Is Diet Selection by Greater Sage-Grouse Influenced by Biomass Availability or Toxins?

Foraging herbivores must meet nutritional requirements by not only finding enough plant biomass to consume, but also finding plants with high protein content and low concentrations of potentially toxic plant secondary metabolites (PSMs). Greater sage-grouse (Centrocercus urophasianus; hereafter, sage-grouse) are sagebrush obligate herbivores that consume relatively high concentrations of PSMs. To meet their nutritional needs and avoid ingesting high amounts of PSMs, sage-grouse may select species of sagebrush for food that have lower concentrations of PSMs than a more abundant species with higher concentration of PSMs. Diet selection by sage-grouse may also be driven by chemical factors at finer scales once a species is selected. For example, different morphotypes of sagebrush (identified by leaf morphology and plant structure) within a patch have different chemical profiles that may influence selection at a patch scale. Our objective was to determine how diet selection is influenced by available biomass and chemical characteristics of morphotypes within a foraging patch, and whether sage-grouse select specific morphotypes of sagebrush to maximize biomass consumed per bite or minimize toxin consumed per bite. For each sagebrush morphotype, we determined density of plants within a patch and available biomass which we calculated as plant volume. We then measured biomass and monoterpene concentrations of the leaves per bite. Our results showed that browsing is not proportional to biomass availability, but that sage-grouse selected sagebrush morphotypes that minimized toxin intake per bite. Our research aims to understand plant-herbivore interactions and how sage-grouse select and use habitats at different spatial scales

Aversion and attraction to harmful plant secondary compounds jointly shape the foraging ecology of a specialist herbivore.

Most herbivorous insect species are restricted to a narrow taxonomic range of host plant species. Herbivore species that feed on mustard plants and their relatives in the Brassicales have evolved highly efficient detoxification mechanisms that actually prevent toxic mustard oils from forming in the bodies of the animals. However, these mechanisms likely were not present during the initial stages of specialization on mustard plants ~100 million years ago. The herbivorous fly Scaptomyza nigrita (Drosophilidae) is a specialist on a single mustard species, bittercress (Cardamine cordifolia; Brassicaceae) and is in a fly lineage that evolved to feed on mustards only in the past 10-20 million years. In contrast to many mustard specialists, S. nigrita does not prevent formation of toxic breakdown products (mustard oils) arising from glucosinolates (GLS), the primary defensive compounds in mustard plants. Therefore, it is an appealing model for dissecting the early stages of host specialization. Because mustard oils actually form in the bodies of S. nigrita, we hypothesized that in lieu of a specialized detoxification mechanism, S. nigrita may mitigate exposure to high GLS levels within plant tissues using behavioral avoidance. Here, we report that jasmonic acid (JA) treatment increased GLS biosynthesis in bittercress, repelled adult female flies, and reduced larval growth. S. nigrita larval damage also induced foliar GLS, especially in apical leaves, which correspondingly displayed the least S. nigrita damage in controlled feeding trials and field surveys. Paradoxically, flies preferred to feed and oviposit on GLS-producing Arabidopsis thaliana despite larvae performing worse in these plants versus non-GLS-producing mutants. GLS may be feeding cues for S. nigrita despite their deterrent and defensive properties, which underscores the diverse relationship a mustard specialist has with its host when lacking a specialized means of mustard oil detoxification

Is Habitat Use by Greater Sage-Grouse Proportional to Availability of Plant Morphotypes?

Greater Sage-grouse (Centrocercus urophasianus; hereafter, sage-grouse) select sagebrush plants for food that are high in protein. However, sagebrush produce toxins called monoterpenes that can inhibit enzymatic reactions and interrupt cellular processes and therefore result in decreased intake by sage-grouse. Moreover, species, subspecies, populations, and morphotypes of sagebrush can vary in the concentration of toxins produced. Preliminary analysis has shown that different morphotypes of sagebrush have different chemical profiles, and this may influence selection at a scale below species. Our research aims to determine whether sage-grouse select specific morphotypes of sagebrush to maximize biomass consumed per bite or minimize toxin consumed per bite and, how that selection changes with plant density or abundance. We flushed radio-marked sage-grouse and identified their foraging site using tracks and fresh pellets. At each used patch, we performed density counts for each morphotype of sagebrush along atransect, and recorded the volume and number of bite marks for each plant. We will evaluate if sage-grouse browse certain morphotypes in proportion to their availability, or if they differentially select morphotypes to browse based on biomass per bite or toxin concentration per bite. This research contributes to a growing understanding of how sage-grouse select and use habitats throughout the year, which is increasingly important as habitat availability decreases, the distribution of specific morphotypes change and remaining landscapes are degraded. Additionally, this research provides insight about plant-herbivore interactions and how herbivores select plants to consume, based on biomass intake rates, toxin concentration, or availability of plants

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

Effects of site-directed mutagenesis of mglA on motility and swarming of Myxococcus xanthus

<p>Abstract</p> <p>Background</p> <p>The <it>mglA </it>gene from the bacterium <it>Myxococcus xanthus </it>encodes a 22kDa protein related to the Ras superfamily of monomeric GTPases. MglA is required for the normal function of A-motility (adventurous), S-motility (social), fruiting body morphogenesis, and sporulation. MglA and its homologs differ from all eukaryotic and other prokaryotic GTPases because they have a threonine (Thr78) in place of the highly conserved aspartate residue of the consensus PM3 (phosphate-magnesium binding) region. To identify residues critical for MglA function or potential protein interactions, and explore the function of Thr78, the phenotypes of 18 <it>mglA </it>mutants were characterized.</p> <p>Results</p> <p>Nine mutants, with mutations predicted to alter residues that bind the guanine base or coordinate magnesium, did not produce detectable MglA. As expected, these mutants were mot^-dev^-because MglA is essential for these processes. Of the remaining nine mutants, seven showed a wild-type distribution pattern for MglA but fell into two categories with regard to function. Five of the seven mutants exhibited mild phenotypes, but two mutants, T78D and P80A, abolished motility and development. The localization pattern of MglA was abolished in two mutants that were mot^-spo^-and dev^-. These two mutants were predicted to alter surface residues at Asp52 and Thr54, which suggests that these residues are critical for proper localization and may define a protein interaction site. Improving the consensus match with Ras at Thr78 abolished function of MglA. Only the conservative serine substitution was tolerated at this position. Merodiploid constructs revealed that a subset of alleles, including <it>mglA</it>D52A, were dominant and also illustrated that changing the balance of MglA and its co-transcribed partner, MglB, affects A-motility.</p> <p>Conclusion</p> <p>Our results suggest that GTP binding is critical for stability of MglA because MglA does not accumulate in mutants that cannot bind GTP. The threonine in PM3 of MglA proteins represents a novel modification of the highly conserved GTPase consensus at this position. The requirement for a hydroxyl group at this position may indicate that MglA is subject to modification under certain conditions. Proper localization of MglA is critical for both motility and development and likely involves protein interactions mediated by residues Asp52 and Thr54.</p

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

Male Greater Sage-Grouse Detectability on Leks

It is unlikely all male sage-grouse are detected during lek counts, which could complicate the use of lek counts as an index to population abundance. Understanding factors that influence detection probabilities will allow managers to more accurately estimate the number of males present on leks. We fitted 410 males with global positioning system and very high frequency transmitters, and uniquely identifiable leg-bands over 4 years in Carbon County, Wyoming. We counted male sage-grouse using commonly used lek-count protocols and evaluated variables associated with our ability to detect marked males using sightability surveys on 22 leks. We evaluated detection probabilities of male sage-grouse based on factors related to bird characteristics such as age or posture, lek and group size, lek characteristics such as vegetation cover or aspect, light conditions, weather, and observer. We then applied the detection probabilities to more accurately estimate male counts on leks. Detection probabilities were generally high (math formula = 0.87) but varied among leks from 0.77 to 0.93. Male sage-grouse detection declined with increasing sagebrush height and bare ground and increased with more snow cover. Detection probabilities were also lower when observers counted from a higher elevation than the lek. Our sightability models predicted detection well and can be used to accurately estimate male abundance on leks from lek counts, which is especially useful where accurate abundance estimates are required or inference about population status is based on only 1 count. Further, it is important to consider lek attendance as a component of counts on leks because it affects availability of male sage-grouse for detection during lek counts. Detection can be maximized by conducting lek counts from 30 minutes before sunrise to 30 minutes after sunrise, although current protocols recommend lek counts can be performed up to 1 hour after sunrise. Detection can also be maximized by conducting lek counts ≥2 days after snowfall, which maximizes attendance and detection. © 2015 The Wildlife Society

Ras GTPase-like protein MglA, a controller of bacterial social-motility in Myxobacteria, has evolved to control bacterial predation by Bdellovibrio

Bdellovibrio bacteriovorus invade Gram-negative bacteria in a predatory process requiring Type IV pili (T4P) at a single invasive pole, and also glide on surfaces to locate prey. Ras-like G-protein MglA, working with MglB and RomR in the deltaproteobacterium Myxococcus xanthus, regulates adventurous gliding and T4P-mediated social motility at both M. xanthus cell poles. Our bioinformatic analyses suggested that the GTPase activating protein (GAP)-encoding gene mglB was lost in Bdellovibrio, but critical residues for MglABd GTP-binding are conserved. Deletion of mglABd abolished prey-invasion, but not gliding, and reduced T4P formation. MglABd interacted with a previously uncharacterised tetratricopeptide repeat (TPR) domain protein Bd2492, which we show localises at the single invasive pole and is required for predation. Bd2492 and RomR also interacted with cyclic-di-GMP-binding receptor CdgA, required for rapid prey-invasion. Bd2492, RomRBd and CdgA localize to the invasive pole and may facilitate MglA-docking. Bd2492 was encoded from an operon encoding a TamAB-like secretion system. The TamA protein and RomR were found, by gene deletion tests, to be essential for viability in both predatory and non-predatory modes. Control proteins, which regulate bipolar T4P-mediated social motility in swarming groups of deltaproteobacteria, have adapted in evolution to regulate the anti-social process of unipolar prey-invasion in the “lone-hunter” Bdellovibrio. Thus GTP-binding proteins and cyclic-di-GMP inputs combine at a regulatory hub, turning on prey-invasion and allowing invasion and killing of bacterial pathogens and consequent predatory growth of Bdellovibrio

Aquilegia Volume 42 No. 2 Spring 2018

https://epublications.regis.edu/aquilegia/1204/thumbnail.jp