Meal Plans

Bacterial populations’ differing strategies for responding to their environment can set genetic routes to speciation.

By Rina Shaikh-Lesko | August 1, 2014

SPLIT DECISION: Recently speciated marine bacteria use different strategies—biofilm growth (red) or mobility (blue)—to obtain nutrients.ILLUSTRATION BY YUTAKA YAWATA, GLYNN GORICK, AND ROMAN STOCKER


The paper
Y. Yawata et al., “Competition–dispersal tradeoff ecologically differentiates recently speciated marine bacterioplankton populations,” PNAS, 111:5622-27, 2014.

The background
Marine bacteria obtain nutrients from clustered particles that float in the resource-poor broth that is ocean water. Yutaka Yawata, a postdoctoral fellow in Roman Stocker’s lab at MIT, and colleagues wondered if differing strategies used by bacteria to secure these scarce nutrients could influence how populations adapt to their microenvironments and, ultimately, drive speciation, or whether speciation happens by more passive routes.

Diverging strains
Yawata and his team studied two recently diverged populations of Vibrio cyclitrophicus—labeled S and L—isolated from different depths in the same ocean region. They found the L population to be skilled at attaching to nutrient particles and developing into biofilms, whereas the S population could swiftly move to unexploited nutrient patches.  

The technique
The researchers used a microfluidic device to create chemical gradients that could be quickly altered to observe how the bacteria respond. They found that S bacteria responded much more quickly to changes in nutrient gradients, while L populations stayed attached to surfaces, where they created biofilms. “They are starting to become two different species on a genetic basis—and on a behavioral basis,” says Yawata.  

The implications
The finding demonstrates that bacteria can actively respond to their environment to secure resources and that they make strategic tradeoffs to do so, characteristics previously shown only in plants and animals. “Behaviors can actually play a role and be barriers to gene flow,” causing populations to diverge even at the microscopic scale, says marine microbiologist Linda Amaral-Zettler of the Marine Biological Laboratory in Woods Hole, Massachusetts.

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Avatar of: James V. Kohl

James V. Kohl

Posts: 526

August 5, 2014

Re: “They are starting to become two different species on a genetic basis—and on a behavioral basis,” says Yawata.  

That statement attests to everything else known about how the epigenetic landscape becomes the physical landscape of DNA in the organized genomes of species from microbes to man.

Ecological variation leads to nutrient-dependent amino acid substitutions that differentiate cell types of individuals of all species, and the metabolism of nutrients to species-specific pheromones controls the physiology of reproduction, which occurs within the biophysical constraints that allow the amino acid substitutions to stablize organism-level thermoregulation.

See for examples: 

Nutrient-dependent/pheromone-controlled adaptive evolution: a model

For an example of this in vertebrates, see Estrogen receptor α polymorphism in a species with alternative behavioral phenotypes  The difference in feeding patterns is clearly linked to morphological and behavioral phenotypes that also make it appear they are starting to become two different species. 

It's called "ecological speciation" because it is nutrient-dependent and pheromone-controlled. Thus, biological facts associated with ecological speciation can be compared to the pseudoscientific nonsense of mutation-initiated natural selection and the evolution of biodiversity in species from microbes to man -- with white-throated sparrows as a vertebrate example (in birds) that parallels what is currently known about these bacteria and about bees. 

Once everyone learns the biological facts about nutrient-dependent pheromone-controlled cell type differentiation in the birds and the bees, we can dispense with theories and "Just-So" stories that claim differences in nutrient uptake in E. coli exemplify mutation-driven evolution. Serious scientists know that the physiology of reproduction in E. coli is nutrient-dependent and pheromone-controlled. No experimental evidence of biologically-based cause and effect suggest the E.coli are mutating into another species or that any species mutates into another species.

All experimental evidence shows that species diversity is nutrient-dependent and pheromone-controlled via conservered molecular mechanisms. See also: Starvation-Induced Transgenerational Inheritance of Small RNAs in C. elegans

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