Directional selection effects on patterns of phenotypic (co)variation in wild populations.

Phenotypic (co)variation is a prerequisite for evolutionary change, and understanding how (co)variation evolves is of crucial importance to the biological sciences. Theoretical models predict that under directional selection, phenotypic (co)variation should evolve in step with the underlying adaptive landscape, increasing the degree of correlation among co-selected traits as well as the amount of genetic variance in the direction of selection. Whether either of these outcomes occurs in natural populations is an open question and thus an important gap in evolutionary theory. Here, we documented changes in the phenotypic (co)variation structure in two separate natural populations in each of two chipmunk species (Tamias alpinus and T. speciosus) undergoing directional selection. In populations where selection was strongest (those of T. alpinus), we observed changes, at least for one population, in phenotypic (co)variation that matched theoretical expectations, namely an increase of both phenotypic integration and (co)variance in the direction of selection and a re-alignment of the major axis of variation with the selection gradient.

Exposure to climate change drives stability or collapse of desert mammal and bird communities.

High exposure to warming from climate change is expected to threaten biodiversity by pushing many species toward extinction. Such exposure is often assessed for all taxa at a location from climate projections, yet species have diverse strategies for buffering against temperature extremes. We compared changes in species occupancy and site-level richness of small mammal and bird communities in protected areas of the Mojave Desert using surveys spanning a century. Small mammal communities remained remarkably stable, whereas birds declined markedly in response to warming and drying. Simulations of heat flux identified different exposure to warming for birds and mammals, which we attribute to microhabitat use. Estimates from climate projections are unlikely to accurately reflect species' exposure without accounting for the effects of microhabitat buffering on heat flux.

Movement therapy without moving - First results on isometric movement training for post-stroke rehabilitation of arm function.

This study explores the use of isometric movement training for arm rehabilitation after stroke. The aim of this approach is to enhance movement skill even when the person training is not moving. This is accomplished by deceptively displaying virtual motions, exploiting known cross-modal sensory interactions between vision and proprioception. This approach can be advantageous in situations where actual movement is prohibitive due to weakness, spasticity, instability, or unsafe conditions. We present early insights on usability of and tolerance to this training approach and quantitative results that can power future clinical trials.

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.

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.

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.

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.

Robot-amplified manual exploration improves load identification.

We tested how manual exploration with anisotropic loading (Viscosity-Only (negative), Inertia-Only, or Combined-Load) influenced skill transfer to the isolated inertial load. Intact subjects (N=39) performed manual exploration with an anisotropic load before evaluation with prescribed circular movements. Combined-Load resulted in lower error (6.89±3.25%) compared to Inertia-Only (8.40±4.32%) and Viscosity-Only (8.17±4.13%) according to radial deviation analysis (% of trial mean radius). An analysis of sensitivity to load variation in normal and catch trials reveals performance differences were likely due to changes in feedforward mass compensation. Analysis of exploration movement revealed higher average speeds (12.0%) and endpoint forces (22.9%) with Combined-Load exploration compared to Inertia-Only. Our findings suggest that free movements amplified by negative viscosity can enhance the ability to identify changes in inertial loading.

Geomyid evolution: the historical, selective, and random basis for divergence patterns within and among species.

Patterns of variation in life history, ecological distribution, genetic and morphological differentiation, and speciation of pocket gophers, family Geomyidae, have been examined in the context of the genetic demography of local populations. Emphasis has been placed on the structure of local breeding populations, dispersal potential leading to effective gene flow, and the influence of patchy distributions due to the availability of suitable soils. The focus of this paper is on those factors contributing to differentiation among geographic segments of species, or among different species--that is, to those processes responsible for converting phenotypically expressed variation within populations to that differentiating among them.

B-chromosome systems in the pocket mouse, Perognathus baileyi: meiosis and C-band studies.

The heterochromatin characteristics and meiotic behavior of the B-chromosome system of the pocket mouse, Perognathus baileyi, and described. B-chromosomes are associated both with a meiotic accumulation mechanism and with an increase in average chiasma frequency in the A-chromosome set in males. Three morphological classes of B-chromosomes are recognizable, and the mechanisms of origin of each are discussed.

Molecular evidence for mating asymmetry and female choice in a pocket gopher (Thomomys) hybrid zone.

This paper presents circumstantial evidence that the mating system of the North American pocket gophers (Rodentia: Geomyidae) is a promiscuous one, with female choice at its base. A molecular marker (a length variant in the mitochondrial Control region [D-loop]) is used to show mating asymmetry in a hybrid zone between the species Thomomys bottae and Thomomys townsendii in north-eastern California. All hybrids result from a bottae mother x townsendii father cross. Because of significant differences in body size and resulting burrow diameter, bottae females must have actively sought their respective townsendii mates for the asymmetry in mating to have occurred, signalling female choice in these subterranean mammals that are otherwise characterized by exclusive-use territories, skewed adult sex ratio in favour of females, and high variance in male reproductive success.

The phosphoinositol sphingolipids of Saccharomyces cerevisiae are highly localized in the plasma membrane.

To investigate the vital function(s) of the phosphoinositol-containing sphingolipids of Saccharomyces cerevisiae, we measured their intracellular distribution and found these lipids to be highly localized in the plasma membrane. Sphingolipids were assayed in organelles which had been uniformly labeled with [3H]inositol or 32P and by chemical measurements of alkali-stable lipid P, of long chain bases, and of very long chain fatty acids. We have developed an improved method for the preparation of plasma membranes which is based on the procedure of Duran et al. (Proc. Natl. Acad. Sci. USA 72:3952-3955, 1975). On the basis of marker enzyme and DNA assays carried out with a number of preparations, the plasma membranes contained less than 10% vacuolar membranes (alpha-mannosidase) and nuclei (DNA); the contamination by the endoplasmic reticulum (NADPH-cytochrome c reductase) varied from 0 to 20%. The plasma membrane preparations showed a 13-fold increase in the specific activity of vanadate-sensitive ATPase, compared with that in the homogenate, with a yield ranging from 50 to 80%. A comparison of the distribution of the ATPase with that of sphingolipids assayed by a variety of methods showed that 80 to 100% of the sphingolipids are localized in the plasma membrane; the sphingolipids constitute about 30% of the total phospholipid content of the plasma membrane. Minor amounts of sphingolipids that were found in isolated mitochondria and nuclei can be attributed to the presence of small amounts of plasma membrane in these fractions. These results suggest that one or more essential functions of these lipids is in the plasma membrane. Furthermore, sphingolipids may be useful chemical markers of the plasma membrane of S. cerevisiae.

Variation in mitochondrial cytochrome b sequence in natural populations of South American akodontine rodents (Muridae: Sigmodontinae).

A 401-bp fragment of the mitochondrial cytochrome b gene was sequenced from polymerase chain reaction-amplified products for 20 natural populations representing 12 species of South American akodontine rodents (Muridae). Variation among these taxa increased with their hierarchical position, from comparisons within local populations to those among different genera. Two individuals from the same local population differed by less than 1% sequence divergence. Sequence divergence among geographic samples within a species was 0.25%-8%, while that among species was 3%-21%. Comparisons of the akodontine sequences with that for the house mouse show 21%-25% sequence difference. A parsimony-based phylogenetic analysis of the data supports the placement of the taxon Microxus within Akodon (sensu stricto), of Bolomys just outside the Akodon cluster, and of Chroeomys as a separate genus quite distinct from the other members of this group. This phylogenetic hypothesis is identical to that determined from electrophoretic data but is quite divergent from the present taxonomy of the group.

Phosphatidylinositol phosphate, phosphatidylinositol bisphosphate, and the phosphoinositol sphingolipids are found in the plasma membrane and stimulate the plasma membrane H(+)-ATPase of Saccharomyces cerevisiae.

Several plasma membrane phospholipids have been studied for their ability to modulate the activity of the plasma membrane H(+)-ATPase of Saccharomyces cerevisiae. We show here that phosphatidylinositol phosphate (PIP), phosphatidylinositol bisphosphate (PIP2), and/or the phosphatidylinositol and PIP kinases are localized primarily in the plasma membrane. Previous in vivo studies with S. cerevisiae have shown that large, rapid, and reversible changes occur in the levels of PIP and PIP2 congruent with changes in cellular ATP levels. We demonstrate here that isolated plasma membranes exhibit the same changes in PIP and PIP2 content when they are supplied with or washed free of ATP. Using a mixed micellar assay we systematically studied the efficacy of the plasma membrane lipids in sustaining the activity of the plasma membrane H(+)-ATPase. We demonstrate for the first time that a number of plasma membrane glycerophospholipids effectively stimulate the ATPase, including PIP, PIP2, and cardiolipin. Phosphoinositol-containing sphingolipids, major components of the plasma membrane, are also shown to stimulate the ATPase at significantly lower levels than the glycerophospholipids and must also be considered as important effectors in vivo.

Genome evolution in pocket gophers (genus Thomomys). I. Heterochromatin variation and speciation potential.

A basic dichotomy exists in the amount and chromosomal position of constitutive heterochromatin (C-bands) in species of pocket gophers, genus Thomomys. Members of the "talpoides-group" of species (e.g., T. talpoides and T. monticola) have C-bands restricted to the centromeric regions. These taxa are characterized by Robertsonian patterns of karyotypic evolution. In contrast, species within the "bottae-group" are characterized by extensive amounts of heterochromatin, placed as whole-arm and apparent whole-chromosome (T. bottae) or as large interstitial blocks (T. umbrinus). These species are characterized by extensive non-Robertsonian variation in karyotype, variation which may be expressed from local population polymorphism to between population or species polytypy. Within T. bottae, the number of whole-arm heterochromatic autosomes is inversely proportional to the number of uniarmed chromosomes in the complement, which ranges from 0 to 36 across the species populations. In all-biarmed karyotypic populations, upward to 60 percent of the linear length of the genome is composed of heterochromatin. Populations with extensive heterochromatin variation and those with similar amounts meet and hybridize freely in nature. The implications of these date for current ideas on the function of heterochromatin, particularly as related to speciation models, are discussed.

Genome evolution in pocket gophers (genus Thomomys). II. Variation in cellular DNA content.

Cellular DNA content (2 C-value) was measured by fluorescence flow cytometry of chromomycin-A3 stained spleen cells in 2 subgenera, 5 species, and 21 subspecies of pocket gophers (genus Thomomys). The data indicate that, in Thomomys: (1) interspecific variation is extensive but, while some congeneric species differ by as much as 230%, others are identical in C-value: (2) intraspecific differentiation can be extensive with C-values differing by as much as 35%; and (3) populations of the same subspecies with apparently similar karyotypes can differ significantly in C-value. The implications of these results for hypotheses of the "adaptive" significance of C-value variation and genome evolution are discussed.

Genome evolution in pocket gophers (genus Thomomys). III. Fluorochrome-revealed heterochromatin heterogeneity.

Heterochromatin is a dominant component of the genome in the bottae group of the pocket gopher genus Thomomys, having had a major role in the karyotypic evolution of member species. Heterochromatin characteristics of two subspecies of T. bottae and one of T. umbrinus were examined with fluorochrome dyes identifying presumptive GC- and AT-rich regions. In two karyotype forms of T. b. fulvus and in T. umbrinus, chromatin that fluoresces brightly with chromomycin A3 is also C-band positive, although not all heterochromatin fluoresces. However, in T. b. bottae, only euchromatic regions fluoresce brightly with chromomycin. Fluorescence patterns produced with DAPI are the reverse of the chromomycin banding in all karyotypic forms. Heterochromatin in these taxa is thus highly differentiated, exhibiting heterogeneity in staining characteristics, and presumably in underlying DNA sequences, both across the genome within a given chromosomal complement as well as among the different karyotypic races and species of the bottae group of pocket gophers.