Biomedical subjects

V A Braithwaite

Publications and source records attributed to V A Braithwaite.

10 recordsLinked to original sources

PubMed2006

Reproductive isolation in a threespine stickleback hybrid zone.

In many estuarine sites, morphological and genetic differences between anadromous and freshwater threespine sticklebacks are maintained despite breeding in sympatry. Here, we investigate the maintenance of this morphological divergence in a natural hybrid zone in the River Tyne, Scotland. We provide a morphological description of the hybrid zone, and using a Bayesian MCMC approach, identified distinct anadromous and freshwater genetic clusters. Anadromous and freshwater sticklebacks breed in spatial and temporal sympatry in the lower reaches of the River Tyne. The frequency of hybrids within these sites (33%) indicates prezygotic isolation is not complete, and suggests that assortative mating is not strong. However, significant heterozygote deficit and cytonuclear disequilibrium in juveniles collected from sympatric sites confirms that barriers to gene flow exist between the morphs in the wild. In addition, we found no evidence of a directional bias in hybridisation, although hybrids with anadromous mothers were more common because anadromous females outnumbered freshwater females within the hybrid zone. We discuss the potential contribution of temporal, spatial, and sexual prezygotic barriers to the observed reproductive isolation as well as postzygotic selection against hybrid zygotes or fry.

Animals↗

PubMed2005

The role of ultraviolet wavelengths in the mate-choice decisions of female three-spined sticklebacks.

Female three-spined sticklebacks have been found to use visual cues when responding sexually towards courting males, often preferring more intensely red-coloured males, and males with blue rather than silver irises. However, traditionally the literature has failed to test preference across the full spectral range to which females might be sensitive, limiting analysis to the human-visible wavelengths of the electromagnetic spectrum. We studied the effects that the addition of ultraviolet wavelengths has on the mate-choice preferences of female sticklebacks using a two-choice paradigm. We found that females preferred males that were viewed across the full spectrum to males whose display lacked an ultraviolet component. Using suitable controls we were able to establish that female preference was sexually motivated and was not caused by a general preference for the manipulated light conditions. Our results indicate that female preference may be due to an enhancement in visual contrast when males are viewed in full spectrum conditions.

Animals↗

PubMed2004

Population variation in lateralized eye use in the poeciliid Brachyraphis episcopi.

Differential use of each hemisphere of the brain for specific tasks is a widespread phenomenon that appears to have arisen in the early history of tetrapod lineage. Despite a high degree of conformity in the development of lateralization among the tetrapods, some variation exists. The mechanisms underlying this variation remain largely unresolved. We exposed fish from regions of high and low predation pressure to a series of visual experiences, including viewing an empty compartment, a novel object and a live predator. Fish from each region differed in their preferential use of each eye to view the scenes. For example, fish from high predation regions viewed a live predator by using their right eye, whereas fish from low predation sites showed no eye preference. These results suggest that the degree of lateralization varies between populations of the same species that have been exposed to different ecological/evolutionary pressures.

Animals↗

PubMed2001

Indirect fitness consequences of mate choice in sticklebacks: offspring of brighter males grow slowly but resist parasitic infections.

'Good genes' models of sexual selection suggest that elaborate male sexual ornaments have evolved as reliable signals of male quality because only males of high genetic viability are able to develop and maintain them. Females benefit from choosing such individuals if quality is heritable. A key prediction is that the offspring of males with elaborate mating displays will perform better than those of less elaborate males, but it has proved difficult to demonstrate such an effect independently of the effects of differences in parental investment. We tested for 'good genes' linked to male ornamentation in the three-spined stickleback Gasterosteus aculeatus using in vitro fertilization to generate maternal half-siblings, which were raised without parental care. Maternal half-siblings sired by brightly coloured males grew less quickly than half-siblings sired by dull males but were more resistant to a controlled disease challenge. Among the offspring that became infected, those with brighter fathers had higher white blood cell counts. This suggests that highly ornamented males confer disease resistance on their offspring. The association with reduced growth suggests a mechanism for the maintenance of heritable variation in both disease resistance and male sexual coloration.

Animals↗

PubMed1999

Spatial working memory in rats: no differences between the sexes.

In a number of mammalian species, males appear to have superior spatial abilities to females. The favoured explanations for this cognitive difference are hormonal, with higher testosterone levels in males than females leading to better spatial performance, and evolutionary, where sexual selection has favoured males with increased spatial abilities for either better navigational skills in hunting or to enable an increased territory size. However, an alternative explanation for this sex difference focuses on the role of varying levels of oestrogen in females in spatial cognition (the 'fertility and parental care' hypothesis). One possibility is that varying oestrogen levels result in variation in spatial learning and memory so that, when tested across the oestrous cycle, females perform as well as males on days of low oestrogen but more poorly on days of high oestrogen. If day in the oestrous cycle is not taken into account then, across an experiment, any sex differences found would always produce male superiority. We used a spatial working memory task in a Morris water maze to test the spatial learning and memory abilities of male and female rats. The rats were tested across a number of consecutive days during which the females went through four oestrous cycles. We found no overall sex differences in latencies to reach a submerged platform in a Morris water maze but, on the day of oestrus (low oestrogen), females took an extra swim to learn the platform's location (a 100% increase over the other days in the cycle). Female swim speed also varied across the oestrous cycle but females were no less active on the day of oestrus. These results oppose the predictions of the fertility and parental care hypothesis.

Animals↗

PubMed1998

Spatial and discrimination learning in rodents infected with the nematode Strongyloides ratti.

Recent work has shown that mice with subclinical parasitic infections suffer impaired spatial learning and memory, as assayed in an open-field water maze. Although the mechanism underlying this effect is not clear, the phenomenon has been reported following infection with both a protozoan parasite (Eimeria vermiformis) and a gastrointestinal nematode (Heligmosomoides polygyrus). In a variety of experiments, we examined the effects of a different gastrointestinal nematode, Strongyloides ratti, on the ability of rats and mice to learn a spatial or a discrimination task. Animals were tested at various stages post-infection, with different levels of infection, using different lines of S. ratti and with varying experimental protocols. All animals learned the tasks, but we found no evidence of an effect of S. ratti infection on learning or memory. Even rats infected with approximately 5000 S. ratti larvae, a dose which has an impact on rat body size, showed no deficit in learning ability. Various reasons for the conflict between our results and those previously reported for E. vermiformis and H. polygyrus are discussed. Our results show that impaired learning and memory following parasitic infection is not a ubiquitous or at least easily replicated phenomenon.

Analysis of Variance↗

PubMed1994

Social-psychological factors affecting help-seeking for emotional problems.

Predictors of the attitudinal measure of orientation toward help-seeking for emotional problems have been shown to include demographic, network, and personality variables. This research determined whether these same variables predict the behavioral outcome measure of help-seeking, both in general and from professional services in particular. Help-seeking in response to emotional problems was studied in a sample of Australian adolescents. General help-seeking was predicted by more symptoms of psychological distress, being female, availability of social support, knowing someone who had sought professional help, and the personality characteristics of high private self-consciousness and willingness to disclose mental health. When only those with evident emotional distress were considered, only gender and willingness to disclose remained significant predictors. These same variables did not account for those who sought professional help rather than relying upon their informal network. Level of psychological distress was the only significant predictor of professional consultation. Psychological symptoms and gender were shown to be more relevant predictors of the behavioral measure of help-seeking than network or personality characteristics.

Adolescent↗

PubMed1987

The Scale of Emotional Arousability: bridging the gap between the neuroticism construct and its measurement.

This paper outlines and evaluates a newly developed measure of neuroticism, the Scale of Emotional Arousability (SEA). The 15-item scale is economical to use, avoids the consistent pattern of negatively worded items that plagues the neuroticism (N) Scale of the Eysenck Personality Inventory (EPI) and comprises of items that focus specifically on emotional arousability, thereby bringing the measurement of neuroticism in line with Eysenck's (1967) original conceptualization. The SEA shows every indication of being psychometrically sound and correlates with related constructs in much the same way as the N Scale of the EPI. The SEA is recommended as an alternative to the EPI for research purposes, particularly where there is a need to measure independently such related constructs as neurosis, self-esteem and private self-consciousness.

Arousal↗

PubMed1986

An exploratory study of poor adjustment styles among retirees.

This paper focuses on the one third of retirees who report difficulty in making the transition from work to retirement. On the basis of Levy's [16] research, it is hypothesized that there are different styles of poor adjustment that have different consequences for the retirees experiencing them. Data from 487 male and female retirees identify four poor adjustment styles--poor health, negativism, change adaptation and retirement reluctance. While the latter two responses to retirement tend to be problems only in the short term, the former two may have far reaching consequences. Health related retirement and negativism about retiring were linked with low activity and involvement, poor physical and mental health, inadequate income and low life satisfaction in the years following retirement.

Adaptation, Psychological↗

PubMed1986

Old age stereotypes: reconciling contradictions.

This study tested the hypothesis that age stereotyping with specific targets would occur when targets were disabled, when information was minimal, when the context was commonplace, and when the measuring instruments were psychometrically sound. In addition, greater compatibility was anticipated between specific and generalized target evaluations when rating scales were anchored to a fixed comparison point. Using between-subject designs, 208 students completed two judgment tasks and reported on the impact that age had on their evaluations. The traditional stereotyping paradigm revealed both positive and negative stereotypes of old age when the target was generalized but not when the target was specific. The qualitative data are used to suggest shortcomings in the use of the traditional stereotyping paradigm with specific targets.

Adolescent↗