| dc.description.abstract | Limited opportunity to establish new conservation areas due to intensive
fragmentation and destruction of once contiguous protected areas as human population
continues to grow is a serious challenge facing wildlife conservation. Knowledge of a
species' social organization, including aspects such as natal dispersal is important in
order to tackle such a challenge. Natal dispersal is an important life history trait that
influences several aspects of a species such as regulation of its gene flow and genetic
structure and in avoiding inbreeding. It provides an opportunity for studying the effects of
change in social context on physiological systems such as reproduction and stress
response. In addition, it provides an opportunity for studying the physiological correlates
of life history trajectories such as pervasiveness of maternal effects and food availability
during critical periods of growth and development. The goals of this study were to
determine (I) the relationship between food availability and timing of natal dispersal (2)
whether the social context of the natal, group suppresses secretion of reproductive
hormones, and consequently whether it represents a stressful period among natal males
(3) effects of maternal life history traits such as maternal parity and dominance rank, and
of food availability during gestation-and lactation on reproductive and stress hormone
secretion in yellow baboons in the Amboseli/Longido basin, l'~uthem Kenya.
Data on rainfall and demography of the Amboseli baboons were collated from the
Amboseli Baboon Research Project database. The Project is a longitudinal study
spanning over three decades. Steroid analysis was done non-invasively, from faecal
samples collected following observed spontaneous defaecation by individually know
male baboons. Faecal concentrations of glucocorticoid (GC) and testosterone (T)
metabolites were measured using 1125 radio-irnmunoassays, using techniques that had
previously been modified and validated for use in the yellow baboon at Princeton
University. Non-invasive hormonal analysis has numerous advantages over invasive
methods such as those involving collection of serum. For example, collection of faecal
samples does not involve animal handling and is therefore free from stress due to animal
immobilization. It is therefore ideal for studies that monitor stress even in endangered
species. In addition, it allows for repetitive collection of samples and suitable for
longitudinal studies that require many samples.
The present results show that male baboons do not show seasonality in the timing
of natal dispersal. However, males that dispersed during months of low food availability
had higher concentrations of faecal GC (fGC) than those that dispersed during months of
high food availability during the last 10 months to dispersal [t test: t 82= 3.074, P < 0.05:
mean ± SE, high food availability = 40.015 ± 2.821; low food availability = 56.035 ±
4.507J. After dispersal, however, the distribution of rGC concentrations between males
that dispersed during months of high food availability and those that dispersed during
months of low food availability were not significantly different (Mann Whitney U, Z = -
0.664, P = 0.507).
The secretion of T was found to be suppressed in natal male baboons.
Concentrations of faecal T (IT) after natal dispersal was significantly higher than that of
natal males (t247= -2.832, P = 0.005). The study attributed the high IT concentration after
natal dispersal to either increased expression of sexual behaviour or increase in
reproductive physiology or both. The differences in IT concentrations between natal and
post-dispersal males were likely due to the change ill social context, that is, from living
with related to living with unfamiliar con-specifics. It was concluded that the social
context in the natal group suppresses the secretion of testosterone. Effect of age was
however not ruled out. The study did not show that natal baboons are stressed, as
indicated by the concentrations of fOC obtained from samples collected before and after
natal dispersal. Concentrations of faecal OC did not differ significantly during dispersal,
which was divided into 4 10-month periods (F 3,245 = 6.646, P = 0.179). Concentrations
of OC among breeding males were found to be significantly higher from those of
dispersing males, 20 months before and after natal dispersal (t377= -5.632, P = 0.000).
The study did not find a directional relationship between concentrations of IT and
neither maternal parity nor dominance rank. Maternal parity did not show any directional
relationship with concentrations of fOe. However, males conceived when their mothers
were low ranking at conception had high mean concentrations of fOC. This relationship
was observed to persist beyond life in the natal group, which suggests that maternal
dominance may pervasively affect the predisposition of male baboons to stress.
Food availability during gestation and lactation did not contribute significantly to
the variations in concentrations of fOC before and after natal dispersal (standard multiple
regressions, food availability during gestation: 20-11 months prior to dispersal =
Adjusted R2 = 0.299, P = 0.177; 10-1 months prior to dispersal, Adjusted R2 = 0.017, P
0.375; 1-10 months post-dispersal, Adjusted R2 = 0.250, Y = 0.250; 11-20 months post-
dispersal, Adjusted IF = 0.364, P = 0.139. Similarly, food availability during gestation
and the first 5 months of lactation did not contribute significantly to variations in IT
concentrations (20-11 months prior to dispersal, Adjusted R2 = -0.173, P = 0.643; 10-1
months prior to dispersal, Adjusted I{i -0.0 I '), P 0.441; 1-10 months post-dispersal,
Adjusted R2 = -0.049, P = 0.489; 11-20 months post-dispersal, Adjusted R2 = 0.322, P =
0.866).
It was concluded that although male baboons do not show seasonality in the
timing of natal dispersal, dispersing during months of low food availability may involve
incurring a metabolic cost. That is, males that disperse during months of low food
availability may be highly vulnerable to the deleterious effects of elevated levels of GCs.
Furthermore, the catabolic role of GCs imply that males that disperse during months of
low food availability join their new groups at a metabolic disadvantage, and have to
replenish their energy reserves before engaging in sexual contests. It is worth noting that
maternal effects or food availability during gestation and lactation did not influence the
secretion of T in male baboons, even when they influenced the secretion of GC. The
disparity in the influence of maternal effects and food availability on the secretion of T
and GC was attributed to a possible evolution of a mechanism that has decoupled
maternal and nutritional influences on t~e hypothalamo-pituitary gonadal axis from those
on the hypothalamo-pituitary adrenal axis. Nevertheless, it is worth mentioning that the
present study sought to investigate the reproductive and stress hormonal correlates more
than 7 years after birth of the males. The potential of the high ecological flexibility of
baboons and other social factors in influencing the secretion of the steroids cannot be
ruled out. Research is needed to study the developmental profiles of reproductive and
stress and stress hormones in the yellow baboons in order to tease social effects from
developmental effects. | en |
