Plant protein and secondary metabolites influence diet selection in a mammalian specialist herbivore

Abstract

For herbivores, nutrient intake is limited by the relatively low nutritional quality of plants and high concentrations of potentially toxic defensive compounds (plant secondary metabolites, PSMs) produced by many plants. In response to phytochemical challenges, some herbivores selectively forage on plants with higher nutrient and lower PSM concentrations relative to other plants. Pygmy rabbits (Brachylagus idahoensis) are dietary specialists that feed on sagebrush (Artemisia spp.) and forage on specific plants more than others within a foraging patch. We predicted that the plants with evidence of heavy foraging (browsed plants) would be of higher dietary quality than plants that were not browsed (unbrowsed). We used model selection to determine which phytochemical variables best explained the difference between browsed and unbrowsed plants. Higher crude protein increased the odds that plants would be browsed by pygmy rabbits and the opposite was the case for certain PSMs. Additionally, because pygmy rabbits can occupy foraging patches (burrows) for consecutive years, their browsing may influence the nutritional and PSM constituents of plants at the burrows. In a post hoc analysis, we did not find a significant relationship between phytochemical concentrations, browse status and burrow occupancy length. We concluded that pygmy rabbits use nutritional and chemical cues while making foraging decisions.

Antioxidant Capacity Of Wyoming Big Sagebrush (Artemisia tridentataSSP.Wyomingensis) Varies Spatially and is Not Related to the Presence of a Sagebrush Dietary Specialist

“…The higher antioxidant activity of samples from the Camas Prairie site for a given amount of polyphenolics could be due to the higher concentration of specific PSMs that have a greater antioxidant activity than others, or it may be due to other classes of PSMs that also have antioxidant capacity that we did not investigate. For example, several monoterpenes, such as (+)-camphene, p -cymene, and borneol, have antioxidant capacity (Kordali et al 2005, Quintans-Júnior et al 2013), and these PSMs are also found in sagebrush (Bray et al 1991, Ulappa et al 2014). …”

“…However, focusing on total polyphenols may dilute our ability to detect the deterrent properties or antioxidant activity of specific polyphenols or other classes of chemical. For example, we recently found that low-browsed sagebrush contained lower concentrations of specific monoterpenes, but not total monoterpenes, than did sagebrush browsed heavily by pygmy rabbits (Ulappa et al 2014). Future studies should investigate the role of specific polyphenols and their mechanism of action, in addition to total polyphenols, to better understand the interactions between chemical defenses, antioxidant capacity, and biotic stress caused by herbivores.…”

“…Damage to leaves by natural or simulated browsing by herbivores can result in induction of PSMs in sagebrush (Karban et al 2006, Shiojiri and Karban 2008). Moreover, the PSMs in sagebrush deter pathogens (Talley et al 2002) and herbivores (Frye et al 2013, Ulappa et al 2014), suggesting that these PSMs have biological activity.…”

Unmanned aerial systems measure structural habitat features for wildlife across multiple scales

“…canopy cover), distance to a burrow refuge (Camp, Rachlow, Woods, Johnson, & Shipley, ) and the variance in phytochemical properties (i.e. crude protein and plant secondary metabolites) of shrubs for food (Nobler, ; Ulappa et al., ). Although we focus our analysis on habitat quality for pygmy rabbits, we note that many of the habitat features that we quantify with UAS are important to a variety of terrestrial vertebrates inhabiting sagebrush steppe, such as the greater sage grouse ( Centrocercus urophasianus ) (Connelly, Wakkinen, Apa, & Reese, ; Fremgen, ; Frye, Connelly, Musil, & Forbey, ).…”

“…canopy cover), distance to a burrow refuge (Camp, Rachlow, Woods, Johnson, & Shipley, 2012) and the variance in phytochemical properties (i.e. crude protein and plant secondary metabolites) of shrubs for food (Nobler, 2016;Ulappa et al, 2014).…”