Current Selection (current + selection)

Distribution by Scientific Domains


Selected Abstracts


SEXUAL DIMORPHISM IN RELATION TO CURRENT SELECTION IN THE HOUSE FINCH

EVOLUTION, Issue 3 2000
Alexander V. Badyaev
Abstract., Sexual dimorphism is thought to have evolved in response to selection pressures that differ between males and females. Our aim in this study was to determine the role of current net selection in shaping and maintaining contemporary sexual dimorphism in a recently established population of the house finch (Carpodacus mexicanus) in Montana. We found strong differences between sexes in direction of selection on sexually dimorphic traits, significant heritabilities of these traits, and a close congruence between current selection and observed sexual dimorphism in Montana house finches. Strong directional selection on sexually dimorphic traits and similar intensities of selection in each sex suggested that sexual dimorphism arises from adaptive responses in males and females, with both sexes being far from their local fitness optimum. This pattern is expected when a recently established population experiences continuous immigration from ecologically distinct areas of a species range or as a result of widely fluctuating selection pressures, as found in our study. Strong and sexually dimorphic selection pressures on heritable morphological traits, in combination with low phenotypic and genetic covariation among these traits during growth, may have accounted for close congruence between current selection and observed sexual dimorphism in the house finch. This conclusion is consistent with the profound adaptive population divergence in sexual dimorphism that accompanied very successful colonization of most of the North America by the house finch over the last 50 years. [source]


Dissociating the role of the caudate nucleus and dorsolateral prefrontal cortex in the monitoring of events within human working memory

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2010
Jean-Sebastien Provost
Abstract There is evidence that the dorsolateral prefrontal cortex is involved in the monitoring of information held in memory whether it is self-ordered or externally triggered. However, the functional contribution of the caudate nucleus in the monitoring of events has not yet been studied. We have previously proposed that the striatum is involved when a novel self-initiated action needs to be generated. The present study aimed to test the hypothesis that the caudate nucleus is significantly more required when the monitoring is self-ordered as opposed to externally triggered. Self-ordered monitoring refers to keeping track of which items have been selected so far in order to perform the current selection. Externally triggered monitoring refers to keeping track of which items have been selected by an outside source. Thirteen healthy young adults were scanned using functional magnetic resonance imaging while performing a monitoring task with three conditions: self-ordered, externally triggered and recognition. As predicted, a significant increase of activity was found in the dorsolateral prefrontal cortex bilaterally when the self-ordered and externally triggered conditions were compared with the recognition condition. Most importantly, significantly increased activity was found in the right caudate nucleus when comparing the self-ordered with the recognition condition or with the externally triggered condition, but not when comparing the externally triggered with the recognition condition. We suggest that the caudate nucleus is involved in the planning of a self-initiated novel action, especially when no clear indication is given for the response choice, and that this may be the case across different domains of cognition. [source]


SEXUAL DIMORPHISM IN RELATION TO CURRENT SELECTION IN THE HOUSE FINCH

EVOLUTION, Issue 3 2000
Alexander V. Badyaev
Abstract., Sexual dimorphism is thought to have evolved in response to selection pressures that differ between males and females. Our aim in this study was to determine the role of current net selection in shaping and maintaining contemporary sexual dimorphism in a recently established population of the house finch (Carpodacus mexicanus) in Montana. We found strong differences between sexes in direction of selection on sexually dimorphic traits, significant heritabilities of these traits, and a close congruence between current selection and observed sexual dimorphism in Montana house finches. Strong directional selection on sexually dimorphic traits and similar intensities of selection in each sex suggested that sexual dimorphism arises from adaptive responses in males and females, with both sexes being far from their local fitness optimum. This pattern is expected when a recently established population experiences continuous immigration from ecologically distinct areas of a species range or as a result of widely fluctuating selection pressures, as found in our study. Strong and sexually dimorphic selection pressures on heritable morphological traits, in combination with low phenotypic and genetic covariation among these traits during growth, may have accounted for close congruence between current selection and observed sexual dimorphism in the house finch. This conclusion is consistent with the profound adaptive population divergence in sexual dimorphism that accompanied very successful colonization of most of the North America by the house finch over the last 50 years. [source]


Fabrication of Direct Fiber-Reinforced Posts: A Structural Design Concept

JOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 4 2001
DOUGLAS A. TERRY DDS
ABSTRACT As the clinician continues the quest for optimal functional and esthetic success of a tooth-restorative complex, the current selection of restorative materials and techniques may prove overwhelming. Although no single system provides the ideal restorative solution for every clinical circumstance, understanding of general design criteria and the components for the various post and core systems available allow the clinician to appropriately select the method and materials compatible with the existing tooth structure and desired result. This article provides a discussion of the various post and core systems, the methods and materials inherent in these systems, and general design principles. Using that basic information and clinical experience, the authors offer an alternative procedure for the rehabilitation of the intraradicular anatomy of the post-endodontic channel with a direct composite resin,the fiber-reinforced post and core system. CLINICAL SIGNIFICANCE Using improved restorative materials that simulate the physical properties and other characteristics of natural teeth in combination with the proper design principles, the clinician can develop a tooth-restorative complex with optimal functional and esthetic results. [source]


Estimation of dominance genetic variances for reproductive traits and growth traits of calves in Japanese Black cattle

ANIMAL SCIENCE JOURNAL, Issue 4 2004
Takafumi ISHIDA
ABSTRACT The dominance genetic effects for reproductive and calf growth abilities in the practical Japanese Black populations were examined using average information (AI) algorithm restricted maximum likelihood (REML) under animal models. The reproductive traits were observed in Japanese Black cattle maintained at Tottori and Okinawa prefectures, and growth traits of calves were observed in cattle at Okinawa. The average of dominance relationships in Tottori ranged from 0.2 to 0.4%, while the level in Okinawa was lower and sparse compared with Tottori. The proportions of the dominance variances to sum of additive and dominance variances () were all 0.02 for reproductive traits in Tottori. In contrast, the proportion was 0.02,0.64 in Okinawa regardless of the level of dominance relationships. These proportions suggested that the dominance might affect the expression of calving interval, days open and gestation length in Okinawa, where breeding units were spread over many islands. Although the dominance variances could not estimate birthweight, w as 0.34 for calf market weight and 0.27 for average daily gain from birth to calf market in Okinawa. These values also suggested that the dominance might affect the early growth of calves. In the near future, genetic relationships will become more complicated with continuation of the current selection and mating systems. Therefore, genetic evaluation accounting for dominance effects would be necessary for particular traits and populations. [source]