Two hypotheses, nutrient constraints and detoxification limitation, have been proposed to explain the lack of specialists among mammalian herbivores. The nutrient constraint hypothesis proposes that dietary specialization in mammalian herbivores is rare because no one plant can provide all requisite nutrients. The detoxification limitation hypothesis suggests that the mammalian detoxification system is incapable of detoxifying high doses of similar secondary compounds present in a diet of a single plant species. We experimentally tested these hypotheses by comparing the performance of specialist and generalist woodrats (Neotoma) on a variety of dietary challenges. Neotoma stephensi is a narrow dietary specialist with a single species, one-seeded juniper, Juniperus monosperma, comprising 85-95% of its diet. Compared with other plants available in the habitat, juniper is low in nitrogen and high in fiber, phenolics, and monoterpenes. The generalist woodrat, N. albigula, also consumes one-seeded juniper, but to a lesser degree. The nutrient constraint hypothesis was examined by feeding both species of woodrats a low-nitrogen, high-fiber diet similar to that found in juniper. We found no differences in body mass change, or apparent digestibility of dry matter or nitrogen between the two species of woodrats after 35 days on this diet. Moreover, both species were in positive nitrogen balance. We tested the detoxification limitation hypothesis by comparing the performance of the generalist and specialist on diets with and without juniper leaves, the preferred foliage of the specialist, as well as on diets with and without α-pinene, the predominant monoterpene in juniper. We found that on the juniper diet, compared with the specialist, the generalist consumed less juniper and lost more mass. Urine pH, a general indicator of overall detoxification processes, declined in both groups on the juniper diet. The generalist consumed half the toxin load of the specialist yet its urine pH was slightly lower. Moreover, the generalist consumed significantly less of the treatment with high concentrations of α-pinene compared to the control treatment, while the specialist consumed the same amount of food regardless of α-pinene concentration. For both groups, urine pH declined as levels of α-pinene in the diet increased. The generalist produced a significantly more acidic urine than the specialist on the treatment with the highest α-pinene concentration. Our results suggest that in this system, specialists detoxify plant secondary compounds differently than generalists and plant secondary compounds may be more important than low nutrient levels in maintaining dietary diversity in generalist herbivores.

Plant secondary metabolites (PSMs) can affect survival, reproduction, and distribution of herbivores. Individuals with a high capacity to tolerate PSMs will experience fewer and smaller adverse effects than less tolerant individuals. Theoretically, the capacity to tolerate PSMs can be acquired during development, modulated during adulthood, or genetically fixed. We studied tolerance to phenolic resin from creosote bush (Larrea tridentata) in two populations of desert woodrats as a first step in understanding phenotypic habituation and genetic adaptation of this species to creosote resin. One population was from Mojave desert habitat where woodrats eat creosote bush, and the other from the Great Basin desert, where creosote bush is not present and woodrats consume mainly juniper (Juniperus osteosperma). For Ͼ1 mo in the laboratory, woodrats from both populations were fed rabbit chow with increasing amounts of phenolic resin extracted from creosote bush until they lost body mass or showed any sign of sickness. Woodrats from the Mojave population maintained body mass at higher concentrations of resin and remained in the experiment longer. There were no differences between populations in food intake across all resin levels; however, maximum resin intake was 25% higher for the Mojave population. Food intake decreased with increasing resin intake. Glucuronic acid excretion in urine, one indicator of detoxification capacity, did not differ between populations. Water consumption increased with increased levels of creosote resin in the diet in woodrats from both populations. The results are consistent with the idea of differential tolerance to creosote bush phenolic resin in desert woodrat populations. Woodrats appear to be a promising natural system to study the developmental or genetic factors underlying vertebrate adaptation to plant secondary metabolites.

SYNOPSIS. Plant secondary compounds are deterrents and toxins to a variety of herbivores. The effect of secondary compounds on water balance of herbivores is virtually unexplored, yet many secondary compounds are renowned for their diuretic effects in humans and laboratory rats. We review data from the ethnopharmocological literature on plants with diuretic effects. We also present our data from experiments on water intake of specialist (Neotoma stephensi) and generalist woodrats (N. albigula) consuming plant secondary compounds from their natural diet. We measured effects of dietary secondary compounds on voluntary water consumption, urine volume and urine osmolarity. Ingestion of secondary compounds increased water intake and urine output and decreased urine osmolarity in both species. However, the generalist was more impacted by dietary secondary compounds than the specialist. Our results combined with that from the literature suggest that diuresis may be a prevalent consequence of ingestion of secondary compounds. Many herbivores live in arid habitats with limited access to free-standing water, thus an increase in the desire for water may have profound consequences on foraging behavior and fitness.

Plant secondary metabolites (PSMs) can affect survival, reproduction, and distribution of herbivores. Individuals with a high capacity to tolerate PSMs will experience fewer and smaller adverse effects than less tolerant individuals. Theoretically, the capacity to tolerate PSMs can be acquired during development, modulated during adulthood, or genetically fixed. We studied tolerance to phenolic resin from creosote bush (Larrea tridentata) in two populations of desert woodrats as a first step in understanding phenotypic habituation and genetic adaptation of this species to creosote resin. One population was from Mojave desert habitat where woodrats eat creosote bush, and the other from the Great Basin desert, where creosote bush is not present and woodrats consume mainly juniper (Juniperus osteosperma). For >1 mo in the laboratory, woodrats from both populations were fed rabbit chow with increasing amounts of phenolic resin extracted from creosote bush until they lost body mass or showed any sign of sickness. Woodrats from the Mojave population maintained body mass at higher concentrations of resin and remained in the experiment longer. There were no differences between populations in food intake across all resin levels; however, maximum resin intake was 25% higher for the Mojave population. Food intake decreased with increasing resin intake. Glucuronic acid excretion in urine, one indicator of detoxification capacity, did not differ between populations. Water consumption increased with increased levels of creosote resin in the diet in woodrats from both populations. The results are consistent with the idea of differential tolerance to creosote bush phenolic resin in desert woodrat populations. Woodrats appear to be a promising natural system to study the developmental or genetic factors underlying vertebrate adaptation to plant secondary metabolites.

Xenarthrans—anteaters, sloths, and armadillos—have essential functions for ecosystem maintenance, such as insect control and nutrient cycling, playing key roles as ecosystem engineers. Because of habitat loss and fragmentation, hunting pressure, and conflicts with domestic dogs, these species have been threatened locally, regionally, or even across their full distribution ranges. The Neotropics harbor 21 species of armadillos, 10 anteaters, and 6 sloths. Our data set includes the families Chlamyphoridae (13), Dasypodidae (7), Myrmecophagidae (3), Bradypodidae (4), and Megalonychidae (2). We have no occurrence data on Dasypus pilosus (Dasypodidae). Regarding Cyclopedidae, until recently, only one species was recognized, but new genetic studies have revealed that the group is represented by seven species. In this data paper, we compiled a total of 42,528 records of 31 species, represented by occurrence and quantitative data, totaling 24,847 unique georeferenced records. The geographic range is from the southern United States, Mexico, and Caribbean countries at the northern portion of the Neotropics, to the austral distribution in Argentina, Paraguay, Chile, and Uruguay. Regarding anteaters, Myrmecophaga tridactyla has the most records (n = 5,941), and Cyclopes sp. have the fewest (n = 240). The armadillo species with the most data is Dasypus novemcinctus (n = 11,588), and the fewest data are recorded for Calyptophractus retusus (n = 33). With regard to sloth species, Bradypus variegatus has the most records (n = 962), and Bradypus pygmaeus has the fewest (n = 12). Our main objective with Neotropical Xenarthrans is to make occurrence and quantitative data available to facilitate more ecological research, particularly if we integrate the xenarthran data with other data sets of Neotropical Series that will become available very soon (i.e., Neotropical Carnivores, Neotropical Invasive Mammals, and Neotropical Hunters and Dogs). Therefore, studies on trophic cascades, hunting pressure, habitat loss, fragmentation effects, species invasion, and climate change effects will be possible with the Neotropical Xenarthrans data set. Please cite this data paper when using its data in publications. We also request that researchers and teachers inform us of how they are using these data.