and non-nociceptive input onto the MDH, the blink reflex (BR) was applied. R1- and R2-components can be evoked by innocuous stimuli, but only the R2 is elicited by painful heat. The BR was elicited by innocuous electrical stimuli applied to the supraorbital nerve. A conditioning painful heat pulse which did not evoke any BR was homotopically applied to the left forehead preceding the electrical stimulus by 75 ms. While R1 remained unchanged, the R2 was facilitated by about 30%. This study demonstrates a convergence of low-threshold mechanoreceptive and nociceptive inputs onto interneurons of the MDH in man.

Adult↗

PubMed2005

The case for feedforward multisensory convergence during early cortical processing.

The prevailing hierarchical model of sensory processing in the brain holds that different modalities of sensory information emanating from a single object are analyzed extensively during passage through their respective unisensory processing streams before they are combined in higher-order 'multisensory' regions of the cortex. Because of this view, multisensory interactions that have been found at early, putatively 'unisensory' cortical processing stages during hemodynamic imaging studies have been assumed to reflect feedback modulations that occur subsequent to multisensory processing in the higher-order multisensory areas. In this paper, we consider findings that challenge an exclusively feedback interpretation of early multisensory integration effects. First, high-density electrical mapping studies in humans have shown that multisensory convergence and integration effects can occur so early in the time course of sensory processing that purely feedback mediation becomes extremely unlikely. Second, direct neural recordings in monkeys show that, in some cases, convergent inputs at early cortical stages have physiological profiles characteristic of feedforward rather than feedback inputs. Third, damage to higher-order integrative regions in humans often spares the ability to integrate across sensory modalities. Finally, recent anatomic tracer studies have reported direct anatomical connections between primary visual and auditory cortex. These findings make it clear that multisensory convergence at early stages of cortical processing results from feedforward as well as feedback and lateral connections, thus using the full range of anatomical connections available in brain circuitry.

Animals↗

PubMed1980

The relation between night myopia and accommodative convergence.

Accommodation and convergence normally bear a tight relation to each other. To the extent that night myopia is due to an actual change in lens convexity, accommodation in night myopia should be accompanied by a commensurate change in convergence. This prediction was shown to be false because of variability in the convergence mechanism.

Accommodation, Ocular↗

PubMed2000

Field data do not support a textbook example of convergent character displacement.

Experimental evidence supporting convergent character displacement is rare; only one example exists and it is in the form of orientation and territory competition experiments performed in the laboratory. However, outcomes of laboratory experiments involving behaviour or competition can be artefacts of unnatural conditions and, therefore, the results of the previous experiments supporting convergent character displacement are equivocal. In this study, we re-examine the evolution of melanic nuptial coloration in male three-spined stickleback (Gasterosteus aculeatus) inhabiting the Chehalis River drainage in Washington State. This novel nuptial coloration has been thought to have evolved in response to competition for nesting territories with the co-distributed Olympic mudminnow (Norzumbra hubbsi), which is also melanic and breeds at the same time. I found that melanic stickleback males did not have an advantage over their red counterparts from typical populations when competing for nesting territories with Olympic mudminnows. Additionally competitive interactions between sticklebacks and mudminnows were rare in both cage experiments and naturally breeding sticklebacks. Finally, melanic coloration in the Chehalis populations did not develop until males were parental, well after the hypothesized territory establishment period. These results refute the only experimental support for convergent character displacement and emphasize the importance of conducting behavioural experiments and observations under natural conditions.

Animals↗

PubMed2005

Local phylogenetic divergence and global evolutionary convergence of skull function in reef fishes of the family Labridae.

The Labridae is one of the most structurally and functionally diversified fish families on coral and rocky reefs around the world, providing a compelling system for examination of evolutionary patterns of functional change. Labrid fishes have evolved a diverse array of skull forms for feeding on prey ranging from molluscs, crustaceans, plankton, detritus, algae, coral and other fishes. The species richness and diversity of feeding ecology in the Labridae make this group a marine analogue to the cichlid fishes. Despite the importance of labrids to coastal reef ecology, we lack evolutionary analysis of feeding biomechanics among labrids. Here, we combine a molecular phylogeny of the Labridae with the biomechanics of skull function to reveal a broad pattern of repeated convergence in labrid feeding systems. Mechanically fast jaw systems have evolved independently at least 14 times from ancestors with forceful jaws. A repeated phylogenetic pattern of functional divergence in local regions of the labrid tree produces an emergent family-wide pattern of global convergence in jaw function. Divergence of close relatives, convergence among higher clades and several unusual 'breakthroughs' in skull function characterize the evolution of functional complexity in one of the most diverse groups of reef fishes.

Animals↗

PubMed2004

Comparative analysis of gene expression for convergent evolution of camera eye between octopus and human.

Although the camera eye of the octopus is very similar to that of humans, phylogenetic and embryological analyses have suggested that their camera eyes have been acquired independently. It has been known as a typical example of convergent evolution. To study the molecular basis of convergent evolution of camera eyes, we conducted a comparative analysis of gene expression in octopus and human camera eyes. We sequenced 16,432 ESTs of the octopus eye, leading to 1052 nonredundant genes that have matches in the protein database. Comparing these 1052 genes with 13,303 already-known ESTs of the human eye, 729 (69.3%) genes were commonly expressed between the human and octopus eyes. On the contrary, when we compared octopus eye ESTs with human connective tissue ESTs, the expression similarity was quite low. To trace the evolutionary changes that are potentially responsible for camera eye formation, we also compared octopus-eye ESTs with the completed genome sequences of other organisms. We found that 1019 out of the 1052 genes had already existed at the common ancestor of bilateria, and 875 genes were conserved between humans and octopuses. It suggests that a larger number of conserved genes and their similar gene expression may be responsible for the convergent evolution of the camera eye.

Animals↗