Abstract
Several studies have emphasized that inbreeding depression (ID) is enhanced under stressful conditions. Additionally, one might imagine a loss of adaptively plastic responses which may further contribute to a reduction in fitness under environmental stress. Here, we quantified ID in inbred families of the cyclical parthenogen Daphnia magna in the absence and presence of fish predation risk. We test whether predator stress affects the degree of ID and if inbred families have a reduced capacity to respond to predator stress by adaptive phenotypic plasticity. We obtained two inbred families through clonal selfing within clones isolated from a fish pond. After mild purging under standardized conditions, we compared life history traits and adaptive plasticity between inbred and outbred lineages (directly hatched from the natural dormant egg bank of the same pond). Initial purging of lineages under standardized conditions differed among inbred families and exceeded that in outbreds. The least purged inbred family exhibited strong ID for most life history traits. Predator-induced stress hardly affected the severity of ID, but the degree to which the capacity for adaptive phenotypic plasticity was retained varied strongly among the inbred families. The least purged family overall lacked the capacity for adaptive phenotypic plasticity, whereas the family that suffered only mild purging exhibited a potential for adaptive plasticity that was comparable to the outbred population. We thus found that inbred offspring may retain the capacity to respond to the presence of fish by adaptive phenotypic plasticity, but this strongly depends on the parental clone engaging in selfing.
Highlights
Inbreeding and inbreeding depression, the reduced fitness of inbred individuals, is an intensively studied field in evolutionary biology (Charlesworth and Charlesworth 1987; Saccheri et al 1998; Keller and Waller 2002; Bakker et al 2010; Bijlsma and Loeschke 2011; Fox et al 2011; Reed et al 2012)
We found evidence for inbreeding depression, even after purging, in several life history traits we studied in our life table experiment, indicated by a significant effect of “Subpopulation” for all the traits we studied here
As we only studied two families here, we can only cautiously make a general conclusion about the effects of stress on inbreeding depression: overall, our results do suggest that the presence of a stressor may increase inbreeding depression in Daphnia magna, but this strongly depends on the family under study
Summary
Inbreeding and inbreeding depression, the reduced fitness of inbred individuals, is an intensively studied field in evolutionary biology (Charlesworth and Charlesworth 1987; Saccheri et al 1998; Keller and Waller 2002; Bakker et al 2010; Bijlsma and Loeschke 2011; Fox et al 2011; Reed et al 2012). Numerous studies report inbreeding in a large variety of taxa, ranging from invertebrates to mammals (e.g., Keller et al 1994; Madsen et al 1996; Wade et al 1996; Saccheri et al 1998; Ross-Gillespie et al 2007; Thunken et al 2007; Jamieson 2011). In these studies, the degree of inbreeding depression varies widely, with some populations showing minor or no effects of inbreeding, while in others inbreeding depression is strong (Keller and Waller 2002).
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