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Biomedical subjects

R Knudsen

Publications and source records attributed to R Knudsen.

13 recordsLinked to original sources
PubMed2006

Parallel evolution of ecomorphological traits in the European whitefish Coregonus lavaretus (L.) species complex during postglacial times.

The extensive phenotypic polymorphism in the European whitefish has triggered evolutionary research in order to disentangle mechanisms underlying diversification. To illuminate the ecological distinctiveness in polymorphic whitefish, and evaluate taxonomic designations, we studied nine Norwegian lakes in three watercourses, which each harboured pairs of divergent whitefish morphs. We compared the morphology and life history of these morphs, documented the extent of genetic differentiation between them, and contrasted the niche use of sympatric morphs along both the habitat and resource axes. In all cases, sympatric morphs differed in the number of gill rakers, a highly heritable trait related to trophic utilization. Individual growth rate, age and size at maturity, diet and habitat use also differed between morphs within lakes, but were remarkably similar across lakes within the same morph. Microsatellite analyses confirmed for all but one pair that sympatric morphs were significantly genetically different, and that similar morphs from different lakes likely have a polyphyletic origin. These results are most compatible with the process of parallel evolution through recurrent postglacial divergence into pelagic and benthic niches in each of these lakes. We propose that sparsely and densely rakered whitefish sympatric pairs may be a likely case of ecological speciation, mediated in oligotrophic lakes with few trophic competitors.

Age Factors↗
PubMed2001

Selective predation on parasitized prey--a comparison between two helminth species with different life-history strategies.

In Lake Fjellfrøsvatn, northern Norway, the larval helminths Cyathocephalus truncatus and Cystidicola farionis use Gammarus lacustris as intermediate hosts and Arctic charr (Salvelinus alpinus) as final hosts. There was sampled 1,433 live G. lacustris from the lake and 1,964 G. lacustris from stomach contents of the charr. Prevalence of infection were, respectively, 0.49% and 3.72% for C. truncatus, and 0.21% and 0.20% for C. farionis. Usually, only 1 parasite was present in each host, and the 2 parasite species never co-occurred. Gammarus lacustris amphipods parasitized by C. truncatus were positively selected by the Arctic charr and were consumed approximately 8 times as often as were the unparasitized amphipods or the amphipods infected with C. farionis. This suggests that G. lacustris amphipods infected with C. truncatus larvae are more susceptible to predation than noninfected specimens, probably because of parasite-induced alterations in behavior or visibility. Alternatively, this could also be explained by selection toward the largest G. lacustris specimens observed, which are also the most frequently parasitized amphipods. However, the data show clearly that this was not a result of size-selective predation by the charr. In contrast, the presence of C. farionis did not increase the susceptibility to predation of its intermediate host. The discrepancy between the 2 helminth species supports the hypothesis that parasite-increased susceptibility to predation is related to the life history strategies of the parasites.

Animals↗
PubMed1997

Patterns of coverage. Uniform versus graded density.

The goal of hair restoration surgery is undetectability. Anything that is unnatural or draws attention to itself is to be avoided. In extensive baldness (Norwood V1-V11) various patterns of coverage with grafting can be constructed. Principally they fall into either the graded or uniform density approaches. If the goal is to provide coverage of the entire area of extensive baldness, the uniform density approach offers the less noticeable result because it draws no attention to any particular part of the balding scalp. If the goal is to provide only frontal forelock reconstruction, both approaches are advocated. In less than ideal grooming situations such as in the wind, exercise, or swimming however, the uniform density approach appears to offer a less noticeable result.

Adult↗
PubMed1996

Fear of injections and report of negative dentist behavior among Caucasian American and Taiwanese adults from dental school clinics.

Fear of injections and reports of negative dentist behavior and associations with dental anxiety and avoidance of treatment were explored among 951 adults from dental school clinics in Iowa City, Iowa and Taipei, Taiwan. Use and fear of anesthetic injections and negative dentist behavior were assessed by written questionnaire to test associations with demographics, overall dental anxiety (Dental Anxiety Scale or "DAS") and utilization behaviors. Frequency and logistic regression analyses showed that use of dental anesthetics for routine treatment was much greater overall among caucasian Americans than Taiwanese, as was fear of injections. Taiwanese and Americans with high dental anxiety (DAS 12) had similar high fear of injections, but inspite of similar fears about dental drilling, high anxiety Taiwanese reported using much less local anesthesia for routine treatments than did high anxiety Americans. Report of condescending remarks to patients ("put downs") by dentists was mainly an American phenomenon associated with high dental anxiety. Avoidance of appointment making was high for persons afraid of injections and for Americans reporting negative dentist behavior. Avoidance was highest in subjects with high dental anxiety. That predominant characteristics or etiologies of dental anxiety can differ by cultural differences in dental health care systems, dentist beliefs and/or expectations of patients within those systems was discussed in relation to the literature.

Adolescent↗
PubMed1980

Neurotensin-induced contractions in venous smooth muscle.

Synthetic neurotensin was shown to be a powerful contractant of the isolated rat portal vein. Concentration-dependent increases in basal tension and frequency of spontaneous contractions were obtained in response to single dose (10-1000 nM, final bath concentrations). The responses reached maxima within 2 min and differed in this respect from comparable responses to angiotensin II, substance P and bradykinin, which were maximal after 2-4 min. The "apparent affinity" for neurotensin (pD2 = 7.5 +/- 0.3, S.D., n = 10) was about 10 times less than for angiotensin II while higher than for both the other peptides and for norepinephrine. The "intrinsic activity" was 0.75 (+/- 0.13, S.D., n = 6) relative to angiotensin II during the first 2 min of the response. A pronounced degree of tachyphylaxis was observed; repetition of the neurotensin dose at the lower range of concentrations (1-10 nM) within 2-4 min was completely ineffective. The results suggest that there is a specific neurotensin receptor in the tissue and that neurotensin-induced contractions may play a part in redistributing the blood flow in the gastrointestinal region following release of this peptide from the ileum into the portal circulation.

Angiotensin II↗