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Biomedical subjects

R W Elwood

Publications and source records attributed to R W Elwood.

At least 19 recordsLinked to original sources
PubMed2005

Ecological impacts of the microsporidian parasite Pleistophora mulleri on its freshwater amphipod host Gammarus duebeni celticus.

The microsporidian parasite, Pleistophora mulleri, infects the abdominal muscle of the freshwater amphipod Gammarus duebeni celticus. We recently showed that P. mulleri infection was associated with G. d. celticus hosts being more vulnerable to predation by the invasive amphipod Gammarus pulex. Parasitized G. d. celticus also had a reduced ability to prey upon other co-occurring amphipods. We suggested the parasite may have pervasive influences on host ecology and behaviour. Here, we examine the association between P. mulleri parasitism and parameters influencing individual host fitness, behaviour and interspecific interactions. We also investigate the relationship between parasite prevalence and host population structure in the field. In our G. d. celticus study population, P. mulleri prevalence was strongly seasonal, ranging from 8.5% in summer to 44.9% in winter. The relative abundance of hosts with the heaviest parasite burden increased during summer, which coincided with high host mortality, suggesting that parasitism may regulate host abundance to some degree. Females were more likely to be parasitized than males and parasitized males were paired with smaller females than unparasitized males. Parasitism was associated with reduction in the host's activity level and reduced both its predation on the isopod Asellus aquaticus and aggression towards precopula pairs of the invasive G. pulex. We discuss the pervasive influence of this parasite on the ecology of its host.

Amphipoda↗
PubMed2001

Decision rules, energy metabolism and vigour of hermit-crab fights.

Aggressive interactions between animals are often settled by the use of repeated signals that reduce the risk of injury from combat but are expected to be costly. The accumulation of lactic acid and the depletion of energy stores may constrain activity rates during and after fights and thus represent significant costs of signalling. We tested this by analysing the concentrations of lactate and glucose in the haemolymph of hermit crabs following agonistic interactions over the ownership of the gastropod shells that they inhabit. Attackers and defenders play distinct roles of sender and receiver that are fixed for the course of the encounter. Attackers perform bouts of 'shell rapping', which vary in vigour between attackers and during the course of the encounter, and are a key predictor of victory. In contrast to the agonistic behaviour of other species, we can quantify the vigour of fighting. We demonstrate, to our knowledge for the first time, an association between the vigour of aggressive activity and a proximate cost of signalling. We show that the lactate concentration in attackers increases with the amount of shell rapping, and that this appears to constrain the vigour of subsequent rapping. Furthermore, attackers, but not defenders, give up when the concentration of lactate is high. Glucose levels in attackers also increase with the amount of rapping they perform, but do not appear to influence their decision to give up. Defenders are more likely to lose when they have particularly low levels of glucose. We conclude that the two roles use different decision rules during these encounters.

Aggression↗
PubMed2001

MicroCog: assessment of cognitive functioning.

MicroCog: Assessment of Cognitive Functioning version 2.1 (Powell, D. H., Kaplan, E. F., Whitla, D., Catlin, R., and Funkenstein, H. H. (1993). The Psychological corporation, San Antonio, TX.) is one of the first computerized assessment batteries commercially developed to detect early signs of cognitive impairment. This paper reviews its psychometric characteristics and relates them to its clinical utility. It concludes that MicroCog provides an accurate, cost-effective screen for early dementia among elderly subjects living in the community and that it can distinguish dementia from depression. Its ability to detect cognitive decline at other ages or to discriminate dementia from other mental disorders has not been established. MicroCog measures different constructs than do traditional neuropsychological tests, making it difficult to relate test performance to current models of cognitive functioning. The review recommends further development of MicroCog and discusses its implications for the future of computer-based neuropsychological assessment.

Cognition Disorders↗
PubMed2000

Cumulative or sequential assessment during hermit crab shell fights: effects of oxygen on decision rules.

Agonistic interactions between animals are often settled by the use of repeated signals which advertise the resource-holding potential of the sender. According to the sequential assessment game this repetition increases the accuracy with which receivers may assess the signal, but under the cumulative assessment model the repeated performances accumulate to give a signal of stamina. These models may be distinguished by the temporal pattern of signalling they predict and by the decision rules used by the contestants. Hermit crabs engage in shell fights over possession of the gastropod shells that they inhabit. During these interactions the two roles of signaller and receiver may be examined separately because they are fixed for the duration of the encounter. Attackers rap their shell against that of the defender in a series of bouts whereas defenders remain tightly withdrawn into their shells for the duration of the contest. At the end of a fight the attacker may evict the defender from its shell or decide to give up without first effecting an eviction; the decision for defenders is either to maintain a grip on its shell or to release the shell and allow itself to be evicted. We manipulated fatigue levels separately for attackers and defenders, by varying the oxygen concentration of the water that they are held in prior to fighting, and examined the effects that this has on the likelihood of each decision and on the temporal pattern of rapping. We show that the vigour of rapping and the likelihood of eviction are reduced when the attacker is subjected to low oxygen but that this treatment has no effect on rates of eviction when applied to defenders. We conclude that defenders compare the vigour of rapping with an absolute threshold rather than with a relative threshold when making their decision. The data are compatible with the cumulative assessment model and with the idea that shell rapping signals the stamina of attackers, but do not fit the predictions of the sequential assessment game.

Animals↗
PubMed2000

Imperfect assessment and limited information preclude optimal strategies in male-male fights in the orb-weaving spider Metellina mengei.

Agonistic behaviour between male orb-web spiders Metellina mengei competing for access to female webs was examined in field experiments to test the major predictions of game theory. Winners of fights were significantly larger than losers, particularly with respect to the length of the first pair of legs, which are sexually dimorphic in this species and used extensively in agonistic encounters. The size of the winning male had no influence on contest intensity or duration, and neither did relative size. However, fight intensity and duration were both positively correlated with the size of the losing male. Resident males won significantly more contests than intruders. Winning intruders were significantly larger than winning residents and it was these winning intruders that tended to produce the longer fights. Female weight and hence reproductive value had a marked influence on fight intensity and duration of fights won by the intruder but not those won by the resident. This indicates that only the resident obtains information about the female. These data are discussed with reference to the discrepancy with theory and a failure of some contestants to obtain information on resource value and relative contestant size necessary to optimize fight strategy.

Aggression↗
PubMed1995

The California Verbal Learning Test: psychometric characteristics and clinical application.

The California Verbal Learning Test (CVLT) is a popular clinical and research test that claims to measure key constructs in cognitive psychology such as repetition learning, serial position effects, semantic organization, intrusions, and proactive interference. The psychometric characteristics of the CVLT are reviewed and related to the test's clinical utility. The utility of the CVLT is shown to be limited by its poor standardization and inflated norms. Further, the validity is limited because the CVLT uses multiple trials whereas the constructs it purports to measure are based on single-trial paradigms. The review proposes modifications to the CVLT and guidelines for its clinical use. It concludes that if the limitations of the CVLT are recognized, it can still make a useful contribution to the clinical assessment of verbal learning and memory.

Adolescent↗
PubMed1993

Delayed recall on the Wechsler Memory Scale-revised: the factor structure revisited.

Although delayed recall tasks are prominent features of the popular Wechsler Memory Scale-Revised (WMS-R), exploratory factor analyses consistently have failed to identify an associated delayed recall factor. The present study tested the hypothesis (Elwood, 1991b) that a delayed recall factor could be found by substituting percent retained (saving) scores for the existing WMS-R delayed recall subtest scores. Principal component analyses of age-corrected WMS-R immediate and save scores in a mixed clinical sample failed to find the hypothesized save factor. Both the scree and MAP tests retained one general memory factor, which accounted for 42.2% of the total variance. Independent statistical programs produced essentially equivalent results. Clinical implications of these findings are discussed.

Adult↗
PubMed1993

The clinical utility of the MMPI-2 in diagnosing unipolar depression among male alcoholics.

The correspondence between Scale 2 elevations on the MMPI-2 and SCID-diagnosed unipolar depression (major depression and dysthymia) and alcohol-induced depression was evaluated among 106 consecutive male admissions to an inpatient alcohol treatment unit. Valid profiles were obtained from 87 subjects, 15% of whom were diagnosed with unipolar depression and another 4.5% with presumed alcohol-induced depression. The sensitivity of Scale 2 (the probability that a depressed subject would obtain an elevated score) ranged from .19 to .42. Positive predictive power (the probability that a subject who obtained an elevated score had a depressive disorder) ranged from .23 to .38. Neither Scale 2 alone nor Scale 2 paired in 2-point code types predicted the presence or absence of comorbid depressive disorders among male alcoholics.

Adult↗
PubMed1991

The Wechsler Memory Scale-Revised: psychometric characteristics and clinical application.

The psychometric characteristics of the Wechsler Memory Scale-Revised (WMS-R) are evaluated and related to its clinical utility. The accuracy of the scale scores is shown to be limited by their high standard error, low reliabilities, and consequent large standard errors of measurement. Specific procedures are discussed for establishing confidence intervals and for testing the significance of differences between scores. It is concluded that the WMS-R, like the original Wechsler Memory Scale, provides only a rough estimate of overall memory functioning. The multidimensional index scores have not been shown effective in describing the nature or the pattern of memory deficits. Recommendations for the clinical use of the WMS-R are provided.

Brain Damage, Chronic↗
PubMed1991

Selectivity in paternal and infanticidal responses by male mice: effects of relatedness, location, and previous sexual partners.

Male mice tend to be infanticidal to unrelated infants but parental to their own offspring. The present study examines three hypotheses that might explain this apparent discrimination. There was no evidence of selective infanticide toward infants encountered for the first time on the basis of kinship, location, or cues associated with previous sexual partners. However, males tended to direct more paternal responses toward their own unfamiliar infants than toward unrelated infants, infants encountered in the male's home cage than those in the cage of another male, and when cues associated with a previous sexual partner were present. Data suggested that the responses of females to male intruders might influence the responses of those males. It was concluded that the infanticidal responses of male mice are mediated by a particular state of the male but that males in a noninfanticidal state may vary their paternal responsiveness on the basis of direct and indirect cues concerning relatedness.

Animals↗
PubMed1990

Responses of infant mice to odors of urine from infanticidal, noninfanticidal, and paternal male mice.

Infant mice responded differently to the odors of urine from isolated-infanticidal, isolated-noninfanticidal, and parental males. More ultrasonic vocalizations were produced in response to urine odors of parental males than to those of isolated-infanticidal males and more to infanticidal than to noninfanticidal males. Infants became agitated in the presence of urine odors of infanticidal males and moved away from the odor source whereas they tended to remain stationary in response to urine odors of parental males. The response to urine odors of noninfanticidal males was intermediate. These data support the hypothesis that infanticidal and parental states have different physiological bases and that this physiological difference results in different chemical composition of urine. The data failed to support the hypothesis that infants will attempt to conceal themselves from infanticidal males by remaining quiet.

Animals↗
PubMed1990

The relationship between infanticide and pregnancy block in mice.

Newly pregnant mice are more likely to exhibit pregnancy block when females are exposed to infanticidal males rather than to noninfanticidal males. These data suggest that females are able to assess the risk to their future infants and adjust their reproductive tactic. Those females that did not exhibit pregnancy block in the presence of infanticidal males suffered a greater loss of pups than those in the presence of noninfanticidal males, demonstrating the advantage of pregnancy block. Females served by infanticidal or noninfanticidal males showed no difference in pregnancy block, but if the litter was produced, there was a greater loss of pups sired by infanticidal males.

Animals↗
PubMed1989

Epileptic tendencies in relation to behavioral responses to a novel environment in the Mongolian gerbil.

The severity of epileptic-like seizures in gerbils (Meriones unguiculatus), placed in an open field, is directly related to their ambulatory activity on subsequent trials. An inverse relationship, however, occurs between seizure severity and oriented, bipedal rearing behavior on subsequent trials. Principal components and multiple linear regression analyses support the hypothesis that ambulation and rearing have different underlying neuronal mechanisms. If these two activities are considered as measures of arousal and attention, respectively, then epileptic-like seizures may be caused by hyperactivity of mechanisms which induce arousal.

Animals↗
PubMed1988

Strain differences in the inhibition of infanticide in male mice (Mus musculus).

The mediating mechanisms for the inhibition of infanticide in male mice were examined in two strains of mice. Both copulation and postcopulatory cohabitation inhibited infanticide in CS1 males whereas only postcopulatory cohabitation inhibited infanticide in CBA males. These data illustrate the difficulties of making conclusions concerning infanticide from single studies using single strains or species.

Animals↗
PubMed1986

Discrimination between conspecific and allospecific infants by male gerbils and mice before and after experience of their own young.

Prior to the birth of their 1st litter, male gerbils generally respond paternally toward both gerbil and mouse pups. Once they have experience of their own pups, however, they continue to respond paternally toward unrelated gerbil pups but kill mouse pups. Male CSI mice, on the other hand, respond paternally to unrelated mouse pups both before and after the birth of their own litter but tend to ignore gerbil pups at these times. These data are discussed with respect to infanticide, onset of paternal care and the narrowing of effective stimuli for eliciting paternal care.

Aggression↗
PubMed1986

What makes male mice paternal?

Both copulation and postcopulatory cohabitation with pregnant females reduce infanticide and enhance paternal responsiveness in male CS1 mice. The effectiveness of copulation in this process, however, depends on the number of occasions that males have previously encountered infants. Infanticidal males which have been subordinated in brief encounters with other males are less likely to commit infanticide in subsequent tests than are those which became dominant to other males. Males which copulate and cohabit with a relatively large female are less likely to be infanticidal than are those with a relatively small female. These data suggest that males are subordinated after copulation by their mates and that this subordination is a factor in the reduction of infanticide and the initiation of paternal responsiveness.

Aggression↗
PubMed1984

Hunger and the vocalizations of infant gerbils.

Infant gerbils were deprived of food by removing their mother from the cage for 3 hr on alternate days, during which time they remained with their father. These infants were compared with a control group which remained with their mother while the father was removed. Litters lost weight when deprived of food but they received similar levels of parental care, warmth, and tactile stimuli to those of nonfood-deprived litters. There were no significant effects on the vocalizations of the young when tested either in isolation or in the nest with other pups. This apparent absence of a mode of communicating nutritional state is discussed with reference to normal interactions between adults and the litter and the role of vocalizations produced in response to heat loss.

Animals↗