title: The effect of inbreeding rate on fitness, inbreeding depression and heterosis over a range of inbreeding coefficients.
abstract: Understanding the effects of inbreeding and genetic drift within populations and hybridization between genetically differentiated populations is important for many basic and applied questions in ecology and evolutionary biology. The magnitudes and even the directions of these effects can be influenced by various factors, especially by the current and historical population size (i.e. inbreeding rate). Using Drosophila littoralis as a model species, we studied the effect of inbreeding rate over a range of inbreeding levels on (i) mean fitness of a population (relative to that of an outbred control population), (ii) within-population inbreeding depression (reduction in fitness of offspring from inbred versus random mating within a population) and (iii) heterosis (increase in fitness of offspring from interpopulation versus within-population random mating). Inbreeding rate was manipulated by using three population sizes (2, 10 and 40), and fitness was measured as offspring survival and fecundity. Fast inbreeding (smaller effective population size) resulted in greater reduction in population mean fitness than slow inbreeding, when populations were compared over similar inbreeding coefficients. Correspondingly, populations with faster inbreeding expressed more heterosis upon interpopulation hybridization. Inbreeding depression within the populations did not have a clear relationship with either the rate or the level of inbreeding.
authors.affiliation: Department of Biological and Environmental Science, University of Jyväskylä Jyväskylä, Finland.
authors.forename: Nina
authors.initials: N
authors.lastname: Pekkala
authors.affiliation: Department of Biological and Environmental Science, University of Jyväskylä Jyväskylä, Finland.
authors.forename: K Emily
authors.initials: KE
authors.lastname: Knott
authors.affiliation: Department of Biological and Environmental Science, University of Jyväskylä Jyväskylä, Finland ; Natural History Museum, University of Jyväskylä Jyväskylä, Finland.
authors.forename: Janne S
authors.initials: JS
authors.lastname: Kotiaho
authors.affiliation: Finnish Institute for Educational Research, University of Jyväskylä Jyväskylä, Finland.
authors.forename: Kari
authors.initials: K
authors.lastname: Nissinen
authors.affiliation: Department of Biological and Environmental Science, University of Jyväskylä Jyväskylä, Finland ; Centre of Excellence in Biological Interactions, University of Jyväskylä Jyväskylä, Finland.
authors.forename: Mikael
authors.initials: M
authors.lastname: Puurtinen
keywords: genetic distance; genetic divergence; genetic drift; interpopulation hybridization; population size