This study examined the relationship between social stress, as measured by fecal glucocorticoid metabolite (FGM) levels, reproductive success, and social rank in wild female yellow-bellied marmots over nine years. The researchers found that lower-ranking females had higher FGM levels and smaller litters compared to higher-ranking females. Additionally, females in larger colonies and those with higher body mass the previous year were more likely to reproduce and have larger litters, while more predators in an area and being younger decreased reproduction chances. Overall, increased social stress from factors like rank was associated with reduced reproductive success in female marmots.

1. We thank all the marmoteers, since 2001, who have helped collect these data. D.T.B was supported by the National Geographic
Society, UCLA (Faculty Senate and the Division of Life Sciences), a Rocky Mountain Biological Laboratory research fellowship, and by
the NSF (IDBR-0754247 and DEB-1119660 to D.T.B., as well as DBI 0242960 and 0731346 to the Rocky Mountain Biological
Laboratory). J.E.S. was supported by funds from Faculty Development Funds and from the Provost’s Office at Mills College as well as
by fellowships from the American Association of University Women, the Institute for Society and Genetics at the University of California
Los Angeles, and the American Philosophical Society.
GRAPHICS: www.adamspestcontrol.com; www.ironphoenix.org
a Department of Ecology and Evolutionary Biology, University of California Los Angeles, Los Angeles, CA USA
b Department of Biology, Mills College, Oakland, CA,USA
c The Rocky Mountain Biological Laboratory, Crested Butte, CO, USA
Fitness & hormonal correlates of social and ecological stressors in
wild yellow-bellied marmot females
Vertebrates’ stress responses can be measured by
glucocorticoid (GC) hormones.
GC Production varies among species & can be
influenced by:
 Reproductively dominant females can be more
stressed to maintain their position
 Reproductively subordinate females can be more
stressed because of violence from reproductively
dominant females
However, individuals with higher FGM had
increased reproductive success. This suggests that
the reproductive skew may be due to factors other
than social rank, such as body mass, colony size,
or predator abundance.
Higher FGM levels =
• More likely to
reproduce
• Larger litter sizes
• Lower social rank
Higher social rank =
• Lower FGM levels
• Larger litter size
Larger colonies =
• Higher FGM levels
• More likely to
• reproduce
• Larger litters
(Graphed on right)
More predators =
• Higher FGM levels
• Less likely to
reproduce
Two year olds =
• Higher FGM levels
• Less likely to
reproduce
Increased mass
previous year =
• Higher FGM levels
• More likely to
reproduce
• Larger litters
Perhaps, in species like marmots (that only
have a single chance per year to reproduce),
reproductive suppression should be rare and
social interactions won’t affect reproductive
success.
What is the relationship between female social
rank and stress in adult females? Is stress
associated with reproductive success?
Kathryn N. Keeley a, Jennifer E. Smith b, & Daniel T. Blumstein a, c
We used long-term data
on yellow-bellied
marmots (YBM; Marmota
flaviventris). YBMs live in
dominance hierarchical
societies with ~50
females in each colony.
𝑪𝑩𝑰 =
(𝑩 + 𝒃 + 𝟏)
(𝑳 + 𝒍 + 𝟏)
B = number of “losers” that the individual has “beaten”
b = number of marmots that the “losers” (B) have “beaten”
L = number of “winners” that have “beaten” the individual
l = number of marmots that have “beaten” the “winners” (L)
YBM were live-
trapped & marked in
the field. Information
& fecal samples were
collected.
• Observe YBM for agonistic behavior
(aggression & accompanied by
biting, chasing, or fighting)
• Record “winners” & “losers” of each
interaction
GC levels were extracted from YBM feces. We called
these Fecal Glucocorticoid Metabolites (FGM) Social
rank hierarchies were calculated with the Clutton-Brock
Index (CBI):
Our models included 9 fixed effects, including:
body mass, predator abundance, age,
and colony size
Lower-ranking females had relatively
higher GC levels and had smaller litters
compared to higher-ranking females
Predator abundance may have sublethal effects on
prey by creating a predator-induced “stress”
Body mass from the previous year indicated that
dominant females may be in better body condition
than their subordinates due to increased access to
resources.
Body condition (e.g. body mass)
Ecology (e.g. predators, food availability)
Sociality (e.g. social rank within group)
 Subordinates may have higher GC (i.e.
because of harassment, lack of resources, etc)
 Dominants may have higher GC (i.e. to
maintain social rank)
 May be no relationship between rank & GC
Not all individuals breed or produce surviving
offspring & GCs may be a mechanism of this
reproductive failure.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
80
100
120
140
160
180
200
220
240
260
-0.1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
Fecalglucocorticoidmetabolites
(ng/gfeces)
Numberofpupssurvivingto
weaning
Relative social rank of adult females
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
low FCMs
large colony
low FCMs
small colony
high FGMs
large colony
high FGMs
small colony
Proportionofadultfemalesthat
reproduced
N = 68 N = 30 N = 116 N = 44
The Effect of FGM and Colony Size on
Reproduction
The Effect of FGM and Rank on Reproductive
Success
We studied 5
colonies in
Gunnison
County, CO from
2003-2011.
1.0
1.5
2.0
2.5
3.0
3.5
Low Heavy
#pupssurvivingtoweaning
0.46
0.48
0.50
0.52
0.54
0.56
0.58
0.60
0.62
low predation high predation
Proportionofadultfemales
thatreproduced
N = 122 N = 151
Number pups weaned
increases with body mass
from the previous year
Females reproduce less with
high predator abundance
N = 139 N = 134