As I’ve mentioned before, I’m primarily interested in the
development of an animal’s hormonal stress response. The main stress hormone in
degus (and humans) is cortisol (CORT), which is regulated by the
hypothalamic-pituitary-adrenal (HPA) axis. Previous work on mice has shown that
experiences after birth (termed “post-natal effects”) can influence the
development of the HPA-axis. Mouse pups that do not receive enough licking and
grooming from their mothers will end up with hyperactive stress responses,
which means that they will secrete high levels of CORT in response to stressors
and will have a harder time bringing CORT levels back to normal after a
stressor has passed. Because stressed mothers lick and groom their pups at a
lower frequency, this means that maternal stress can affect the development of
the offspring stress response.
One of my main research goals is to see if stressed mothers
produce pups with altered stress responses. The other main goal of my research
is to determine whether the degu’s social structure can help buffer the
negative effects of post-natal stress. Because degu females live in social
groups and will care for other female’s pups (this reproductive strategy is
called “plural breeding with communal care”), if one mother in the social group
is stressed, then other females within the group may be able to compensate for
the lack of maternal care.
In 2011 and 2012, I did a manipulative field experiment
where I implanted certain degu mothers with CORT pellets after they gave birth.
In some social groups all the mothers were implanted with CORT, while in other
groups 0% or 50% of the mothers received CORT implants. After the pups emerged
three weeks later, I trapped them and took blood samples to determine their
stress responses.
However, one thing that I was not able to do in the field
was to confirm that the CORT pellets decreased the amount or quality of maternal
care. Because degus spend the first few weeks of their lives underground in
burrows, it’s impossible to observe mother-pup interactions during this
important time. So, what I’m doing now is basically replicating my field
experiment in the lab so I can also observe the behavior of the mothers and
pups.
Currently, I have 32 pregnant female degus in my
collaborator’s animal rooms at the Universidad Católica de Chile. My females
are housed in pairs in acrylic terrariums, and as soon as they give birth I
will implant certain females with CORT and start filming them with a home
security camera system. I’ll be watching the videotapes later and will score
behaviors such as time spent at the nest, how often the pups nurse, and the
rate of licking and grooming. When the pups are about three weeks of age, I’ll
take blood samples so I can compare their stress responses to those pups that I
caught in the field.So that’s a basic overview of what I’m doing this year, and stay tuned for more posts! I’ll be writing about the importance of flexibility and contingency plans in scientific research, the comparison between doing lab and field research, and the different theories about why the HPA-axis is plastic during development.
