Habitat fragmentation, genetic diversity, and inbreeding depression in a threatened grassland legume: is genetic rescue necessary?

Abstract

Kincaid's lupine (Lupinus oreganus), a threatened perennial legume of western Oregon grasslands, is composed of small, fragmented populations that have consistently low natural seed set, suggesting they may have accumulated high enough levels of genetic load to be candidates for genetic rescue. We used simple sequence repeat (SSR) loci, both nuclear DNA and chloroplast DNA, to screen populations throughout the species' range for evidence of severe inbreeding and recent genetic bottlenecks due to habitat fragmentation. After genotyping about 40% of the known populations, only one of 24 populations had strong statistical evidence for a recent genetic bottleneck (H e [ H eq ). Both mean nSSR fixation coefficients and genetic diversity did not statistically differ between very small, small, medium, and large lupine population size classes. Within population chloroplast DNA haplotype number was high for an animal pollinated species, &4.2 haplotypes/population, and within population haplotype diversity was also relatively evenly distributed. Within population patterns of nSSR and cpSSR genetic diversity suggest that genetic diversity has not been lost over the last century of habitat fragmentation. With genet lifespan thought to exceed 100 years, overlap of several to many generations, and substantial reductions in seed set from inbreeding depression that shifts cohort composition towards those generated by outcrossing events, Kincaid's lupine is likely maintain the currently high levels of within population genetic diversity. The case of Kincaid's lupine provides an example of how the assumptions of severe inbreeding depression with small population size and habitat fragmentation can be inaccurate.

Comparative Landscape Genetics of Three Closely Related Sympatric Hesperid Butterflies with Diverging Ecological Traits

“…However, there are also examples where genetic diversities in rare species exceed those of their common congeners [77]–[79]. This contrasting pattern to neutral genetic theory might be a result from hybridization ([80], but see [78]) or because of time-lags that display the past genetic diversity, when connectivity between populations was much higher than today [79], [81]. Indeed, genetic differentiation responds to habitat changes quicker than genetic diversity [82]–[83] so that the high genetic diversity observed for T. aceton may not yet reflect the negative consequences of on-going habitat alterations for this species.…”

Contemporary pollen-mediated gene immigration reflects the historical isolation of a rare, animal-pollinated shrub in a fragmented landscape

“…teretifolius is experiencing some deleterious effects of fragmentation. Reduced diversity within populations following fragmentation has been found in several species (Honnay and Jacquemyn, 2007;Aguilar et al, 2008) but not all fragmentation events result in erosion of genetic diversity (Young et al, 1996;Aquilar et al, 2008;Severns et al, 2011;Wang et al, 2011). When fragmentation has caused changes, meta-analyses indicate large negative effects on allelic diversity and outcrossing rates, but non-significant overall effects on inbreeding coefficients measured in adults.…”

Analysis of genetic diversity and population structure of Bellamya quadrata from lakes of middle and lower Yangtze River

“…The diversity we currently observe may represent past population connectivity patterns and indicate a genetic debt (Severns et al 2011;Habel and Zachos 2013). In the case of harvesting pressure and fragmentation of the habitat, Bellamya species may suffer particularly under fragmentation due to their high genetic diversity and intermediate ecological amplitude (Richards and van Oppen 2012;Habel and Schmitt 2012).…”