Experimentally Elvated Tesosterone and
Female Parental Care in the Dark-eyed Junco
Experimental elevation of plasma testosterone (T) in male dark-eyed
juncos (Junco
hyemalis) has been shown to decrease male parental care, but
results in an
overall fitness increase due to increased mating success. This
shift from
parental care behaviors to behaviors associated with mate acquisition
results
in an overall fitness increase for male dark-eyed juncos creating a
kind of
paradox: if male fitness could be higher if T were higher, what
prevents
evolution from favoring higher levels of T?
It has been hypothesized that the potential benefits associated with
higher
levels of T in males may be offset by deleterious effects in females
(Clotfelter et al. 2004). Since it is proposed the T could
be
mediating parental care behaviors in males, I have focused on parental
care in
the female junco with the expectation that because females invest the
most time
and energy via nest construction, incubation, and nestling brooding and
nestling feeding, alterations in their parental care behavior will
greatly
impact fitness. In juncos, previous studies have shown elevated T
in
female juncos does not suppress parental behaviors when females are
incubating
(Clotfelter et al. 2004) but the effect of experimentally elevated T on
other
aspects of female parental care remains to be discovered.
To assess the possible means of female constraint in the junco, I ask
if elevated
T impairs female parental care, particularly care associated with
nestling
brooding, feeding and nest defense and whether any
alterations in behavior could be related to
fitness. We found that treatment with testosterone significantly
reduced
the amount of time females spent brooding nestlings, the total time
females spent
on the nest, and intensity of nest defense. Additionally, treatment
with T
reduced both nest success and the probability of producing at least one
fledgling. Collectively our findings suggest that female juncos with
naturally
higher levels of testosterone may be selected against.
Our findings also provide provisional support
for the hypothesis that response to selection favoring higher
testosterone in
males might be constrained if it led to a correlated response in
females.
Publications
O’Neal, D.M., Reichard, D.G.,
Pavlis, K.,
Ketterson, E.D. (in review). Consequences of experimentally elevated
testosterone on female parental care and reproductive success in the
dark-eyed
junco. Hormones and Behavior.
Clotfelter ED, O'Neal DM et
al. (2004) Consequences of elevating plasma
testosterone in females of a socially monogamous songbird: evidence of
constraints on male evolution? Hormones and Behavior. 46:
171-178.
Presented
Papers
Does
Testosterone Mediate Parental Care Behaviors in the Female Dark-eyed
Junco?
Society for Integrative and Comparative Biology. January 2007. Oral
Presentation
Testosterone
in Female Birds. North American Ornithological Conference. October
2006.
Invited Speaker
Testosterone
and Parental Care in Female Dark-eyed Juncos: A case of behavioral
insensitivity? Mountain
Lake Biological
Station.
June 2006. Oral Presentation