Silicon-based plant defences, tooth wear and voles

Abstract

Plant-herbivore interactions are hypothesized to drive vole population cycles through the grazing-induced production of phytoliths in leaves. Phytoliths act as mechanical defences because they deter herbivory and lower growth rates in mammals. However, how phytoliths impair herbivore performance is still unknown. Here, we tested whether the amount of phytoliths changes tooth wear patterns. If confirmed, abrasion from phytoliths could play a role in population crashes. We applied dental microwear texture analysis (DMTA) to laboratory and wild voles. Lab voles were fed two pelleted diets with differing amounts of silicon, which produced similar dental textures. This was most probably due to the loss of food mechanical properties through pelletization and/or the small difference in silicon concentration between diets. Wild voles were trapped in Poland during spring and summer, and every year across a population cycle. In spring, voles feed on silica-rich monocotyledons, while in the summer they also include silicadepleted dicotyledons. This was reflected in the results; the amount of silica therefore leaves a traceable record in the dental microwear texture of voles. Furthermore, voles from different phases of population cycles have different microwear textures. We tentatively propose that these differences result from grazing-induced phytolith concentrations. We hypothesize that the high amount of phytoliths in response to intense grazing in peak years may result in malocclusion and other dental abnormalities, which would explain how these silicon-based plant defences help provoke population crashes. DMTA could then be used to reconstruct vole population dynamics using teeth from pellets or palaeontological material.

Functions of phytoliths in vascular plants: an evolutionary perspective

“…, ; Calandra et al . ). A study of Japanese sika deer ( Cervus nippon ) across (mainly closed) habitats similarly found that both the degree of mesowear (measuring the macroscopic effects of abrasion during the tooth's lifespan) and molar wear rates were correlated with the dietary percentage of grass as well as the phytolith content of ingested grasses (Ozaki Kubo & Yamada ).…”

The ecology of herbivore‐induced silicon defences in grasses

“…Furthermore, Calandra et al . () found effects of silicon on microwear patterns in the teeth of voles and have proposed this as a mechanism by which silicon may contribute to population crashes. Hummel et al .…”

Association of leaf silicon content with chronic wind exposure across and within herbaceous plant species

“…The common view has been that the main function of foliar Si accretions in solid form (e.g., phytoliths) is to protect plant tissues from herbivory (Cooke et al, ; Epstein, ; Hartley & DeGabriel, ; Hartley, Fitt, McLarnon, & Wade, ), especially from being eaten by (mostly mammalian) vertebrates (Massey & Hartley, ; Massey, Massey, Ennos, & Hartley, ; Strömberg et al, ; Teaford, Lucas, Ungar, & Glander, ; Wieczorek, Zub, Szafrańska, Książek, & Konarzewski, ) or invertebrates (Garbuzov, Reidinger, & Hartley, ; Hunt, Dean, Webster, Johnson, & Ennos, ; Johnson et al, ; Massey & Hartley, ; Reynolds, Keeping, & Meyer, ; Ryalls, Hartley, & Johnson, ; Soininen, Bråthen, Jusdado, Reidinger, & Hartley, ), and to act as a potentially cheap alternative to cellulose or lignin (Cooke & Leishman, ; Raven, ; Schoelynck et al, ). Silicon is even thought to have played a central role in the co‐evolution of grasses and their mammalian grazers, which had to evolve teeth that could withstand chronic erosion by foliar phytoliths, although this role is still under active debate (Calandra, Zub, Szafrańska, Zalewski, & Merceron, ; Hartley & DeGabriel, ; Strömberg et al, ). However, horsetails (Equisetopsida), which generally have a very high tissue Si concentration ([Si]; in milligrams per gram dry weight; Hodson, White, Mead, & Broadley, ), are known to have been abundant as early as the Carboniferous (Trembath‐Reichert, Wilson, McGlynn, & Fischer, ), when herbivorous vertebrates had hardly evolved or not yet evolved (Sues, ).…”