Vascular, cardiac, and renal lesions attributed to primary systemic hypertension in western pygmy marmosets (Cebuella pygmaea)

In a retrospective study of a western pygmy marmoset ( Cebuella pygmaea) colony, postmortem examination of 1/8 juvenile and 29/47 adult animals identified vascular, cardiac, and renal lesions consistent with systemic hypertension. This included frequent renal arteriolar hypertrophy, hyaline and proliferative arteriolosclerosis, fibrinoid necrosis of arterioles, glomerulosclerosis, and nephrosclerosis. Affected animals ranged from 0.6 to 12 years of age (mean 6 years) and had an observed male predominance. Genealogical relatedness was evident in several breeding pairs and spanned multiple generations. Concurrent cardiac and renal disease was commonly identified, although frequently subclinical, and both were important causes of morbidity and mortality in affected animals. Cardiomegaly and hypertrophy were typical features and were accompanied by left atrial thrombosis in 10 animals. Signs of heart failure included chronic pulmonary edema in 20 cases and body cavity effusions in 17. In the kidneys, 19 cases had glomerular disease and hypertensive vasculopathy, and 26 cases had nephrosclerosis or glomerulosclerosis. Common extrarenal secondary causes of hypertension were excluded by necropsy examination. The pathogenesis is suggested to involve primary hypertension leading to renal and cardiac disease. Elevated sympathetic activity might be an underlying factor in the frequent development of primary systemic hypertension in the pygmy marmoset, as for the owl monkey.

Pygmy Marmoset Exudate Feeding Stimulates Exudate Production

Exudates are an important renewable resource for many primates. Exudate renewability is based on observations of primates repeatedly depleting exudate sites and measures of exudate trees’ daily replenishment rates, but the role of the consumer in the renewal process is unclear. Trees’ exudate production may be independent of the consumer, remaining unchanged regardless of depletion frequency, but since trees produce exudates as a physiological response to fungal infection, they may produce more exudates with more frequent depletion. To test these competing hypotheses, we employed a within-subjects experimental design in which we exposed pygmy marmosets’ exudate holes to two treatment conditions: collecting exudates after 5 h and collecting exudates every hour for five consecutive hours. To compare production outputs between treatments, we used generalised linear mixed modelling in which log-transformed production data were a function of treatment with exudate holes nested within trees as a random effect. The model indicated that the cumulative production of hourly exudate removal was significantly greater than the amount accumulated after 5 h. Furthermore, the random effect of holes nested within trees had the greatest impact on variation in differences between treatments, but another unknown source also contributed to the observed variation. These results support the hypothesis that consumers partly drive exudate production, and although it is unknown what other factors, such as fungal load and healing trajectory, may influence variation between treatments, we conclude that pygmy marmosets can stimulate exudate production by consuming exudates.

Cognitive Components of Vocal Communication: A Case Study

Communication among nonhuman animals is often presented as rigid and inflexible, reflecting emotional states rather than having any cognitive basis. Using the world’s smallest monkey, the pygmy marmoset (Cebuella pygmaea), with the smallest absolute brain size amongst simian primates as a case study, I review the role of cognition in the development and usage of vocalizations in pygmy marmosets and present new data on the instrumental use of babbling and of food associated vocalizations. Pygmy marmosets have several contact calls that differ in the psychoacoustic properties for sound localization as well as the distance at which they carry through the rainforest. Marmosets use these calls strategically based on distance from neighbors. Marmosets alter spectral and temporal aspects of call structure when exposed to new groups and when newly mated. They display population specific vocal dialects. Young pygmy marmosets engage in extensive babbling behavior rewarded by parents that helps the young develop adult vocal structures, but older monkeys also use babbling instrumentally in conflict situations. Specific food referential calls generally relate to food preferences, but food calls are suppressed in the presence of animate prey. Unmated animals systematically combine a long distance call with food calls as though advertising for mates. Taken together, these examples show that even small brained primates use their vocal signals flexibly and strategically in response to a variety of environmental and social conditions.