On the interpretation of the operation of natural selection in class-structured populations

Abstract

Biological adaptation is the outcome of allele-frequency change by natural selection. At the same time, populations are usually class structured as individuals occupy different states such as age, sex, or stage. This is known to result in the differential transmission of alleles through non-heritable fitness differences called class transmission, also affecting allele-frequency change even in the absence of selection. How does one then isolate the allele-frequency change due to selection from that owing to class transmission? We decompose one-generational allele-frequency change in terms of effects of selection and class transmission, and show how reproductive values can be used to reach a decomposition between any two distant generations of the evolutionary process. This provides a missing relationship between multigenerational allele-frequency change and the operation of selection. It also allows to define a measure of fitness summarizing the effect of selection in a multigenerational evolutionary process, which connects asymptotically to invasion fitness.