|Dennis, R - UNIVERSITY OF MARYLAND|
|Estevez, I - UNIVERSITY OF MARYLAND|
|Newberry, R - WASHINGTON STATE UNIV|
|CHENG, HENG WEI|
Submitted to: Journal of the National Academy of Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 24, 2006
Publication Date: N/A
Interpretive Summary: Artificial marking for identification is an integral part of animal experimentation that is employed in many disciplines. Our results demonstrate that application of artificial identification marks to only a proportion of the individuals in a group can alter aggressive behavior, BM and endocrine parameters. We conclude that, when artificial marking is required, both the number and proportion of animals marked within a study population should be taken into consideration in experimental design and interpretation of results. This research should be used by other scientists in their research to improve the reliability of their results.
Technical Abstract: Artificial marking for identification is an integral part of animal experimentation that is employed in many disciplines. The impact of marking on experimental results is rarely considered despite evidence that changes in phenotypic appearance can modify animal behaviour and reproductive success. Here we present evidence that artificial marking of individuals within a group has frequency dependent effects on behaviour and physiology. Using the domestic fowl (Gallus gallus domesticus) as a model, we demonstrate that when 20% or 50% of individuals within a group were artificially marked, the marked birds received more aggression and had lower body mass (BM) than the unmarked individuals within the same group. Furthermore, in groups where only a small proportion of individuals was marked, we report evidence of increased endocrine stress and depressed “fight or flight” response in marked individuals. These effects were imperceptible when all birds in a group were marked. This finding has important implications for animal research because, when only a subset of group members is artificially marked and used for data collection, the results obtained may not be representative of the population.