Host Bias in Diet-Source Microbiome Transmission in Wild Cohabitating Herbivores: New Knowledge for the Evolution of Herbivory and Plant Defense

We discovered a host bias among cohabitating herbivores (leaf-eating insects and deer), where a significant portion of the herbivorous insect gut microbiome may originate from the diet, while in deer, only a tiny fraction of the gut microbiome is of dietary origin. We speculated that the putative difference in the oxygenation level in the host digestion systems would lead to these host biases in plant-source (diet) microbiome transmission due to the oxygenation living condition of the dietary plant's symbiotic microbiome.

On the evolutionary advantage of multi-cusped teeth

A hallmark of mammalian evolution is a progressive complexity in postcanine tooth morphology. However, the driving force for this complexity remains unclear: whether to expand the versatility in diet source, or to bolster tooth structural integrity. In this study, we take a quantitative approach to this question by examining the roles of number, position and height of multiple cusps in determining sustainable bite forces. Our approach is to use an extended finite-element methodology with due provision for step-by-step growth of an embedded crack to determine how fracture progresses with increasing occlusal load. We argue that multi-cusp postcanine teeth are well configured to withstand high bite forces provided that multiple cusps are contacted simultaneously to share the load. However, contact on a single near-wall cusp diminishes the strength. Location of the load points and cusp height, rather than cusp number or radius, are principal governing factors. Given these findings, we conclude that while complex tooth structures can enhance durability, increases in cusp number are more likely to be driven by the demands of food manipulation. Structural integrity of complex teeth is maintained when individual cusps remain sufficiently distant from the side walls and do not become excessively tall relative to tooth width.

Inherent variation in carbon and nitrogen isotopic assimilation in the freshwater macro-invertebrate Cherax destructor

Individual variability in diet source selection has often been cited as the main factor for intra-specific variation of isotopic signatures among food-web consumers. We conducted a laboratory study to test how well the individual variability of the δ13C and δ15N ratios in the muscle of an omnivore consumer (yabby: Cherax destructor) corresponded to the variability of various diet types and diet combinations. We found that C. destructor muscle isotope signatures varied in concert with the composition of single-source diets, and that this variability was low. However, when fed the same proportional mixture of multiple diet sources, comparatively high isotopic variability was observed among specimens. Results suggest that a substantial component of isotopic variability in wild populations may be owing to inherent differences in uptake, absorption, and sequestration among individuals, which is distinct from behaviourally driven individualised diet selection. Considering the potential of such individual variability in assimilation to be present in many different consumer populations, we suggest further testing for a range of species and inclusion of this source of variation, for interpretation of isotopic data for trophic ecology.