2, Holobiont
“The world was to me a secret which I desired to divine.”
— Victor Frankenstein.
There is a deep plurality in Victor Frankenstein’s words; a plurality that resonates within my own ethos. The Frankenstein; or, The Modern Prometheus narrative follows Victor Frankenstein’s own eureka moment in successfully quickening the inanimate with life… with sapience. Some adaptations frame the creature as a mosaic of cadaver scraps.
The holobiont is a mosaic composing the host and a hefty medley of microorganisms (i.e. the host’s microbiota). Thus, the holobiont is an ecological unit; a dance shared between the host and its microbiota.
“Are we more microbial than human?”
— Richard Losick.
Our microbiota contribute to ~3% of our body mass yet the human to microbiome cell ratio estimates ~ 30:39 respectively on a 1e+12 scale (we’re talking trillions). Losick’s question, in tandem with the context of stats, lean towards reframing our understanding of the individual.
Wing size is a discriminant characteristic between the wasp species N. giraulti, N. longicornis and the N. vitripennis; all from the Nasonia genus. On the phylogenetic tree (consider this a family tree of species) the N. vitripennis is a distant relative to both the N. giraulti and N. longicornis. Any attempts at breeding N. vitripennis with its distant relatives results in hybrid lethality (the offspring between distant relatives’ die).
Brucker and Bordenstein’s study presents evidence that this “lethality is conditional on the microbiome”; hence, alluding that a host’s microbial communities may function as a unit of natural selection. In an event analogous to the Modern Prometheus, their study produced viable hybrids. A controlled antibacterial diet led to germ-free hybrids, as a result of flushing the microbiome local to the gut — lethality negated. Eureka, Life! On reintroducing a conventional diet — morbidity reinstated. Eureka, natura naturans rescued!
Granted that I have glossed over the relevant Bateson-Dobzhansky-Muller model of genetic incompatibilities, I remain hopeful that this oversimplified account of Brucker and Bordenstein’s findings invokes an appreciation of this dance between host and microbiome and its potential as a unit of evolutionary selection.
And with this appreciation we can accordingly draw assumptions, along the phylogenetic tree, of many budding bifurcations. Holobionts emerging from these tributaries meandering around selective pressures. Each holobiont, a mosaic of genomes echoing that dynamic gambol.
Like Aphrodite’s conception from sea froth; the holobiont surfaces as a symphony from a myriad of coupled gene regulation systems, a Himalayas of gene expression & silencing spanning over the hologenome: the orchestra of all the genes from the host and its microbial community. The following triple pendulum is a very simple model of these coupled dynamics:
The path traced out by the pendulum corresponds to the holobiont which in itself encompasses the entire system (natura naturans & natura naturata). Homeostasis reflects this self-regulating symphony; conserving survival through a scale invariance of stability throughout the holobiont.
