Differentiating siliceous particulate matter in the diets of mammalian herbivores

Abstract

1. Silica is crucial to terrestrial plant life and geochemical cycling on Earth. It is also implicated in the evolution of mammalian teeth, but there is debate over which type of siliceous particle has exerted the strongest selective pressure on tooth morphology.2. Debate revolves around the amorphous silica bodies (phytoliths) present in plants and the various forms of siliceous grit-that is, crystalline quartz (sand, soil, dust)-on plant surfaces. The problem is that conventional measures of silica often quantify both particle types simultaneously.3. Here we describe a protocol that relies on heavy-liquid flotation to separate and quantify siliceous particulate matter in the diets of herbivores. The method is reproducible and well suited to detecting species-or population-level differences in silica ingestion. In addition, we detected meaningful variation within the digestive tracts of cows, an outcome that supports the premise of ruminal fluid 'washing' of siliceous grit. 4. We used bootstrap resampling to estimate the sample sizes needed to compare species, populations or individuals in space and time. We found that a minimum sample of 12 individuals is necessary if the species is a browser or as many as 55 if the species is a grazer, which are more variable. But a sample size of 20 is adequate for detecting statistical differences. We conclude by suggesting that our protocol for differentiating and quantifying silica holds promise for testing competing hypotheses on the evolution of dental traits.

Comparative study of feeding and rumination behaviour of goats and sheep fed mixed grass hay of different chop length

“…Besides other, well‐described advantages, the ruminant forestomach physiology also represents a mechanism that washes off dust, sand or grit from the ingested feed prior to rumination (Hatt, et al, 2019; Valerio et al, 2022). Free‐ranging ruminants have been reported to ingest significant levels of soil inadvertently with their diet (Beyer et al, 1994; Fannin et al, 2022; Hummel et al, 2011; Madden, 2014; Sanson et al, 2017). Shifting the majority of mastication to that phase where these external abrasives have been removed from the feed will distinctively protect dental tissue from wear, and may therefore represent an important adaptation.…”

The Ruminant sorting mechanism protects teeth from abrasives

“…It was long suspected that this mechanism provides material to rumination from which abrasives have been washed off. This was supported by indirect evidence from slaughter or feeding experiments in ruminants and camelids fed diets contaminated with sand, in which the dorsal forestomach contents, from which material for regurgitation is recruited, had low silica concentrations (11)(12)(13)(14). However, direct evidence investigating actually chewed material in live animals has been missing so far.…”

Food-washing monkeys recognize the law of diminishing returns

“…S1). It is a modest difference, perhaps, but it is freighted with tness consequences when extrapolated over years of life 20 . It follows that monkeys should compulsively wash sand from food whenever the opportunity avails itself, a prediction that motivated our eld experiment.…”