Digestive strategies and food choice in mantled howler monkeys Alouatta palliata mexicana: bases of their dietary flexibility

Sour, but acceptable: Taste responsiveness to five food-associated acids in zoo-housed white-faced sakis, Pithecia pithecia

White-faced sakis (Pithecia pithecia) are commonly considered as frugivores but are unusual among primates as they do not specialize on ripe fruits but rather include a high proportion of unripe fruits into their diet, even during seasons when ripe fruits are available. Using a two-bottle preference test of short duration we therefore assessed whether this dietary specialization affects the taste responsiveness and sour-taste tolerance of four adult white-faced sakis for five food-associated acids. We found taste preference thresholds of the sakis to be 1-10 mM for citric acid, 0.5-20 mM for ascorbic acid, 2-10 mM for malic acid, 0.1-1 mM for tannic acid, and 2-20 mM for acetic acid, respectively. When given the choice between a reference solution of 50 mM sucrose and mixtures containing varying concentrations of sucrose plus citric acid, the sakis displayed a high sour-taste tolerance and required only 100 mM of sucrose (when mixed with 10 mM citric acid) or 200 mM of sucrose (when mixed with 30 or 50 mM citric acid), respectively, to prefer the sweet-sour mixture over the purely sweet 50 mM sucrose reference solution. These results demonstrate that white-faced sakis have a well-developed taste sensitivity for food-associated acids which is not inferior to that of primates specializing on ripe fruits. Compared to other platyrrhine primates, the sakis displayed a markedly higher sour-taste tolerance. These results may therefore reflect an evolutionary adaptation to the dietary specialization of the white-faced sakis to sour-tasting unripe fruits.

Sloth metabolism may make survival untenable under climate change scenarios

Although climate change is predicted to have a substantial effect on the energetic requirements of organisms, the longer-term implications are often unclear. Sloths are limited by the rate at which they can acquire energy and are unable to regulate core body temperature (Tb) to the extent seen in most mammals. Therefore, the metabolic impacts of climate change on sloths are expected to be profound. Here we use indirect calorimetry to measure the oxygen consumption (VO2) and Tb of highland and lowland two-fingered sloths (Choloepus hoffmanni) when exposed to a range of different ambient temperatures (Ta) (18 °C -34 °C), and additionally record changes in Tb and posture over several days in response to natural fluctuations in Ta. We use the resultant data to predict the impact of future climate change on the metabolic rate and Tb of the different sloth populations. The metabolic responses of sloths originating from the two sites differed at high Ta's, with lowland sloths invoking metabolic depression as temperatures rose above their apparent 'thermally-active zone' (TAZ), whereas highland sloths showed increased RMR. Based on climate change estimates for the year 2100, we predict that high-altitude sloths are likely to experience a substantial increase in metabolic rate which, due to their intrinsic energy processing limitations and restricted geographical plasticity, may make their survival untenable in a warming climate.

Lead exposure and its relationship with fecal cortisol levels in black howler monkeys (Alouatta pigra)

Efficiently detecting early environmental threats to wildlife is vital for conservation. Beyond obvious dangers like habitat loss or deforestation, our study focuses on one of the most hazardous toxic metals for wildlife: lead (Pb). Pb is a widespread, cumulative, and insidious environmental pollutant that can trigger a wide range of physiological, biochemical, and behavioral disorders. In fact, Pb can cause permanent dysfunction of the major stress system, the hypothalamic pituitary adrenal (HPA) axis. We analyzed Pb and cortisol concentrations in fecal samples from Alouatta pigra in southern Mexico. Fecal samples were collected across six sites categorized as free-ranging (n = 65; conserved and disturbed) and from captive animals (n = 58). Additionally, we collected soil samples (n = 35). We found that Pb was present in 28% of fecal samples and 83% of soil samples. There was a positive relation between fecal and soil Pb levels, and fecal Pb concentration was negatively associated with cortisol levels. However, the claim of Pb being a direct interference with HPA axis requires further investigation. Given our findings, assessing wildlife exposure can be a valuable tool for understanding potential Pb exposure levels in the environment and its possible implications for human health. It can also serve as an early warning system of these consequences.

Food preferences and nutrient composition in captive Southern brown howler monkeys, Alouatta guariba clamitans

Studies of food preferences in captive primates have so far mainly been restricted to frugivorous species. It was therefore the aim of the present study to assess the occurrence of spontaneous food preferences in a mainly folivorous primate, the captive Southern brown howler monkey, and to analyze whether these preferences correlate with nutrient composition. Using a two-alternative choice test, we presented ten male and five female adult Alouatta guariba clamitans with all possible binary combinations of ten types of food that are part of their diet in captivity and recorded their choice behavior. We found the howler monkeys to display the following rank order of preference: banana > mango > watermelon > papaya > beetroot > apple > pear > orange > cucumber > tomato. This preference ranking significantly and positively correlated with the total carbohydrate content and with the sucrose content of the food items. We also found significant positive correlations between the food preference ranking and the content of the minerals copper and magnesium. Male and female howler monkeys did not differ significantly in their food preference rankings. These results suggest this howler monkeys under human care are not opportunistic, but selective feeders with regard to maximizing their net gain of energy as only the content of carbohydrates, but not the contents of total energy, proteins, or lipids significantly correlated with the displayed food preferences. Thus, the food preferences of this primate are similar to those reported in several species of frugivorous primates tested with cultivated fruits and vegetables.

Comparative gastrointestinal organ lengths among Amazonian primates (Primates: Platyrrhini)

OBJECTIVES

The morphological features of the gastrointestinal tract (GIT) in mammals reflect a species' food niche breadth and dietary adaptations. For many wild mammals, the relationship between the structure of the GIT and diet is still poorly understood, for example, the GIT for frugivorous primates is usually classified as unspecialized and homogeneous. Here, we compare the GIT structure of 13 primate species from the three families of extant platyrrhines (Atelidae, Pitheciidae, and Cebidae) in Amazonia, and discuss possible evolutionary adaptations to different diets and trophic niches.

METHODS

We measured the length of the esophagus, stomach, small intestine, large intestine, cecum, colon, and rectum of the digestive tracts of 289 primate specimens. We determined the allometric relationships of the different tubular organs with the total length of the GIT as a proxy of specimen body size. Allometric parameters were used to establish the quotients of differentiation of every organ for each primate specimen.

RESULTS

There was a high differentiation in structure of the digestive organs among genera. Alouatta specimens clearly separated from the other genera based on dissimilarities in gastric, colonic, and rectal quotients, likely linked to the fermentation of plant contents. In contrast, all cebines (Sapajus, Cebus, and Saimiri) and Cacajao species had similar small intestine quotients, which is expected due to their high rates of animal matter consumed.

CONCLUSIONS

We show that diverse adaptations in digestive structure exist among frugivorous primates, which in turn reflect different dietary patterns within this group that may enable the geographic coexistence of different primate species.

Influence of tannic acid concentration on the physicochemical characteristics of saliva of spider monkeys (Ateles geoffroyi)

Tannins are a chemical defense mechanism of plants consumed by herbivores. Variations in salivary physicochemical characteristics such as pH, total protein concentration (TP), and presence of proline-rich proteins (PRPs) in animals have been reported as a mechanism to protect the oral cavity when consuming food with variations in pH and tannins. Variations in salivary physiochemistry as adaptations for consuming tannin-rich foods have been found in omnivorous and folivorous primates, but have not yet been reported in frugivorous species such as spider monkeys. We therefore assessed changes in pH using test strips, TP concentration by measuring absorbance at 595 nm in a spectrophotometer and salivary PRPs using the SDS-PAGE electrophoresis technique in the saliva of nine captive spider monkeys in response to the consumption of solutions with different concentrations of tannic acid. The results showed variations in pH, TP concentration and the presence and variation of possible salivary PRPs associated with tannic acid concentration. These findings suggest that spider monkeys may tailor their salivary physicochemical characteristics in response to the ingestion of potentially toxic compounds.

Anthropogenic edges impact howler monkey (Alouatta palliata) feeding behaviour in a Costa Rican rainforest

Anthropogenic forest fragmentation impacts many aspects of animal behaviour, including feeding ecology. With forests increasingly fragmented in tropical regions due to human development, the proportion of forest edge (≤ 100 m from clear-cut regions) is higher relative to forest interior. Forest edges differ in vegetation from interior, making it important to better understand how anthropogenic edges impact the feeding behaviour of primates such as mantled howler monkeys (Alouatta palliata). We predicted that howler monkeys would feed on higher-quality plant resources, from a larger number of tree families, and from larger trees in forest interior compared to anthropogenic forest edge. We surveyed howler monkey feeding behaviour across forest zones in a fragmented rainforest in Costa Rica, La Suerte Biological Research Station. We observed individual monkeys for 30-minute periods, collecting data on their feeding behaviour and tree use at 2-minute intervals. We measured feeding trees and recorded the plant parts and taxonomy of resources consumed. Monkeys consumed more leaves and fewer stems and fed from a smaller number of tree families in the forest interior, while they consumed fewer leaves and more stems and fed from a larger number of tree families in the forest edge. Monkeys also fed from larger, taller trees in the forest interior than the edge. The differences in howler monkey feeding behaviour between forest zones attest to the impact of human disturbance on howler monkey feeding ecology.

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.

Postural behavior of howler monkeys (Alouatta palliata, A. macconnelli, and A. caraya) during sleep: an assessment across the genus range

Sleep is the longest and most continuous behavioral phase in the 24 h cycle of mammals. However, selection of postures, substrates, and tree parts during sleep has not been adequately explored, as well as their evolutionary consequences. The present study investigates postural behavior, substrate, and tree part use during sleep in three howler species (A. palliata, A. macconnelli, and A. caraya) in Nicaragua, French Guiana, and Argentina. All three species were consistent in the use of a crouched ball-like sit-in posture on large, horizontal, unramified, or bifurcated substrates, and in avoiding the periphery of tree crowns. The regularities of these sleeping patterns are very likely functionally associated with protection from potential predators and extreme weather conditions, biomechanical stability, thermoregulation, and enhancement of the digestive process of hard-to-decompose plant material.

Visual detection and fruit selection by the mantled howler monkey (Alouatta palliata)

Howler monkeys (platyrrhini) have evolved routine trichromatic color vision independently from catarrhines, which presents an opportunity to test hypotheses concerning the adaptive value of distinguishing reddish from greenish hues. A longstanding hypothesis posits that trichromacy aids in the efficient detection of reddish-ripe fruits, which could be an advantage for the detection of the nutritional content of the fruit, such as sugars. In the present study, we assessed fruit visual conspicuity and selection based on color and sucrose content by wild mantled howler monkeys (Alouatta palliata) on Agaltepec Island, Mexico. We used colorimetry to classify dietary fruits as cryptic (greenish) or conspicuous (reddish) against their background leaves. Species-specific color models indicate that trichromatic howler monkeys should be more efficient in discriminating the conspicuous ripe fruits from leaves compared to detecting cryptic ripe fruits from leaves. We found howler monkeys consume more cryptic fruits compared to conspicuous fruits, and that they consume more unripe fruits than ripe fruits. The consumption (acceptance) of fruit was independent of sucrose content, and thus this disaccharide may not play an essential role in mantled howler food selection. Our findings suggest that routine trichromatic color vision may aid in the detection and discrimination of conspicuously colored fruits, but that the final decision whether to accept or reject a fruit probably involves the use of other senses in addition to vision.

Historical antecedents and recent innovations in pitheciid (titi, saki, and uakari) feeding ecology

The modern pitheciids (titis, sakis, and uakaris) of northern South America represent one of the earliest radiations of platyrrhines and demonstrate morphological adaptations and ecological strategies for seed eating. While seeds can provide reliable resources for relatively long periods of time, they are often well protected by thick husks and hard seed coverings. Seeds also tend to be rich in lipids, but they may also be high in indigestible fiber. Even though seed eaters are found in each major primate radiation, only the pitheciids demonstrate primary adaptations for eating seeds. In this partly historical, partly contemporary review, I examine the ecological and anatomical correlates of seed eating. It is dedicated to two well-known field primatologists: ecologist and conservationist J. Márcio Ayres; and anatomist and ecologist Warren G. Kinzey. Using observations in Kinzey (1992, Am J Phys Anthropol, 88, pp. 499-514) as a framework, I provide context and analysis for the intervening three decades of pitheciid research to identify what we know about this understudied group of primates and propose directions for future work.

Salivary proteome of a Neotropical primate: potential roles in host defense and oral food perception

BACKGROUND

Saliva contains a very complex mixture of proteins for defense against microbiological pathogens and for oral food perception. Howler monkeys are Neotropical primates that can consume a mostly leaf diet. They are well known to thrive in highly disturbed habitats where they may cope with a diversity of dietary challenges and infection risks. We aimed to describe the salivary proteome of howlers to contribute to better understanding of their physiology.

METHODS

We analyzed the salivary proteins of wild black howler monkeys (Alouatta pigra), by SDS-PAGE-1-D and Nano LC-MS/MS and categorized them by their function involved in host defense and oral food perception.

RESULTS

Our proteomic analysis identified 156 proteins in howler saliva including a number of host defense peptides that are the first line of defense in mammals, such as defensin, cathelicidin, dermcidin, and lactotransferrin, and proteins with anti-bacterial, anti-fungal, and anti-viral capacity, such as IgA, IgG, IgM, BPI, salivary heat shock 70 kDa protein, beta-2-microbulin, and protein S-100. We also identified key proteins necessary for taste perception, including salivary carbonic anhydrase VI, cystatin D, IgA, and fatty acid-binding protein. Proteins to detect astringent foods were identifying, including four members of cystatins (A, B, C and D), lactoperoxidase, and histidine-rich proteins. No chitinase and amylase were identified as would be expected because howlers do not eat insects and little starch. These findings provide basic information to future studies in oral biology, ingestive physiology, and physiological ecology of mammals and non-human primates.

Duplication and parallel evolution of the pancreatic ribonuclease gene (RNASE1) in folivorous non-colobine primates, the howler monkeys (Alouatta spp.)

In foregut-fermenting mammals (e.g., colobine monkeys, artiodactyl ruminants) the enzymes pancreatic ribonuclease (RNASE1) and lysozyme C (LYZ), originally involved in immune defense, have evolved new digestive functions. Howler monkeys are folivorous non-colobine primates that lack the multi-chambered stomachs of colobines and instead digest leaves using fermentation in the caeco-colic region. We present data on the RNASE1 and LYZ genes of four species of howler monkey (Alouatta spp.). We find that howler monkey LYZ is conserved and does not share the substitutions found in colobine and cow sequences, whereas RNASE1 was duplicated in the common ancestor of A. palliata, A. seniculus, A. sara, and A. pigra. While the parent gene (RNASE1) is conserved, the daughter gene (RNASE1B) has multiple amino acid substitutions that are parallel to those found in RNASE1B genes of colobines. The duplicated RNase in Alouatta has biochemical changes similar to those in colobines, suggesting a novel, possibly digestive function. These findings suggest that pancreatic ribonuclease has, in parallel, evolved a new role for digesting the products of microbial fermentation in both foregut- and hindgut-fermenting folivorous primates. This may be a vital digestive enzyme adaptation allowing howler monkeys to survive on leaves during periods of low fruit availability.

Spatial aggregation of fruits explains food selection in a neotropical primate (Alouatta pigra)

The availability and spatial distribution of food resources affect animal behavior and survival. Black howler monkeys (Alouatta pigra) have a foraging strategy to balance their nutrient intake that involves mixing their consumption of leaves and fruits. The spatial aggregation of food items should impact this strategy, but how it does so is largely unknown. We quantified how leaf and fruit intake combined (here termed food set selection) was spatially aggregated in patches and how food aggregation varied across seasons. Using variograms we estimated patch diameter and with Generalized Least Square models determined the effect of food spatial aggregation on food selection. Only fruits were structured in patches in the season of highest availability (dry-season). The patches of food set selection had a diameter between 6.9 and 14 m and were explained by those of mature fruit availability which were between 18 and 19 m in diameter. Our results suggest that the spatial pattern of food selection is influenced by patches of large fruit-bearing trees, not by particular species. Fruit also occur along spatial gradients, but these do not explain food selection, suggesting that howlers maximize food intake in response to local aggregation of fruit that are limiting during certain seasons. We demonstrate how the independent spatial modelling of resources and behavior enables the definition of patches and testing their spatial relationship.

The Influence of Leaf Consumption on Time Allocation in Black Howler Monkeys (Alouatta pigra)

The analysis of factors that determine variation in time budgets is important to understand the interactions between environment, behaviour and fitness. We tested the hypothesis that changes in the dietary patterns of black howler monkeys (Alouatta pigra) caused by a decrease in the availability of preferred foods are a main determinant of variation in time budgets. We predicted that individuals would trade off travel time for resting time (i.e., minimize energy expenditure) as the diet included more leaves. We conducted our study in the Mexican state of Campeche between 2005 and 2008, where we studied the behaviour of 28 adult males and 32 adult females belonging to 14 different groups for a total of 3,747.2 focal sampling hours. Study groups lived in forest fragments with variation in habitat quality. Individuals showed different rest:travel trade-offs in response to leaf consumption according to the quality of the forest fragments they lived in. Individuals that lived in high-quality fragments increased resting time under more folivorous regimes, whereas those living in low-quality fragments increased travel time. Our results suggest that howler monkeys living in low-quality fragments spend more time foraging to compensate for the low quality of the available resources.

Salivary tannin-binding proteins are a pervasive strategy used by the folivorous/frugivorous black howler monkey

Dietary tannins can affect protein digestion and absorption, be toxic, and influence food selection by being astringent and bitter tasting. Animals that usually ingest tannins may regularly secrete tannin-binding salivary proteins (TBSPs) to counteract the negative effects of tannins or TBSPs production can be induced by a tannin-rich diet. In the wild, many primates regularly eat a diet that contains tannin-rich leaves and unripe fruit and it has been speculated that they have the physiological ability to cope with dietary tannins; however, details of their strategy remains unclear. Our research details the salivary protein composition of wild and zoo-living black howler monkeys (Alouatta pigra) feeding on natural versus manufactured low-tannin diets, and examines differences in TBSPs, mainly proline-rich proteins (PRPs), to determine whether production of these proteins is dependent on the tannin content of their food. We measured the pH, flow rate, and concentration of total protein and trichloroacetic acid soluble proteins (an index of PRPs) in saliva. Howler monkeys produced slightly alkaline saliva that may aid in the binding interaction between tannin and salivary proteins. We used gel electrophoresis to describe the salivary protein profile and this analysis along with a tannin-binding assay allowed us to detect several TBSPs in all individuals. We found no differences in the characteristics of saliva between wild and zoo-living monkeys. Our results suggest that black howler monkeys always secrete TBSPs even when fed on foods low in tannins. This strategy of constantly using this salivary anti-tannin defense enables them to obtain nutrients from plants that sometimes contain high levels of tannins and may help immediately to overcome the astringent sensation of their food allowing howler monkeys to eat tanniferous plants.

Howler monkey foraging ecology suggests convergent evolution of routine trichromacy as an adaptation for folivory

Primates possess remarkably variable color vision, and the ecological and social factors shaping this variation remain heavily debated. Here, we test whether central tenants of the folivory hypothesis of routine trichromacy hold for the foraging ecology of howler monkeys. Howler monkeys (genus Alouatta) and paleotropical primates (Parvorder: Catarrhini) have independently acquired routine trichromacy through fixation of distinct mid- to long-wavelength-sensitive (M/LWS) opsin genes on the X-chromosome. The presence of routine trichromacy in howlers, while other diurnal neotropical monkeys (Platyrrhini) possess polymorphic trichromacy, is poorly understood. A selective force proposed to explain the evolution of routine trichromacy in catarrhines-reliance on young, red leaves-has received scant attention in howlers, a gap we fill in this study. We recorded diet, sequenced M/LWS opsin genes in four social groups of Alouatta palliata, and conducted colorimetric analysis of leaves consumed in Sector Santa Rosa, Costa Rica. For a majority of food species, including Ficus trees, an important resource year-round, young leaves were more chromatically conspicuous from mature leaves to trichromatic than to hypothetical dichromatic phenotypes. We found that 18% of opsin genes were MWS/LWS hybrids; when combined with previous research, the incidence of hybrid M/LWS opsins in this species is 13%. In visual models of food discrimination ability, the hybrid trichromatic phenotype performed slightly poorer than normal trichromacy, but substantially better than dichromacy. Our results provide support for the folivory hypothesis of routine trichromacy. Similar ecological pressures, that is, the search for young, reddish leaves, may have driven the independent evolution of routine trichromacy in primates on separate continents. We discuss our results in the context of balancing selection acting on New World monkey opsin genes and hypothesize that howlers experience stronger selection against dichromatic phenotypes than other sympatric species, which rely more heavily on cryptic foods.