Abstract:
Biologically inert material in feces may confound interpretations
of noninvasive fecal endocrine data, because it may induce
variance related to differences in foraging behavior rather than
to differences in endocrine activity. We evaluated two different
enzyme immunoassays (EIAs) for the noninvasive evaluation
of adrenocortical activity in ground-feeding aardwolves (Proteles
cristata) and tested the influence of soil content in aardwolf feces on the interpretation of fecal glucocorticoid metabolite
data. Using adrenocorticotropic hormone (ACTH) challenges
for validation, we successfully identified a cortisol EIA suitable
for assessing adrenocortical activity in aardwolves. An alternatively
tested 11-oxoetiocholanolone EIA failed to detect a
biologically relevant signal after ACTH administration. Although
the proportion of inorganic content in aardwolf feces
did not alter qualitative conclusions from the endocrine data,
the data related to mass of organic content had a larger amount
of variance attributed to relevant biological contrasts and a
lower amount of variance attributed to individual variation,
compared with data related to total dry mass of extracted material.
Compared with data expressed as dry mass of extracted
material, data expressed as mass of organic content may provide
a more refined and statistically powerful measure of endocrine
activity in species that ingest large amounts of indigestible
material.
