The Different Sources of Variation in Inbreeding Depression, Heterosis and Outbreeding Depression in a Metapopulation ofPhysa acuta

Abstract

Understanding how parental distance affects offspring fitness, i.e., the effects of inbreeding and outbreeding in natural populations, is a major goal in evolutionary biology. While inbreeding is often associated with fitness reduction (inbreeding depression), interpopulation outcrossing may have either positive (heterosis) or negative (outbreeding depression) effects. Within a metapopulation, all phenomena may occur with various intensities depending on the focal population (especially its effective size) and the trait studied. However, little is known about interpopulation variation at this scale. We here examine variation in inbreeding depression, heterosis, and outbreeding depression on life-history traits across a full-life cycle, within a metapopulation of the hermaphroditic snail Physa acuta. We show that all three phenomena can co-occur at this scale, although they are not always expressed on the same traits. A large variation in inbreeding depression, heterosis, and outbreeding depression is observed among local populations. We provide evidence that, as expected from theory, small and isolated populations enjoy higher heterosis upon outcrossing than do large, open populations. These results emphasize the need for an integrated theory accounting for the effects of both deleterious mutations and genetic incompatibilities within metapopulations and to take into account the variability of the focal population to understand the genetic consequences of inbreeding and outbreeding at this scale.T HE importance of inbreeding and outbreeding on fitness has been recognized for a long time (Darwin 1876;Dobzhansky 1936;Wright 1937;Crow 1948) and has more recently reclaimed importance on theoretical

Within- and among-population impact of genetic erosion on adult fitness-related traits in the European tree frog Hyla arborea

“…Within-and among-population impact of genetic erosion E Luquet et al First, the expression of fixed deleterious alleles can be specific to a life stage or an environment (Ouborg et al, 2010). Especially in species exhibiting complex life cycle like amphibians, the gene pools expressed during larval and adult stages, in aquatic and terrestrial habitats, respectively, can have different fixation loads and therefore different detrimental effects (Husband and Schemske, 1996;Koelewijn et al, 1999;Escobar et al, 2008).…”

“…Several environmental factors could be responsible to these variations among populations, but determining these factors was beyond the scope of this study. A challenging experiment would be to compare in controlled conditions the detrimental effects of fixation loads at different life stages from embryos to adults on the same cohorts (see Escobar et al, 2008).…”

Contrasting the distribution of phenotypic and molecular variation in the freshwater snail Biomphalaria pfeifferi, the intermediate host of Schistosoma mansoni

“…Freshwater snails of the Basommatophoran group offer excellent biological models to address these issues (Städler and Jarne, 1997;Charbonnel et al, 2002c;Chapuis et al, 2007;Escobar et al, 2008).…”

“…Several studies using neutral genetic markers have also concluded that the population genetic structure at short spatial scale is affected by habitat characteristics (hydrological permanence or habitat openness; for example, Charbonnel et al, 2002c;Trouvé et al, 2003;Bousset et al, 2004). For example, less variation is maintained in closed (for example, ponds) than in open (for example, rivers) habitats (Bousset et al, 2004;Escobar et al, 2008). However, two studies only have compared neutral and phenotypic variation, the first in the lymnaeid Galba truncatula (Chapuis et al, 2007) and the second in the physid Physa acuta (Escobar et al, 2008).…”

“…For example, less variation is maintained in closed (for example, ponds) than in open (for example, rivers) habitats (Bousset et al, 2004;Escobar et al, 2008). However, two studies only have compared neutral and phenotypic variation, the first in the lymnaeid Galba truncatula (Chapuis et al, 2007) and the second in the physid Physa acuta (Escobar et al, 2008). No study has untill now been conducted in the planorbids, the largest Basommatophoran family.…”