Preferences of Specialist and Generalist Mammalian Herbivores for Mixtures versus Individual Plant Secondary Metabolites

Herbivores that forage on chemically defended plants consume complex mixtures of plant secondary metabolites (PSMs). However, the mechanisms by which herbivores tolerate mixtures of PSMs are relatively poorly understood. As such, it remains difficult to predict how PSMs, singly or as complex mixtures, influence diet selection by herbivores. Although relative rates of detoxification of PSMs have been used to explain tolerance of PSMs by dietary specialist herbivores, few studies have used the rate of detoxification of individual PSMs to understand dietary preferences of individual herbivores for individual versus mixtures of PSMs. We coupled in vivo experiments using captive feeding trials with in vitro experiments using enzymatic detoxification assays to evaluate the dietary preferences and detoxification capacities of pygmy rabbits (Brachylagus idahoensis), dietary specialists on sagebrush (Artemisia spp.), and mountain cottontails (Sylvilagus nuttallii), dietary generalists. We compared preference for five single PSMs in sagebrush compared to a mixture containing those same five PSMs. We hypothesized that relative preference for individual PSMs would coincide with faster detoxification capacity for those PSMs by specialists and generalists. Pygmy rabbits generally showed little preference among individual PSMs compared to mixed PSMs, whereas mountain cottontails exhibited stronger preferences. Pygmy rabbits had faster detoxification capacities for all PSMs and consumed higher concentrations of individual PSMs versus a mixture than cottontails. However, detoxification capacity for an individual PSM did not generally coincide with preferences or avoidance of individual PSMs by either species. Cottontails avoided, but pygmy rabbits preferred, camphor, the PSM with the slowest detoxification rate by both species. Both species avoided β-pinene despite it having one of the fastest detoxification rate. Taken together our in vivo and in vitro results add to existing evidence that detoxification capacity is higher in dietary specialist than generalist herbivores. However, results also suggest that alternative mechanisms such as absorption and the pharmacological action of individual or mixtures of PSMs may play a role in determining preference of PSMs within herbivore species

Using an Ultraviolet Light Test to Improve Sagebrush Identification and Predict Forage Quality for Wildlife

Sagebrush identification can be improved by using a relatively easy ultraviolet (UV) light test on specimens. Sagebrush produces a variety of water-soluble polyphenols called coumarins, which fluoresce a blue color under UV light and can help differentiate species, subspecies, and hybrids. We tested 16 different sagebrush taxa (including species and subspecies) from herbarium specimens and found 3 taxa (low sagebrush, Artemisia arbuscula; Wyoming sagebrush, A. tridentata wyomingensis; and basin sagebrush, A. t. tridentata) that were often misidentified. We show that the UV light test can greatly improve identification of these species. Moreover, given that the UV+ chemicals that discriminate taxa are also considered an indirect biomarker of sagebrush palatability for some herbivores, the UV light test can be used to predict forage quality for threatened species like sage-grouse (Centrocercus spp.) and pygmy rabbits (Brachylagus idahoensis). Collecting voucher specimens of sagebrush at wildlife study sites and comparing their UV intensity to historical herbarium specimens could help identify both current and changing availability of palatable sagebrush for wildlife. We found that even herbarium specimens \u3e80 years old still fluoresce under UV light

Effects of Mowing and Tebuthiuron on the Nutritional Quality of Wyoming Big Sagebrush

Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle & Young) is the most abundant and widely distributed subspecies of big sagebrush and has been treated through chemical application, mechanical treatments, and prescribed burning in efforts thought to improve habitat conditions for species such as greater sage-grouse (Centrocercus urophasianus) and mule deer (Odocoileus hemionus). Although the response of structural attributes of sagebrush communities to treatments is well understood, there is a need to identify how treatments influence the quality of sagebrush as winter food for wildlife. Our purpose was to identify how mowing and tebuthiuron treatments influenced dietary quality of Wyoming big sagebrush in central Wyoming. Two study areas were mowed in January and February 2014 and tebuthiuron was applied in two study areas in May 2014. We constructed 6 exclosures in each of these four study areas (24 total), which encompassed 30 m x 30 m areas of treated and untreated sagebrush within each exclosure. Samples of current annual growth were collected from 18 sagebrush plants from treated and 12 plants from control portions of mowing exclosures during November 2013–2015 and tebuthiuron exclosures during November 2014–2015. Samples were analyzed for crude protein and plant secondary metabolites known to influence dietary selection of sagebrush by sage-grouse and other sagebrush occurring herbivores. Our results suggest mowing and tebuthiuron treatments may slightly increase crude protein concentrations directly after treatments without immediate changes in plant secondary metabolites. Slight increases in dietary quality of sagebrush following treatments coupled with potential trade-offs with loss of biomass associated with treatments corroborates previous research that treating Wyoming big sagebrush may have little benefit for sage-grouse and other sagebrush-dependent wildlife. Future work should evaluate not only how treatments influence sage-grouse habitat use and 2 reproductive success, but how treatments influence other wildlife species in fragile sagebrush ecosystems

Using Age as a Predictor of Chemotypes for Low Sagebrush (\u3cem\u3eArtemisia Arbuscula\u3c/em\u3e): Can Age Help Us Manage Sage-Grouse Foraging Habitat?

The defensive chemistry of plants limit intake by herbivores. In addition, the spatial and temporal variation of plant chemicals constrains habitat use by herbivores. As such, management of herbivores requires that we properly conserve and manage for the most palatable chemical profiles of plants, or chemotypes. However, management of palatable plants requires that we first identify parameters that influence chemotypes. We hypothesized that the age of a plant is one parameter that influences chemotypes and could be managed. To test this hypothesis, we counted the annual ring growth to determine age and used gas chromatography to determine chemotypes of small (tall) and medium (15cm-30cm tall) low sagebrush (Artemisia arbuscula). We focused on low sagebrush as it is a preferred food source for greater sage-grouse (Centrocercus urophasianus) at our study site. In addition, we tested whether the circumference at the base of the plant is correlated with annual ring growth. Correlating age and circumference may yield a simple, nonintrusive method to estimate the age of sagebrush in the field without counting annual rings. Understanding how age influences palatability of plants is an important factor in assessing and managing grouse habitat. Using a parameter like age, which may be simple to assess in field, to manage sage-steppe habitats could save time and money. We expect if the younger plants are more palatable, reseeding and replanting could be effective methods to make restored habitats more ideal for foraging grouse. Alternatively, if older plants are more palatable the consequences of mowing and herbicide could dramatically outweigh any potential benefits

All Leaves Are Not Created Equal: Variation Among Leaves in Chemical Defenses and Nutritional Quality

Coevolution among plants and herbivores has led to variation in plant defenses and herbivore foraging. Plants must defend against herbivores, whereas herbivores must find ways to overcome plant defenses and meet nutritional needs. Variation in plant quality is important because it can influence selection of plants by herbivores for food. Few studies have investigated the variation occurring within a single plant. Sagebrush offers an excellent system for studying the variation in dietary and chemical quality within a plant. First, variation in nutrition and chemical content exists between subspecies (Kelsey 1982) and between plants of a single subspecies of sagebrush from different geographic locations (Welch 1981). Second, sagebrush has two types of leaves, ephemeral and persistent, and our preliminary data demonstrates that pygmy rabbits prefer ephemeral over persistent leaves leaf types indicating leaf types differ in quality

Ambient Temperature Influences Diet Selection and Physiology of an Herbivorous Mammal, \u3cem\u3eNeotoma albigula\u3c/em\u3e

The whitethroat woodrat (Neotoma albigula) eats juniper (Juniperus monosperma), but the amount of juniper in its diet varies seasonally. We tested whether changes in juniper consumption are due to changes in ambient temperature and what the physiological consequences of consuming plant secondary compounds (PSCs) at different ambient temperatures might be. Woodrats were acclimated to either 20ºC or 28ºC. Later, they were given two diets to choose from (50% juniper and a nontoxic control) for 7 d. Food intake, resting metabolic rate (RMR), and body temperature (Tb) were measured over the last 2 d. Woodrats at 28ºC ate significantly less juniper, both proportionally and absolutely, than woodrats at 20ºC. RMRs were higher for woodrats consuming juniper regardless of ambient temperature, and Tb was higher for woodrats consuming juniper at 28ºC than for woodrats eating control diet at 28ºC. Thus, juniper consumption by N. albigula is influenced by ambient temperature. We conclude that juniper may influence thermoregulation in N. albigula in ways that are helpful at low temperatures but harmful at warmer temperatures in that juniper PSCs may be more toxic at warmer temperatures. The results suggest that increases in ambient temperature associated with climate change could significantly influence foraging behavior of mammalian herbivores

Phytochemistry Predicts Habitat Selection by an Avian Herbivore at Multiple Spatial Scales

Animal habitat selection is a process that functions at multiple, hierarchically structured spatial scales. Thus multi-scale analyses should be the basis for inferences about factors driving the habitat selection process. Vertebrate herbivores forage selectively on the basis of phytochemistry, but few studies have investigated the influence of selective foraging (i.e., fine-scale habitat selection) on habitat selection at larger scales. We tested the hypothesis that phytochemistry is integral to the habitat selection process for vertebrate herbivores. We predicted that habitats selected at three spatial scales would be characterized by higher nutrient concentrations and lower concentrations of plant secondary metabolites (PSMs) than unused habitats. We used the Greater Sage-Grouse (Centrocercus urophasianus), an avian herbivore with a seasonally specialized diet of sagebrush, to test our hypothesis. Sage-Grouse selected a habitat type (black sagebrush, Artemisia nova) with lower PSM concentrations than the alternative (Wyoming big sagebrush, A. tridentata wyomingensis). Within black sagebrush habitat, Sage-Grouse selected patches and individual plants within those patches that were higher in nutrient concentrations and lower in PSM concentrations than those not used. Our results provide the first evidence for multi-scale habitat selection by an avian herbivore on the basis of phytochemistry, and they suggest that phytochemistry may be a fundamental driver of habitat selection for vertebrate herbivores

Plant Driven Movement: Does Plant Quality Affect the Foraging Patterns of Successful Male Sage-Grouse (Centrocercus Urophasianus)?

The structural and dietary quality of plants is highly variable across the landscape and may influence energy acquisition by herbivores needed for energy dependent activities. For sage-grouse, male display efforts are energetically expensive, with successful males expending up to four times their basal metabolic rate to display. Previous work found that males who had the greatest energy expenditure during the lekking season also lost the least weight and foraged farthest from the lek. We hypothesized that the energetic benefit of foraging farther from the lek is due to higher quality food or cover compared to near lek vegetation. To initially test this hypothesis, we quantified the structural and nutritional quality of sagebrush at different distances away from the lek as well as at patches used by sage-grouse for foraging and roosting. We found no difference in density, percent cover, or height of live or dead sagebrush among different distances (edge, 100, 200, 400 or 800 m) away from leks, but there was a trend for plants near the lek edge to have higher crude protein than those farther away from leks. We found no difference in percent grass, percent forbs, volume of sagebrush, or crude protein of sagebrush among forage, roost, or near lek (100 m from edge) patches, but forage patches tended to have taller sagebrush than roost or near lek patches. The preliminary results suggest that selection for off-lek patches by male sage-grouse may not be driven by the structural or nutritional quality of plants. We propose that plant chemical components may be more indicative of off-lek habitat use by male sage-grouse during the lekking period

Conservation of Sharp-Tailed Grouse (\u3cem\u3eTympanuchus phasianellus columbianus\u3c/em\u3e) Through Fecal DNA Extraction

Columbian Sharp-tailed Grouse (Tympanuchus phasianellus columbianus) are the rarest of the six extant Sharp-tailed Grouse subspecies. This subspecies experienced a 90% range contraction over the last century and have been extirpated from several states (Figure 1). In Washington alone, populations that once numbered hundreds of thousands of individuals now consist of fewer than 1,000 birds. Conservation efforts—including conservation translocations and habitat management—are underway to help bolster this imperiled subspecies across their range. However, little is known about the ecology of this charismatic species and the factors that may be contributing towards higher rates of decline. The collection of fecal pellets presents an opportunity to better understand Columbian Sharp-tailed Grouse across their range, by providing information on their diet and host ID. As a HERC Fellow in the Conservation Genetics Lab at Boise State University, I have been exploring the potential to use non-invasively collected fecal samples to understand how we can best capture different DNA types, which can be used to better inform the conservation and management of this charismatic grouse

Seasonal temperature acclimatization in a semi-fossorial mammal and the role of burrows as thermal refuges.

Small mammals in habitats with strong seasonal variation in the thermal environment often exhibit physiological and behavioral adaptations for coping with thermal extremes and reducing thermoregulatory costs. Burrows are especially important for providing thermal refuge when above-ground temperatures require high regulatory costs (e.g., water or energy) or exceed the physiological tolerances of an organism. Our objective was to explore the role of burrows as thermal refuges for a small endotherm, the pygmy rabbit (Brachylagus idahoensis), during the summer and winter by quantifying energetic costs associated with resting above and below ground. We used indirect calorimetry to determine the relationship between energy expenditure and ambient temperature over a range of temperatures that pygmy rabbits experience in their natural habitat. We also measured the temperature of above- and below-ground rest sites used by pygmy rabbits in eastern Idaho, USA, during summer and winter and estimated the seasonal thermoregulatory costs of resting in the two microsites. Although pygmy rabbits demonstrated seasonal physiological acclimatization, the burrow was an important thermal refuge, especially in winter. Thermoregulatory costs were lower inside the burrow than in above-ground rest sites for more than 50% of the winter season. In contrast, thermal heterogeneity provided by above-ground rest sites during summer reduced the role of burrows as a thermal refuge during all but the hottest periods of the afternoon. Our findings contribute to an understanding of the ecology of small mammals in seasonal environments and demonstrate the importance of burrows as thermal refuge for pygmy rabbits