Socioendocrinology
In
collaboration with Drs J.A. French and S.E. Glickman, we are using levels
of steroid hormones excreted in feces to study relationships among hormonal,
ecological, and behavioral variables in wild and captive hyenas. Current
& former students worked with Dr French develop suitable extraction
protocols and assays with which to measure excreted corticosterone, estrogen,
and androgens in hyena feces. After immunological validation of these
assays had been completed, Drs Glickman and N. Place then used captive
Berkeley hyenas to validate these assays in vivo, and they also examined
effects of early treatment with anti-androgens on the hypothalamic-pituitary-gonadal
axis in this species (Place et al 2002a). Dr Stephanie Dloniak has found
that interacting with large aggressive females represents a significant
“challenge” for male hyenas. Dr Dloniak has also found support
for the hypothesis suggesting that concentrations of circulating and excreted
androgens vary with maternal social rank during pregnancy, and that offspring
behavioral phenotype varies with maternal androgen levels during pregnancy.
This suggests that a special form of non- genetical "inheritance"
might occur in mammals analogous to maternal deposition of androgens in
the yolk of bird eggs (eg., Schwabl et al 1997). In a related analysis
with Dr M. Spencer we found that circulating levels of insulin-like growth
factor (IGF-I) in young hyenas increase with maternal rank, suggesting
yet another possible mechanism of non-genetical "inheritance."
There is no relationship between concentrations of excreted glucocorticoids
(GCs) and social rank in hyenas, thus corroborating work by Goymann et
al (2001), but male androgen levels increase dramatically when they disperse
to a new clan (Holekamp & Smale 1998; Holekamp & Sisk 2003). We
plan to continue our endocrine work and add tests of an hypothesis suggesting
that excretion of GCs is affected by differential exposure to interspecific
competition.