Natural Selection Essay

The relative importance of genetic drift and natural selection on flower colour in the annual desert plant Linanthus parryae, whose dominant blue and recessive white phenotypes are controlled mostly by one gene, is debated. Epling and Dobzhansky found that spatial distribution of blue- and white-flowering plants was consistent with genetic drift, and Wright found that spatial distribution was consistent with that expected in isolation by distance, both supporting the predominant importance of genetic drift. Epling later changed his argument to support natural selection, after he and his colleagues found little annual variation in colour distribution over 15 years. Schemske and Bierzychudek challenged Wright’s “isolation by distance” theory, that genetic drift creates trait frequencies that are then acted on by natural selection, to further support the importance of natural selection. Natural selection appears to be the most important mechanism for flower colour in L. parryae because of stable annual spatial distribution and variation in colour distribution in different ecological environments.
Natural selection likely
parryae varies with environmental differences on either side of the ravine, suggesting different colour morphs are selectively favoured in different conditions. Significant differences were found in the abundance of 7 out of the 10 most common plant species, species richnesses, and soil compositions, and white- and blue-flowered plants produced more seeds on the side of the ravine they were most abundant on. Environment-driven selection is demonstrated in Placostylus snails on New Caledonia, which have morphological shell differences and similarities depending on their local environment, regardless of genetic similarities and proximity of populations. Higher fitness in an environment may promote the abundance of particular traits, such as colour morph in L.