First response to food odors (and pheromones?)
November 26, 2013 | James Kohl
Locusts reveal how neurons distinguish multiple odors
November 25th, 2013 in Neuroscience
Excerpt: “Our sense of smell is often the first response to environmental stimuli. Odors trigger neurons in the brain that alert us to take action.”
My comment: In desert locusts, a profound shift in life history is brought about solely by the presence of conspecifics. Aversive memory is switched to appetitive. The switch indicates to me that the ecological niche construction, which leads to social niche construction and to neurogenic niche construction in other species, is nutrient-dependent and pheromone-controlled.
For example, sans the neurogenic niche construction, this is what occurs in yeasts. Adaptations occur via one signaling pathway that links nutrient availability to the pheromone-controlled physiology of reproduction. Thus, it seems likely that neurogenic niche construction is not required for adaptive evolution to occur.
Theoretically, however, the switches in life history could occur outside the context of how the epigenetic landscape becomes the physical landscape of DNA in the organized genome. There might be no need for the de novo creation of olfactory receptor genes and de novo creation of species-specific pheromones that control the physiology of reproduction in species from microbes to man.
Alternatively, the change in the diet of the desert locusts may be due to something they instinctively “know,” or learn from experience, about how preferential ingestion of plants with toxic compounds makes them unpalatable to predators. If that’s true, in theory, peppered moths could have survived bird predation if their larva continued to eat the lead- and manganese-contaminated leaves associated with industrial melanism. Unfortunately, that alternative hypothesis is no longer testable via experiments in nature. When pollution was controlled, the peppered moths changed back to fawn-colored moths.
That fact indicates snake predation of monkeys in trees might have led to evolution of the human brain and visual acuity/specificity for snake detection, regardless of dietary changes — unless our ancestors decided to eat toxic substances to avoid snake predation. Maybe some monkeys did, and they were among those who are not our ancestors.
That raises the question of why locusts that ate toxic substances are believed to be the ancestors of other locusts who survived predation by eating toxic substances. Clearly, further study is required to determine whether predators are responsible for natural selection in moths, locusts, and primates, or if adaptive evolution is nutrient-dependent and pheromone-controlled in species from microbes to man.