Posted on: 02 March, 2017
Author: Alexander P
In Ips the alleles which control both production and reception of pheromones are codominant and autosomal. If a male Ips which is heterozygous for a mutant pheromone allele breeds a female which is he... In Ips the alleles which control both production and reception of pheromones are codominant and autosomal. If a male Ips which is heterozygous for a mutant pheromone allele breeds a female which is heterozygous for a receptor allele keyed to the mutant pheromone, 1/4 of the progeny will be doubly heterozygous, l /2 will carry one mutant allele, and 1/4 will carry no mutant alleles. If it is assumed that each female mates with the male which is theoretically the most attractive to her, 1/96 of the following generation would be expected to be homozygous for both of the mutant alleles. If the mutation were between cis and trans isomers of the pheromone and if a mixture of the pheromones is inhibitory, as suggested by Roelofs and Comeau (1969), the pheromone mixture produced by the hetero- zygous genotype would be totally unattractive. Hence, the criteria necessary for mate-finding among mutant types would be lost in the first generation. The hypothesis of Roelofs and Comeau (1969) requires totally dominant mutations or simultaneous mutation of both pheromone alleles. However, females homozygous for mutant pheromone alleles would produce unattractive heterozygous daughters after mating with a male having receptor mutations but normal alleles for pheromone production according to http://sundowndivers.org/best-pheromones-2017-review/ Allopatric Pheromone changes Transition in pheromone systems in geographic isolation encounters some of the difficulties in shift of pheromone systems outlined above, but it does not require that entities with identical genomes (except for pheromone systems) compete for the same niche. Changing of the geographic range of a species by immigration or by disruption (as by glaciation, etc.) results in intensive selection for genotypes suited, for the new situation. New combinations of genes which convey superior survival are continually disrupted by panmictic mating in the general population and be- tween adjacent populations. Any gene which helps to prevent outmating of highly adapted genotypes would itself have survival value. Hence, a change in the phero- mone system could be co-adaptive with genes which convey high survival value in the modied environment. This mechanism could result in a shift in pheromone systems without direct pressure on the pheromone system itself. It is probable that evolution of the pheromone system is usually accomplished by direct selection pressure. The force involved could be selection for pheromone bouquets least attractive to natural enemies and/or disruptive selection for repro- ductive isolation of species using the same pheromones. Predators and parasites have broken the chemical code of bark beetles and capitalized upon pheromone systems to locate their host or prey (Rice 1969, inter alia). These natural enemies could exert considerable selection pressure on the pheromone system of bark bee- tles by their differential response to various components of a pheromone bouquet (Vite and Williamson 1970; Pitman and Vité 1971). Variations in the pheromone system of a widely distributed species may result from selection pressure to mini- mize mortality to the natural enemies which occur in different parts of its range. In Idaho and California 1. pint’ from New York were four times more attractive to the black-bellied clerid, Enoclerus lecontei (Wolcott) than were the western I. pini (Lanier et al. l972). However, the eastern clerid species, Enoclerus nigripes (Say) and Thamzsimus dubius (F.), did not distinguish between the eastern and western Ips pim‘ males (Piston and Lanier 1973). Clearly, selection pressure against the eastern pheromone could be considerable in the west. Source: Free Articles from ArticlesFactory.com Alexander P is a blogger that studies pheromones. He is from Los Angeles, CA.