Overlap Zone Research Articles

Mitotic motors and chromosome segregation: the mechanism of anaphase B

Anaphase B spindle elongation plays an important role in chromosome segregation. In the present paper, we discuss our model for anaphase B in Drosophila syncytial embryos, in which spindle elongation depends on an ip (interpolar) MT (microtubule) sliding filament mechanism generated by homotetrameric kinesin-5 motors acting in concert with poleward ipMT flux, which acts as an 'on/off' switch. Specifically, the pre-anaphase B spindle is maintained at a steady-state length by the balance between ipMT sliding and ipMT depolymerization at spindle poles, producing poleward flux. Cyclin B degradation at anaphase B onset triggers: (i) an MT catastrophe gradient causing ipMT plus ends to invade the overlap zone where ipMT sliding forces are generated; and (ii) the inhibition of ipMT minus-end depolymerization so flux is turned 'off', tipping the balance of forces to allow outward ipMT sliding to push apart the spindle poles. We briefly comment on the relationship of this model to anaphase B in other systems.

A review of the Acanthopagrus bifasciatus species complex (Pisces: Sparidae) from the Indian Ocean, with redescriptions of A. bifasciatus (Forsskål 1775) and A. catenula (Lacepède 1801) YUKIO IWATSUKI (Japan) & PHILLIP C. HEEMSTRA (South Africa)

The Doublebar Seabream, Acanthopagrus bifasciatus (Forsskål 1775) with two conspicuous vertical black bars across the head has long been recognized as a distinctive species from the Red Sea and Western Indian Ocean. Two distinct colour patterns are associated with two allopatric populations except southern Oman and Somalia which appears to be a zone of overlap: a northern population (Red Sea, through Persian Gulf, to Pakistan) with dorsal and caudal fins immaculate yellow; and a southern population (east coast of Africa from the Horn of Africa to South Africa, Madagascar, and Mascarene Islands) having the dorsal fin with a wide black margin and caudal fin rear margin with a narrow black edge (and both black margins disappearing with growth in specimens over 30 cm SL). Both populations resulted in the two valid species: A. bifasciatus for the northern population and A. catenula (Lacepède 1801) for the southern population. Nominal species (junior synonyms) of the two species are discussed.

Taxonomic recommendations for British birds: seventh report

Taxonomic recommendations for British birds: seventh report

System size, energy, centrality and pseudorapidity dependence of charged-particle density in Au+Au and Cu+Cu collisions at RHIC

Charged particle pseudorapidity distributions are presented from the PHOBOS experiment at RHIC, measured in Au+Au and Cu+Cu collisions at $\sqrt {s_{NN} } $ =19.6, 22.4, 62.4, 130 and 200 GeV, as a function of collision centrality. The presentation includes the recently analyzed Cu+Cu data at 22.4 GeV. The measurements were made by the same detector setup over a broad range in pseudorapidity, |η| < 5.4, allowing for a reliable systematic study of particle production as a function of energy, centrality and system size. Comparing Cu+Cu and Au+Au results, we find that the total number of produced charged particles and the overall shape (height and width) of the pseudorapidity distributions are determined by the number of nucleon participants, N part. Detailed comparisons reveal that the matching of the shape of the Cu+Cu and Au+Au pseudorapidity distributions over the full range of η is better for the same N part/2A value than for the same N part value, where A denotes the mass number. In other words, it is the geometry of the nuclear overlap zone, rather than just the number of nucleon participants that drives the detailed shape of the pseudorapidity distribution and its centrality dependence.

Determination of Inadvertent Atrial Capture During Para-Hisian Pacing

Inadvertent capture of the atrium will lead to spurious results during para-Hisian pacing. We sought to establish whether the stimulation-to-atrial electrogram interval at the proximal coronary sinus (stim-PCS) or high right atrium (stim-HRA) could signal inadvertent atrial capture. Para-Hisian pacing with and without intentional atrial capture was performed in 31 patients. Stim-HRA and stim-PCS intervals were measured with atrial capture, His plus para-Hisian ventricular (H+V) capture, and para-Hisian ventricular (V) capture alone. The mean stim-HRA interval was significantly shorter with atrial capture (66 ± 18 ms) than with H+V (121 ± 27 ms, P < 0.001) or V capture alone (174 ± 38 ms, P < 0.001). The mean stim-PCS interval was significantly shorter with atrial capture (51 ± 16 ms) than with H+V (92 ± 22 ms, P<0.001) or V capture alone (146 ± 33 ms, P < 0.001). A stim-PCS < 60 ms (stim-HRA < 70 ms) was observed only with atrial capture. A stim-PCS >90 ms (stim-HRA >100 ms) was observed only in the absence of atrial capture. A stim-HRA of < 85 ms was highly specific and stim-PCS of < 85 ms highly sensitive at identifying atrial capture. Stim-HRA intervals of 75 to 97 ms and stim-PCS intervals of 65 to 88 ms were observed with either atrial, His, or para-Hisian ventricular capture without atrial capture. In this overlap zone, all patients demonstrated a stim-PCS or stim-HRA interval prolongation of at least 20 ms when the catheter was advanced to avoid deliberate atrial pacing. The QRS morphology was of limited value in distinguishing atrial capture due to concurrent ventricular or H+V capture, as observed in 20 of 31 (65%) patients. Stim-PCS and stim-HRA intervals can be used to monitor for inadvertent atrial capture during para-Hisian pacing. A stim-PCS < 60 ms (or stim-HRA < 70 ms) and stim-PCS > 90 ms (or stim-HRA > 100 ms) were observed only with and without atrial capture, respectively, but there was significant overlap between these values. Deliberate atrial capture and loss of capture reliably identifies atrial capture regardless of intervals.

Genetic Barcode RFLP Analysis of the Nelson's and Saltmarsh Sparrow Hybrid Zone

Abstract Hybridization between Saltmarsh Sparrow (Ammodramus caudacutus) and Nelson's Sparrow (A. nelsoni) has been documented in areas where the two species occur sympatrically, increasing the difficulty of accurate species identification. We developed a DNA barcoding restriction fragment length polymorphism (RFLP) test to discriminate between Nelson's Sparrows and Saltmarsh Sparrows and applied it to 426 putative Saltmarsh Sparrows sampled from Maine to New York, USA. All individuals were identified in the field as Saltmarsh Sparrows based on morphology, but 34 (8%) had Nelson's specific mitochondrial DNA, indicating they were of hybrid origin. This discrepancy in morphological and genetic data highlights the difficulties associated with accurate field identification and may hinder conservation efforts by confounding attempts to identify and monitor “pure” populations. Mitochondrial DNA of Nelson's Sparrow was prevalent at the most southern point of the previously documented overlap zone and was also fo...

Coexistence patterns of two invasive thistle species, Carduus nutans and C. acanthoides, at three spatial scales

To better understand the competitive processes involved in invasion by congeners, we examine coexistence patterns of two invasive species, Carduus nutans and C. acanthoides, at three spatial scales. A roadside survey of 5 × 5 km blocks in a previously identified overlap zone provided information about the regional scale. At smaller scales, we surveyed four fields of natural co-occurrence, quantifying the spatial patterns at the field scale by randomly placed 1 × 1 m quadrats and at the smallest scale by detailing plant position within the quadrats. The patterns observed are strikingly different at the different scales. At the regional scale, there is positive local autocorrelation in both species but negative cross-correlation between them, consistent with previous surveys. However, at the field scale, there is positive local autocorrelation in both species, and we generally see a positive association between the two species. At the plot scale, when excluding areas of joint absence, there is again a negative association between the two species. This pattern can also be seen at the field scale when excluding plots with joint absence. These results suggest that, at the scale of a field, the strongest factor determining location is aggregation in favorable habitats, which is a stronger force than the competition-induced segregation evidenced at small scales. Lottery competition for spatially aggregated safe sites thus appears to drive the patterns observed at the field scale, while the regional scale pattern may be a result of restricted natural dispersal and invasion history.

Spatial and temporal interactions of sympatric mountain lions in Arizona

Spatial and temporal interactions among individual members of populations can have direct applications to habitat management of mountain lions (Puma concolor). Our objectives were to evaluate home range overlap and spatial/temporal use of overlap zones (OZ) of mountain lions in Arizona. We incorporated spatial data with genetic analyses to assess relatedness between mountain lions with overlapping home ranges. We recorded the space use patterns of 29 radio-collared mountain lions in Arizona from August 2005 to August 2008. We genotyped 28 mountain lions and estimated the degree of relatedness among individuals. For 26 pairs of temporally overlapping mountain lions, 18 overlapped spatially and temporally and eight had corresponding genetic information. Home range overlap ranged from 1.18% to 46.38% ( $$ \overline x = {\text{24}}.{\text{43}} $$ , SE = 2.96). Male–male pairs were located within 1 km of each other on average, 0.04% of the time, whereas male–female pairs on average were 3.0%. Two male–male pairs exhibited symmetrical spatial avoidance and two symmetrical spatial attractions to the OZ. We observed simultaneous temporal attraction in three male–male pairs and four male–female pairs. Individuals from Tucson were slightly related to one another within the population (n = 13, mean R = 0.0373 ± 0.0151) whereas lions from Payson (n = 6, mean R = −0.0079 ± 0.0356) and Prescott (n = 9, mean R = −0.0242 ± 0.0452) were not as related. Overall, males were less related to other males (n = 20, mean R = −0.0495 ± 0.0161) than females were related to other females (n = 8, mean R = 0.0015 ± 0.0839). Genetic distance was positively correlated with geographic distance (r 2 = 0.22, P = 0.001). Spatial requirements and interactions influence social behavior and can play a role in determining population density.

Anaphase B spindle dynamics in Drosophila S2 cells: Comparison with embryo spindles

BackgroundIn the Drosophila melanogaster syncytial blastoderm stage embryo anaphase B is initiated by a cell cycle switch in which the suppression of microtubule minus end depolymerization and spatial reorganization of the plus ends of outwardly sliding interpolar microtubules triggers spindle elongation. RNA interference in Drosophila cultured S2 cells may present a useful tool for identifying novel components of this switch, but given the diversity of spindle design, it is important to first determine the extent of conservation of the mechanism of anaphase B in the two systems.ResultsThe basic mechanism, involving an inverse correlation between poleward flux and spindle elongation is qualitatively similar in these systems, but quantitative differences exist. In S2 cells, poleward flux is only partially suppressed and the rate of anaphase B spindle elongation increases with the extent of suppression. Also, EB1-labelled microtubule plus ends redistribute away from the poles and towards the interpolar microtubule overlap zone, but this is less pronounced in S2 cells than in embryos. Finally, as in embryos, tubulin FRAP experiments revealed a reduction in the percentage recovery after photobleaching at regions proximal to the pole.ConclusionsThe basic features of the anaphase B switch, involving the suppression of poleward flux and reorganization of growing microtubule plus ends, is conserved in these systems. Thus S2 cells may be useful for rapidly identifying novel components of this switch. The quantitative differences likely reflect the adaptation of embryonic spindles for rapid, streamlined mitoses.

Of Least Concern? Range Extension by Rhesus Macaques (Macaca mulatta) Threatens Long-Term Survival of Bonnet Macaques (M. radiata) in Peninsular India

Rhesus and bonnet macaques are the 2 most common and widely distributed of the 8 macaque species of India. Rhesus macaques are widely distributed across southern and southeastern Asia, whereas bonnet macaques are restricted to peninsular India. We studied the current distributional limits of the 2 species, examined patterns of their coexistence in the interspecific border zones, and evaluated losses in the distributional range of bonnet macaques over the last 3 decades. Our results indicate that whereas rhesus macaques have extended their geographical range into the southern peninsula, bonnet macaques have been displaced from many areas within their former distributional range. The southern and the northern distributional limits for rhesus and bonnet macaques, respectively, currently run parallel to each other in the western part of the country, are separated by a large gap in central India, and converge on the eastern coast of the peninsula to form a distribution overlap zone. This overlap region is characterized by the presence of mixed-species troops, with pure troops of both species sometimes occurring even in close proximity to one another. The range extension of rhesus macaque—a natural process in some areas and a direct consequence of introduction by humans in other regions—poses grave implications for the endemic and declining populations of bonnet macaques in southern India.

Mysterious magno.

Fish have three otolithic endorgans that may be involved in auditory processing: saccule, lagena, and utricle. One or more of those endorgans may serve a vestibular (tilt) function. In general, vestibular inputs are distributed more ventrally than auditory inputs in the medulla of teleost fishes, but there are zones of overlap with the more dorsal auditory sites. The octaval nucleus magnocellularis (Magno) receives overlapping input from all three endorgans, but Magno is not part of the ascending auditory circuit in the oyster toadfish, Opsanus tau, and the sensory role of this nucleus is unknown. Extracellular recordings were conducted in Magno and neurobiotin was injected at successful recording sites to confirm location and label local cell types. Sinusoidal particle motion stimuli (50–303 Hz) were presented at multiple stimulus levels to assess relative sensitivity. The data indicate that some cells in Magno respond to auditory frequencies at biologically relevant levels. While these results are suggestive, many attempts to record auditory responses in the divisions of Magno were negative, indicating that only a subset of cells is auditory.

Chiroptera, mid-Calima River basin, Pacific slope of the Western Andes, Valle del Cauca, Colombia

The Calima River Basin is part of the Chocó Biogeográfico Ecoregion in the Pacific Coast of Colombia. Here, we compile a bat species checklist recorded for the Basin and describe the bat diversity patterns found in the mid-Calima Basin (the gradient from 300 – 1,400 m a.s.l.). The checklist comprises 55 bat species for the Basin. In the mid-Calima, 31 bat species occur (permanently or seasonally). Our results show complementary diversity patterns of bat assemblages living below and above 1,000 m. We also identified an overlap zone between 800 – 1,200 m a.s.l. where at least three pairs of sister species coexists. The sampled area is located where the Chocó and the Andes biogeographical regions are connected. The Calima River Basin has high bat richness, high variation in species composition along the elevational gradient, and harbours threatened and endemic species, highlighting its importance for conservation.

Dobzhansky’s rule and reinforcement of prezygotic reproductive isolation in zones of secondary contact

It is well known that closely related sympatric species are usually more different in characters involved in species recognition (e.g., in visual and acoustic signals) than allopatric species of the same evolutionary age. In this article I call this phenomenon Dobzhansky's rule in accordance with the name of the scientist who first discovered it. There are two alternative explanations for this pattern. Under hypothesis of reinforcement by Dobzhansky, these species-specific differences evolve in situ, exactly in zone of overlap between two populations. Under hypothesis of differential fusion by Templeton, the differences originate in geographically separated regions, and only those populations that have evolved such differences can persist in secondary sympatry. These evolutionary scenarios are significantly different. The scenario by Dobzhansky is an essentially sympatric model, in which natural selection reinforces pre-zygotic isolation between divergent populations by selecting against unfit hybrids. The scenario by Templeton is based on classic allopatric speciation model that consider the formation of reproductive isolation to be a by-product of divergent evolution. In this work we show that the sympatric distribution of sister taxa of Agrodiaetus butterflies strongly correlates with differences in male wing colour. We also use a new quantitative phylogenetic test to distinguish between the models by Dobzhansky and by Templeton and to demonstrate that the pattern observed is, most likely, the result of reinforcement.

Location and group size influence decisions in simulated intergroup encounters in banded mongooses

In social species that cooperatively defend territories the decision to retreat or attack in contests between groups is likely to depend on ecological and social factors. Previous studies have emphasized the importance of the encounter location or the size of competing groups on the outcome. In addition, the identity of the intruder, whether familiar or stranger, may also play a role. To test whether the same factors affect the resident group’s decisions already at the beginning of contests, we simulated intergroup encounters in banded mongooses (Mungos mungo). When spotting rival groups banded mongooses emit ‘‘screeching calls’’ which lead group members to bunch up. With playbacks of these calls, we tested how the groups’ response was affected by the following factors: 1) the location of the playback in relation to their territory (exclusive use vs. overlap); 2) the number of resident individuals; and 3) the origin of calls (neighbor vs. stranger) used. Subjects were more likely to approach the loudspeakers and arrive within 1 m of the speakers in the exclusive use zone than in the overlap zone. Moreover, larger groups tended to be more likely to move toward the loudspeakers and were also more likely to arrive there. The origin of calls used in the playbacks did not affect the groups’ responses. These findings exemplify the importance of the combined effect of location and group size on group decisions during impending intergroup contest. Key words: banded mongooses, group decision, group size, intergroup encounter, Mungos mungo, territory. [Behav Ecol]

Regionalization in Fine-Grid GFS MOS 6-h Quantitative Precipitation Forecasts

Abstract The recent emergence of the National Digital Forecast Database as the flagship product of the National Weather Service has resulted in an increased demand for forecast guidance products on fine-mesh grids. Unfortunately, fine-grid forecasts with geographically regionalized statistical models are usually plagued by nonmeteorological discontinuities at regional boundaries. This study treats the problem in a regionalized Global Forecast System (GFS)-based model output statistics (MOS) application that produces 6-h probabilistic quantitative precipitation forecasts (PQPFs) on a 4-km grid up to 192 h in advance. The technique involves incorporating areal overlap in the geographical regionalization and weighting multiple PQPFs in region-overlap zones. The degree of overlap ranges from about 20 km along meteorologically significant regional boundaries to about 150 km at quasi-arbitrary boundaries. The forecast-weighting constants for a grid point in an overlap zone vary in direct proportion to the distances to the closest associated regional boundaries. The application of the region-overlap and forecast-weighting techniques resulted in retention of sharp PQPF gradients along meteorologically significant regional boundaries and prevention of artificial discontinuities at quasi-arbitrary boundaries. The eradication of the discontinuities in the forecast patterns was achieved without sacrificing forecast skill. While the regionalization was customized for producing high-spatial-resolution 6-h PQPFs over the contiguous United States with a specialized gridded MOS application, the region-overlap and forecast-weighting techniques may have general applicability. Also, the quality of the 6-h PQPFs was not strongly dependent on customization of the regionalization.

Population structure, timing of divergence and contact between lineages in the endangered Hastings River mouse (Pseudomys oralis)

Management of threatened species requires understanding their genetic structure, particularly when the potential for cryptic lineages exists for species with a broad geographic range. The Hastings River mouse (Pseudomys oralis) is an endangered species found along the eastern coast of Australia. Previous genetic investigation revealed two mitochondrial lineages, separated by an unsampled gap in northern New South Wales. Using new samples from within this gap and from throughout the species’ range, we recovered two evolutionary lineages in agreement with previous studies. Importantly, we identified Washpool National Park as the area of lineage overlap, located at the northern limit of the Macleay–McPherson Overlap Zone. We confirmed limited haplotype sharing between localities, suggesting low levels of gene flow. Historical demography suggested recent population expansion and decline for Lineages I and II, respectively. Our dating estimates placed lineage divergence at 300 000–900 000 years ago, at the lower limit of percentage divergence between other sister species in Pseudomys. While these results support separate management consideration for each lineage, nuclear markers are needed to evaluate whether these lineages represent separate species. In addition, comparative phylogeographic analyses of divergence times among lineages of other species distributed across the Macleay–McPherson Overlap Zone are needed to determine the significance of this biogeographic contact zone for ecological communities in the region generally.

Coexistence and Habitat Preference of Two Honeyeaters and a Sunbird on Lombok, Indonesia

On the island of Lombok, Indonesia, three nectarivorous birds partially coexist: the two closely related and very similar Lichmera honeyeaters and a sunbird (Cinnyris jugularis). We investigated how these species segregated ecologically in areas where they coexisted by evaluating foraging visits and aggressive interactions at rich and poor nectar resources in different habitats (forest and open areas) along an altitudinal gradient (800–1600 m asl). The two honeyeaters were partially segregated by altitude. In the zone of overlap, Lichmera limbata dominated the richest forest resources, while Lichmera lombokia dominated the richest resources in open land. The sunbird, C. jugularis, was only observed in open habitats and mostly at poor resource patches. In the three-species community in open habitats a dominance hierarchy was apparent with L. lombokia as the superior species and C. jugularis as the inferior species. Studies on how segregated species interact in their transition zone can help us to understand interactions between otherwise ecologically segregated species.

Hybridisation and climate change: brown argus butterflies in Britain (Polyommatus subgenus Aricia)

Distribution changes brought about by climate change are likely to alter levels of hybridisation between related taxa, and may threaten some species. 2. Nuclear (Tpi) and mitochondrial (cytB) DNA sequence data give evidence for introgression between two related Polyommatus (subgenus Aricia) butterfly species in a 150-200 km wide overlap zone in northern England and North Wales. A history of hybridisation is evident from the mixture of genotypes present within this region: some populations contain southern-origin (Polyommatus agestis )m tDNA and northern-origin (Polyommatus artaxerxes) Tpi alleles, and many populations contain mixtures of Tpi alleles. 3. The timing of the original hybridisation is unknown, but could be immediately post-glacial or much more recent in origin. 4. Both species are now beginning to shift northwards, associated with recent climatic warming. 5. It is thus expected that anthropogenic climate change will unleash a new spate of hybridisation, potentially threatening the long-term survival of the northern species in Britain.

The Effect of Adhesive for Fillet on Stress in Weld-Bonded Joints

The influence of the fillet with different elastic modulus on the stress distributed in weld-bonded aluminum alloy single lap joint was investigated using elasto-plastic finite element method. The results show that the peak values of the stress along the mid-bondline at the points near the fillet edge were increased as the elastic modulus of the fillet increased. But at points near the both ends of the adherend in over lap zone as well as in the region of the nugget the peak stresses were decreased except longitudinal stress Sx. The peak value of Seqv decreased first, and then it increased again as the elastic modulus in fillet increased. The load-bearing capacity of the whole weld-bonded joints may be improved for the fillet with Adhesive B (825 MPa) for the relative high stress region in nugget was wider and the stress distribution in overlap zone was more uniform.

The Organization of the Forelimb Representation of the C57BL/6 Mouse Motor Cortex as Defined by Intracortical Microstimulation and Cytoarchitecture

The organization of forelimb representation areas of the monkey, cat, and rat motor cortices has been studied in depth, but its characterization in the mouse lags far behind. We used intracortical microstimulation (ICMS) and cytoarchitectonics to characterize the general organization of the C57BL/6 mouse motor cortex, and the forelimb representation in more detail. We found that the forelimb region spans a large area of frontal cortex, bordered primarily by vibrissa, neck, shoulder, and hindlimb representations. It included a large caudal forelimb area, dominated by digit representation, and a small rostral forelimb area, containing elbow and wrist representations. When the entire motor cortex was mapped, the forelimb was found to be the largest movement representation, followed by head and hindlimb representations. The ICMS-defined motor cortex spanned cytoarchitecturally identified lateral agranular cortex (AGl) and also extended into medial agranular cortex. Forelimb and hindlimb representations extended into granular cortex in a region that also had cytoarchitectural characteristics of AGl, consistent with the primary motor-somatosensory overlap zone (OL) characterized in rats. Thus, the mouse motor cortex has homologies with the rat in having 2 forelimb representations and an OL but is distinct in the predominance of digit representations.