Inbreeding and fitness in the freshwater snail Lymnaea peregra: An evaluation over two generations of self-fertilization

Inbreeding depression was estimated from an outbreeding population of the f reshwater snail Lymnaea peregra, on the basis of two successive generations of enforced selfing and outcrossing, and 70 maternal lineages. Outcrossing was analyzed under two treatments, groups of two and five individuals. The fitness parameters measured included fecundity, growth, and survival. In t he first generation, we contrasted three treatments (selfers vs, paired out crossers and group outcrossers). Very similar results were obtained between the two outcrossing treatments, A strong self-fertilization depression (wh ich includes parental fecundity and progeny fitness) was detected in the se lfing treatment (about 90%). In the second generation, there was again mark ed evidence for self-fertilization depression, with the highest contributio ns coming from parental fecundity and progeny hatching rate. Our results su ggest that the decreased parental fecundity is a consequence of the mating system in the previous generation, although the role of partial self-incomp atibility and the copulation behavior could not be ruled out. Hatching rate and early survival data are suggestive of purging of lethal mutations. Sig nificant variation in fitness among selfing lineages was found for most fit ness traits. Our experimental design also allowed to test for interactions among fitness loci. Only one trait of the nine studied behaved as expected under synergistic interactions. However we cannot rule out some purging dur ing the experiment, which could have biased results towards linearity. Inbr eeding depression was also inferred from the change of inbreeding level acr oss generations in the same population. We obtained a Value similar to the experimental estimate.