The Enemy Within: How Does a Bacterium Inhibit the Foraging Aptitude and Risk Management Behavior of Allenby's Gerbils?

On the use of antibiotics in plasticity research: Gastropod shells unveil a tale of caution

Through phenotypic plasticity, individual genotypes can produce multiple phenotypes dependent on the environment. In the modern world, anthropogenic influences such as man-made pharmaceuticals are increasingly prevalent. They might alter observable patterns of plasticity and distort our conclusions regarding the adaptive potential of natural populations. Antibiotics are nowadays nearly ubiquitous in aquatic environments and prophylactic antibiotic use is also becoming more common to optimize animal survival and reproductive output in artificial settings. In the well-studied plasticity model system Physella acuta, prophylactic erythromycin treatment acts against gram-positive bacteria and thereby reduces mortality. Here, we study its consequences for inducible defence formation in the same species. In a 2 × 2 split-clutch design, we reared 635 P. acuta in either the presence or absence of this antibiotic, followed by 28-day exposure to either high or low predation risk as perceived through conspecific alarm cues. Under antibiotic treatment, risk-induced increases in shell thickness, a well-known plastic response in this model system, were larger and consistently detectable. Antibiotic treatment reduced shell thickness in low-risk individuals, suggesting that in controls, undiscovered pathogen infection increased shell thickness under low risk. Family variation in risk-induced plasticity was low, but the large variation in responses to antibiotics among families suggests different pathogen susceptibility between genotypes. Lastly, individuals that developed thicker shells had reduced total mass, which highlights resource trade-offs. Antibiotics thus have the potential to uncover a larger extent of plasticity, but might counterintuitively distort plasticity estimates for natural populations where pathogens are a part of natural ecology.

Mycoplasmataceae dominate microbial community differences between gut regions in mammals with a simple gut architecture

Faunivorous mammals with simple guts are thought to rely primarily on endogenously produced enzymes to digest food, in part because they lack fermentation chambers for facilitating mutualistic interactions with microbes. However, variation in microbial community composition along the length of the gastrointestinal tract has yet to be assessed in faunivorous species with simple guts. We tested for differences in bacterial taxon abundances and community compositions between the small intestines and colons of 26 individuals representing four species of shrew in the genus Crocidura. We sampled these hosts from a single locality on Sulawesi Island, Indonesia, to control for potential geographic and temporal variation. Bacterial community composition differed significantly between the two gut regions and members of the family Mycoplasmataceae contributed substantially to these differences. Three operational taxonomic units (OTUs) of an unclassified genus in this family were more abundant in the small intestine, whereas 1 OTU of genus Ureaplasma was more abundant in the colon. Species of Ureaplasma encode an enzyme that degrades urea, a metabolic byproduct of protein catabolism. Additionally, a Hafnia–Obesumbacterium OTU, a genus known to produce chitinase in bat gastrointestinal tracts, was also more abundant in the colon compared to the small intestine. The presence of putative chitinase- and urease-producing bacteria in shrew guts suggests mutualisms with microorganisms play a role in facilitating the protein-rich, faunivorous diets of simple gut mammals.

Finding a Home: Stopping Theory and Its Application to Home Range Establishment in a Novel Environment

Familiarity with the landscape increases foraging efficiency and safety. Thus, when animals are confronted with a novel environment, either by natural dispersal or translocation, establishing a home range becomes a priority. While the search for a home range carries a cost of functioning in an unfamiliar environment, ceasing the search carries a cost of missed opportunities. Thus, when to establish a home range is essentially a weighted sum of a two-criteria cost-minimization problem. The process is predominantly heuristic, where the animal must decide how to study the environment and, consequently, when to stop searching and establish a home range in a manner that will reduce the cost and maximize or at least satisfice its fitness. These issues fall within the framework of optimal stopping theory. In this paper we review stopping theory and three stopping rules relevant to home range establishment: the best-of-n rule, the threshold rule, and the comparative Bayes rule. We then describe how these rules can be distinguished from movement data, hypothesize when each rule should be practiced, and speculate what and how environmental factors and animal attributes affect the stopping time. We provide a set of stopping-theory-related predictions that are testable within the context of translocation projects and discuss some management implications.

Using Free-Range Laboratory Mice to Explore Foraging, Lifestyle, and Diet Issues in Cancer

As cancer progresses, its impact should manifest in the foraging behavior of its host much like the effects of endo-parasites that hinder foraging aptitudes and risk management abilities. Furthermore, the lifestyle of the host can impact tumor growth and quality of life. To approach these questions, we conducted novel experiments by letting C57BL/6 laboratory mice, with or without oral squamous cell carcinoma, free range in a large outdoor vivarium. Our goals were to: (1) determine whether one could conduct experiments with a mouse model under free range conditions, (2) measure effects of cancer burden on foraging metrics, (3) compare tumor growth rates with laboratory housed mice, and (4) begin to sort out confounding factors such as diet. With or without cancer, the C57BL/6 laboratory mice dealt with natural climatic conditions and illumination, found shelter or dug burrows, sought out food from experimental food patches, and responded to risk factors associated with microhabitat by foraging more thoroughly in food patches under bush (safe) than in the open (risky). We quantified foraging using giving-up densities of food left behind in the food patches. The mice’s patch use changed over time, and was affected by disease status, sex, and microhabitat. Males, which were larger, consumed more food and had lower giving-up densities than females. Relative to cancer-free mice, mice with growing tumors lost weight, harvested more food, and increasingly relied on patches in the bush microhabitat. The tumors of free-ranging mice in the vivarium grew slower than those of their cohort that were housed in mouse cages in animal facilities. Numerous interesting factors could explain the difference in tumor growth rates: activity levels, stress, weather, food intake, diet, and more. To tease apart one of these intertwined factors, we found that tumors grew faster when mice in the laboratory were fed on millet rather than laboratory mouse chow. While just a start, these novel experiments and framework show how free-ranging mice provide a model that can test a broader range of hypotheses and use a broader range of metrics regarding cancer progression and its consequences for the host.