Topographic Subdivisions Research Articles

Biogeographic inferences across spatial and evolutionary scales.

The field of biogeography unites landscape genetics and phylogeography under a common conceptual framework. Landscape genetics traditionally focuses on recent-time, population-based, spatial genetics processes at small geographical scales, while phylogeography typically investigates deep past, lineage- and species-based processes at large geographical scales. Here, we evaluate the link between landscape genetics and phylogeographical methods using the western fence lizard (Sceloporus occidentalis) as a model species. First, we conducted replicated landscape genetics studies across several geographical scales to investigate how population genetics inferences change depending on the spatial extent of the study area. Then, we carried out a phylogeographical study of population structure at two evolutionary scales informed by inferences derived from landscape genetics results to identify concordance and conflict between these sets of methods. We found significant concordance in landscape genetics processes at all but the largest geographical scale. Phylogeographical results indicate major clades are restricted to distinct river drainages or distinct hydrological regions. At a more recent timescale, we find minor clades are restricted to single river canyons in the majority of cases, while the remainder of river canyons include samples from at most two clades. Overall, the broad-scale pattern implicating stream and river valleys as key features linking populations in the landscape genetics results, and high degree of clade specificity within major topographic subdivisions in the phylogeographical results, is consistent. As landscape genetics and phylogeography share many of the same objectives, synthesizing theory, models and methods between these fields will help bring about a better understanding of ecological and evolutionary processes structuring genetic variation across space and time.

Coastal barrier morphogenic categories in Mississippi Delta plain development

Coastal barriers are defined as shore-parallel, aggraded-prograded supratidal beach ridge sets and individual single ridge-landforms, composed of sand and/or gravel. Island, spit, and mainland barriers represent the three major topographic subdivisions. In terms of bathymetric and hydrographic characteristics, bottom sediment types and associated habitats, barriers separate the marine offshore from inshore facies. This definition is not uniformly accepted and applied in the literature. Barriers impose reduced salinities inshore, diminish storm impact and moderate inland inundation, protect critical habitats and may mark ancient longshore transport directions, shore and sea-level positions. A wide range of dimensions, topography, and other factors characterize mainland strandplains. Shoal aggradation appears to be the prime island-forming mechanism, followed by accretion around semi-consolidated, elevated cores. Smaller islands may also form by barrier spit fragmentation. Detachment of dune ridges from the mainland shore is an often cited but at best unlikely mode of island genesis. Review of the literature and remote-sensed images created new insights, utilized barrier definitions and genetic theories, as applied in the Mississippi Delta Complex. A three-stage concept, involving dune ridge or barrier spit-detachment by marine encroachment and landward shift of fragmented transgressive islands forms the basis of a recent invited Marine Geology research article. That model assumes spit-growth from delta headlands, followed by splintering into landward-migrating islands. Submerged, they become permanent shoals. For several reasons, this “island-cycle” hypothesis is questionable and a reassessment of the geomorphic and stratigraphic context of this delta coast is required.Contradicting the geomorphic setting of assumed Stage 1, key component of the cycle-model, evidence is lacking for subrecent delta lobes and erosional headland in spawning barrier islands. In addition, the delta headland-flanking islands reveal only progradational (regressive) development and in situ disintegration,. Transgressive landward migrations is known only from the Chandeleur chain's prehistory. Sand from decaying Terrebonne-Lafourche 6 Subdelta headland was the dominant source for the Caminada Strandplain and for the shoal /or island predecessor of Grand Isle. Wave refraction around an inferred Lafourche delta lobe (dated provisionally between ∼2900 - ∼ 2300 yrs. BP) and its decayed erosional headland remnant resulted in diametric reversal of littoral sand transport. An earlier proferred ∼750–300 yrs. BP Caminada Strandplain age range is now replaced by a loosely defined ∼2200- to- ∼800 yrs. BP value, based on ages of Grand Isle and reworked delta hinterland sediments incorporated into the Strandplain.

Regional and local topography subdivision and landform mapping using SRTM-derived data: a case study in southeastern Brazil

Topographic subdivisions and landforms are important relief characteristics that serve as a basis for several types of regional and local planning. This paper presents an assessment of the application of a global landform classification method on a regional scale using Sao Paulo State as the study area and on a local scale using the city of Sao Paulo as the study area. In addition, a new approach that includes elevation derivatives for local analysis is presented. The study hypothesizes that the automated object-based classification of topography from shuttle radar topography mission (SRTM) data method could also be used for local mapping when supported by elevation derivative data. SRTM data were used in the regional approach and post-processed elevation data derived from SRTM were used for the local analysis. The results were compared with the best available geomorphological maps and topographic surface descriptions of the region. The new method resulted in a regional-scale product in which the boundaries and features of the topography matched those in the geomorphological maps and in the literature. The method did not perform well when classifying the local topographic subdivisions of Sao Paulo, even when using the interpolated elevation data. However, the surface edges and shapes identified in the topographic maps were represented in the resulting map. To refine the results, a new approach was proposed using data derived from a digital elevation model, such as drainage densities, horizontal and vertical curvatures, and slope gradients. The use of these products in the image segmentation process and classification criteria was fundamental for obtaining the results. Theoretical thresholds were used to define the relief classes, and landform characteristics were taken into account in developing the landform map. The success of this new approach is attributed to the comprehensive database that supported the topographic subdivision analysis. In summary, this study indicates that a method developed for use on a global scale can be replicated for use on a regional scale but not on a local scale. The new approach produced reasonable results and can be used in other regions. Greater detail can be obtained using various thresholds of horizontal and vertical curvatures, for example, when delineating hazard areas. The products have potential applications in urban planning, ecological-economic zoning, urban drainage, hazard mitigation, environmental issues, erosional dynamics and transportation planning.

Probabilistic topography of human corpus callosum using cytoarchitectural parcellation and high angular resolution diffusion imaging tractography

The function of the corpus callosum (CC) is to distribute perceptual, motor, cognitive, learned, and voluntary information between the two hemispheres of the brain. Accurate parcellation of the CC according to fiber composition and fiber connection is of upmost important. In this work, population-based probabilistic connection topographies of the CC, in the standard Montreal Neurological Institute (MNI) space, are estimated by incorporating anatomical cytoarchitectural parcellation with high angular resolution diffusion imaging (HARDI) tractography. First, callosal fibers are extracted using multiple fiber assignment by continuous tracking algorithm based on q-ball imaging (QBI), on 12 healthy and young subjects. Then, the fiber tracts are aligned in the standard MNI coordinate system based on a tract-based transformation scheme. Next, twenty-eight Brodmann's areas on the surface of cortical cortex are registered to the MNI space to parcellate the aligned callosal fibers. Finally, the population-based topological subdivisions of the midsagittal CC to each cortical target are then mapped. And the resulting subdivisions of the CC that connect to the frontal and somatosensory associated cortex are also showed. To our knowledge, it is the first topographic subdivisions of the CC done using HARDI tractography and cytoarchitectonic information. In conclusion, this sophisticated topography of the CC may serve as a landmark to further understand the correlations between the CC, brain intercommunication, and functional cytoarchitectures.

Reduced retrograde labelling with fluorescent tracer accompanies neuronal atrophy of basal forebrain cholinergic neurons in aged rats

During ageing, basal forebrain cholinergic neurons are prone to degeneration for unknown reasons. In this study we morphometrically evaluated the retrograde labelling of basal forebrain neurons obtained after injection of FluoroGold into multiple sites in the cerebral neocortex in aged (24–33 months) as compared with young adult (four to six months) male Sprague–Dawley rats. In addition, we looked for differences in the distribution of degenerative changes in topographic subdivisions of the basal forebrain cholinergic complex of neurons identified by immunohistochemical detection of the cholinergic markers choline acetyltransferase or low-affinity neurotrophin receptor. After injection of FluoroGold into the cerebral neocortex, the number of retrogradely labelled neurons in the horizontal diagonal band/substantia innominata and basal nucleus was significantly lower in aged rats, by 41% and 48%, respectively. In aged rats injected with FluoroGold, as well as in non-injected aged rats, the numbers of neurons immunoreactive for choline acetyltransferase and low-affinity neurotrophin receptor were significantly lower, by 23–27% in the basal forebrain system as a whole, with no significant difference in the degree of decline amongst different subdivisions (i.e. medial septum, diagonal band, substantia innominata and basal nucleus). The ratios of the number of neurons labelled with Fluoro Gold as compared with the number of neurons immunoreactive for either cholinergic marker were significantly lower in aged rats, by 32–37%, indicating that the decline in the number of neurons retrogradely transporting tracer was greater than the decline in the number of immunoreactive neurons in aged animals. Immunoreactive as well as retrogradely labelled neurons showed a significant shrinkage of cell surface area of 6–13% in different subdivisions of the basal forebrain cholinergic system in aged rats. These findings confirm significant loss and atrophy of basal forebrain cholinergic neurons in aged rats, and demonstrate significantly reduced retrograde labelling of these neurons with fluorescent tracer applied to their target cortex. This reduced retrograde labelling suggests an impairment of either uptake or retrograde transport mechanisms in these neurons in aged rats. Such an impairment may contribute to the degenerative changes of basal forebrain cholinergic neurons observed in ageing and age-related degenerative conditions such as Alzheimer's disease.

Alcohol effects on paraventricular hypothalamic nucleus morphometry.

The morphometric effects of postnatal exposure to alcohol on the neurons of the paraventricular hypothalamic nucleus (PVN) have been studied in four different topographic subdivisions of the nucleus: rostral, intermediate medial, intermediate lateral and caudal. Male mice were exposed to alcohol during lactation and after weaning by addition of 20% of ethanol to the drinking water that was first ingested by the mother and thereafter by the experimental animals themselves. Animals were sacrificed at the 25th, 35th, 45th, 55th and 100th postnatal day. Nuclear sizes of the PVN neurons (Perimeter, area and maximum diameter) were determined in both control and experimental alcohol-treated groups. The shape of these neuronal nuclei was also determined and compared. PVN responds globally to alcohol exposure, showing a decrease in the neuronal nuclear sizes in the four studied PVN subdivisions of the alcohol-treated mice at the 35th and 45th and 100th day. We suggest that these decreases could be related to changes in gonadal hormone levels induced by alcohol exposure and/or disturbances of brain neurotransmitter and neuropeptide metabolism caused by ethanol.

Differential changes in cell size and number in topographic subdivisions of human basal nucleus in normal aging

The age-related cell loss of the nucleus basalis of Meynert is of considerable importance because loss of its neurons may be followed by cognitive decline. Compared to the number found at ages 16–29 years, we found that 50% of the total population of neurons is lost by 90 years of age. This change in number is accompanied by modifications in the morphometric features, including a 17.3% increase in cell size by 60 years of age as compared with values at 16 years, and followed by a gradual decline. Topographic differences were seen both in the neuronal loss and in morphometry: in relation to the youngest group, the posterior subdivision is the most severely affected by 90 years (64.5% decrease in number and 10% reduction in neuronal size), followed by the intermediate subdivision (42% loss of neurons accompanied by 4% increase in cell size). In the anterior subdivision no significant decrease in the number of neurons could be detected, although a 15% increase in cell size occurred.

Topographic organization of the karyometric response to neonatal castration of the male mouse in the paraventricular and ventromedial hypothalamic nuclei.

We have analysed the karyometric development of four topographic subdivisions of the paraventricular nucleus (rostral, medial, lateral and caudal) and three topographic subdivisions of the ventromedial nucleus (ventral, central and dorsal) of the hypothalamus in neonatally castrated male mice. Castration at birth produces a decrease of the nuclear sizes from the 10th to the 35th postnatal day, but after this age, no differences were detected in comparison with the sizes of the control male mice. Neonatal gonadal hormone deprivation also produces changes in the nuclear shape of the nuclei, that tend to be more spherical in both centres, as we could establish after the study of the form factor parameter (perimeter/area ratio). We have found differences in the response of both hypothalamic nuclei to neonatal castration and differences in the response of the topographic subdivisions of both of them.

Karyometric development of four topographic subdivisions of the paraventricular nucleus in normal and castrated mice

A karyometric study of the spontaneous development of four topographic subdivisions in the paraventricular nucleus was made in male albino mice from the 5th to the 190th day of postnatal life. Anoter 25 animals were castrated at 20 days and examined at 25, 35, 45, 55 and 85 days of life. A comparison was established between both groups of mice.

Fades, topography, and sedimentary processes in the Catskill Sea (Devonian), New York and Pennsylvania

Topography of the floor of the sea bordering the Catskill Delta (referred to here as the Catskill Sea) differed markedly from modern continental-margin configurations. Data from exposures in New York and Pennsylvania indicate that the Catskill Sea floor was a subdued surface with three topographic subdivisions. Nearest the shore was the basin margin , a low-gradient, shelf-like surface. Seaward, this gave way to the clinoform , the gradient of which was not much greater. The clinoform merged seaward into the basin floor. A sandstone and shale sequence with abundant fauna developed on the basin margin; thin turbidites and gray, silty shales with both transported and pelagic fauna were deposited on the clinoform and silt-stones and black shales with pelagic fauna formed on the basin floor. Boundaries between facies and between the inferred topographic subdivisions on which they formed reflect the different sedimentary processes active on the sea floor and not geophysical discontinuities. The basin margin was affected mainly by deltaic processes, waves, tides, and, perhaps, internal waves. Turbidity currents deposited the majority of clinoform sediments with a lesser contribution from pelagic sedimentation. Pelagic deposits dominate on the basin floor.

The cortico-cortical connections to area 5 of the parietal lobe from the primary somatic sensory cortex of the monkey.

The projection of the primary somatic sensory area (SI) upon area 5 of the parietal lobe of the monkey has been studied with axonal degeneration methods. No overlap occurs between the projection of the different topographic subdivisions of SI, but within the projection of each individual subdivision there is spatial convergence within the cortex of area 5 containing the same representation. The projections from the different cytoarchitectonic areas of SI overlap in area 5, and the number of fibres arising from area 3b is less than from areas 1 and 2. The degeneration after a small lesion in the trunk and face region of SI occupies a continuous antero-posterior zone of area 5, but after similar lesions in the distal limb region of SI the degeneration in area 5 is in three separate bands. In the projection of SI upon area 5 there is a reversal in the antero-posterior dimension with area 3 projecting more posteriorly than areas 1 and 2.

Representation of head and face in postcentral gyrus of the macaque.

The receptive field and submodality characteristics of individual neurons within the cytoarchitectural and topographic subdivisions of the head and face areas of the postcentral gyrus (SI) were determined with the technique of extracellular recording. Correlation of the single-unit data with the intracortical location of the recording electrode provided a detailed description of the functional organization within each of the several cytoarchitecturally distinct regions contributing to the representation of the head and face in SI. The data indicate that the functional organization of the SI cortex which receives its principal input from trigeminal mechanoreceptors is comparable to the organization within those SI regions which receive their input from the mechanoreceptors of the limbs, trunk, and tail. In each topographic subdivision of the SI cortex 1) a single region in the periphery is represented several times in widely separated locations, each time in a context of different submodalities and peripheral receptive fields; and 2) neurons belonging to the different submodality classes are segregated so that projections from cutaneous afferents terminate mainly in cytoarchitectural area 3 in the adjacent anterior portion of area 1, while projections from the afferents innervating deep tissues terminate mainly in cytoarchitectural area 3a, area 2, and the posterior part of each 1. Although the mechanoreceptor input to SI is segregated according to submodality and the mechanoreceptors from most body regions project to multiple widely separated regions within SI, neurons with receptive fields confined to the ophthalmic division of the trigeminal peripheral innervation field are found within a restricted region of the anterior postcentral gyral crown which is positioned symmetrically about the junction of cytoarchitectural areas 1 and 3. Neurons with receptive fields confined to the maxillary division of the trigeminal innervation field are found within a ring of cortex which a) completely surrounds the representation of the ophthalmic field, and b) includes parts of cytoarchitectural area 2, 1, 3, and 3a. SI neurons with receptive fields restricted to the mandibular division of the trigeminal innervation field occupy the largest portion of the SI face area and form a ring of cortical cell columns which completely surrounds that cortical region which receives its input from the maxillary peripheral innervation field.