DOI: 10.5061/dryad.6782r
title: Data from: Plasma markers of oxidative stress are uncorrelated in a wild mammal

description: Oxidative stress, which results from an imbalance between the production
 of potentially damaging reactive oxygen species versus antioxidant
 defenses and repair mechanisms, has been proposed as an important mediator
 of life-history trade-offs. A plethora of biomarkers associated with
 oxidative stress exist, but few ecological studies have examined the
 relationships among different markers in organisms experiencing natural
 conditions or tested whether those relationships are stable across
 different environments and demographic groups. It is therefore not clear
 to what extent studies of different markers can be compared, or whether
 studies that focus on a single marker can draw general conclusions
 regarding oxidative stress. We measured widely used markers of oxidative
 damage (protein carbonyls and malondialdehyde) and antioxidant defense
 (superoxide dismutase and total antioxidant capacity) from 706 plasma
 samples collected over a 4-year period in a wild population of Soay sheep
 on St Kilda. We quantified the correlation structure among these four
 markers across the entire sample set and also within separate years, age
 groups (lambs and adults), and sexes. We found some moderately strong
 correlations between some pairs of markers when data from all 4 years were
 pooled. However, these correlations were caused by considerable among-year
 variation in mean marker values; correlation coefficients were small and
 not significantly different from zero after accounting for among-year
 variation. Furthermore, within each year, age, and sex subgroup, the
 pairwise correlation coefficients among the four markers were weak,
 nonsignificant, and distributed around zero. In addition, principal
 component analysis confirmed that the four markers represented four
 independent axes of variation. Our results suggest that plasma markers of
 oxidative stress may vary dramatically among years, presumably due to
 environmental conditions, and that this variation can induce
 population-level correlations among markers even in the absence of any
 correlations within contemporaneous subgroups. The absence of any
 consistent correlations within years or demographic subgroups implies that
 care must be taken when generalizing from observed relationships with
 oxidative stress markers, as each marker may reflect different and
 potentially uncoupled biochemical processes.
description: ECE-2015-07-00379 Dryad
 DataThe data contained in
 this file come from a much larger database curated by the Soay sheep
 project. If you are interested in using the data we strongly recommend you
 contact us, as we most likely have additional data that could be useful to
 you and can assist with interpretation of results based on the biology of
 the system. Note that the individual identity codes in this file have been
 re-coded and will not correspond with those in other data files from the
 Soay sheep project which you may find in data repositories. Please contact
 Dan Nussey (dan.nussey@ed.ac.uk) if you think you would be interested in
 using the data.