How Species Diversify
November 2, 2012 | James Kohl
Science 2 November 2012: Vol. 338 no. 6107 pp. 619-621 DOI:10.1126/science.1224818
Article excerpt: “The heterogeneous light conditions in this lake led to diversifying selection on opsin genes as a function of water depth. The divergence in opsins, in turn, affects sexual selection, because differences in color perception influence the female preference for male coloration (17). Here, the interplay between natural and sexual selection resulted in speciation in the absence of geographic barriers through selection on a sensory system (“sensory drive”).”
My comment: There is no animal model of female preference for male coloration that is not primarily dependent on sex differences in species-specific pheromones. Pheromones, not coloration, are responsible for epigenetic effects on intracellular signaling and stochastic gene expression in hormone-secreting nerve cells of tissue in vertebrate brains.
In mammals, these hormone-secreting nerve cells are the gonadotropin releasing hormone (GnRH) nerve cells that control the hypothalamic-pituitary-gonadal (HPG) axis and hypothalamic-pituitary adrenal (HPA) axis.
GnRH control of the HPG and HPA axis controls the adaptive evolution of behavior that links nutrient chemical-dependent individual survival to speciation via the metabolism of the nutrient chemicals to pheromones, which control reproduction. The reciprocal relationships are clear: 1) nutrient chemicals -> food acquisition 2) pheromones -> mate acquisition 3) adaptive evolution -> speciation via behaviors required for appropriate food choice and best mate choice in all animal species.
Cichlid species diversify via selection for food and pheromones like every other species on this planet. Attributing their diversity to selection for color (or a “sensory drive” associated with visual input) ignores the obvious fact that “Olfaction and odor receptors provide a clear evolutionary trail that can be followed from unicellular organisms to insects to humans.”
The molecular mechanisms are conserved across species and they result in species radiation (i.e., diversity). Thus, the perspective on evolution offered in this article is the wrong perspective. It is olfactory/pheromonal input that is responsible for the sensory drive and species diversity of Cichlids and the diversity of all species.