Journal of Experimental Biology - Latest Issue

• How consistent is ‘the dynamic gut’? Complex physiological responses to dietary fiber and protein across three rodent species

  ABSTRACT

  To efficiently digest food resources that may vary spatially and temporally, animals maintain physiological flexibility across levels of organization. For example, in response to dietary shifts, animals may exhibit changes in the expression of digestive enzymes, the size of digestive organs or the structure of their gut microbiome. A ‘Grand Challenge’ in comparative physiology is to understand how components of flexibility across organizational levels may scale to cumulatively determine organismal performance. Here, we conducted feeding trials on three rodent species with disparate feeding strategies: herbivorous montane voles (Microtus montanus), omnivorous white-footed mice (Peromyscus leucopus) and carnivorous grasshopper mice (Onychomys torridus). For each species, four groups of individuals were presented with diets that varied in carbohydrate, fiber and protein content. After 4–5 weeks, we measured organismal performance in the form of nutrient digestibility (dry matter, nitrogen, fiber). We also measured gut anatomy and organ size, and conducted enzyme assays on various tissues to measure activities of carbohydrases and peptidases. We found some shared physiological responses, e.g. fiber generally increased gut size across species. However, the specifics of these responses were distinct across species, suggesting different capacities for flexibility. Thus, in the context of digestion, we still lack an understanding of how flexibility across organizational levels may scale to determine whole-animal performance.

• Gut bacterial and fungal communities of three rodent species respond uniquely to dietary fiber and protein manipulation

  ABSTRACT

  Diet and host identity play fundamental roles in digestive physiology and the assembly of gut microbial communities. Research shows that microbial communities are plastic, with abundances of taxa and community interactions exhibiting changes in response to diet. Few studies considering the influence of diet on host and microbial plasticity disentangle the unique roles of specific nutrients, such as protein and fiber. Additionally, in the context of host–microbiome interactions, few studies have explored how host dietary strategies shape the plastic responses of microbial communities within the host digestive tract. To address these current gaps, we fed rodents with distinct dietary strategies (Peromyscus leucopus, Microtus montanus and Onychomys torridus) diets varying in fiber and protein content. Species varied in the degree of cecum size plasticity, with the carnivore showing no significant changes and the omnivore responding to both fiber and protein manipulation. There were also differences in the diversity indices of bacterial and fungal communities across hosts, and the microbes driving those differences were largely unique across rodent species. Additionally, community network interactions varied across treatments, and hub taxa that play a role in regulating network properties were identified. For example, bacteria in the Eubacterium groups, which are known to aid in fiber fermentation, were identified as hub taxa in all three species, but no group shared the same Eubacterium as a hub taxa. Overall, our data suggest that hosts with unique dietary strategies and their microbiomes respond uniquely to changes in the nutrient composition of their diets.

• Multigenerational exposure to glyphosate has only modest effects on life-history traits, stress tolerance and microbiome in a field cricket

  ABSTRACT

  Glyphosate is the most used herbicide worldwide, and it can be toxic to off-target species, such as insects. Although GLY-based herbicides (GBHs) can influence insect microbiomes, little is known about its cascading effects on fitness-related traits, such as life history or stress tolerance, especially in the context of long-term, multigenerational exposure. Thus, we exposed the variable field cricket, Gryllus lineaticeps, to GBH within and across generations to examine the potential role of GBH in developmental plasticity and evolution. Specifically, we measured its effects on life-history traits (e.g. developmental duration, adult body size and mass, and a life-history trade-off between investment into reproduction and flight), stress (heat and desiccation) tolerance and the gut microbiome. One generation of exposure to GBH reduced desiccation tolerance, which was also lower in flight-capable individuals. However, after 11 generations of exposure to GBH, this cost of GBH disappeared, and GBH exposure instead increased adult body size and mass in flight-incapable individuals. Flight capacity had a stronger effect on the gut bacterial community than GBH exposure, where flight-capable individuals contained more than twice as many Family Oscillospiraceae and fewer than half as many Family Erysipelotrichaceae. The effects of both flight capacity and GBH on the microbiome were only evident in generation 1. Together, our results indicate that GBH exposure may have quite modest long-term effects on stress tolerance and the gut microbiome. However, GBH may facilitate the evolution of flightlessness given its potential benefits to flight-incapable individuals, which exhibit greater reproductive potential and tolerance to climate stressors compared with flight-capable individuals.

• Osmoregulatory contributions of the corticotropin-releasing factor system in the intestine of Atlantic salmon

• Co-option of immune and digestive cellular machinery to support photosymbiosis in amoebocytes of the upside-down jellyfish Cassiopea xamachana

  ABSTRACT

  The upside-down jellyfish Cassiopea spp. host their algal symbionts inside a subset of amoebocytes, phagocytic cells that also play innate immune functions akin to macrophages from vertebrate animals. Amoebocyte precursors phagocytose algae from the jellyfish gut and store them inside intracellular compartments called symbiosomes. Subsequently, the precursors migrate to the mesoglea, differentiate into symbiotic amoebocytes, and roam throughout the jellyfish body, where the algae remain photosynthetically active and supply the jellyfish host with a significant portion of their organic carbon needs. Here, we show that the amoebocyte symbiosome membrane contains V-H⁺-ATPase (VHA), the proton pump that acidifies phagosomes and lysosomes in all eukaryotes. Many symbiotic amoebocytes also abundantly express a carbonic anhydrase (CA), an enzyme that reversibly hydrates CO₂ into H⁺ and HCO₃⁻. Moreover, we found that the symbiosome lumen is pronouncedly acidic and that pharmacological inhibition of VHA or CA activities significantly decreases photosynthetic oxygen production in live jellyfish. These results point to a carbon concentrating mechanism (CCM) that co-opts VHA and CA from the phago-lysosomal machinery that ubiquitously mediates food digestion and innate immune responses. Analogous VHA-dependent CCMs have been previously described in reef-building corals, anemones and giant clams; however, these other two cnidarians host their dinoflagellate algae inside gastrodermal cells – not in amoebocytes – and the clam hosts theirs within the gut lumen. Thus, our study identifies an example of convergent evolution at the cellular level that might broadly apply to invertebrate–microbe photosymbioses while also providing evolutionary links with intracellular and extracellular food digestion and the immune system.