Female reproductive energetics in mantled howler monkeys (Alouatta palliata): A follow-up study.

OBJECTIVE: Reproduction entails several challenges to primate females, among which energetic costs are remarkable at certain stages of the reproductive cycle. Still, females may use behavioral and physiological strategies to cope with those challenges. We had previously reported covariation between female energetic condition through the reproductive cycle and time-budget adjustments in mantled howler monkeys (Alouatta palliata). Accordingly, we suggested that behavioral flexibility allowed coping with the energetic challenges of reproduction. Subsequent evidence from the same population, however, suggested otherwise, so we performed a follow-up study on the variation in female reproductive energetics based on a larger sample of females. METHODS: We studied 48 free-ranging adult females at Los Tuxtlas (Mexico). We assessed energy balance via urinary C-peptide concentrations (2717 urine samples), behavioral energy intake and expenditure (5728 sampling hours), and physiological energy expenditure via fecal triiodothyronine metabolites (fTH3; 3138 fecal samples). RESULTS: We found that energy balance varied among reproductive states: (a) cycling was a period of low C-peptide concentrations; (b) the highest C-peptide concentrations occurred during gestation; and (c) the beginning of lactation marked a notable decrease in C-peptide concentrations, which then improved at mid-lactation to again decline at lactation offset. These peaks and valleys in energy balance did not seem to be associated with variation in energy acquisition but were rather mirrored by activity levels and fTH3 during lactation. DISCUSSION: Energy balance was not preserved through the reproductive cycle, supporting previous contentions that the reproductive performance of female mantled howler monkeys may be energetically constrained. The contrast between these and results that we have previously reported, highlights the importance of conducting follow-up studies to continually improve our understanding of the reproductive energetics of primate females.

Long-lasting behavioral and neuroendocrine changes provoked in rabbits by cancelling a single nursing bout in early lactation.

To restore estrus in lactating doe rabbits, nursing was prevented on lactation day 10 and allowed again from day 12 onward. This "biostimulation" procedure, used to accelerate reproduction, allows kit survival despite a 48 hr fast. Yet, the consequences of "biostimulation" on their psychobiological and neuroendocrine development are largely unknown. Therefore, we determined, in adult males and females, tested in the morning or afternoon: corticosteroid secretion (baseline and reactive), sexual behavior, and responses in six tests measuring stress/anxiety. The latter were not affected by maternal deprivation or time of testing in either sex. The lordosis quotient was reduced in deprived does (relative to controls), an effect eliminated when only non-kins (of both groups) were compared. Deprived males showed altered sexual behavior, evidenced by a large number of mounts not culminating in ejaculation. Corticosterone and cortisol secretion increased (relative to baseline) following i.m. saline in all groups, but the magnitude of the response was affected by maternal deprivation, time of day, and sex. Results indicate that particular behaviors and reactivity to stress have different thresholds regarding the effects of mother-litter separation in early lactation.

Energetic constraints on the reproduction of female mantled howlers.

The reproductive process of female primates is energetically constrained. However, while there is extensive evidence about factors that influence the maintenance of gestation and lactation, less is known about energetic correlates of cycling and the occurrence of conception in wild primates. We examined how female physical condition affected the occurrence of conception and interbirth intervals (IBI) in female mantled howler monkeys, a species in which females experience long non-conceptive periods. For 6 years we followed 7 females at La Flor de Catemaco (Los Tuxtlas, Mexico). In addition to noting the presence of dependent immatures, we collected fecal samples that were analyzed for thyroid hormone and glucocorticoid metabolite concentrations (N = 1,460). Conception was more likely following months when females were not lactating and had higher thyroid hormone and lower glucocorticoid levels. IBIs were shorter when females had higher thyroid hormone and lower glucocorticoid levels, and when the infant at the beginning of the interval died. Due to their obvious impact on female fecundity and fertility, gestation and lactation are the stages of the reproductive process that have traditionally received more attention in studies of female reproductive performance. Still, the cycling stage accounts for a large proportion of IBIs in many primate species. Here we demonstrate that the reproductive rates of female mantled howler monkeys are energetically constrained: both the occurrence of conception and IBI are positively affected by female energetic condition.