Strategies for the Use of Fallback Foods in Apes

Researchers have suggested that fallback foods (FBFs) shape primate food processing adaptations, whereas preferred foods drive harvesting adaptations, and that the dietary importance of FBFs is central in determining the expression of a variety of traits. We examine these hypotheses in extant apes. First, we compare the nature and dietary importance of FBFs used by each taxon. FBF importance appears greatest in gorillas, followed by chimpanzees and siamangs, and least in orangutans and gibbons (bonobos are difficult to place). Next, we compare 20 traits among taxa to assess whether the relative expression of traits expected for consumption of FBFs matches their observed dietary importance. Trait manifestation generally conforms to predictions based on dietary importance of FBFs. However, some departures from predictions exist, particularly for orang-utans, which express relatively more food harvesting and processing traits predicted for consuming large amounts of FBFs than expected based on observed dietary importance. This is probably due to the chemical, mechanical, and phenological properties of the apes’ main FBFs, in particular high importance of figs for chimpanzees and hylobatids, compared to use of bark and leaves—plus figs in at least some Sumatran populations—by orang-utans. This may have permitted more specialized harvesting adaptations in chimpanzees and hylobatids, and required enhanced processing adaptations in orang-utans. Possible intercontinental differences in the availability and quality of preferred and FBFs may also be important. Our analysis supports previous hypotheses suggesting a critical influence of the dietary importance and quality of FBFs on ape ecology and, consequently, evolution

Cryo-scanning transmission electron tomography of vitrified cells

Cryo-electron tomography (CET) of fully hydrated, vitrified biological specimens has emerged as a vital tool for biological research. For cellular studies, the conventional imaging modality of transmission electron microscopy places stringent constraints on sample thickness because of its dependence on phase coherence for contrast generation. Here we demonstrate the feasibility of using scanning transmission electron microscopy for cryo-tomography of unstained vitrified specimens (CSTET). We compare CSTET and CET for the imaging of whole bacteria and human tissue culture cells, finding favorable contrast and detail in the CSTET reconstructions. Particularly at high sample tilts, the CSTET signals contain more informative data than energy-filtered CET phase contrast images, resulting in improved depth resolution. Careful control over dose delivery permits relatively high cumulative exposures before the onset of observable beam damage. The increase in acceptable specimen thickness broadens the applicability of electron cryo-tomography