Trade-offs between immunity and testosterone in male African ground squirrels.
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Date
2018-08-23
Authors
O'Brien, Kelsey
Waterman, Jane
Anderson, W. Gary
Bennett, Nigel
Journal Title
Journal ISSN
Volume Title
Publisher
The Company of Biologists
Abstract
The immunocompetence handicap hypothesis (ICHH) proposes that
testosterone has both beneficial effects on male reproductive
potential and negative effects by suppressing the immune system.
However, support for the ICHH has been variable and an alternative
hypothesis suggests that testosterone may be acting indirectly via
cortisol to suppress immunity (the stress-linked ICHH). A third
hypothesis is that increased energetic investment in immunity
results in the suppression of testosterone. We tested these
hypotheses in male Cape ground squirrels (Xerus inauris) through
two separate manipulations: first, by triggering a strong immune
response using a lipopolysaccharide (LPS) injection and, secondly,
by increasing circulating testosterone using silastic testosterone
implants. Responding to an immune challenge significantly reduced
testosterone, supporting the immune suppression hypothesis,
while increasing circulating testosterone had no effect on
immunocompetence, body mass, ectoparasite abundances or
cortisol levels, failing to support either the ICHH or stress-linked
ICHH. Our results add to the increasing body of literature that
challenges the ICHH, and we conclude that the trade-off between
testosterone and immunity is mediated through immune activation
and not through testosterone in male Cape ground squirrels. Being
able to test the ICHH, stress-linked ICHH and immune suppression
hypotheses in a free-ranging mammal gives us a unique opportunity
to examine the mechanisms mediating this trade-off.
Description
Keywords
immunocompetence handicap hypothesis, cortisol, LPS, lipopolysaccharide, Stress-linked ICHH, Cape ground squirrels, Xerus inauris
Citation
O’Brien, KA, Waterman JM, Anderson WG, Bennett NC. 2018. Trade-offs between immunity and testosterone in male African ground squirrels. Journal of Experimental Biology. 221