Evolutionary effects of contagious and familial transmission

Abstract

Two models involving non-Mendelian transmission of a discrete valued trait through within- and across-generation contagion are proposed in an investigation of the joint evolution of phenotype and genotype. A single locus with 2 alleles determines susceptibility to contagion. The incorporation of within-generation contagious transmission extends the parameter ranges allowing phenotypic polymorphism and introduces a new phenotypic equilibrium configuration. The latter is characterized by a threshold in the initial value of the trait which determines whether the trait can increase. Phenotypic evolution is accelerated by within-generation contagion, but the rate of genetic evolution is retarded relative to that under uniparental transmission across generations. The 2nd model studied allows the trait to be acquired, at genotype-dependent rates, even if the transmitting parent does not have the trait. Both the pattern of phenotypic transmission and the selection on the trait influence the course of evolution. Some important aspects of the structure of the 1 locus-2 allele model are preserved with more alleles. At equilibrium, the leading eigenvalue of the transmission-selection matrix assumes the role of genotypic fitness.