Specific Migration Patterns Research Articles

Exploring the Control Circuit of Cell Migration by Mathematical Modeling

We have developed a top-down, rule-based mathematical model to explore the basic principles that coordinate mechanochemical events during animal cell migration, particularly the local-stimulation-global-inhibition model suggested originally for chemotaxis. Cells were modeled as a shape machine that protrudes or retracts in response to a combination of local protrusion and global retraction signals. Using an optimization algorithm to identify parameters that generate specific shapes and migration patterns, we show that the mechanism of local stimulation global inhibition can readily account for the behavior of Dictyostelium under a large collection of conditions. Within this collection, some parameters showed strong correlation, indicating that a normal phenotype may be maintained by complementation among functional modules. In addition, comparison of parameters for control and nocodazole-treated Dictyostelium identified the most prominent effect of microtubules as regulating the rates of retraction and protrusion signal decay, and the extent of global inhibition. Other changes in parameters can lead to profound transformations from amoeboid cells into cells mimicking keratocytes, neurons, or fibroblasts. Thus, a simple circuit of local stimulation-global inhibition can account for a wide range of cell behaviors. A similar top-down approach may be applied to other complex problems and combined with molecular manipulations to define specific protein functions.

Periodic, spatially structured matrix model for the study of anchovy ( Engraulis encrasicolus) population dynamics in N Aegean Sea (E. Mediterranean)

The development of a periodic, spatially structured population matrix model for the study of North Aegean Sea anchovy population structure and dynamics is presented on the basis of its life-cycle, and the ecosystem environmental features. System heterogeneity and species life-cycle leaded to model development on seasonal scale and sub-regional basis, incorporating survival, fecundity and migration rates. Several methodological aspects concerning the periodic dynamics on a seasonal basis combined with the existence of spatial heterogeneity and age—season specific migration patterns are examined and discussed. Special attention is devoted to a possible inflow of recruits originated from Black Sea Waters, introducing a “source-sink” effect in the model and resulting in reducible projection matrices. The model also accounts for a possible outflow from the study area, structurally implemented by another virtual “sink” sub-area incorporation. A first attempt was made to calibrate the model using parameters provided by older studies and original data provided by the ANREC project focused on the anchovy—environment interactions and carried out in the area. Then the model was used to check the efficiency of various fishing limitations in space and/or time and the results confirmed the importance of the fishing activity over the spawning grounds.

Dynamic in-lake spawning migrations by female sockeye salmon

Abstract – Precise homing by salmon to natal habitats is considered the primary mechanism in the evolution of population-specific traits, yet few studies have focused on this final phase of their spawning migration. We radio tagged 157 female sockeye salmon (Oncorhynchus nerka) as they entered Lake Clark, Alaska, and tracked them every 1–10 days to their spawning locations. Contrary to past research, no specific shoreline migration pattern was observed (e.g., clockwise) nor did fish enter a tributary unless they spawned in that tributary. Tributary spawning fish migrated faster (mean = 4.7 km·day−1, SD = 2.7, vs. 1.6 km·day−1, SD = 2.1) and more directly (mean linearity = 0.8, SD = 0.2, vs. 0.4, SD = 0.2) than Lake Clark beach spawning fish. Although radio-tagged salmon migrated to within 5 km of their final spawning location in an average of 21.2 days (SD = 13.2), some fish migrated five times the distance necessary and over 50 days to reach their spawning destination. These results demonstrate the dynamic nature of this final phase of migration and support studies indicating a higher degree of homing precision by tributary spawning fish.

Dynamic in‐lake spawning migrations by female sockeye salmon

Abstract – Precise homing by salmon to natal habitats is considered the primary mechanism in the evolution of population‐specific traits, yet few studies have focused on this final phase of their spawning migration. We radio tagged 157 female sockeye salmon (Oncorhynchus nerka) as they entered Lake Clark, Alaska, and tracked them every 1–10 days to their spawning locations. Contrary to past research, no specific shoreline migration pattern was observed (e.g., clockwise) nor did fish enter a tributary unless they spawned in that tributary. Tributary spawning fish migrated faster (mean = 4.7 km·day−1, SD = 2.7, vs. 1.6 km·day−1, SD = 2.1) and more directly (mean linearity = 0.8, SD = 0.2, vs. 0.4, SD = 0.2) than Lake Clark beach spawning fish. Although radio‐tagged salmon migrated to within 5 km of their final spawning location in an average of 21.2 days (SD = 13.2), some fish migrated five times the distance necessary and over 50 days to reach their spawning destination. These results demonstrate the dynamic nature of this final phase of migration and support studies indicating a higher degree of homing precision by tributary spawning fish.

Site‐specific expression of CD11b and SIRPα (CD172a) on dendritic cells: implications for their migration patterns in the gut immune system

Dendritic cells (DC) in the intestinal tract play a major role in directing the mucosal immune system towards tolerance or immunity. We analyzed whether different mucosal DC subsets in pigs have specific functions, localizations, or migration patterns in vivo. Therefore, we collected physiologically migrating DC by pseudo-afferent cannulation of the intestinal duct in eight Gottingen minipigs. Lymph DC were phenotypically and functionally characterized and compared to DC found on histological sections of porcine small intestine and mesenteric lymph nodes (MLN). Four different DC subpopulations were detected. Lamina propria (LP) DC were mainly CD11b(+) signal regulatory protein alpha (SIRPalpha)(+), DC in Peyer's patches were mainly CD11b(-)/SIRPalpha(+) in subepithelial domes and CD11b(-)/SIRPalpha(-) in interfollicular regions, whereas MLN DC were largely CD11b(+)/SIRPalpha(-). Of these four subsets, only the CD11b(+)/SIRPalpha(+) DC and the CD11b(+)/SIRPalpha(-) DC were present in lymph. This suggests that DC migration to MLN largely originates from the LP. Lymph DC expressed high levels of MHC class II and costimulatory molecules and had a low capacity for FITC-dextran uptake, indicating a mature phenotype. However, lymph DC did not induce PBMC proliferation in MLR, and migration was not significantly influenced by mucosal antigen application.

Fluoride distribution in water and the governing factors of environment in arid north-west China

In arid areas of north-west China, fluorides occur predominantly as NaF and KF. They are fairly ubiquitous in both natural surface waters such as rivers, lakes and reservoirs, and in ground-water. Abundant fluoride sources, a relatively closed hydrological network, and the dry climate of the arid inland basin provide favorable conditions to the dissolution, migration and enrichment of fluoride. The formation of inland river systems has led to specific fluoride migration and distribution patterns. This has resulted in three main hydro-chemical zones: (1) leaching-runoff; (2) runoff-evaporation and (3) dissolution-evaporative enrichment zones. In Cretaceous and lower Pleistocene lake deposit depressions and on the margin of desert areas, F−is not only enriched in ground water compared to surface waters, but also shows a vertical zoning, i.e. the greater the depth the greater the F−content. F−enrichment and deficiency are closely related to the hydro-chemical characteristics of the body of water. Generally, low-SO2−4and low-Ca2+alkaline waters environments, e.g. Cl−•–HCO−3–Na+or HCO−3–Na+waters, are favorable to the dissolution and enrichment of F−.

Priority‐Setting Tool Applied to Canada's Landbirds Based on Concern and Responsibility for Species

Abstract: As a contribution to Partners in Flight–Canada, the Canadian Wildlife Service developed a ranking system to help set priorities for landbird species. Two complementary species lists were generated: one with scores for “concern” representing vulnerability and population trend, and one for “responsibility” for regionally characteristic fauna. The concern score gave equal weight to vulnerability, a composite score based on abundance and breadth of range, and population trend, because its purpose was to give early warning of potential problems. Responsibility scores were scale‐free and were assigned for the season in which the species is most abundant. Other systems for identifying species of concern may be more appropriate for other jurisdictions or organisms, but the responsibility ranking is widely applicable. This system is a coarse filter that generates preliminary ranks; additional information should be considered in deciding how to allocate scarce resources for conservation. Unrefined results are nonetheless useful for a variety of purposes, as illustrated by the scores for Canadian landbirds. About 25% of Canada's high‐responsibility species are also of high concern. These high‐concern species are not associated with specific habitats or migration patterns. Conservation of species ranking high on concern and responsibility merits cooperation with the United States and Mexico in particular. The scores identified improved monitoring as a priority conservation activity for Canada.

Denaturing gradient gel electrophoresis analysis for the detection of point mutations in the Chlamydia trachomatis major outer-membrane protein gene.

Fifty clinical strains of Chlamydia trachomatis were studied by denaturing gradient gel electrophoresis (DGGE) of bacterial DNA amplified by the polymerase chain reaction (PCR). The strains belonged to the three most commonly encountered serovars in developed countries--D, E and F. Six reference strains, including the serovar Da strain, were also studied. The DNA sequences explored encompassed the four variable domains (VDs) of omp1, the gene encoding the major outer-membrane protein (MOMP). The corresponding regions in the MOMP contain the species-, subspecies- and serovar-specific epitopes. The four distinct serovars were clearly differentiated by specific migration pattern. No sequence variations were observed among strains of serovar F. However, variant strains within serovars D and E were found, which exhibited migration patterns different from those of the reference strains and these were sequenced directly. According to the observed sequence variations, serovar D strains could be divided into three stable representative groups (D, D1 and D2). Two variants were identified among serovar E strains. No biological differences were observed for the variant strains in terms of growth properties, ecology or pathogenicity. All the nucleotide substitutions detected in the VDs were non-synonymous at the protein level and, for the serovar D strains, could account for differences identified by specific monoclonal antibodies. These substitutions could be involved in antigenic drift, driven by the immune pressure of the host, leading to the emergence of serovariants. The data may explain, in part, chlamydial infection recurrences and could have critical implications for developing rational vaccine strategies.

Zooplankton spatial patterns in two lakes with contrasting fish community structure

Horizontal and temporal patterns in crustacean zooplankton communities were analyzed in two small, oligotrophic lakes which were morphologically and chemically similar, but had contrasting fish communities. Ranger Lake was dominated by two bass species and the planktivores numbered 1200 ind. ha−1. There were significant differences in the distribution of zooplankton taxa and size classes between sampling stations. In Ranger Lake, the smallest size classes were more abundant at the deeper stations and the larger individuals were more abundant at the shallower stations. In Mouse Lake, the smaller individuals were more common at the shallow stations and the larger individuals were more common at the deeper stations. These differences suggest medium scale patterns induced by vectorial forces, but modified by species specific migration patterns. We tested the hypothesis that horizontal heterogeneity should be influenced by planktivore density and found that none of the taxa showed significant between-lake differences in the variance-mean regressions. We also tested the hypothesis that larger taxa should be more heterogeneous and we found that cladocerans were more heterogeneous than copepods and nauplii. In terms of sampling methodology our data suggest that the between-station variability was so high that a single mid-lake sample would certainly lead to completely unacceptable errors in the estimation of population densities and biomasses.

β2‐Adrenergic stimulation causes detachment of natural killer cells from cultured endothelium

Physical exercise, mental stress, or infusion of beta-adrenergic agonists result in an increase in the number of natural killer (NK) cells in the peripheral circulation. In view of the specific migration pattern of NK cells in vivo, it has been suggested that these cells may be released from the marginating pool in blood vessels. In the present report, the in vitro effect of catecholamines on the adhesion of NK cells to unstimulated human endothelial cells (EC) was characterized. Peripheral blood mononuclear cells were allowed to adhere to monolayers of EC, after which the adherent lymphocyte fraction was analyzed phenotypically by flow cytometry. NK cells were found to adhere preferentially to EC, a process that was reversed by the addition of various adrenergic agonists. Catecholamines selectively affected adhesion of NK cells and had no effect on T cell adhesion to EC, as was determined by the use of purified cell populations. Detachment of NK cells from EC could be achieved by short incubations (5 min) with epinephrine (EPI) and was concentration-dependent, with an ED50 of 2 x 10(-10)M. Using a panel of alpha- and beta-adrenergic agonists and antagonists, we show that the detachment of NK cells is mediated via beta 2-adrenergic receptors. In line with the lower affinity for beta 2-adrenergic receptors, norepinephrine was less effective than EPI in inducing detachment of NK cells from EC. Direct activation of adenylate-cyclase with forskolin gave similar results as observed with EPI, indicating that signaling through cAMP is necessary to induce detachment of NK cells from EC. The results of the present study lend support to the hypothesis that catecholamines, via beta 2-adrenergic receptors, can induce recruitment of NK cells from the marginating pool to the circulating pool, by changing the adhesive interactions between NK cells and EC.

Electrophoretic karyotyping of typical and atypical Candida albicans

Electrophoretic karyotypes of atypical isolates of Candida albicans, e.g., strains that were germ tube negative, failed to express proteinase activity, demonstrated low virulence for mice, formed hyperchlamydoconidia, produced hyperhyphae, or were sucrose negative (including the type strain of Candida stellatoidea), were compared with those of typical C. albicans. Karyotypes of whole-cell DNA of classical C. albicans examined with transverse alternating-field electrophoresis under specific conditions were composed of seven DNA bands with a specific migration pattern. Certain atypical strains and representatives of the three serotypes of C. stellatoidea produced discrete karyotypes with 5 to 10 bands. All isolates demonstrated a significant degree of DNA relatedness, suggesting their conspecificity. Densitometric tracings of DNA bands provided an objective and standardized method for comparing bands within the gels.

Diel Vertical Migrations by Juvenile Sockeye Salmon and the Antipredation Window

Diel migrations between habitats containing different levels of food abundance is a common phenomenon among marine organisms, both vertebrate and invertebrate. We hypothesize that in many cases this behavior constitutes a response to diel changes in the relationship between potential feeding rates and predation risks in the different habitats. For planktivores that locate their prey by sight (such as juvenile sockeye salmon) and that in turn are subject to predators that use sight to locate them, the diel time profiles of potential feeding rate and predation risk in near-surface waters may be determined largely by the relative densities of prey at the two trophic levels. A simple model of aquatic predation leads us to hypothesize the existence of brief "antipredation windows" for feeding at dawn and dusk. If this hypothesis is valid, then the optimal behavior for pelagic planktivores is to migrate into surface waters to feed during these two daily windows and to migrate to deeper, less illuminated waters during daylight hours. (Our model does not predict any specific nocturnal migration pattern.) Our arguments can also be used to predict optimal migration patterns for contact-feeding zooplankton subject to visual predation. The resulting predictions agree qualitatively with many observed patterns of diel vertical migration.

AFRICAN MIGRANTS IN NIGERIA

SummaryOwing to the regular alternation of wet and dry seasons and to the relatively simple arrangement of vegetation zones, migration is a well‐developed phenomenon in the northern tropics of Africa. Nigeria is well placed for its study. While a vast amount remains to be learned, a systematic treatment of the 672 Nigerian bird species shows that at least 126 of them are migrant. Species newly shown to be migratory include the sunbird Nectarinia pulchella, the bunting Fringillaria (Emberiza) tahapisi, and the sparrow Gymnoris (Petronia) dentata, and corroborative evidence is adduced for many more. New interpretations are placed on the movements of the bustard Neotis denhami, the Painted Snipe Rostratula benghalensis, and other species.Most families that are migrant in the temperate zone (e.g. storks, cuckoos, nightjars, hirundines) have several migrants among their tropical representatives, except flycatchers, thrushes, warblers and shrikes. Important tropical migrant families include the kingfishers and sunbirds.The following ecological correlates emerge:migration appears to be more important at lower than higher trophic levels in the ecosystem;only one primary lowland rain forest and one montane forest species migrate;95% of African migrants in Nigeria inhabit the five savanna zones, where the 120 migrants comprise 28% of the avifauna;most savanna migrants cross one, two or three vegetation zone boundaries; few are restricted within a single zone or cross four boundaries;twice as many savanna species are eurytopic (habitat‐tolerant) as stenotopic (habitat‐tied), and twice the proportion of eurytopic as stenotopic species are migrant;the majority of migrants move so as to avoid the winter drought in northern Nigeria (insectivores being little affected) and also the heaviest summer rains in southern savannas;migration is initiated by climatic factors such as rains, dry desert winds, etc.Three to six Nigerian species cross the Equator, but the stork Anastomus lamelligerus is shown to breed in Nigeria and the Chad basin and may not be a trans‐equatorial migrant. A quail, a crake, a coucal and five cuckoos have space‐time distribution patterns (motograms) in Nigeria that suggest equatorial migration.Motograms figured for 60 species show great variation. Nearly all land‐bird migrants move with the progression of the sun and the inter‐tropical front, north in spring and south in autumn. The basic pattern is thus a summer wet‐season range at higher latitude than the winter dry‐season range, and specific patterns vary according to the absolute and relative latitudinal limits af each season, and to speed and dates of migration.Comparison of congeneric migrants having different breeding seasons or motogram patterns suggests that a specific migration pattern is fixed by ecological necessity, and reproduction occurs at that time in the year when the species is stationary longest. Breeding seasons may span migration periods, leading to two‐stage early‐rains migration in e.g. the kingfisher Halcyon leucocephala.Water‐bird migrations are complicated by opportunist breeding and responses to floods and changing water levels in rivers. A few species move with the typical land‐bird pattern; others concentrate at perennial marshes in arid northern savannas, and may disperse in all directions from the few west African breeding stations.