is concerned with the ABIOTIC and BIOTIC environment into which an individual or group changes is born and hopes to thrive must meet its biological NEEDS.
All the processes we categorize mainly as Development, Evolution, or Physiology occur in response to an environment that is more or less stable, but never static.
So, although we document circumstances with static photos–like frames from a motion picture, fragments of a relentless dynamism–must be always in mind. I believe it helps to deploy some of the cognitive grace invited by poetry & art to emphasize what the student of ethology must know:
SO, As we turned to DEEP ETHOLOGY to identify the connections and meanings of phenomena, we became highly aware of the multiplicity of connections to our environments–although some eem to have priority in our reasoning. We detect stimuli with our senses, turn the information into percepts and concepts. THIS IS intrinsically interesting, but often only gets our attention when our well-being is challenged. This second reason to understand how the environment affects us is often framed in clinical terms and those of health. We try our best to cope with environments that challenge our ability to meet our biological needs. Environmental influences that do not use the familiar sensory pathways draw us quickly into levels of organization. We must find the detectable corollaries of environmental challenges of which our familiar senses are necessarily unaware. For example, look at …
Eight ways the environment affects our bodies
1. Oxidative stress and inflammation
Many environmental pollutants contain extremely aggressive chemicals called reactive oxygen species. These can overwhelm our natural antioxidant defences and cause inflammation, cell death and organ damage.
2. Genomic alterations and mutations
Mutagens in pollutants damage DNA and trigger cancer and other chronic diseases.
3. Epigenetic alterations
Air pollution, pesticides and heavy metals have been shown to induce harmful changes in gene expression during our lifetimes through effects such as DNA methylation and histone modification, which are known to be linked to the process of ageing.
4. Mitochondrial dysfunction
Mutagens and reactive oxygen species can also damage the genome and epigenome of mitochondria, our cells’ power packs. Such damage seems to increase the risk of conditions such as type 2 diabetes and breast cancer.
5. Endocrine disruption
Many chemicals found in the environment, food and consumer products disrupt the regulation of hormones, something that might be associated with type 2 diabetes and age-related thyroid dysfunction.
6. Altered cell communication
Some pollutants directly interfere with cell-to-cell communication, and prematurely aged cells can become dysfunctional communicators. The result can be “inflammaging”, or system-wide chronic inflammation that is a hallmark of ageing.
7. Altered microbiome communities
Toxic environmental substances reaching the gut can alter its microbial communities, increasing susceptibility to allergies and infections.
8. Impaired nervous system function
Noise pollution can disrupt the autonomic nervous system, leading to hikes in blood pressure and cardiovascular disease. Microscopic particles in air pollution reach the brain through the olfactory nerve and interfere with cognition.
MICROBIOME: (item 7, above) has been enlarged beyond the gut and emerges as significant in theoretical as well as practical ways. READ A&O notes on “We are holobionts”. An update (introduced by Kelly et al 2022) concludes, “Given their abundance, interactions among diverse microbial communities will likely influence host physiology. … Some emerging clinical evidence indicates that the “soup” of metabolites and signaling molecules produced by the gut microbiota could influence many diseases, not to mention behavioral states, but there are few examples of verified mechanisms.”)
MORE on microbiome-behavior connections:
· Modulating brain function with microbiota. (Microbial metabolites identified in animal models and human neurological diseases could be therapeutic targets” JA Poster 2022 https://www.science.org/doi/10.1126/science.abo4220 -cut & paste URL into browser)
· Microbiota–brain axis: Context and causality (Gut bacteria influence the brain and behavior, but causation in humans remains unclear.” JF Cryan & SK Mazmanian 2022 https://www.science.org/doi/10.1126/science.abo4442 -cut & paste URL into browser)
[i] Tissue Stem Cells: Architects of Their Niches Elaine Fuchs1,* and Helen M. Blau Cell Stem Cell. Author manuscript; available in PMC 2021 Feb 4. Published in final edited form as: Cell Stem Cell. 2020 Oct 1; 27(4): 532–556. doi: 10.1016/j.stem.2020.09.011
- Billions of cells are lost daily from our body’s tissues, which are in a perpetual state of flux throughout our lifetime. The molecular engines that drive this turnover are self-renewing tissue stem cells. The work horses are stem cell-generated, short-lived progenitors that balance proliferation and differentiation, thereby maintaining tissue homeostasis. The homeostatic requirements for cellular replacements are tissue and context specific. They are continual in blood, epidermis, and intestine, episodic in the hair follicle and lactating mammary gland, and limited in brain and muscle. However, even largely quiescent stem cells, such as those of the muscle, can be mobilized into action when their tissue is injured. To guard against infection and heal wounds, the normal homeostatic cues—termed the “milieu interieur” in 1865 by Claude Bernard—must be overridden in ways that are still being determined.
- Understanding stem cell behaviors necessitates knowledge of their local environment or “niche.” Increasing evidence shows that whether quiescent or active, stem cells are not simple passive responders to their niches; rather, they play an integral role in creating and communicating with their niches that envelope them. Regenerative signals, emanating either from a build up in crosstalk with niche factors or from marked environmental changes upon injury, alter stem cell behavior and disrupt the homeostatic equilibrium of the tissue. In part, the stem cells’ own progenies can become important niche components: while early short-lived progenitors can send transient activating cues back to their stem cell parents to fuel their self-renewal and boost tissue growth (Blau et al., 2015; Hsu et al., 2014; Mondal et al., 2014; Porpiglia et al., 2017), differentiated progeny can home back to their niche to halt further proliferation and tissue regeneration and restore homeostasis (Montarras et al., 2005; Sato et al., 2011; Yu and Scadden, 2016). In this way, tissue regeneration is orchestrated by a delicate balance of temporally coordinated cellular interactions and molecular feedback circuits in which stem cells play a central role.
- Heterologous stem cell niche components include the basement membrane, rich in extracellular matrix and stem cell growth factors, as well as blood vessels, lymphatic capillaries, nerves, stromal, adipose, and a variety of tissue-resident immune cells that function with stem cells to guard against tissue damage and pathogens. The beauty of having immune cells as integral constituents of stem cell niches is that many are mobile, able to migrate to local lymph nodes and stimulate non-resident immune cells, which can then travel through the circulation to the site of tissue damage and contribute to the inflammatory response that clears pathogens and damaged cells from the tissue (Fan and Rudensky, 2016). Reinstating homeostasis, however, relies upon tissue repair, which is incompatible with inflammation. Since the stem cells are responsible for the reparative phase of the response, there must be intricate immune-stem cell communication to ensure not only that the pathogen invasion is under control, but also that the inflammation is subsequently dampened in order to facilitate repair (Arnold et al., 2007; Burzyn et al., 2013; Fan and Rudensky, 2016). How this happens is still largely a mystery, but a few clues are beginning to emerge.
- Here we review how stem cells serve as architects of their own niche. This microenvironment envelops the stem cell and dictates its function during homeostasis while allowing it to rapidly mobilize its tissue regenerating energies when an injury occurs. We focus on two markedly different tissues—the skin epithelium and the skeletal muscle—both of which are subjected to stress and damage throughout life. We highlight features of the stem cells and their niches and discuss how they combine context-specific and universal mechanisms to maintain tissue fitness. We discuss increasing evidence that tissue stem cells sense and communicate with an amazingly diverse array of niche components. As we are beginning to learn, this complexity enables stem cells to not only deflect minor insults and maintain homeostasis, but also remain poised to sense and respond to natural regenerative stimuli and to the diverse array of tissue damage and other stresses they encounter throughout their lifetime. Given the complexity of stem cell niches, it is also perhaps not surprising that across many different tissues, including muscle and skin, aging often involves a breakdown of extrinsic niche components, rather than the intrinsic self-renewal capacity of its stem cell residents (Blau et al., 2015; Ge et al., 2020; Pentinmikko et al., 2019; Raaijmakers, 2019; Segel et al., 2019; Tierney and Sacco, 2016). An additional consequence of aging-associated changes is an increase in tissue stiffness that can disrupt homeostatic stem cell mechanosensing (Cosgrove et al., 2014; Gilbert et al., 2010; Madl et al., 2018).
Although all domains of DEEP ETHOLOGY manifest extensive interconnectedness, it is, for most of us, more apparent in the web of life described in ECOLOGY. The ENVIRONMENT in which all organisms find themselves must–in the course of natural selection–provide for all biological needs, and all organisms compete for limited resources to meet those needs. (Whatever resource(s) might be in shortest supply is termed “selection pressure.” The flexibility of an individual (or species) in coping with these pressures results in different patterns: sexual selection (selection pressure if “female choice”), ecological selection, stabilizing selection, disruptive selection and directional selection, each describing the patterns of successful coping with pressure.
[we will revisit selection pressure relative to biological NEEDS when visiting PHYSIOLOGY: the first response of individuals to the real or perceived or even threatened inability to meet a biological need evokes a STRESS RESPONSE.]