Inbreeding Depression and Genetic Rescue in a Plant Metapopulation

Abstract

While migration of individuals has been shown to increase the persistence of small isolated populations through a process known as the "rescue effect," the demographic effects that pollen-mediated gene flow may have in plant populations are not known empirically. This study investigates the role that inbreeding depression plays in newly colonized populations of a common, dioecious, weedy species, Silene alba. Experimental greenhouse studies presented here show that S. alba displays high levels of inbreeding depression (expressed as lowered germination success) in progeny produced with inbreeding coefficients of 0.125 (half-sib mated), 0.250 (full-sib mated), and 0.375 (second-generation sib mated). In addition, it is shown that the degree of inbreeding depression in 12 natural colonies varies with the degree of isolation from other established populations. Significantly, data from experimental populations showed that gene flow into patches comprised of full sibs was higher than those observed into patches comprised of unrelated individuals and may serve to mitigate the effects of inbreeding depression. It is suggested that population connectivity through pollen-mediated gene flow may have substantial effects on the persistence of isolated colonies and on the spatial structure of a metapopulation in general.

Silene as a model system in ecology and evolution

“…Pollinators play a role in prezygotic reproductive isolation and genetic structure (Richards, 2000;Teixeira and Bernasconi, 2007), but are also important seed predators in Silene (Jolivet and Bernasconi, 2006;Kephart, 2006). Most species are pollinated by moths or bumblebees and have extensively differentiated floral morphologies and scent profiles (Jurgens et al, 2002; Silene as a model system in ecology and evolution…”

Evidence for inbreeding depression and post-pollination selection against inbreeding in the dioecious plant Silene latifolia

“…latifolia occurs in meta-populations that often include also very small populations. Seeds disperse by gravity, leading to a potentially frequent risk of inbreeding under natural circumstances (Richards, 2000). On the other hand, naturally pollinated fruits are often sired by several fathers (Teixeira and Bernasconi, 2007), and pollen carry-over may hence provide the opportunity for post-pollination pre-or post-zygotic selection against inbreeding.…”

“…The variation in inbreeding depression on overall fitness was mainly explained by inbreeding depression on germination success and on flower and fruit production. Inbreeding depression has previously been reported in other populations of the same species (on seed germination; Richards, 2000), and in congeneric species with mixed mating systems, for example, S. acaulis (Delph, 2004), S. vulgaris and S. flos-cuculi (L.) Clairv.…”

“…This species shows limited seed dispersal and restricted pollen transfer among neighbouring plants (McCauley, 1997;Wright and Meagher, 2004;M Barluenga et al unpublished data). Inbreeding is probably common, and Richards (2000) showed that S. latifolia sustains inbreeding depression on seed germination. Also, pollen competition is likely in this species: in an earlier study, we detected frequent multiple paternity within fruits (Teixeira and Bernasconi, 2007).…”

“…Negative effects of inbreeding on reproductive traits and offspring establishment have been documented in several plant species (for example, Richards, 2000;Fishman, 2001). Because of the detrimental effects of inbreeding on fitness, mechanisms should arise to avoid fertilizations by related pollen (Bernasconi et al, , 2004, as has been found in some animal species, where unrelated males are preferred at mating (for example, Hoffman et al, 2007) or fertilization (Foerster et al, 2006;Simmons et al, 2006).…”