Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

The Theory of Island Biogeography

Gut microbial induction of host immune maturation exemplifies host-microbe mutualism. We colonized germ-free (GF) mice with mouse microbiota (MMb) or human microbiota (HMb) to determine whether small intestinal immune maturation depends on a coevolved host-specific microbiota. Gut bacterial numbers and phylum abundance were similar in MMb and HMb mice, but bacterial species differed, especially the Firmicutes. HMb mouse intestines had low levels of CD4(+) and CD8(+) T cells, few proliferating T cells, few dendritic cells, and low antimicrobial peptide expression--all characteristics of GF mice. Rat microbiota also failed to fully expand intestinal T cell numbers in mice. Colonizing GF or HMb mice with mouse-segmented filamentous bacteria (SFB) partially restored T cell numbers, suggesting that SFB and other MMb organisms are required for full immune maturation in mice. Importantly, MMb conferred better protection against Salmonella infection than HMb. A host-specific microbiota appears to be critical for a healthy immune system.

Gut Immune Maturation Depends Upon Colonization with Host-Specific Microbiota

https://pure.bond.edu.au/ws/files/32288082/AM_Dietary_fiber_intervention_on_gut_microbiota_composition_in_healthy_adults.pdf

Dietary fiber intervention on gut microbiota composition in healthy adults: a systematic review and meta-analysis.

Affective Neuroscience: The Foundations of Human and Animal Emotions.

The microorganisms within the intestinal tract (termed gut microbiota) have been shown to interact with the gut-brain axis, a bidirectional communication system between the gut and the brain mediated by hormonal, immune, and neural signals. Through these interactions, the microbiota might affect behaviors, including feeding behavior, digestive/absorptive processes (e.g., by modulating intestinal motility and the intestinal barrier), metabolism, as well as the immune response, with repercussions on the energy homeostasis and health of the host. To date, research in this field has mostly focused on mammals. Studies on non-mammalian models such as fish may provide novel insights into the specific mechanisms involved in the microbiota-brain-gut axis. This review describes our current knowledge on the possible effects of microbiota on feeding, digestive processes, growth, and energy homeostasis in fish, with emphasis on the influence of brain and gut hormones, environmental factors, and inter-specific differences.

/pdf/gut-microbiota-and-energy-homeostasis-in-fish-20ma2uvxjc.pdf

Gut Microbiota and Energy Homeostasis in Fish.

Growing evidence indicates that the mammalian microbiome can affect behaviour, and several symbionts even produce neurotransmitters. One common explanation for these observations is that symbionts have evolved to manipulate host behaviour for their benefit. Here, we evaluate the manipulation hypothesis by applying evolutionary theory to recent work on the gut-brain axis. Although the theory predicts manipulation by symbionts under certain conditions, these appear rarely satisfied by the genetically diverse communities of the mammalian microbiome. Specifically, any symbiont investing its resources to manipulate host behaviour is expected to be outcompeted within the microbiome by strains that do not manipulate and redirect their resources into growth and survival. Moreover, current data provide no clear evidence for manipulation. Instead, we show how behavioural effects can readily arise as a by-product of natural selection on microorganisms to grow within the host and natural selection on hosts to depend upon their symbionts. We argue that understanding why the microbiome influences behaviour requires a focus on microbial ecology and local effects within the host.

/pdf/why-does-the-microbiome-affect-behaviour-3zaffo37uy.pdf

Why does the microbiome affect behaviour

Gut microbiome composition and diversity are related to human personality traits

Host-associated microbiomes play an increasingly appreciated role in animal metabolism, immunity and health. The microbes in turn depend on their host for resources and can be transmitted across the host's social network. In this Perspective, we describe how animal social interactions and networks may provide channels for microbial transmission. We propose the 'social microbiome' as the microbial metacommunity of an animal social group. We then consider the various social and environmental forces that are likely to influence the social microbiome at multiple scales, including at the individual level, within social groups, between groups, within populations and species, and finally between species. Through our comprehensive discussion of the ways in which sociobiological and ecological factors may affect microbial transmission, we outline new research directions for the field.

Microbial transmission in animal social networks and the social microbiome.

Microbes colonise all multicellular life, and the gut microbiome has been shown to influence a range of host physiological and behavioural phenotypes. One of the most intriguing and least understood of these influences lies in the domain of the microbiome's interactions with host social behaviour, with new evidence revealing that the gut microbiome makes important contributions to animal sociality. However, little is known about the biological processes through which the microbiome might influence host social behaviour. Here, we synthesise evidence of the gut microbiome's interactions with various aspects of host sociality, including sociability, social cognition, social stress, and autism. We discuss evidence of microbial associations with the most likely physiological mediators of animal social interaction. These include the structure and function of regions of the 'social' brain (the amygdala, the prefrontal cortex, and the hippocampus) and the regulation of 'social' signalling molecules (glucocorticoids including corticosterone and cortisol, sex hormones including testosterone, oestrogens, and progestogens, neuropeptide hormones such as oxytocin and arginine vasopressin, and monoamine neurotransmitters such as serotonin and dopamine). We also discuss microbiome-associated host genetic and epigenetic processes relevant to social behaviour. We then review research on microbial interactions with olfaction in insects and mammals, which contribute to social signalling and communication. Following these discussions, we examine evidence of microbial associations with emotion and social behaviour in humans, focussing on psychobiotic studies, microbe-depression correlations, early human development, autism, and issues of statistical power, replication, and causality. We analyse how the putative physiological mediators of the microbiome-sociality connection may be investigated, and discuss issues relating to the interpretation of results. We also suggest that other candidate molecules should be studied, insofar as they exert effects on social behaviour and are known to interact with the microbiome. Finally, we consider different models of the sequence of microbial effects on host physiological development, and how these may contribute to host social behaviour.

The role of the microbiome in the neurobiology of social behaviour.

Studies on microbiome diversity are flooding the current literature, yet lessons from ecology clearly demonstrate that diversity is just one factor to consider when analyzing an ecosystem, along with its stability, structure and function. Measures of diversity may be a useful tool for interpreting metagenomic data but the question remains as to how informative they are and what insight they may provide into the state of the microbiome. A study utilizing mathematical modeling to investigate the ecological dynamics of microbial communities has shown that diversity and stability may not always be concomitant. This finding is pertinent to the gut microbiome field, especially since diversity comparisons between healthy and pathological states frequently yield contradictory results. There is a need to broaden our approach to the analysis of microbiome data if we are to better understand this complex ecological community and its role in human health and disease.

https://www.tandfonline.com/doi/pdf/10.1080/19490976.2016.1241933

Katerina V.-A. Johnson

Papers

Why does the microbiome affect behaviour

Gut microbiome composition and diversity are related to human personality traits

Microbial transmission in animal social networks and the social microbiome.

The role of the microbiome in the neurobiology of social behaviour.

Microbiome: Should we diversify from diversity?