Patterns of pollen dispersal in a small population of the Canarian endemic palm (Phoenix canariensis).

The genetic diversity of small populations is greatly influenced by local dispersal patterns and genetic connectivity among populations, with pollen dispersal being the major component of gene flow in many plants species. Patterns of pollen dispersal, mating system parameters and spatial genetic structure were investigated in a small isolated population of the emblematic palm Phoenix canariensis in Gran Canaria island (Canary Islands). All adult palms present in the study population (n=182), as well as 616 seeds collected from 22 female palms, were mapped and genotyped at 8 microsatellite loci. Mating system analysis revealed an average of 5.8 effective pollen donors (Nep) per female. There was strong variation in correlated paternity rates across maternal progenies (ranging from null to 0.9) that could not be explained by the location and density of local males around focal females. Paternity analysis revealed a mean effective pollen dispersal distance of ∼71 m, with ∼70% of effective pollen originating from a distance of <75 m, and 90% from <200 m. A spatially explicit mating model indicated a leptokurtic pollen dispersal kernel, significant pollen immigration (12%) from external palm groves and a directional pollen dispersal pattern that seems consistent with local altitudinal air movement. No evidence of inbreeding or genetic diversity erosion was found, but spatial genetic structure was detected in the small palm population. Overall, the results suggest substantial pollen dispersal over the studied population, genetic connectivity among different palm groves and some resilience to neutral genetic erosion and subsequently to fragmentation.

Genetic structure of the Canarian palm tree (Phoenix canariensis) at the island scale: does the 'island within islands' concept apply to species with high colonisation ability?

Oceanic islands are dynamic settings that often promote within-island patterns of strong population differentiation. Species with high colonisation abilities, however, are less likely to be affected by genetic barriers, but island size may impact on species genetic structure regardless of dispersal ability. The aim of the present study was to identify the patterns and factors responsible for the structure of genetic diversity at the island scale in Phoenix canariensis, a palm species with high dispersal potential. To this end, we conducted extensive population sampling on the three Canary Islands where the species is more abundant and assessed patterns of genetic variation at eight microsatellite loci, considering different within-island scales. Our analyses revealed significant genetic structure on each of the three islands analysed, but the patterns and level of structure differed greatly among islands. Thus, genetic differentiation fitted an isolation-by-distance pattern on islands with high population densities (La Gomera and Gran Canaria), but such a pattern was not found on Tenerife due to strong isolation between colonised areas. In addition, we found a positive correlation between population geographic isolation and fine-scale genetic structure. This study highlights that island size is not necessarily a factor causing strong population differentiation on large islands, whereas high colonisation ability does not always promote genetic connectivity among neighbouring populations. The spatial distribution of populations (i.e. landscape occupancy) can thus be a more important driver of plant genetic structure than other island, or species' life-history attributes.

A comparison of non-linear non-parametric models for epilepsy data.

EEG spike and wave (SW) activity has been described through a non-parametric stochastic model estimated by the Nadaraya-Watson (NW) method. In this paper the performance of the NW, the local linear polynomial regression and support vector machines (SVM) methods were compared. The noise-free realizations obtained by the NW and SVM methods reproduced SW better than as reported in previous works. The tuning parameters had to be estimated manually. Adding dynamical noise, only the NW method was capable of generating SW similar to training data. The standard deviation of the dynamical noise was estimated by means of the correlation dimension.

Multivariate Box-Cox transformations with applications to neurometric data.

The Box-Cox power transform methodology for achieving Gaussianity is developed for a variety of models useful in neurometric statistical analysis. Algorithms are proposed for estimating the optimal transformations in the univariate and multivariate cases. Their use is briefly illustrated with neurometric data.

Allozyme variation and structure of the Canarian endemic palm tree Phoenix canariensis (Arecaceae): implications for conservation.

Electrophoretic analysis of 18 allozyme loci was used to estimate the levels and structuring of genetic variation within and among natural populations of the protected endemic palm species from the Canary Islands (Phoenix canariensis) to evaluate its genetic relationship with the widespread congener P. dactylifera, and to assess comparatively the genetic variation in the populations where the two species coexist with morphologically intermediate plants (mixed populations). Our survey revealed that the within-population component explains roughly 75% of the genetic variation levels detected in P. canariensis (A=1.59; P=41.8; He=0.158), which rank higher than those reported for other species of the Arecaceae. A Principal Component analysis (PCA) based on allele frequencies consistently separates populations of P. canariensis and P. dactylifera, and reveals a close genetic relationship between P. canariensis and the mixed populations. Reduced levels of genetic variation in P. canariensis with respect to P. dactylifera, the fact that the genetic makeup of the Canarian endemic (with no unique alleles) is a subset of that found in P. dactylifera, and the high genetic identity between both species strongly suggest that P. canariensis is recently derived from a common ancestor closely related to P. dactylifera.

Allozyme diversity in three endemic species of Cistus (Cistaceae) from the Canary Islands: intraspecific and interspecific comparisons and implications for genetic conservation.

Patterns of variation at 13 isozyme loci were examined in 11 populations in three Cistus species strictly endemic to the Canary Islands. Cistus osbaeckiaefolius and C. chinamadensis display low levels of isozyme variation associated with moderate to high interpopulation differentiation, which probably arose through historical bottlenecks in a landscape of habitat fragmentation, grazing, and human influence. By contrast, C. symphytifolius ranks among the subset of narrow endemics with high levels of isozyme variation and features different degrees of genetic structuring that are closely associated with taxonomic ascription. Low interpopulation differentiation in var. leucophyllus is possibly a reflection of its recent origin or of moderate levels of gene flow between its populations. High interpopulation differentiation in var. symphytifolius probably arose due to slight ecological differences between populations coupled with low levels of gene flow. Interpretation of neighbor-joining trees in the light of geological data substantiates the hypothesis that C. symphytifolius (or a very close relative) might be the ancestor of the other stands of Cistus in the islands. Conservation implications of our survey are the identification of the two populations of C. chinamadensis with the highest allele and genotype richness for preservation on genetic grounds and advice to prevent artificial gene flow in this taxon lest it might disrupt locally adapted gene combinations. All populations of C. osbaeckiaefolius should be given conservation priority on ecological grounds despite their genetic depauperation.

On the structure of EEG development.

Two different descriptions of EEG maturation are compared: a broad-band spectral parameters (BBSPs) model and a recently developed xi-alpha (xi alpha) model. 'Developmental equations' were obtained for both parameter sets using 1 min, eyes closed EEG sample from 165 normal children (5-12 years old). At each age, the xi alpha parameter set described the average spectrum more closely than the BBSP developmental equations. Furthermore, a more detailed picture of changes of spectral shape with age is possible with the xi alpha model. A computer simulation illustrates the possible appearance of fixed frequency bands as a byproduct of inadequate statistical models.

Brain electrical field measurements unaffected by linked earlobes reference.

Recent theoretical analysis supports the possibility that using a linked earlobe reference in EEG studies might appreciatively distort the measured electrical field due to current flow over a low resistance path across the wire joining both ears. Such an effect would invalidate published quantitative EEG norms. Evidence for the balancing effect of this distortion was sought for in the EEG of 4 patients with well localized unilateral lesions, a situation in which this distortion would be most apparent. Statistical tests failed to reveal significant differences between EEGs recorded when ears were linked or unlinked. An analysis of the equivalent circuit reveals that a high skin/electrode impedance effectively makes the linked ear reference behave as an ordinary reference.

A parametric model for multichannel EEG spectra.

The EEG is modelled as the superposition of two component processes: the xi and the alpha processes. In the frequency domain, the xi process is always present and appears as a spectral peak with maximum amplitude at very low frequencies, while the alpha process is characterized by a spectral peak with its maximum located in the traditional alpha band (7-13 Hz), and is not necessarily always present. The multivariate properties of EEG spectra are adequately modelled with frequency independent coherence matrices for each process. Multichannel EEG studies reveal interesting properties: (1) the generalized coherence for alpha is much larger than for xi, indicating increased functional coupling for the alpha process; (2) the alpha coherence matrix has reduced dimensionality, possibly related to a small number of generators; (3) xi coherences are zero phase with magnitudes that decrease exponentially with interelectrode distance; and (4) alpha coherences have significant nonzero phase shifts.

The estimation of event related potentials affected by random shifts and scalings.

There is considerable evidence for trial to trial variability of the event related potentials (ERPs) within a given subject's recording. This variability influences the outcome of usual procedures in ERP analysis. Better results may be obtained if the sources of variability are explicitly taken into account in an appropriate model. This paper considers a probabilistic model, the random shift and scaling (RSS) model, where the response is modified by a random time shift and a random scale factor. In addition to this, an additional random scale factor which affects both the response and the background noise is taken into account. This time shift and these scale factors are handled as nuisance parameters. Maximum likelihood and least squares estimators of these parameters and the waveform of response are derived for the RSS model. It is shown that the Woody estimate of the ERP reported in earlier work can be derived by restricting the assumptions for the RSS model. Test statistics for hypotheses on means are obtained for the RSS model and a new type of discriminant function. The usefulness of the method is illustrated by means of simulation studies. Receiver operating characteristic (ROC) curves are used to demonstrate that the new type of discriminant performs better than the usual Fisher's Linear Discriminant.

Current source density estimation and interpolation based on the spherical harmonic Fourier expansion.

A method for the spatial analysis of EEG and EP data, based on the spherical harmonic Fourier expansion (SHE) of scalp potential measurements, is described. This model provides efficient and accurate formulas for: (1) the computation of the surface Laplacian and (2) the interpolation of electrical potentials, current source densities, test statistics and other derived variables. Physiologically based simulation experiments show that the SHE method gives better estimates of the surface Laplacian than the commonly used finite difference method. Cross-validation studies for the objective comparison of different interpolation methods demonstrate the superiority of the SHE over the commonly used methods based on the weighted (inverse distance) average of the nearest three and four neighbor values.

Model parameters estimation when the evoked potential recordings are affected by a random scale factor.

In many situations an important source of the average evoked potentials (EPs) variability is a random scale factor affecting each recording. As a result, the outcome of any EP detection method may be greatly affected. However, using an appropriate probabilistic model these scale factor can be estimated, and the performance of any available detection index improved by data rescaling. In this paper the Maximum Likelihood Estimators of the waveform of the response and the scale factor affecting both background noise and this waveform are obtained. Also, an iterative algorithm for model parameters estimation is presented and its convergence is examined in a simulation study. The Linear Discriminant function is computed using simulated test data in both situations, before and after rescaling of recordings. The performance of these statistics is evaluated by mean of ROC curves.

A parametric model for multichannel EEG spectra

El EEG es modelado como la superposición de dos procesos componentes: y alfa. En el dominio de la frecuencia, el proceso siempre está presente y aparece como un pico espectral centrado en o Hz, mientras que el pico espectral del proceso alfa está centrado en la banda tradicional alfa (17-13 Hz), y no siempre está presente. Se postula que el processo es generado por el sistema de proyección tálamo-cortical generalizado y que su propagación ocurre mediante conecciones corticales de corto alcance, mientras que el proceso alfa está relacionado al sistema de proyección tálamo-cortical específico y se propaga vía fibras de asociación cortico-corticales de largo alcance

Modelo paramétrico para el análisis de potenciales relacionados a eventos múltiples / Parametric model for the analysis of potentials related to multiple events

En este trabajo se presenta un método para la estimación de los potenciales relacionados a eventos (PRE) contenidos en segmentos de electroencefalograma (EEG). El modelo presupone que en el dominio del tiempo los potenciales relacionados a eventos múltiples (PREM) se superponen aditivamente. Cada componente es de morfología constante pero su amplitud y latencia pueden variar. Se presenta un algoritmo máximo verosímil para la estimación de la forma de onda de cada componente que utiliza una estimación a priori de sus latencias. El algoritmo fue valiado con PREM simulados por computadora y utilizado en la descripción de potenciales evocados auditivos de tallo cerebral de humanos y potenciales evocados auditivos de latencia media de humanos y primates

Métodos de máxima potencia para la detección estadística de potenciales evocados en el dominio de la frecuencia / Methods of maximal potential for detection statistics evoked potentials in the frequency domain

El presente trabajo presenta un nuevo método para la detección de Potenciales Evocados en el dominio de la frecuencia. El cual consiste en la comparación de dos muestras de registros mediante la versión en el campo complejo del estadígrafo T2 de Hotelling para dos muestras. Una muestra está formada por segmentos de EEG y la otra por segmentos registrados durante la estimulación. Las curvas Características de Operación del Receptor muestran que una expresión aproximada del estadígrafo T2 de Hotelling para dos muestras es mejor que la medida de sincronía presentada por Fridman y que la expresión aproximada del estadígrafo T2 para una muestra desarrollada en nuestro grupo. Para determinar la composición espectral del Potencial Evocado se emplearon estadígrafos análogos. En el campo complejo, a la t de Student para una y dos muestras. Cuando está presente una señal independiente del estímulo sólo el estadígrafo para dos muestras es capaz de revelar la estructura espectral del PE

Current source density estimation: a new method

En este trabajo se describe un nuevo método para la estimulación de la densidad de fuentes de corrientes para el EEG (electroencefalograma) y los PEs (potenciales evocados). El método consiste en que la distribución del potencial eléctrico sobre la cabeza es expandida en términos de armónicos esféricos. Condicionada a poseer una curvatura media cuadrática mínima. Esta técnica posse ventajas significativas sobre los métodos descritos en la literatura actual, como son aquellos basados en el cálculo del Laplaciano de superficie mediante diferencias finitas. Además, mediante este nuevo método es posible construir imágenes con información eléctrica sin la necesidad de utilizar funciones arbitrarias para la interpolación

Análisis multivariado del electroencefalograma en escolares cubanos de 7 a 11 años / Multivariate analysis of electroencephalography in cuban students of 7 to 11 years

Se estudió una muestra de 96 niños normales entre 7 y 11 años de edad, con el objetivo de ensayar nuevas estrategias de análisis del EEG. Se definieron 3 medidas globales que contienen valiosa información que resume las características más importantes evaluadas en el análisis del EEG en el dominio de la frecuencia. Se utilizaron análisis multivariados que permiten conocer desviaciones con respecto a una norma, encontrándose que las medidas globales son capaces de evaluar las regularidades que rigen la maduración del EEG

Estudio de la influencia de algunas variables biológicas sobre las características del electroencefalograma / Study of influence the soma biological variables about characteristics of electroencephalogram

Se realizó el análisis cuantitativo de 1 minuto de actividad electroencefalográfica (EEG) en 192 niños normales entre 5 y 12 años de edad. El espectro de frecuencias del EEG se ajustó mediante dos modelos diferentes (Medidas Espectrales de Banda Ancha y Medidas de Modelo XI-ALFA) obteniéndose dos grupos de variables cuantitativos. Se aplicaron técnicas estadísticas multivariables para comparar la variables cuantitativos de diferentes submuestras de esta población para estudiar el efecto del sexo, los antecedentes de riesgos biológicos, la circunferencia cefálica y el cociente de inteligencia sobre las mismas

Análisis cuantitativo de la maduración del electroencefalograma en niños de edad escolar / Quantitative analysis of electroencephhalogram maturation in school children

Se describen las variaciones con la edad de las variables cuantitativas obtenidas del Electroencefalograma mediante dos modelos de ajuste diferentes en un grupo de 192 niños normales entre 5 y 12 años de edad. Se aplican técnicas de regresión no lineal para lograr mejores ajustes de las curvas de regresión. Se comparon los resultados obtenidos con los dos modelos y se discuten las ventajas del nuevo modelo Xi-Alfa sobre el tradicional análisis de Banda Ancha

Análisis cuantitativo del electroencefalograma en niños retrasados mentales ligeros / Quantitative analysis of electroencefalography in midly mentally retarded children

Se calcularon dos conjuntos diferentes de medidas cuantitativas del EEG en un grupo de 63 niños con Retraso Mental Ligero, comparándose mediante técnicas estadisticas uni y multivariadas con un grupo de niños normales. Se estudiaron medidas cuantitativas globales que permiten hacer inferencias sobre la fisiopatologia de este tipo de trastorno. Se comparan los resultados obtenidos con ambos grupos de medidas cuantitativas