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J L Patton

Publications and source records attributed to J L Patton.

At least 19 recordsLinked to original sources
PubMed2001

Testing models of diversification in mice in the Abrothrix olivaceus/xanthorhinus complex in Chile and Argentina.

Samples of the forest-dwelling mouse Abrothrix olivaceus and the steppe-dwelling A. xanthorhinus across a transect between 45 and 47 degrees S in southern Chile were analysed using the mitochondrial cytochrome b (cyt b) sequence, substantially adding to the data presented previously for these taxa from Argentina and Chile. The level of variation in the cyt b sequence throughout the entire olivaceus/xanthorhinus complex is comparable to that seen within a single species in many South American sigmodontine rodents, consistent with a previous conclusion that both taxa are sub-species of A. olivaceus. Haplotypes of xanthorhinus have not yet achieved reciprocal monophyly relative to those of olivaceus. We evaluate competing hypotheses for the morphological divergence of xanthorhinus and olivaceus by allopatry in Pleistocene refuges versus postglacial diversification across ecological gradients. Two contrasting patterns are predicted for plots of the distribution of pairwise genetic differences, depending on whether the taxa diverged in allopatric refuges or through selection across a gradient. Examples of both modes of diversification are found in this complex.

Animals↗
PubMed2000

Riverine barriers and the geographic distribution of Amazonian species.

Rivers have been suggested to have played an important role in shaping present-day patterns of ecological and genetic variation among Amazonian species and communities. Recent molecular studies have provided mixed support for the hypothesis that large lowland Amazonian rivers have functioned as significant impediments to gene flow among populations of neotropical species. To date, no study has systematically evaluated the impact that riverine barriers might have on structuring whole Amazonian communities. Our analyses of the phylogeography of frogs and small mammals indicate that a putative riverine barrier (the Juruá River) does not relate to present-day patterns of community similarity and species richness. Rather, our results imply a significant impact of the Andean orogenic axis and associated thrust-and-fold lowland dynamics in shaping patterns of biotic diversity along the Juruá. Combined results of this and other studies significantly weaken the postulated role of rivers as major drivers of Amazonian diversification.

Animals↗
PubMed2000

Relative stability improves with experience in a dynamic standing task.

This study tested the hypothesis that subjects improve their relative stability as they learn a dynamic pulling task. Healthy adult subjects practiced making brief horizontal pulls (<300 ms) on a handle to a range of target forces ranging from 20 to 80% of their estimated maximum for 5 days. They were instructed to always keep their feet flat and begin and end their motion in an upright posture. In order to do this, subjects had to develop the appropriate body momentum prior to the pull and then recover their balance following the pull. We analyzed relative stability during balance recovery, using two measures: spatial safety margin (minimum distance of the center of pressure, COP, to the edges of the feet) and temporal safety margin (minimum extrapolated time for the COP to reach the edges of the feet). We hypothesized that: (1) spatial and temporal safety margins would be uncorrelated; (2) safety-margin means would increase with practice; and (3) safety-margin standard deviations would decrease with practice. Two experiments were conducted: one where subjects practiced three force targets and positioned their initial COP in a small window, and one where subjects practiced two force targets with no initial COP constraint. Results showed that spatial and temporal safety margins were correlated but shared less than 6% variance, indicating that they reflected different aspects of control. Safety-margin averages increased with practice and standard deviations decreased with practice, indicating that the stability of balance control in the execution of this task became more robust. We suggest that the nervous system could use safety margins in both feedback and feedforward control of balance.

Adult↗
PubMed2000

Practice-related changes in lumbar loading during rapid voluntary pulls made while standing.

OBJECTIVE: To determine if five days of practice on a novel dynamic, multi-joint pulling task resulted in lower magnitudes of lumbar loading or a more consistent relationship between pulling force and lumbar loading. DESIGN: A repeated measures design compared how practice influenced the magnitude of lumbar torque and the correlations between lumbar torque and pulling force. BACKGROUND: Previous studies suggest that practice can decrease the magnitude of lumbar loading on simple manual material handling tasks, but it is unknown whether practice reduces lumbar loading for more complex tasks. Neither is it known whether the consistency of lumbar loading increases with practice. METHODS: Ten healthy adults practiced impulse-like horizontal pulls to targets equaling 20%, 40% and 80% of their estimated maximal dynamic pulling force over 5 days. Movements were unrestrained, other than keeping the feet flat on the ground. We used a four-segment, sagittal plane inverse dynamics model to compute lumbar, hip, knee, and ankle torques on days 1 and 5 from ground reaction forces and moments, pulling forces, and kinematics. RESULTS: An analysis of variance showed significant practice-related changes in lumbar torque at the time of peak pulling force (lumbar torque(peakPF)). The lumbar torque(peakPF) decreased for the 20% pulls, did not change for the 40% pulls, and increased for the 80% pulls. Two subjects showed a significant decrease in lumbar torque(peakPF) for all three force levels. Coefficients of determination between pulling force and lumbar torque (r(2)(PF,LT): a measure of the consistency of the relationship between these two variables) were significantly higher on day 5 than day 1. CONCLUSIONS: Practice on a novel pulling task changed the magnitude of lumbar torques and increased their correlation with pulling force, suggesting that subjects learned strategies that improve motor control of lumbar torques. Relevance The study showed that the magnitude and consistency of lumbar loading changed spontaneously as subjects practiced a novel multijoint pulling task. Such changes may decrease the risk of low-back injury.

Adult↗
PubMed2000

Population genetic structure of two ecologically distinct Amazonian spiny rats: separating history and current ecology.

Population history and current demographic and ecological factors determine the amount of genetic variation within and the degree of differentiation among populations. Differences in the life history and ecology of codistributed species may lead to differences in hierarchical population genetic structure. Here, we compare patterns of genetic diversity and structure of two species of spiny rats in the genus Proechimys from the Rio Jurui of western Amazonian Brazil. Based on the ecological and life-history differences between the two species, we make predictions as to how they might differ in patterns of genetic diversity and structure. We use mitochondrial sequence data from the cytochrome b gene to test these predictions. Although both species maintain nearly the same number of mitochondrial haplotypes across the sampled range, they differ in levels of genetic diversity and geographic structure. Patterns of gene flow are also different between the two species with average M-values of nearly three in P. steerei and less than one in P. simonsi. Our initial predictions are largely upheld by the genetic data and where conflicting hypotheses arise, we suggest further studies that may allow us to distinguish among evolutionary scenarios. Separating the effects of history and ongoing demography on patterns of genetic diversity is challenging. Combining genetic analyses with field studies remains essential to disentangling these complex processes.

Animals↗
PubMed1999

Evaluation of a model that determines the stability limits of dynamic balance.

A recent model of balance control has revealed two types of boundaries describing stability limits for center of mass (CM) dynamics: torque boundaries and state boundaries. The purpose of this study was to determine if these boundaries correctly characterize empirical data. We analyzed 2367 trials from 10 subjects who recovered their balance after they voluntarily pulled on a handle. We hypothesized that if model predictions were valid, both types of boundaries should encompass the empirical trajectories. We also hypothesized that each trajectory's nearest distance to the torque boundaries (the torque safety margin) would be correlated with the center of pressure (COP) safety margin, defined as the COP's nearest distance to the edge of the feet. The results supported the accuracy of the model-derived boundaries, with torque boundaries encompassing 100% and state boundaries encompassing 99.8% of the trials. Moreover, torque safety margins were highly correlated with COP safety margins, supporting the use of COP safety margins for estimating relative stability in dynamic tasks where balance is maintained. The distributions of the trajectories also suggested that a safety margin-oriented control strategy might be a robust alternative to the hypothesis that the central nervous system strives to optimize motion. The distinctions among different safety margins are discussed.

Adult↗
PubMed1998

Molecular phylogeography and the evolution and conservation of Amazonian mammals.

The phylogeographic structure of 15 genera of Amazonian marsupials and rodents is summarized based on comparative sequence of the mitochondrial cytochrome b gene. The data are limited in geographical coverage, with samples widely scattered throughout Amazonia from the base of the Andes in Peru to the Guianan coast and eastern Brazil. We use this approach to define species boundaries, based minimally on the principle of reciprocal monophyly, in conjunction with morphological or other genetic discontinuities. The taxa so defined are older than previously appreciated, with many lineages dating from 1 to more than 3 Myr, and thus apparently predating the early Pleistocene. We relate patterns of concordant geographical shifts with underlying tectonic history and to current positions of major rivers. Finally, we provide comments on the utility of these data and patterns to conservation, articulating a need to incorporate phylogeographic information as part of the rationale in establishing conservation priorities at the organismal and geographical area levels.

Animals↗
PubMed1997

Learned changes in the complexity of movement organization during multijoint, standing pulls.

This paper tests the hypothesis that the central nervous system (CNS) learns to organize multijoint movements during a multijoint 'bouncing pull' task such that, after practice, motion of the anterior-posterior center of mass (CMAP) more closely resembles that of a conservative, one degree of freedom (DF), inverted pendulum model. The task requires standing human subjects to produce precise peak pulling forces on a handle while maintaining balance-goals that can be easily accomplished if movement is organized as in the model. Ten freely standing subjects practiced making brief, bouncing pulls in the horizontal direction to target forces (20-80% of maximum) for 5 days. Pulling force, body kinematic and force plate data were recorded. An eight-segment analysis determined sagittal-plane CM motion. We compared the effects of practice on the regression-based fit between actual and model-simulated CMAP trajectories, and on measures of CMAP phase plane symmetry and parameter constancy that the model predicts. If the CNS learns to organize movements like the inverted pendulum model, then model fit should improve and all other measures should approach zero after practice. The fit between modeled and actual CMAP motion did not improve significantly with practice, except for moderate force pulls. Nor did practice increase phase plane symmetry or parameter constancy. Specifically, practice did not decrease the differences between the pre-impact and rebound positions or speeds of the CMAP, although speed difference increased with pulling force. CMAP at the end of the movement was anterior to its initial position; the anterior shift increased after practice. Differences between the pre-pull and balance-recovery ankle torque (TA) impulses were greater on day 5 and correlated with the anterior shift in CMAP. These results suggest that practice separately influenced the force production and balance recovery phases. A modified model with damping could not explain the observed behaviors. A modified model using the actual time-varying TA profiles improved fit at lower force levels, but did not explain the increased postural shift after practice. We conclude that the CNS does not learn to organize movements like the conservative, inverted pendulum model, but rather learned a more complex form of organization that capitalized on more time-varying controls and more intersegmental dynamics. We hypothesize that at least one additional DF and at least one time-varying parameter will be needed to explain fully how the CNS learns to organize multijoint, bouncing pulls made while standing.

Adult↗
PubMed1997

Phylogenetic evidence of mitochondrial DNA introgression among pocket gophers in New Mexico (family Geomyidae).

Mitochondrial DNA (mtDNA) variation in the cytochrome b gene was determined for two divergent taxa of pocket gophers, Thomomys bottae actuosus and T. b. ruidosae. These two taxa hybridize in a narrow contact zone, but introgression of nuclear markers such as allozymes or chromosomes does not extend much beyond the hybrid zone (Patton et al. 1979). We found that despite their distinctness, the two subspecies shared very similar mtDNA haplotypes. By a comparison of phylogenetic histories derived from nuclear markers (allozymes) and from mtDNA haplotypes sampled in different populations of T. bottae from New Mexico, we show that apparent similarity is due to an introgression of T. b. ruidosae mtDNA into T. b. actuosus nuclear background. Evidence of introgression is not limited to the present-day contact zone between these two taxa, but extends at least 75 km away from it. The actuosus haplotype coexists along with the ruidosae mtDNA in the Gallinas Mts., which are inhabited by otherwise pure T. b. actuosus, while further north only typical actuosus haplotypes were detected. Of several potential mechanisms which could lead to such a geographical pattern of variation, we argue that a combination of range shifts due to climatic fluctuations, and genetic drift are most likely. Horizontal gene transfers due to hybridization are historical events which seem rather common among pocket gophers. Although they can be identified with careful phylogenetic study using independent data sets, the potential for misinterpreting a gene tree as an organismal tree is great in this and other groups of animals.

Animals↗
PubMed1996

Human herpesvirus 6: infection and disease following autologous and allogeneic bone marrow transplantation.

Human herpesvirus 6 activity (HHV-6) was studied in 15 allogeneic and 11 autologous marrow transplantation patients. After transplantation, HHV-6 was isolated from the peripheral blood mononuclear cells of 12 of 26 patients (6 allogeneic and 6 autologous). All isolates were variant B. Eleven of 26 and 12 of 19 patients showed salivary shedding of HHV-6 DNA before and after transplantation, respectively. The antibody titer increased in 7 of 26 patients. Thus, 23 of 26 patients showed evidence of active HHV-6 infection either by virus isolation, salivary shedding, or increases in antibody titers. The fraction of saliva specimens positive in 19 patients was negatively associated with their antibody titers (P= .005). The proportion of cultures positive increased after transplantation (P = .007). Sinusitis was associated with HHV-6 isolation in autologous recipients (P= .002). In allogeneic patients, active human cytomegalovirus infection was associated with HHV-6 isolation (P = .04). No association was observed between HHV-6 infection and GVHD, pneumonia, delay in engraftment, or marrow suppression. Of the 120 clinical events analyzed in 26 patients, HHV-6 was defined as a probable cause of 16 events in 9 patients based on the propinquity of HHV-6 activity and the clinical event plus the absence of other identified causes of the event.

Adult↗
PubMed1996

The simultaneous diversification of South American echimyid rodents (Hystricognathi) based on complete cytochrome b sequences.

Variation in the complete nucleotide sequence of the mitochondrial cytochrome b gene was examined for 32 individuals representing 12 supraspecific taxa of South American rodents of the family Echimyidae (Hystricognathi). Representative genera of four other New World hystricognath families, the Old World porcupine Hystrix, and the myomorph murid rodents Rattus and Mus were used as outgroups in phylogenetic reconstructions. Monopoly of the family Echimyidae is strongly supported, a result fully consistent with existing morphological and paleontological data relative to the taxa examined. However, relationships among most supraspecific taxa within the family are poorly resolved. Poor resolution appears not to result from lack of data, but to a rapid, nearly simultaneous divergence of most Recent taxa. Generic groupings that are moderately to strongly supported include the tree rats of the Brazilian Atlantic Forest (Nelomys) and Amazonia (Echimys, Makalata) and the Amazonian arboreal spiny rats Mesomys and Lonchothrix. However, the two subgenera of the terrestrial spiny rats, Proechimys, do not form a monophyletic unit, and elevation of the Atlantic Forest Trinomys to generic status is supported. The genus Hoplomys is closely related to Proechimys (sensu stricto), a finding supported by other molecular data.

Animals↗
PubMed1996

Hierarchical genetic structure and gene flow in three sympatric species of Amazonian rodents.

The population genetic structure of three species of Amazonian rodents (Oligoryzomys microtis, Oryzomys capito, and Mesomys hispidus) is examined for mtDNA sequence haplotypes of the cytochrome b gene by hierarchical analysis of variance and gene flow estimates based on fixation indices (NST) and coalescence methods. Species samples are from the same localities along 1000 km of the Rio Juruá in western Amazonian Brazil, but each species differs in important life history traits such as population size and reproductive rate. Average haplotype differentiation, hierarchical haplotype apportionment, and gene flow estimates are contrasted in discussing the current and past population structure. Two species exhibit isolation by distance patterns wherein gene flow is largely limited to geographically adjacent localities. Mesomys exhibits this pattern throughout its range along the river. More than 75% of haplotype variation is apportioned among localities and regions, and estimates of Nm for pair-wise comparisons are nearly always less than 1. Oligoryzomys shows weak isolation by distance, but only over the largest geographical distances. Nm values for this species are nearly always above 1 and most (about 80%) of haplotype variation is contained within local populations. In contrast, Oryzomys exhibits no genetic structure throughout its entire distribution; Nm values average 17 and nearly 90% of the total haplotype variance is contained within local populations. Although gene flow estimates are high, the pattern of Nm as a function of geographical distance suggests that this species experienced a more recent invasion of the region and is still in genetic disequilibrium under its current demographic conditions.

Animals↗
PubMed1996

Evaluation of immunoassays for detection of antibodies to human herpesvirus 7.

An enzyme immunoassay (EIA), an immunoblot assay (IB), and an indirect immunofluorescence assay were developed for detection of human herpesvirus 7 (HHV-7) antibodies in human serum. Cross-absorption studies with EIA or IFA using HHV-7 and human herpesvirus 6 (HHV-6) antigens indicated that most human sera contain cross-reactive HHV-6 and HHV-7 antibodies and that the degree of cross-reactivity varies between individual serum specimens. Inhibition of homologous antibody activity by absorption with heterologous virus ranged from 0 to 57% by EIA. However, for every sample tested, absorption with homologous virus removed more activity than did heterologous virus. An 89-kDa protein was identified as an HHV-7-specific serologic marker by IB. Activity to this protein was not removed by absorption with HHV-6 antigen. Of the three assays, the EIA was the most sensitive (94%), while the IB was the most specific (94%). Approximately 80% of specimens collected from German adults and children older than 2 years were positive for HHV-7 antibodies by these assays.

Adolescent↗
PubMed1996

Riverine barriers and gene flow in Amazonian saddle-back tamarins.

We describe patterns of genotypic and phenotypic variation in saddle-back tamarin (Saguinus fuscicollis) populations along the central and upper Rio Juruá, western Brazilian Amazonia. The genetic data are sequence haplotypes of the mitochondrial cytochrome b gene; phenotypic data are pelage colour variants that define sharply demarcated subspecies of this extremely variable tamarin species. We show that gene flow occurs between adjacent subspecies, but that this phenomenon is restricted to the headwater section of the river, which is consistent with expectations from the riverine barrier hypothesis. In this model, the major first-order tributaries of the Amazon form effective barriers to dispersal, with between-bank gene flow limited to the narrowed sections of headwater streams and parallel divergence increasing along both banks from the headwaters to the mouth of a given river. In meandering rivers such as the Rio Juruá, we suggest passive transfer through river channel dynamics as the main mechanism permitting genetic contact between populations on opposite banks of the river. Finally, we argue that in the case of plant and animal species that are largely restricted to unflooded (terra firme) forests, such as tamarins, seasonally flooded (várzea) forest can operate as a critical additional barrier to between-bank gene flow.

Animals↗
PubMed1995

Detection of Epstein-Barr virus-specific antibodies by means of baculovirus-expressed EBV gp125.

A major antigenic component of the Epstein-Barr virus viral capsid antigen (VCA) complex is the glycoprotein, gp125. Baculovirus-expressed gp125 reacted with Epstein-Barr virus IgG antibodies in a panel of 44 serum specimens using an immunoblot assay with over 97% sensitivity, and 100% specificity as compared to anti-VCA reactivity in an immunofluorescence assay. In addition, no evidence for cross-reactivity was seen in reactions with members of a panel of human serum specimens of known reactivity with each of the other known human herpesviruses. Thus, baculovirus-expressed gp125 should prove a stable platform on which new Epstein-Barr virus-specific serodiagnostic tests can be built.

Animals↗
PubMed1995

Production and reutilization of an extracellular phosphatidylinositol catabolite, glycerophosphoinositol, by Saccharomyces cerevisiae.

Phosphatidylinositol catabolism in Saccharomyces cerevisiae is known to result in the formation of extracellular glycerophosphoinositol (GroPIns). We now report that S. cerevisiae not only produces but also reutilizes extracellular GroPIns and that these processes are regulated in response to inositol availability. A wild-type strain uniformly prelabeled with [3H] inositol displayed dramatically higher extracellular GroPIns levels when cultured in medium containing inositol than when cultured in medium lacking inositol. This difference in extracellular accumulation of GroPIns in response to inositol availability was shown to be a result of both regulated production and regulated reutilization. In a strain in which a negative regulator of phospholipid and inositol biosynthesis had been deleted (an opi1 mutant), this pattern of extracellular GroPIns accumulation in response to inositol availability was altered. An inositol permease mutant (itr1 itr2), which is unable to transport free inositol, was able to incorporate label from exogenous glycerophospho [3H]inositol, indicating that the inositol label did not enter the cell solely via the transporters encoded by itr1 and itr2. Kinetic studies of a wild-type strain and an itr1 itr2 mutant strain revealed that at least two mechanisms exist for the utilization of exogenous GroPIns: an inositol transporter-dependent mechanism and an inositol transporter-independent mechanism. The inositol transporter-independent pathway of exogenous GroPIns utilization displayed saturation kinetics and was energy dependent. Labeling studies employing [14C]glycerophospho[3H] inositol indicated that, while GroPIns enters the cell intact, the inositol moiety but not the glycerol moiety is incorporated into lipids.

Biological Transport, Active↗
PubMed1994

The Saccharomyces cerevisiae PLB1 gene encodes a protein required for lysophospholipase and phospholipase B activity.

Several enzymes with lysophospholipase/phospholipase B activity have been described from the budding yeast Saccharomyces cerevisiae. In vitro, these enzymes are capable of hydrolyzing all phospholipids that can be extracted from yeast cells. Two forms of the enzyme have been isolated from plasma membranes and a third from culture supernatants and the periplasmic space, but their biological roles have not been determined. These highly glycosylated enzymes were reported to have very similar catalytic properties but differed with respect to apparent molecular weight. We isolated a gene from S. cerevisiae, encoding a protein predicted to share 45% amino acid sequence identity with phospholipase B from Penicillium notatum. This yeast gene, designated PLB1, was mapped to the left arm of chromosome VIII. No residual lysophospholipase/phospholipase B activity was detected upon assay of extracts or culture supernatants of a plb1 delta mutant. Thus, either the PLB1 gene encodes all of the previously detected isoforms of phospholipase B or its gene product is required for their expression or activation. Deletion of PLB1 did not result in any apparent phenotypic defect, suggesting either that we failed to identify the growth conditions that would betray such a defect or that Plb1p is functionally redundant with another protein, whose activity has gone undetected. A plb1 delta mutant released wild-type levels of the soluble phosphatidylinositol metabolite glycerophosphoinositol into the growth medium but released greatly reduced levels of the corresponding phosphatidylcholine and phosphatidylethanolamine metabolites. These results indicate that PLB1 is principally responsible for the production of the deacylation products of phosphatidylcholine and phosphatidylethanolamine but not phosphatidylinositol.

Amino Acid Sequence↗