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Articles by A. Peters
Total Records ( 3 ) for A. Peters
  M. L Roberts , E Ras and A. Peters
 

A central assumption of models of sexual selection, including the immunocompetence handicap hypothesis, is that the male sex hormone testosterone (T) is responsible for the expression of male sexual signaling; however, this has been questioned for colorful avian plumage. In this experiment, we manipulated T in juvenile male blue tits (Cyanistes caeruleus) during the molt and measured crown ultraviolet (UV) chroma (a sexually selected trait) immediately after molt and in the following spring during the breeding season, as well as recording preening behavior during spring. We found that males that were implanted with T during the molt had higher crown UV chroma than control males (C-males) in the subsequent breeding season but not immediately after molt. We also found that testosterone-treated males preened more than C-males during the spring but not during the preceding molt. These results suggest not only that T influences plumage coloration during the mate attraction period, possibly by increasing preening behavior, but also that exogenous T administered during the juvenile molt may have organizational effects in the subsequent breeding season. Because our study supports the assumption that T enhances the expression of male sexually selected plumage coloration, the results indicate that T could enforce costliness, and therefore honesty, of male plumage color as a signal of quality to females.

  W. Rathmann , B. Kowall , M. Heier , C. Herder , R. Holle , B. Thorand , K. Strassburger , A. Peters , H.-E. Wichmann , G. Giani and C. Meisinger
  Background  The aim was to derive Type 2 diabetes prediction models for the older population and to check to what degree addition of 2-h glucose measurements (oral glucose tolerance test) and biomarkers improves the predictive power of risk scores which are based on non-biochemical as well as conventional clinical parameters.

Methods  Oral glucose tolerance tests were carried out in a population-based sample of 1353 subjects, aged 55-74 years (62% response) in Augsburg (Southern Germany) from 1999 to 2001. The cohort was reinvestigated in 2006-2008. Of those individuals without diabetes at baseline, 887 (74%) participated in the follow-up. Ninety-three (10.5%) validated diabetes cases occurred during the follow-up. In logistic regression analyses for model 1, variables were selected from personal characteristics and additional variables were selected from routinely measurable blood parameters (model 2) and from 2-h glucose, adiponectin, insulin and homeostasis model assessment of insulin resistance (HOMA-IR) (model 3).

Results  Age, sex, BMI, parental diabetes, smoking and hypertension were selected for model 1. Model 2 additionally included fasting glucose, HbA1c and uric acid. The same variables plus 2-h glucose were selected for model 3. The area under the receiver operating characteristic curve significantly increased from 0.763 (model 1) to 0.844 (model 2) and 0.886 (model 3) (P < 0.01). Biomarkers such as adiponectin and insulin did not improve the predictive abilities of models 2 and 3. Cross-validation and bootstrap-corrected model performance indicated high internal validity.

Conclusions  This longitudinal study in an older population provides models to predict the future risk of Type 2 diabetes. The OGTT, but not biomarkers, improved discrimination of incident diabetes.

  M Roberts and A. Peters
  Mark Roberts and Anne Peters

In this experiment we manipulated testosterone (T) and condition in juvenile male blue tits (Cyanistes caeruleus) during the moult, to test whether T's supposed immunosuppressive qualities are condition-dependent. To achieve this, we used T and control implants in combination with a dietary manipulation. We measured responses to both phytohaemagglutinin (PHA) and humoral immune challenges during the period of the treatments (moult) and also in the following breeding season (spring). During moult, males fed the enhanced diet were in better condition but there was no difference in humoral response between the dietary groups. T males produced a greater humoral antibody response than control (C) males. In the spring, males that had been previously treated with high T again exhibited higher antibody responses than C males. High T levels during moult were associated with a low PHA response but only in males with low body mass: heavier males that had high T exhibited the highest PHA responses. In the spring, the pattern of PHA responses...

 
 
 
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