title: The importance of the timescale of the fitness metric for estimates of selection on phenotypic traits during a period of demographic change.
abstract: Although fitness is central to the evolutionary process, metrics vary by timescale. Different timescales may give rise to different estimates of selection, especially during demographic transitions caused by rapid environmental and socioeconomic change. In this study, we used a dataset of a human population in Finland from 1775 to 1950 to compare two fitness metrics and their estimates of selection pressures, before and during a demographic transition. Both metrics, lifetime reproductive success and an annual metric of individual performance, declined while selection on the ages at first and last reproduction remained nearly constant, favouring individuals with wider reproductive windows. The ability to partition the annual metric into contributions from reproduction and survival revealed the short-term effects of a famine and the reversal of selection pressure via the survival component of annual fitness. Although the metrics generally agreed, the annual metric detected the effects of environmental variation and demographic change occurring within a generation.
authors.affiliation: Department of Ecology and Evolutionary Biology, Yale University, 165 Prospect Street CT, 06520-8102, New Haven, CT, USA.
authors.forename: Katherine
authors.initials: K
authors.lastname: Scranton
authors.affiliation: Department of Biology, University of Turku, FI-20014, Turku, Finland.
authors.forename: Virpi
authors.initials: V
authors.lastname: Lummaa
authors.affiliation: Department of Ecology and Evolutionary Biology, Yale University, 165 Prospect Street CT, 06520-8102, New Haven, CT, USA.
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Stearns
mesh_terms: D001723:Birth Rate; D005387:Finland; D056084:Genetic Fitness / Q000235:genetics*; D006801:Humans; D011157:Population Dynamics; D012641:Selection, Genetic; D013997:Time Factors
keywords: Demographic change; fitness; fitness timescale; life-history traits; phenotypic selection