page_title: Koinophilia
section_title: Effects of diets and environmental conditions
hierarchical_section_title: Koinophilia / Effects of diets and environmental conditions
caption_attribution_description: English: An image created using a combination of Wikimedia Commons images (File:Europe satellite globe.jpg; File:Corvus corone -near Canford Cliffs, Poole, England-8.jpg; and File:Nebelkrähe Corvus cornix.jpg) to illustrate the distribution of the Carrion Crow Corvus corone and Hooded Crow Corvus cornix across across Europe. The white line indicates the contact zone between the two species - the Carrion Crows occurring to west and south of the line; the Hooded Crows to the east and north of the line. A second version of this map, File:Distribution of hooded and carrion crows across Europe by their Latin names.JPG with only the Latin names of the birds mentioned can be used for Wikipedia purposes in languages other than English.
context_page_description: Koinophilia is an evolutionary hypothesis proposing that during sexual selection, animals preferentially seek mates with a minimum of unusual or mutant features, including functionality, appearance and behavior. Koinophilia intends to explain the clustering of sexual organisms into species and other issues described by Darwin's Dilemma. The term derives from the Greek, koinos, "common", "that which is shared", and philia, "fondness".
  Natural selection causes beneficial inherited features to become more common at the expense of their disadvantageous counterparts. The koinophilia hypothesis proposes that a sexually-reproducing animal would therefore be expected to avoid individuals with rare or unusual features, and to prefer to mate with individuals displaying a predominance of common or average features. Mutants with strange, odd or peculiar features would be avoided because most mutations that manifest themselves as changes in appearance, functionality or behavior are disadvantageous. Because it is impossible to judge whether a new mutation is beneficial or not, koinophilic animals avoid them all, at the cost of avoiding the very occasional potentially beneficial mutation.
context_section_description: The best-documented creations of new species in the laboratory were performed in the late 1980s. William Rice and G.W. Salt bred fruit flies, Drosophila melanogaster, using a maze with three different choices of habitat, such as light/dark and wet/dry. Each generation was placed into the maze, and the groups of flies that came out of two of the eight exits were set apart to breed with each other in their respective groups. After thirty-five generations, the two groups and their offspring were isolated reproductively because of their strong habitat preferences: they mated only within the areas they preferred, and so did not mate with flies that preferred the other areas. The history of such attempts is described in Rice and Hostert (1993).
  Diane Dodd used a laboratory experiment to show how reproductive isolation can evolve in Drosophila pseudoobscura fruit flies after several generations by placing them in different media, starch- or maltose-based media.
  Dodd's experiment has been easy for many others to replicate, including with other kinds of fruit flies and foods.
   The carrion crow (Corvus corone) and hooded crow (Corvus cornix) are two closely related species whose geographical distribution across Europe is illustrated in the accompanying diagram. It is believed that this distribution might have resulted from the glaciation cycles during the Pleistocene, which caused the parent population to split into isolates which subsequently re-expanded their ranges when the climate warmed causing secondary contact. Jelmer W. Poelstra and coworkers sequenced almost the entire genomes of both species in populations at varying distances from the contact zone to find that the two species were genetically identical, both in their DNA and in its expression (in the form of RNA), except for the lack of expression of a small portion (<0.28%) of the genome (situated on avian chromosome 18) in the hooded crow, which imparts the lighter plumage coloration on its torso. Thus the two species can viably hybridize, and occasionally do so at the contact zone, but the all-black carrion crows on the one side of the contact zone mate almost exclusively with other all-black carrion crows, while the same occurs among the hooded crows on the other side of the contact zone. It is therefore clear that it is only the outward appearance of the two species that inhibits hybridization. The authors attribute this to assortative mating, the advantage of which is not clear, and it would lead to the rapid appearance of streams of new lineages, and possibly even species, through mutual attraction between mutants. Unnikrishnan and  Akhila propose, instead, that koinophilia is a more precise explanation for the resistance to hybridization across the contact zone, despite the absence of physiological, anatomical or genetic barriers to such hybridization.
caption: A map of Europe indicating the distribution of the carrion and hooded crows on either side of a contact zone (white line) separating the two species.
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