Genetic diversity in nature at the protein and DNA levels: Patterns and Theory

The evolutionary significance of genetic diversity of proteins and DNAS (nuclear and mitochondrial) in natural populations of plants and animals was reviewed using the environmental-genetic correlation methodology at three geographic levels: (1) local: several species of wild cereals, landsnails and barnacles in Israel; (2) regional: 38 species in Israel; of these, 21 range from the Mediterranean region to the Negev desert; also included were two species of wild cereals in the Near East Fertile Crescent; and (3) global: 1111 species of animals and plants ranging worldwide. The species involved in these local, regional, and global analyses are largely taxonomically unrelated. They vary in their ecologies, demographies, life histories, and other biological variables. They were mostly tested for allozymic diversity by routine horizontal starch gel electrophoresis at 25 gene loci on average (range 14-50 loci). In addition, several studies were reviewed on nuclear and mitochondrial DNA polymorphisms (restriction fragment length polymorphisms, RFLPs) in animals and plants in Israel and the correlation was explored between RFLPS and allozymes. The following results were found at all three geographic levels: (1) The levels of genetic diversity vary nonrandomly among populations, species, and higher taxa, and (2) genetic diversity is partly correlated with, and predictable, primarily by ecological factors. These results corroborate the adaptive, environmental theory of genetic diversity, and they were confirmed for several allozyme loci in controlled laboratory experiments on pollution biology. The genetic patterns obtained are inconsistent with the neutral theory of molecular evolution. By contrast, natural selection in its various forms appears to be a major differentiating and orienting force of evolutionary change in protein and DNA polymorphisms.