Poleward Movement Research Articles

Age-specific differences in the seasonal spatial distribution of butterfish (Peprilus triacanthus)

The spatial distribution of butterfish (Peprilus triacanthus) in the Northwest Atlantic Ocean was investigated using a suite of spatial indicators based on Northeast Fisheries Science Center spring and fall bottom trawl survey data, 1982–2013. In the spring, ages 2 and 3 were found farther northeast and deeper than age 1 butterfish, while in the fall, age 3 butterfish were found farther northeast and deeper than ages 0 and 1. There was no significant northward movement of butterfish in spring or fall over the course of either time-series. However, there was a significant increase in the area occupied by ages 1–3 in the spring that was correlated with surface temperature. This illustrates that responses to climate change may be manifested as range expansions, rather than poleward movement of the centre of gravity (i.e. bivariate weighted mean location of the population). Two changes were observed over the course of the fall time series, both for ages 1 and 2: increased spatial dispersion; and a decrease in depth. The former result would have been masked, while the latter would have been erroneously generalized to all age classes, if an age-specific analysis had not been done. This study demonstrates the importance of an age-based and seasonal analysis. It is also shown how a spatial distribution analyses can inform stock assessments by providing insights into diverging survey indices and availability to surveys in general. Similarly, spatial distribution analyses can be used to verify the spatial equilibrium assumption for the calculation of biological reference points.

Patterns and drivers of megabenthic secondary production on the Barents Sea shelf

Megabenthos plays a major role in the overall energy flow on Arctic shelves, but information on megabenthic secondary production on large spatial scales is scarce. Here, we estimated for the first time megabenthic secondary production for the entire Bar- ents Sea shelf by applying a species-based empirical model to an extensive dataset from the joint Norwe- gianRussian ecosystem survey. Spatial patterns and relationships were analyzed within a GIS. The environ- mental drivers behind the observed production pattern were identified by applying an ordinary least squares regression model. Geographically weighted regression (GWR) was used to examine the varying relationship of secondary production and the environment on a shelf- wide scale. Significantly higher megabenthic second- ary production was found in the northeastern, season- ally ice-covered regions of the Barents Sea than in the permanently ice-free southwest. The environmental parameters that significantly relate to the observed pat- tern are bottom temperature and salinity, sea ice cover, new primary production, trawling pressure, and bottom current speed. The GWR proved to be a versatile tool for analyzing the regionally varying relationships of benthic secondary production and its environmental drivers (R 2 = 0.73). The observed pattern indicates tight pelagicbenthic coupling in the realm of the productive marginal ice zone. Ongoing decrease of winter sea ice extent and the associated poleward movement of the seasonal ice edge point towards a distinct decline of benthic secondary production in the northeastern Barents Sea in the future.

The Poleward Motion of Extratropical Cyclones from a Potential Vorticity Tendency Analysis

Abstract The poleward propagation of midlatitude storms is studied using a potential vorticity (PV) tendency analysis of cyclone-tracking composites, in an idealized zonally symmetric moist GCM. A detailed PV budget reveals the important role of the upper-level PV and diabatic heating associated with latent heat release. During the growth stage, the classic picture of baroclinic instability emerges, with an upper-level PV to the west of a low-level PV associated with the cyclone. This configuration not only promotes intensification, but also a poleward tendency that results from the nonlinear advection of the low-level anomaly by the upper-level PV. The separate contributions of the upper- and lower-level PV as well as the surface temperature anomaly are analyzed using a piecewise PV inversion, which shows the importance of the upper-level PV anomaly in advecting the cyclone poleward. The PV analysis also emphasizes the crucial role played by latent heat release in the poleward motion of the cyclone. The latent heat release tends to maximize on the northeastern side of cyclones, where the warm and moist air ascends. A positive PV tendency results at lower levels, propagating the anomaly eastward and poleward. It is also shown here that stronger cyclones have stronger latent heat release and poleward advection, hence, larger poleward propagation. Time development of the cyclone composites shows that the poleward propagation increases during the growth stage of the cyclone, as both processes intensify. However, during the decay stage, the vertical alignment of the upper and lower PV anomalies implies that these processes no longer contribute to a poleward tendency.

Nonlinear Zonal Wind Response to ENSO in the CMIP5 Models: Roles of the Zonal and Meridional Shift of the ITCZ/SPCZ and the Simulated Climatological Precipitation*

Abstract The observed equatorial Pacific zonal wind response during El Niño tends to be stronger than during La Niña. Most global coupled climate models in phase 5 of CMIP (CMIP5) exhibit such nonlinearity, although weaker than observed. The wind response nonlinearity can be reproduced by driving a linear shallow water atmospheric model with a model’s or the observed precipitation anomalies, which can be decomposed into two main components: the zonal and meridional redistribution of the climatological precipitation. Both redistributions contribute comparably to the total rainfall anomalies, whereas the zonal redistribution plays the dominant role in the zonal wind response. The meridional redistribution component plays an indirect role in the nonlinear wind response by limiting the zonal redistribution during La Niña and thus enhancing the nonlinearity in the wind response significantly. During La Niña, the poleward movement of the ITCZ/SPCZ reduces the equatorial zonal-mean precipitation available for the zonal redistribution and its resulting zonal wind response. Conversely, during El Niño, the equatorward movement of the ITCZ and SPCZ do not limit the zonal redistribution of precipitation. The linear equatorial zonal wind response to ENSO is found to have a significant linear correlation with the equatorial central Pacific climatological precipitation and SST among the CMIP5 models. However, no linear correlation is found between the nonlinear equatorial zonal wind response and the climatological precipitation.

Climate and stock influences on the spread and locations of catches in the northeast Atlantic mackerel fishery

The poleward movements of northeast Atlantic (NEA) mackerel (Scomber scombrus) catches, possibly linked to climate change, are causing a major international disagreement over quotas. We present an analysis of spatially resolved catch data from 1977 to 2013 that shows how a northward shift is only part of the change in the fishery. There was a 30-yr trend for declining catches per ICES rectangle (0.5° latitude by 1°-degree longitude) until 2011–2013. Catches also moved further offshore, to areas of deeper waters. Segmented regressions suggested discontinuities in the temporal pattern of change in catch-related variables. In particular, the number of ICES rectangles fished rose sharply around 1987. Generalized additive models (GAMs) suggest that much of the movement of fishing activity to areas of deeper water can be associated with variation in the Atlantic Multidecadal Oscillation (AMO) and the North Atlantic Oscillation (NAO). GAM models had a lower predictive error than linear or simple autoregressive models of change in catch-related variables. Although climate indices can be linked to some of the changes in catch, it may be difficult to extrapolate future patterns in the catch: some of the GAM smoothers are non-linear, and the oceanographic processes linked to climate index values are not homogenous across the area occupied by mackerel. A practical implication of the reported changes in catch since 1977 is that vessels are now reportedly fishing further offshore, which has implications for fuel consumption and profitability of the fishery.

TPX2 phosphorylation maintains metaphase spindle length by regulating microtubule flux.

A steady-state metaphase spindle maintains constant length, although the microtubules undergo intensive dynamics. Tubulin dimers are incorporated at plus ends of spindle microtubules while they are removed from the minus ends, resulting in poleward movement. Such microtubule flux is regulated by the microtubule rescue factors CLASPs at kinetochores and depolymerizing protein Kif2a at the poles, along with other regulators of microtubule dynamics. How microtubule polymerization and depolymerization are coordinated remains unclear. Here we show that TPX2, a microtubule-bundling protein and activator of Aurora A, plays an important role. TPX2 was phosphorylated by Aurora A during mitosis. Its phospho-null mutant caused short metaphase spindles coupled with low microtubule flux rate. Interestingly, phosphorylation of TPX2 regulated its interaction with CLASP1 but not Kif2a. The effect of its mutant in shortening the spindle could be rescued by codepletion of CLASP1 and Kif2a that abolished microtubule flux. Together we propose that Aurora A-dependent TPX2 phosphorylation controls mitotic spindle length through regulating microtubule flux.

Kinetochore-independent chromosome segregation driven by lateral microtubule bundles.

During cell division, chromosomes attach to spindle microtubules at sites called kinetochores, and force generated at the kinetochore-microtubule interface is the main driver of chromosome movement. Surprisingly, kinetochores are not required for chromosome segregation on acentrosomal spindles in Caenorhabditis elegans oocytes, but the mechanism driving chromosomes apart in their absence is not understood. In this study, we show that lateral microtubule-chromosome associations established during prometaphase remain intact during anaphase to facilitate separation, defining a novel form of kinetochore-independent segregation. Chromosome dynamics during congression and segregation are controlled by opposing forces; plus-end directed forces are mediated by a protein complex that forms a ring around the chromosome center and dynein on chromosome arms provides a minus-end force. At anaphase onset, ring removal shifts the balance between these forces, triggering poleward movement along lateral microtubule bundles. This represents an elegant strategy for controlling chromosomal movements during cell division distinct from the canonical kinetochore-driven mechanism.

Expertly validated models and phylogenetically-controlled analysis suggests responses to climate change are related to species traits in the order lagomorpha.

Climate change during the past five decades has impacted significantly on natural ecosystems, and the rate of current climate change is of great concern among conservation biologists. Species Distribution Models (SDMs) have been used widely to project changes in species’ bioclimatic envelopes under future climate scenarios. Here, we aimed to advance this technique by assessing future changes in the bioclimatic envelopes of an entire mammalian order, the Lagomorpha, using a novel framework for model validation based jointly on subjective expert evaluation and objective model evaluation statistics. SDMs were built using climatic, topographical, and habitat variables for all 87 lagomorph species under past and current climate scenarios. Expert evaluation and Kappa values were used to validate past and current models and only those deemed ‘modellable’ within our framework were projected under future climate scenarios (58 species). Phylogenetically-controlled regressions were used to test whether species traits correlated with predicted responses to climate change. Climate change is likely to impact more than two-thirds of lagomorph species, with leporids (rabbits, hares, and jackrabbits) likely to undertake poleward shifts with little overall change in range extent, whilst pikas are likely to show extreme shifts to higher altitudes associated with marked range declines, including the likely extinction of Kozlov’s Pika (Ochotona koslowi). Smaller-bodied species were more likely to exhibit range contractions and elevational increases, but showing little poleward movement, and fecund species were more likely to shift latitudinally and elevationally. Our results suggest that species traits may be important indicators of future climate change and we believe multi-species approaches, as demonstrated here, are likely to lead to more effective mitigation measures and conservation management. We strongly advocate studies minimising data gaps in our knowledge of the Order, specifically collecting more specimens for biodiversity archives and targeting data deficient geographic regions.

Holocene shifts of the southern westerlies across the South Atlantic

AbstractThe southern westerly winds (SWW) exert a crucial influence over the world ocean and climate. Nevertheless, a comprehensive understanding of the Holocene temporal and spatial evolution of the SWW remains a significant challenge due to the sparsity of high‐resolution marine archives and appropriate SWW proxies. Here we present a north‐south transect of high‐resolution planktonic foraminiferal oxygen isotope records from the western South Atlantic. Our proxy records reveal Holocene migrations of the Brazil‐Malvinas Confluence (BMC), a highly sensitive feature for changes in the position and strength of the northern portion of the SWW. Through the tight coupling of the BMC position to the large‐scale wind field, the records allow a quantitative reconstruction of Holocene latitudinal displacements of the SWW across the South Atlantic. Our data reveal a gradual poleward movement of the SWW by about 1–1.5° from the early to the mid‐Holocene. Afterward, variability in the SWW is dominated by millennial scale displacements on the order of 1° in latitude with no recognizable longer‐term trend. These findings are confronted with results from a state‐of‐the‐art transient Holocene climate simulation using a comprehensive coupled atmosphere‐ocean general circulation model. Proxy‐inferred and modeled SWW shifts compare qualitatively, but the model underestimates both orbitally forced multimillennial and internal millennial SWW variability by almost an order of magnitude. The underestimated natural variability implies a substantial uncertainty in model projections of future SWW shifts.

Polar electrostatic forces drive poleward chromosome motions.

Recent experiments revealing nanoscale electrostatic force generation at kinetochores for chromosome motions have prompted models for interactions between positively charged molecules in kinetochores and negative charge at and near the plus ends of microtubules. A clear picture of how kinetochores and centrosomes establish and maintain a dynamic coupling to microtubules for force generation during the complex motions of mitosis remains elusive. The molecular cell biology paradigm requires that specific molecules, or molecular geometries, for polar force generation be identified. While progress has been made regarding explanations of kinetochore-based chromosome motility, molecular machinery for chromosome poleward movements at centrosomes has yet to be identified. The present work concerns polar generation of poleward force in terms of experimentally known electric charge distributions at microtubule minus ends and centrosomes interacting over nanometer distances.

Saturn’s auroral morphology and field-aligned currents during a solar wind compression

On 21–22 April 2013, during a coordinated auroral observing campaign, instruments onboard Cassini and the Hubble Space Telescope observed Saturn’s aurora while Cassini traversed Saturn’s high latitude auroral field lines. Signatures of upward and downward field-aligned currents were detected in the nightside magnetosphere in the magnetic field and plasma measurements. The location of the upward current corresponded to the bright ultraviolet auroral arc seen in the auroral images, and the downward current region was located poleward of the upward current in an aurorally dark region. Within the polar cap magnetic field and plasma fluctuations were identified with periods of ∼20 and ∼60min. The northern and southern auroral ovals were observed to rock in latitude in phase with the respective northern and southern planetary period oscillations. A solar wind compression impacted Saturn’s magnetosphere at the start of 22 April 2013, identified by an intensification and extension to lower frequencies of the Saturn kilometric radiation, with the following sequence of effects: (1) intensification of the auroral field-aligned currents; (2) appearance of a localised, intense bulge in the dawnside (04–06 LT) aurora while the midnight sector aurora remained fainter and narrow; and (3) latitudinal broadening and poleward contraction of the nightside aurora, where the poleward motion in this sector is opposite to that expected from a model of the auroral oval’s usual oscillation. These observations are interpreted as the response to tail reconnection events, initially involving Vasyliunas-type reconnection of closed mass-loaded magnetotail field lines, and then proceeding onto open lobe field lines, causing the contraction of the polar cap region on the night side.

Centrosome dynamics as a source of chromosomal instability.

Accurate segregation of duplicated chromosomes between two daughter cells depends on bipolar spindle formation, a metaphase state in which sister kinetochores are attached to microtubules emanating from opposite spindle poles. To ensure bi-orientation, cells possess surveillance systems that safeguard against microtubule-kinetochore attachment defects, including the spindle assembly checkpoint and the error correction machinery. However, recent developments have identified centrosome dynamics--that is, centrosome disjunction and poleward movement of duplicated centrosomes--as a central target for deregulation of bi-orientation in cancer cells. In this review, we discuss novel insights into the mechanisms that underlie centrosome dynamics and discuss how these mechanisms are perturbed in cancer cells to drive chromosome mis-segregation and advance neoplastic transformation.

Photoperiod constraints on tree phenology, performance and migration in a warming world.

Increasing temperatures should facilitate the poleward movement of species distributions through a variety of processes, including increasing the growing season length. However, in temperate and boreal latitudes, temperature is not the only cue used by trees to determine seasonality, as changes in photoperiod provide a more consistent, reliable annual signal of seasonality than temperature. Here, we discuss how day length may limit the ability of tree species to respond to climate warming in situ, focusing on the implications of photoperiodic sensing for extending the growing season and affecting plant phenology and growth, as well as the potential role of photoperiod in controlling carbon uptake and water fluxes in forests. We also review whether there are patterns across plant functional types (based on successional strategy, xylem anatomy and leaf morphology) in their sensitivity to photoperiod that we can use to predict which species or groups might be more successful in migrating as the climate warms, or may be more successfully used for forestry and agriculture through assisted migration schemes.

The Extended Cycle of Solar Activity and the Sun’s 22-Year Magnetic Cycle

The Sun has two characteristic migrations of surface features—the equatorward movement of sunspots and the poleward movement of high-latitude prominences. The first of these migrations is a defining aspect of the 11-yr Schwabe cycle and the second is a tracer of the process that culminates in solar polarity reversal, signaling the onset of the 22-yr magnetic cycle on the Sun. Zonal flows (torsional oscillations of the Sun’s differential rotation) have been identified for both of these migrations. Helioseismology observations of these zonal flows provide support for the extended (>11-yr cycle) of solar activity and offer promise of a long-term precursor for predicting the amplitude of the Schwabe cycle. We review the growth of observational evidence for the extended and 22-yr magnetic cycles and discuss: (1) the significance of latitude ∼50∘ on the Sun; (2) the “over-extended” cycle; and (3) the outlook for solar cycle 25.

Historical analogues of the recent extreme minima observed in the Atlantic meridional overturning circulation at 26°N

Observations of the Atlantic meridional overturning circulation (AMOC) by the RAPID 26°N array show a pronounced minimum in the northward transport over the winter of 2009/10, substantially lower than any observed since the initial deployment in April 2004. It was followed by a second minimum in the winter of 2010/2011. We demonstrate that ocean models forced with observed surface fluxes reproduce the observed minima. Examining output from five ocean model simulations we identify several historical events which exhibit similar characteristics to those observed in the winter of 2009/10, including instances of individual events, and two clear examples of pairs of events which happened in consecutive years, one in 1969/70 and another in 1978/79. In all cases the absolute minimum, associated with a short, sharp reduction in the Ekman component, occurs in winter. AMOC anomalies are coherent between the Equator and 50°N and in some cases propagation attributable to the poleward movement of the anomaly in the wind field is observed. We also observe a low frequency (decadal) mode of variability in the anomalies, associated with the North Atlantic Oscillation (NAO). Where pairs of events have occurred in consecutive years we find that atmospheric conditions during the first winter correspond to a strongly negative Arctic Oscillation (AO) index. Atmospheric conditions during the second winter are indicative of a more regional negative NAO phase, and we suggest that this persistence is linked to re-emergence of sea surface temperature anomalies in the North Atlantic for the events of 1969/70 and 2009/10. The events of 1978/79 do not exhibit re-emergence, indicating that the atmospheric memory for this pair of events originates elsewhere. Observation of AO patterns associated with cold winters over northwest Europe may be indicative for the occurrence of a second extreme winter over northwest Europe.

Direct kinetochore-spindle pole connections are not required for chromosome segregation.

Segregation of genetic material occurs when chromosomes move to opposite spindle poles during mitosis. This movement depends on K-fibers, specialized microtubule (MT) bundles attached to the chromosomes' kinetochores. A long-standing assumption is that continuous K-fibers connect every kinetochore to a spindle pole and the force for chromosome movement is produced at the kinetochore and coupled with MT depolymerization. However, we found that chromosomes still maintained their position at the spindle equator during metaphase and segregated properly during anaphase when one of their K-fibers was severed near the kinetochore with a laser microbeam. We also found that, in normal fully assembled spindles, K-fibers of some chromosomes did not extend to the spindle pole. These K-fibers connected to adjacent K-fibers and/or nonkinetochore MTs. Poleward movement of chromosomes with short K-fibers was uncoupled from MT depolymerization at the kinetochore. Instead, these chromosomes moved by dynein-mediated transport of the entire K-fiber/kinetochore assembly. Thus, at least two distinct parallel mechanisms drive chromosome segregation in mammalian cells.

Climate change and Southern Ocean ecosystems I: how changes in physical habitats directly affect marine biota.

Antarctic and Southern Ocean (ASO) marine ecosystems have been changing for at least the last 30 years, including in response to increasing ocean temperatures and changes in the extent and seasonality of sea ice; the magnitude and direction of these changes differ between regions around Antarctica that could see populations of the same species changing differently in different regions. This article reviews current and expected changes in ASO physical habitats in response to climate change. It then reviews how these changes may impact the autecology of marine biota of this polar region: microbes, zooplankton, salps, Antarctic krill, fish, cephalopods, marine mammals, seabirds, and benthos. The general prognosis for ASO marine habitats is for an overall warming and freshening, strengthening of westerly winds, with a potential pole-ward movement of those winds and the frontal systems, and an increase in ocean eddy activity. Many habitat parameters will have regionally specific changes, particularly relating to sea ice characteristics and seasonal dynamics. Lower trophic levels are expected to move south as the ocean conditions in which they are currently found move pole-ward. For Antarctic krill and finfish, the latitudinal breadth of their range will depend on their tolerance of warming oceans and changes to productivity. Ocean acidification is a concern not only for calcifying organisms but also for crustaceans such as Antarctic krill; it is also likely to be the most important change in benthic habitats over the coming century. For marine mammals and birds, the expected changes primarily relate to their flexibility in moving to alternative locations for food and the energetic cost of longer or more complex foraging trips for those that are bound to breeding colonies. Few species are sufficiently well studied to make comprehensive species-specific vulnerability assessments possible. Priorities for future work are discussed.

The dynamics of microtubule minus ends in the human mitotic spindle.

During mitotic spindle assembly, γ-tubulin ring complexes (γTuRCs) nucleate microtubules at centrosomes, around chromosomes, and, by interaction with augmin, from pre-existing microtubules. How different populations of microtubules are organized to form a bipolar spindle is poorly understood, in part because we lack information on the dynamics of microtubule minus ends. Here we show that γTuRC is associated with minus ends of non-centrosomal spindle microtubules. Recruitment of γTuRC to spindles occurs preferentially at pole-distal regions, requires nucleation and/or interaction with minus ends, and is followed by sorting of minus-end-bound γTuRC towards the poles. Poleward movement of γTuRC exceeds k-fibre flux, involves the motors dynein, HSET (also known as KIFC1; a kinesin-14 family member) and Eg5 (also known as KIF11; a kinesin-5 family member), and slows down in pole-proximal regions, resulting in the accumulation of minus ends. Thus, in addition to nucleation, γTuRC actively contributes to spindle architecture by organizing microtubule minus ends.

B56-PP2A regulates motor dynamics for mitotic chromosome alignment.

Proper alignment of duplicated chromosomes at the metaphase plate involves both motor-driven chromosome movement and the functional and physical end-on connection (K-fiber formation) between the kinetochore and the plus-end of microtubules. The B56 family of protein phosphatase 2A (PP2A) regulatory subunits (B56-PP2A), through their interaction with the mitotic checkpoint protein BUBR1, are required for proper chromosome alignment, but the underlying mechanism(s) has remained elusive. Here, we show that B56-PP2A promotes chromosome alignment primarily by balancing chromosome movement towards the metaphase plate, rather than by directly establishing stable K-fibers. Notably, the poleward movement of chromosomes in cells depleted of the B56 family can be rescued by depletion of HSET (also known as kinesin-14 or KIFC1), a major minus-end-directed motor protein. Strikingly, K-fiber formation can be restored if chromosome movement to the metaphase plate is rescued in B56-depleted cells. Furthermore, the B56-BUBR1 interaction is required for promoting motor-driven chromosome movement towards the metaphase plate. Thus, we propose that B56-PP2A functions in mitotic chromosome alignment by balancing chromosome movement towards the metaphase plate, which is essential for the subsequent establishment of stable and functional kinetochore-microtubule attachments, and mitotic exit.

Stability of kinetochore‐microtubule attachment and the role of different KMN network components in Drosophila

Kinetochores bind spindle microtubules and also act as signaling centers that monitor this interaction. Defects in kinetochore assembly lead to chromosome missegregation and aneuploidy. The interaction between microtubules and chromosomes involves a conserved super-complex of proteins, known as the KNL1Mis12Ndc80 (KMN) network, composed by the KNL1 (Spc105), Mis12, and Ndc80 complexes. Previous studies indicate that all components of the network are required for kinetochore-microtubule attachment and all play relevant functions in chromosome congression, biorientation, and segregation. Here, we report a comparative study addressing the role of the different KMN components using dsRNA and in vivo fluorescence microscopy in Drosophila S2 cells allowing us to suggest that different KMN network components might perform different roles in chromosome segregation and the mitotic checkpoint signaling. Depletion of different components results in mostly lateral kinetochore-microtubule attachments that are relatively stable on depletion of Mis12 or Ndc80 but very unstable after Spc105 depletion. In vivo analysis on depletion of Mis12, Ndc80, and to some extent Spc105, shows that lateral kinetochore-microtubule interactions are still functional allowing poleward kinetochore movement. We also find that different KMN network components affect differently the localization of spindle assembly checkpoint (SAC) proteins at kinetochores. Depletion of Ndc80 and Spc105 abolishes the mitotic checkpoint, whereas depletion of Mis12 causes a delay in mitotic progression. Taken together, our results suggest that Mis12 and Ndc80 complexes help to properly orient microtubule attachment, whereas Spc105 plays a predominant role in the kinetochore-microtubule attachment as well as in the poleward movement of chromosomes, SAC response, and cell viability.