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PubMed1999

Genetic evidence of an early exit of Homo sapiens sapiens from Africa through eastern Africa.

The out-of-Africa scenario has hitherto provided little evidence for the precise route by which modern humans left Africa. Two major routes of dispersal have been hypothesized: one through North Africa into the Levant, documented by fossil remains, and one through Ethiopia along South Asia, for which little, if any, evidence exists. Mitochondrial DNA (mtDNA) can be used to trace maternal ancestry. The geographic distribution and variation of mtDNAs can be highly informative in defining potential range expansions and migration routes in the distant past. The mitochondrial haplogroup M, first regarded as an ancient marker of East-Asian origin, has been found at high frequency in India and Ethiopia, raising the question of its origin. (A haplogroup is a group of haplotypes that share some sequence variations.) Its variation and geographical distribution suggest that Asian haplogroup M separated from eastern-African haplogroup M more than 50,000 years ago. Two other variants (489C and 10873C) also support a single origin of haplogroup M in Africa. These findings, together with the virtual absence of haplogroup M in the Levant and its high frequency in the South-Arabian peninsula, render M the first genetic indicator for the hypothesized exit route from Africa through eastern Africa/western India. This was possibly the only successful early dispersal event of modern humans out of Africa.

Africa↗

PubMed2003

Ontogeny of the human amygdala.

Data on the fetal development of the human amygdala is reviewed with special reference to major ontogenetic events. In the fifth gestational month, the inferior portion of the amygdala reveals cell-dense columns merging with the ganglionic eminence (proliferative zone) in Nissl-stained sections. These columns contain vimentin-positive fibers and can therefore be regarded as migrational routes. In the sixth and seventh months, distinct reorganization of the cytoarchitectonics takes place. The sequential occurrence of afferens can be visualized using anti-GAP-43; moreover, outgrowing axons appear to reach the periphery of the ganglionic eminence. The latter may thus represent an intermediate target for growing axons using anti-calbindin and anti-calretinin. Migrating and immature amygdaloid neurons can be shown in the fifth month. From the eighth month onwards, various nonpyramidal neurons and pyramidal neurons are immunolabeled. Transient expression of calretinin in pyramidal neurons is observed. When punctate calbindin and calretinin immunostaining in the fifth and eighth months is compared, distinct redistribution is observed. On the whole, it is apparent that the amygdala has reached a high degree of maturity in the eighth month. At this developmental stage, AKAP79, being enriched in postsynaptic densities, shows a characteristic nuclear-specific distribution pattern. The latter largely corresponds to the expression pattern of NMDAR1. Thus, AKAP79 may have a preference for anchoring enzymes to glutamate receptors. The aforementioned results provide a basis for investigations on subtle changes in pathologically altered material, such as hemorrhage, in the ganglionic eminence of preterm infants.

Amygdala↗

PubMed1999

Estimating the size of a transient population.

Migratory populations often stop over for short periods of time at predictable sites along their migration routes. These staging areas can be heavily used and are potentially critical to the survival of the migrants. This paper presents a method for estimating the number of individuals using such an area and their average residence time. The estimator is based on daily population estimates and records of repeat sightings of identifiable individuals. Its application is illustrated with observations on a population of migrating birds, some of which could be identified from bands that were readable from a distance.

Animals↗

PubMed2005

Assortative mating as a mechanism for rapid evolution of a migratory divide.

There have been numerous recent observations of changes in the behavior and dynamics of migratory bird populations, but the plasticity of the migratory trait and our inability to track small animals over large distances have hindered investigation of the mechanisms behind migratory change. We used habitat-specific stable isotope signatures to show that recently evolved allopatric wintering populations of European blackcaps Sylvia atricapilla pair assortatively on their sympatric breeding grounds. Birds wintering further north also produce larger clutches and fledge more young. These findings describe an important process in the evolution of migratory divides, new migration routes, and wintering quarters. Temporal segregation of breeding is a way in which subpopulations of vertebrates may become isolated in sympatry.

Animal Migration↗

PubMed2003

Risk of inter-river transmission of Gyrodactylus salaris by migrating Atlantic salmon smolts, estimated by Monte Carlo simulation.

The possibility of Gyrodactylus salaris infection of wild North Atlantic salmon Salmo salar spreading to new rivers poses a major threat in Norway. This freshwater parasite can survive for some time in brackish water, and it has been suggested that smolts leaving infected rivers could transport vital parasites to new rivers. A Monte Carlo simulation model was used to estimate the risk that infected smolts would ascend a new river. Data from an infected watercourse in Norway, where the salmon population is maintained constant by cultivation, were used. The model included information on prevalence of infection, hydrographical conditions, survival of G. salaris in brackish water, fish population characteristics, and smolt behaviour during seaward migration. The annual risk was estimated for 3 neighbouring rivers situated at different distances from the index river. For the nearest river, which shares the same brackish water zone with the index river, the model estimated an annual risk of 31% that at least 1 infected smolt would ascend this river. The results of the simulation were highly sensitive to the water salinity along the migration route. For the other rivers, the annual risk was lower than 0.5%. Risk was positively correlated with the number of fish leaving the index river, indicating control of this number as a possible tool in risk management.

Animal Migration↗

PubMed1983

Isthmic origin of neurons of the rat substantia nigra.

This study provides new data on the time of origin, the generation site and the migration route of the young neurons of the substantia nigra of the rat during embryogenesis. The neurons of the substantia nigra are generated on day 12, 13, 14 and 15 of gestation. They settle following a light spatiotemporal rostrocaudal gradient from day 12 to 15. The neurons of the substantia nigra are generated at two different points of the basal plate at the level of the fovea isthmi (meso-isthmic junction) and migrate in radial pattern as two definite streams toward the ventral mesencephalon. From this point they move rostralwards along the surface towards their final site. The main findings of this work are the disclosure that the neurons of the substantia nigra are generated in the region of the isthmus rhombencephali and that its cells do not migrate between existing cells of the mesencephalic tegmentum but first migrate ventralwards in a radial pattern and then rostrally towards their definite site. Numerous neurons of the basal mesencephalon and of the midline structures of the caudal mesencephalon are apparently derived from the region of the fovea isthmi.

Animals↗

PubMed1981

Migratory kinetics of Cuterebra fontinella (Diptera: cuterebridae) in the white-footed mouse, Peromyscus leucopus.

Larvae of the rodent botfly, Cuterebra fontinella, follow a consistent migration route thorough their natural host, the white-footed mouse, Peromyscus leucopus. Larvae that enter the eye or nares spend about 48 hr in the nasal cavity and then follow a caudally oriented path that leads through the nasal passage, trachea, thoracic and abdominal cavities, and ends in the subcutaneous tissues of the posteroventral abdominal region. Larvae that enter mice through the anus or by injection into the subcutaneous tissues of the back begin their migration from the trachea and from that point follow the usual path to the terminus.

Abdomen↗

PubMed1996

Migration and evolution of lesser long-nosed bats Leptonycteris curasoae, inferred from mitochondrial DNA.

We used sequence variation within 297 bp of control region mitochondrial DNA (mtDNA) amplified from 53 lesser long-nosed bats, Leptonycteris curasoae (Phyllostomidae: Glossophaginae) captured at 13 locations in south-western United States and Mexico and one site in Venezuela to infer population structure and possible migration routes of this endangered nectar- and fruit-eating species. Phylogenetic analysis using maximum parsimony and UPGMA confirmed species and subspecies distinctions within Leptonycteris and revealed two clades exhibiting 3% sequence divergence within the Mexican subspecies, L. c. yerbabuenae. Even though many roots contained L. c. yerbabuenae from both clades, weak population structure was detected both by a correlation between genetic differentiation, F(st), and geographical distance and by a cladistic estimate of the number of migration events required to align bat sequences with geographical location on maximum parsimony, as compared to random, trees. Three results suggest that L. c. yerbabuenae are more likely to migrate between sites along the Pacific coast of Mexico or along the foothills of the Sierra Madre Occidental than between these regions. (1) Seventeen of 20 bats which shared an identical sequence were captured up to 1800 km apart but within the same putative migration corridor. (2) Residuals from a regression of F(st) on distance were greater between than within these regions. (3) Fewer migration events were required to align bats with these two groups than expected from random assignment. We recommend analysing independent genetic data and monitoring bat visitation to roost sites during migration to confirm these postulated movements.

Animals↗

PubMed1997

Cell migration in the developing chick diencephalon.

We previously reported that retrovirally marked clones in the mature chick diencephalon were widely dispersed in the mediolateral, dorsoventral and rostrocaudal planes. The current study was undertaken to define the migration routes that led to the dispersion. Embryos were infected between stages 10 and 14 with a retroviral stock encoding alkaline phosphatase and a library of molecular tags. Embryos were harvested 2.5-5.5 days later and the brains were fixed and serially sectioned. Sibling relationships were determined following PCR amplification and sequencing of the molecular tag. On embryonic day 4, all clones were organized in radial columns spanning the neuroepithelium, which was composed primarily of a ventricular zone at this age. No tangential migration was seen in the ventricular zone. On embryonic day 5, most clones remained radial with many cells located in the ventricular zone; however, a few clones had cells migrating perpendicular to the radial column, in either a rostrocaudal or dorsoventral direction. The tangential migration began just beyond the basal limit of the ventricular zone. On embryonic days 6 and 7, many clones had cells migrating perpendicular to the radial column, which spanned from the ventricular to the pial surface. The migrating cells appeared to be aligned along axes that were perpendicular to the radial column. Using a combination of DiI tracing, immunohistochemistry and electron microscopy, we have determined that axonal tracts are present and are aligned with the migrating cells, suggesting that they support the non-radial cell migration. These data indicate that migration along pathways independent of radial glia occur outside of the ventricular zone in more than 50% of the clones in the chick diencephalon.

Animals↗

PubMed2002

The metapopulation dynamics of an infectious disease: tuberculosis in possums.

An SEI metapopulation model is developed for the spread of an infectious agent by migration. The model portrays two age classes on a number of patches connected by migration routes which are used as host animals mature. A feature of this model is that the basic reproduction ratio may be computed directly, using a scheme that separates topography, demography, and epidemiology. We also provide formulas for individual patch basic reproduction numbers and discuss their connection with the basic reproduction ratio for the system. The model is applied to the problem of spatial spread of bovine tuberculosis in a possum population. The temporal dynamics of infection are investigated for some generic networks of migration links, and the basic reproduction ratio is computed-its value is not greatly different from that for a homogeneous model. Three scenarios are considered for the control of bovine tuberculosis in possums where the spatial aspect is shown to be crucial for the design of disease management operations.

Animal Migration↗

PubMed2003

Role of Phox2b and Mash1 in the generation of the vestibular efferent nucleus.

The inner ear (vestibular and cochlear) efferent neurons are a group of atypical motor-like hindbrain neurons which innervate inner ear hair cells and their sensory afferents. They are born in the fourth rhombomere, in close association with facial branchial motor neurons, from which they subsequently part through a specific migration route. Here, we demonstrate that the inner ear efferents depend on Phox2b for their differentiation, behaving in that respect like hindbrain visceral and branchial motor neurons. We also show that the vestibular efferent nucleus is no longer present at its usual site in mice inactivated for the bHLH transcription factor Mash 1. The concomitant appearance of an ectopic branchial-like nucleus at the location where both inner ear efferents and facial branchial motor neurons are born suggests that Mash1 is required for the migration of a subpopulation of rhombomere 4-derived efferents.

Animals↗

PubMed1996

The invisible community: undocumented Polish workers in Athens.

"This article describes the development of an economic migration from Poland to Greece and the creation of a migrant community in Athens. It presents the development of a new migration route by political immigrants. It then describes how the Polish political emigrants heading for Greece in the mid-1980s established the pillar institutions which were inherited by the Polish undocumented workers who have followed, and which have served the latter well. The article proceeds to highlight the work milieu of the Polish undocumented workers in Athens, and discusses the role played by the ¿Polish church', i.e., the Roman Catholic church to which Poles were given access. It concludes by considering the future prospects of this migration and of the Polish migrant community in Greece."

Acculturation↗

PubMed2004

Ice Ages and the mitochondrial DNA chronology of human dispersals: a review.

Modern DNA, in particular maternally inherited mitochondrial DNA (mtDNA), is now routinely used to trace ancient human migration routes and to obtain absolute dates for genetic prehistory. The errors on absolute genetic dates are often large (50% or more) and depend partly on the inherent evolutionary signal in the DNA data, and partly on our imperfect knowledge of the DNA mutation rate. Despite their imprecision, the genetic dates do provide an independent, consistent and global chronology linking living humans with their ancestors. Combining this chronology with archaeological and climatological data, most of our own mtDNA studies during the past decade strongly imply a major role for palaeoclimate in determining conditions for prehistoric migrations and demographic expansions. This paper summarizes our interpretation of the genetic findings, covering the initial and modest spread of humans within Africa more than 100 ka, the striking re-expansion within Africa 60-80 ka, leading ultimately to the out-of-Africa migration of a single, small group which settled in Australia, Eurasia and America during windows of opportunity at least partly dictated by fluctuations in sea-levels and climatic conditions.

Climate↗

PubMed2005

[Studies on the spatial distribution and environmental factors of highly pathogenic avian influenza in Mainland China, using geographic information system technology].

OBJECTIVE: To analyze the spatial distribution of highly pathogenic avian influenza (HPAI) and to explore environmental factors associated with HPAI using geographic information system (GIS) techniques in Mainland China. METHODS: Databases were set up using the information of HPAI during epidemics in 2004, and linked to digital maps at provincial and county administrative layers in the country through the ArcGIS 8.3 software. Spatial cluster analyses, spatial statistics analyses and tracking analyses on epidemic situation of HPAI were implemented. Environmental factors associated with HPAI were also analyzed on data related to weather, vegetation and migratory birds etc. RESULTS: Findings from spatial cluster analyses showed that high incidence area was centralized in 113.261 degrees ordm; east longitude and 23. 119 degrees ordm; north latitude with a radius of 1090.52 kilometers (relative risk= 2.646, P value= 0.001). Spatial statistical analyses showed that HPAI took place mainly in capital cities of provinces and surrounding areas as well as in the circumference areas of arterial rivers, lakes and seacoasts. Results also showed that HPAI occurrences were associated with low air temperature, high relative humidity and high air pressure as well as with east & central migration routes of migratory birds. The average normalized difference vegetation index was 0.36 +/- 0.11 in epidemic areas of HPAI. CONCLUSION: HPAI was unrandomly distributed and geographically clustered in China.

Animal Migration↗

PubMed1992

The origin of the luteinizing hormone-releasing hormone (LHRH) neurons in newts (Cynops pyrrhogaster): the effect of olfactory placode ablation.

Neurons containing luteinizing hormone-releasing hormone (LHRH) are first detected in newt embryos (Cynops pyrrhogaster) in the olfactory epithelium and ventromedial portion of the olfactory nerve, after which they sequentially appear in the intracerebral course of the terminal nerve at prometamorphosis, and in the septo-preoptic area at postmetamorphosis. In adults, however, LHRH-immunoreactive cells are rarely seen in the nasal region, and their distribution shifts into the brain, suggesting their migration. In order to ascertain the origin and possible migration route of these neurons in newt larvae, the effect of unilateral or bilateral olfactory placodectomy on the LHRH neuronal system has been studied. Removal of the olfactory placode results in the absence of LHRH-immunoreactive cells in the nasal and brain regions of the operated side, whereas the subsequent growth and the LHRH-immunoreactive cellular distribution in the contralateral side are identical to those of normal larvae. Following bilateral placodectomy, no LHRH immunoreactivity is detected on either side of the olfactory-brain axis. These results suggest that LHRH neurons of the newt, Cynops pyrrhogaster, originate in the olfactory placode and then migrate into the brain during embryonic development.

Animals↗

PubMedDate not supplied

Recruitment of lymphocytes and dendritic cells from the blood to the bronchoalveolar space and the draining lymph nodes after a single intrabronchial application of the lipopeptide MALP-2.

OBJECTIVE: It has been shown previously that the synthetic macrophage-activating lipopeptide, MALP-2, is a potent stimulator of the respiratory immune system and an effective adjuvant in the induction of mucosal immune responses. In this study, the migration route of leukocytes from the blood to the bronchoalveolar space and then to the draining lymph nodes was investigated. METHODS: MALP-2 was intratracheally instilled into lungs of Lewis rats. Bronchoalveolar lavage cells as well as cell preparations of other lung compartments such as the marginal vascular pool, the interstitial pool and also the draining lymph nodes were examined 3 days later. RESULTS: The application of MALP-2 induced a pronounced leukocyte accumulation in the bronchoalveolar space and the lung interstitium but not in the marginal vascular pool. A tendency to increased lymphocyte and dendritic cell numbers was observed in the draining lymph nodes. CONCLUSION: Our data indicate the migration of blood cells into the lung interstitium and the bronchoalveolar space in response to MALP-2. Thus, the immune reaction induced by MALP-2 might be of relevance as an adjuvant treatment in inhalant vaccination strategies in the lung.

Animals↗

PubMed2000

Reproductive ecology of the blue crab, Callinectes danae Smith, 1869 in the Conceição Lagoon system, Santa Catarina Isle, Brazil.

Abundance of ovigerous females, size of the first gonadal maturation and the possible migration, route of the blue crab Callinectes danae from the Conceição Lagoon system, Santa Catarina Isle, Brazil, are described. This lagoon is connected with the coastal area through a canal. A total of 1,124 crabs was caught during a 19 month sampling period. The reproduction and recruitment of juveniles occurred all year-round, with two peaks of abundance (February and September), correlated with the presence of ovigerous females (June and January). The mean carapace width at which the crabs attained gonadal maturity for the first time was 9.4 cm in males and 8.4 cm in females. The Conceição Lagoon is a growth, reproduction, and spawning area for the species. However, egg eclosion occurs outside the lagoon following migration of ovigerous females to the open sea. After hatching the eggs, some females return to the lagoon, but males stay there for most of their life cycle.

Animals↗

PubMed1986

Migration of host astrocytes into superior cervical sympathetic ganglia autografted into the septal nuclei or choroid fissure of adult rats.

Adult astrocytes and their processes, identified by glial fibrillary acidic protein immunohistochemistry and by electron microscopy, migrate into superior cervical ganglia auto-transplanted into the choroid fissure or septal nuclei of adult rats. Migration routes were along the blood vessels, and along the Schwann cell bundles of the transplant. Ultrastructurally, astrocytic processes could be seen to lie in direct contact with Schwann cell processes within the basal lamina enwrapping the Schwann cell and its associated axons. Around the region of the host/transplant interface, the astrocytes were transformed into flattened cells with many short, irregular, fringe-like processes, but within the depths of the transplant mass they resumed a more stellate configuration. Glial fibrillary acidic protein immunoreactivity was present within the intrinsic satellite and Schwann cells of the grafted ganglia, but at a much lower level than in the host astrocytes. It is concluded that reactive astrocytes from adult host central nervous system migrate into peripheral ganglionic transplants, where they differentiate and establish organized arrangements with the ganglionic elements.

Animals↗