Although herbivory is widespread among mammals, few species have adopted a strategy of dietary sp... more Although herbivory is widespread among mammals, few species have adopted a strategy of dietary specialization. Feeding on a single plant species often exposes herbivores to high doses of similar plant secondary metabolites (PSMs), which may exceed the animal's detoxification capacities. Therefore, theory predicts that specialists will have unique detoxification mechanisms to process high levels of dietary toxins. To evaluate this hypothesis, we compared liver metabolism of a juniper specialist, Neotoma stephensi (diet >85% juniper), to that of a sympatric generalist, N. albigula (diet ≤30% juniper). Specifically, we quantified the content of a key detoxification enzyme, cytochrome P450 2B (CYP2B) in liver microsomes, as well as the microsomal turnover of α-pinene, the most abundant terpene in the juniper species consumed by the specialist woodrat. In both Neotoma species, a 30% juniper diet increased CYP2B content (2-3x) and α-pinene turnover rates (4-fold). In N. stephensi, ...
Terpenes, volatile plant secondary compounds produced by woody plants, have historically been tho... more Terpenes, volatile plant secondary compounds produced by woody plants, have historically been thought to act as feeding deterrents for mammalian herbivores. However, three species of woodrats, Neotoma stephensi, N. lepida, and N. albigula, regularly consume juniper, which is high in terpenes, and N. stephensi and N. lepida are considered juniper specialists. By investigating the terpene profiles in Juniperus monosperma and J. osteosperma, which are browsed or avoided by woodrats in the field, and recording the caching and consumption of juniper foliage by woodrats in the lab, we have evidence that terpenes may serve as feeding and/or foraging cues. The obligate specialist N. stephensi chose to forage on trees higher in p-cymene and preferred to consume juniper rather than caching it in a laboratory setting. These observations provide evidence that terpenes serve as a feeding cue and that the obligate specialist’s physiological mechanism for metabolizing the terpenes present in juniper may negate the need for caching. The facultative specialist N. lepida chose to forage on trees lower in four terpenes and cached more juniper than the obligate specialist N. stephensi, providing evidence that terpenes serve as a feeding deterrent for N. lepida and that this woodrat species relies on behavioral mechanisms to minimize terpene intake. The generalist N. albigula foraged on trees with higher terpenes levels but consumed the least amount of juniper in the lab and preferred to cache juniper rather than consume it, evidence that terpenes act as foraging but not feeding cues in the generalist. Our findings suggest that volatile plant secondary compounds can act as feeding and/or foraging cues and not just feeding deterrents in mammalian herbivores.
To be considered a dietary specialist, mammalian herbivores must consume large quantities of a pl... more To be considered a dietary specialist, mammalian herbivores must consume large quantities of a plant species considered "difficult" with respect to nutrient or toxin content, and possess specialized adaptations to deal with plant defensive compounds or low nutritional content. Populations of Neotoma lepida in the Great Basin consume Juniperus osteosperma, a plant heavily defended by terpenes, but a detailed dietary analysis of this population is lacking. Therefore, we investigated the extent of dietary specialization in this species in comparison with the better-studied specialist species, N. stephensi. Microhistological analysis of feces from N. lepida revealed that greater than 90 % of their diet in nature was comprised of juniper. In laboratory tolerance trials, N. lepida tolerated a diet of 80 % J. osteosperma, similar to that observed for N. stephensi. There was no difference in the abilities of N. lepida and N. stephensi to metabolize hexobarbital, a proxy compound for terpene metabolism. In preference tests of native and non-native juniper species, N. lepida did not exhibit a preference for its native or co-occurring juniper, J. osteosperma, over the non-native species, J. monosperma, whereas N. stephensi preferred its native or co-occurring juniper J. monosperma over non-native J. osteosperma. Behavioral and habitat differences between these woodrat species lead to the categorization of N. stephensi as an obligate juniper specialist with a small range that overlaps that of its preferred food, J. monosperma, and N. lepida as a facultative juniper specialist with a large range, and only a portion of its distribution containing populations that feed extensively on J. osteosperma.
To be considered a dietary specialist, mammalian herbivores must consume large quantities of a pl... more To be considered a dietary specialist, mammalian herbivores must consume large quantities of a plant species considered Bdifficult^ with respect to nutrient or toxin content, and possess specialized adaptations to deal with plant defensive compounds or low nutritional content. Populations of Neotoma lepida in the Great Basin consume Juniperus osteosperma, a plant heavily defended by terpenes, but a detailed dietary analysis of this population is lacking. Therefore, we investigated the extent of dietary specialization in this species in comparison with the better-studied specialist species, N. stephensi. Microhistological analysis of feces from N. lepida revealed that greater than 90 % of their diet in nature was comprised of juniper. In laboratory tolerance trials, N. lepida tolerated a diet of 80 % J. osteosperma, similar to that observed for N. stephensi. There was no difference in the abilities of N. lepida and N. stephensi to metabolize hexobar-bital, a proxy compound for terpene metabolism. In preference tests of native and non-native juniper species, N. lepida did not exhibit a preference for its native or co-occurring juniper, J. osteosperma, over the non-native species, J. monosperma, whereas N. stephensi preferred its native or co-occurring juniper J. monosperma over non-native J. osteosperma. Behavioral and habitat differences between these woodrat species lead to the categorization of N. stephensi as an obligate juniper specialist with a small range that overlaps that of its preferred food, J. monosperma, and N. lepida as a facultative juniper specialist with a large range, and only a portion of its distribution containing populations that feed extensively on J. osteosperma.
Although herbivory is widespread among mammals, few species have adopted a strategy of dietary sp... more Although herbivory is widespread among mammals, few species have adopted a strategy of dietary specialization. Feeding on a single plant species often exposes herbivores to high doses of similar plant secondary metabolites (PSMs), which may exceed the animal's detoxification capacities. Therefore, theory predicts that specialists will have unique detoxification mechanisms to process high levels of dietary toxins. To evaluate this hypothesis, we compared liver metabolism of a juniper specialist, Neotoma stephensi (diet >85% juniper), to that of a sympatric generalist, N. albigula (diet ≤30% juniper). Specifically, we quantified the content of a key detoxification enzyme, cytochrome P450 2B (CYP2B) in liver microsomes, as well as the microsomal turnover of α-pinene, the most abundant terpene in the juniper species consumed by the specialist woodrat. In both Neotoma species, a 30% juniper diet increased CYP2B content (2-3x) and α-pinene turnover rates (4-fold). In N. stephensi, ...
Terpenes, volatile plant secondary compounds produced by woody plants, have historically been tho... more Terpenes, volatile plant secondary compounds produced by woody plants, have historically been thought to act as feeding deterrents for mammalian herbivores. However, three species of woodrats, Neotoma stephensi, N. lepida, and N. albigula, regularly consume juniper, which is high in terpenes, and N. stephensi and N. lepida are considered juniper specialists. By investigating the terpene profiles in Juniperus monosperma and J. osteosperma, which are browsed or avoided by woodrats in the field, and recording the caching and consumption of juniper foliage by woodrats in the lab, we have evidence that terpenes may serve as feeding and/or foraging cues. The obligate specialist N. stephensi chose to forage on trees higher in p-cymene and preferred to consume juniper rather than caching it in a laboratory setting. These observations provide evidence that terpenes serve as a feeding cue and that the obligate specialist’s physiological mechanism for metabolizing the terpenes present in juniper may negate the need for caching. The facultative specialist N. lepida chose to forage on trees lower in four terpenes and cached more juniper than the obligate specialist N. stephensi, providing evidence that terpenes serve as a feeding deterrent for N. lepida and that this woodrat species relies on behavioral mechanisms to minimize terpene intake. The generalist N. albigula foraged on trees with higher terpenes levels but consumed the least amount of juniper in the lab and preferred to cache juniper rather than consume it, evidence that terpenes act as foraging but not feeding cues in the generalist. Our findings suggest that volatile plant secondary compounds can act as feeding and/or foraging cues and not just feeding deterrents in mammalian herbivores.
To be considered a dietary specialist, mammalian herbivores must consume large quantities of a pl... more To be considered a dietary specialist, mammalian herbivores must consume large quantities of a plant species considered "difficult" with respect to nutrient or toxin content, and possess specialized adaptations to deal with plant defensive compounds or low nutritional content. Populations of Neotoma lepida in the Great Basin consume Juniperus osteosperma, a plant heavily defended by terpenes, but a detailed dietary analysis of this population is lacking. Therefore, we investigated the extent of dietary specialization in this species in comparison with the better-studied specialist species, N. stephensi. Microhistological analysis of feces from N. lepida revealed that greater than 90 % of their diet in nature was comprised of juniper. In laboratory tolerance trials, N. lepida tolerated a diet of 80 % J. osteosperma, similar to that observed for N. stephensi. There was no difference in the abilities of N. lepida and N. stephensi to metabolize hexobarbital, a proxy compound for terpene metabolism. In preference tests of native and non-native juniper species, N. lepida did not exhibit a preference for its native or co-occurring juniper, J. osteosperma, over the non-native species, J. monosperma, whereas N. stephensi preferred its native or co-occurring juniper J. monosperma over non-native J. osteosperma. Behavioral and habitat differences between these woodrat species lead to the categorization of N. stephensi as an obligate juniper specialist with a small range that overlaps that of its preferred food, J. monosperma, and N. lepida as a facultative juniper specialist with a large range, and only a portion of its distribution containing populations that feed extensively on J. osteosperma.
To be considered a dietary specialist, mammalian herbivores must consume large quantities of a pl... more To be considered a dietary specialist, mammalian herbivores must consume large quantities of a plant species considered Bdifficult^ with respect to nutrient or toxin content, and possess specialized adaptations to deal with plant defensive compounds or low nutritional content. Populations of Neotoma lepida in the Great Basin consume Juniperus osteosperma, a plant heavily defended by terpenes, but a detailed dietary analysis of this population is lacking. Therefore, we investigated the extent of dietary specialization in this species in comparison with the better-studied specialist species, N. stephensi. Microhistological analysis of feces from N. lepida revealed that greater than 90 % of their diet in nature was comprised of juniper. In laboratory tolerance trials, N. lepida tolerated a diet of 80 % J. osteosperma, similar to that observed for N. stephensi. There was no difference in the abilities of N. lepida and N. stephensi to metabolize hexobar-bital, a proxy compound for terpene metabolism. In preference tests of native and non-native juniper species, N. lepida did not exhibit a preference for its native or co-occurring juniper, J. osteosperma, over the non-native species, J. monosperma, whereas N. stephensi preferred its native or co-occurring juniper J. monosperma over non-native J. osteosperma. Behavioral and habitat differences between these woodrat species lead to the categorization of N. stephensi as an obligate juniper specialist with a small range that overlaps that of its preferred food, J. monosperma, and N. lepida as a facultative juniper specialist with a large range, and only a portion of its distribution containing populations that feed extensively on J. osteosperma.
Uploads
Papers by Michele Skopec