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Biomedical subjects

C L Nunn

Publications and source records attributed to C L Nunn.

7 recordsLinked to original sources
PubMed2000

Promiscuity and the primate immune system.

The behavioral and ecological factors involved in immune system evolution remain poorly explored. We present a phylogenetic analysis of white blood cell counts in primates to test three hypotheses related to disease risk: increases in risk are expected with group size or population density, exposure to soil-borne pathogens, and mating promiscuity. White blood cell counts were significantly greater in species where females have more mating partners, indicating that the risk of sexually transmitted disease is likely to be a major factor leading to systematic differences in the primate immune system.

Animals↗
PubMed2000

Comparative tests of primate cognition: different scaling methods produce different results.

Although early comparative studies supported hypotheses that ecological demands selected for primate cognition, later work indicated that social demands were more important. One difference between earlier and later studies is that earlier studies scaled brain structures by (A) taking residuals from an interspecific regression of the brain structure in question on body mass, whereas later studies scaled them by (B) taking residuals from an interspecific regression of the brain structure in question on another brain structure or by (C) taking ratios of the brain structure in question to another brain structure. We conducted a series of comparative tests to explore the possibility that the different methods are responsible for the discrepancy between earlier and later studies. Specifically, we tested the ability of a social variable - group size - and an ecological variable - home range size - to explain variation in the non-V1 isocortex (isocortex minus primary visual cortex) when this structure was scaled with the three different methods. In multiple regression analysis, group size was a better predictor of the non-V1 isocortex with method (B). With methods (A) and (C), however, results were ambiguous: either home range size or group size explained more of the variation, depending on the inclusion of outliers, the use of independent contrasts, and whether home range size was scaled relative to body mass. We examine the three scaling methods and find no reasonable basis for preferring any of them. Hence, our results do not allow a distinction between social and ecological hypotheses. The general implications of our study are that (1) previous comparative studies are inconclusive and (2) further research is needed to develop a scaling method where relative measures of brain structure size are demonstrated to correspond with behavioral performance.

Animals↗
PubMed1999

How quickly do brains catch up with bodies? A comparative method for detecting evolutionary lag.

A trait may be at odds with theoretical expectation because it is still in the process of responding to a recent selective force. Such a situation can be termed evolutionary lag. Although many cases of evolutionary lag have been suggested, almost all of the arguments have focused on trait fitness. An alternative approach is to examine the prediction that trait expression is a function of the time over which the trait could evolve. Here we present a phylogenetic comparative method for using this 'time' approach and we apply the method to a long-standing lag hypothesis: evolutionary changes in brain size lag behind evolutionary changes in body size. We tested the prediction in primates that brain mass contrast residuals, calculated from a regression of pairwise brain mass contrasts on positive pairwise body mass contrasts, are correlated with the time since the paired species diverged. Contrary to the brain size lag hypothesis, time since divergence was not significantly correlated with brain mass contrast residuals. We found the same result when we accounted for socioecology, used alternative body mass estimates and used male rather than female values. These tests do not support the brain size lag hypothesis. Therefore, body mass need not be viewed as a suspect variable in comparative neuroanatomical studies and relative brain size should not be used to infer recent evolutionary changes in body size.

Animals↗
PubMed1995

A simulation test of Smith's "Degrees of freedom" correction for comparative studies.

Computer simulation was used to test Smith's (1994) correction for phylogenetic nonindependence in comparative studies. Smith's method find effective N, which is computed using nested analysis of variance, and uses this value in place of observed N as the baseline degrees of freedom (df) for calculating statistical significance levels. If Smith's formula finds the correct df, distributions of computer-generated statistics from simulations with observed N nonindependent species should match theoretical distributions (from statistical tables) with the df based on effective N. The computer program developed to test Smith's method simulates character evolution down user-specified phylogenies. Parameters were systematically varied to discover their effects on Smith's method. In simulations in which the phylogeny and taxonomy were identical (tests of narrow-sense validity), Smith's method always gave conservative statistical results when the taxonomy had fewer than five levels. This conservative departure gave way to a liberal deviation in type I error rates in simulations using more than five taxonomic levels, except when species values were nearly independent. Reducing the number of taxonomic levels used in the analysis, and thereby eliminating available information regarding evolutionary relationships, also increased type I error rates (broad-sense validity), indicating that this may be inappropriate under conditions shown to have high type I error rates. However, the use of taxonomic categories over more accurate phylogenies did not create a liberal bias in all cases in the analysis performed here. The effect of correlated trait evolution was ambiguous but, relative to other parameters, negligible.

Analysis of Variance↗
PubMed1989

Correlation of carotid bruits and carotid atherosclerosis detected by B-mode real-time ultrasonography.

The extent of carotid atherosclerosis evaluated by B-mode real-time ultrasound and the presence of bruits established by carotid phonoangiography were determined in 1,107 patients. Unilateral bruit was associated with increased atherosclerosis compared with no bruit (p less than or equal to 0.0001). However, there was no association between laterality of the bruit and the degree of atherosclerosis (p = 0.66). There was marginal evidence that patients with bilateral bruits had more severe atherosclerosis than patients with unilateral bruit (p = 0.046). The relation between bruit and atherosclerosis categorized by B-mode ultrasound was not sufficient to reliably predict the presence or absence of disease in an individual patient, though the presence of a bruit should be viewed as a risk factor for, or an indicator of, increased risk of systemic atherosclerosis.

Auscultation↗
PubMed1988

Three-dimensional transcranial Doppler blood flow mapping in patients with cerebrovascular disorders.

We investigated 60 patients with cerebrovascular disorders using a three-dimensional transcranial Doppler blood flow mapping system. A composite display of the circle of Willis is created with computer assistance, allowing accurate vessel identification and optimal data documentation of blood flow velocity and direction in the basal cerebral arteries. The basilar artery was insonated in every patient; the middle cerebral artery and the most distal internal carotid artery were found in 95% of the patients, the anterior cerebral artery in 85%, and the posterior cerebral artery in 84%. Insonation problems occurred predominantly in elderly women. Transcranial Doppler blood flow mapping showed an abnormal result in 23 of 60 patients (38%). An intracranial stenosis with greater than 50% diameter reduction or occlusion was found in 10 of 31 patients (32%) with completed stroke, reversible ischemic neurologic deficit, or transient ischemic attack. Collateral blood flow mechanisms could be demonstrated in patients with extracranial carotid artery occlusions. Intra-arterial cerebral angiography performed in 21 patients confirmed the transcranial Doppler blood flow mapping diagnosis in 19 (90.5%). In one patient an arteriovenous malformation diagnosed by transcranial Doppler blood flow mapping was confirmed by magnetic resonance imaging.

Adolescent↗