Abstract
Many species suffer from anthropogenic habitat fragmentation. The resulting small and isolated populations are more prone to extinction due to, amongst others, genetic erosion, inbreeding depression and Allee-effects. Genetic rescue can help mitigate such problems, but might result in outbreeding depression. We evaluated offspring fitness after selfing and outcrossing within and among three very small and isolated remnant populations of the heterostylous plant Primula vulgaris. We used greenhouse-grown offspring from these populations to test several fitness components. One population was fixed for the pin-morph, and was outcrossed with another population in the field to obtain seeds. Genetic diversity of parent and offspring populations was studied using microsatellites. Morph and population-specific heterosis, inbreeding and outbreeding depression were observed for fruit and seed set, seed weight and cumulative fitness. Highest fitness was observed in the field-outcrossed F1-population, which also showed outbreeding depression following subsequent between-population (back)crossing. Despite outbreeding depression, fitness was still relatively high. Inbreeding coefficients indicated that the offspring were more inbred than their parent populations. Offspring heterozygosity and inbreeding coefficients correlated with observed fitness. One population is evolving homostyly, showing a thrum morph with an elongated style and high autonomous fruit and seed set. This has important implications for conservation strategies such as genetic rescue, as the mating system will be altered by the introduction of homostyles.
Highlights
Human activities have fragmented the habitats of many species
This can result from mixing gene pools of ecologically and genetically distant populations, which may lead to a breakdown of epistatic gene complexes associated with local adaptation (Lynch 1991; Dudash and Fenster 2000; Luijten et al 2002; Tallmon et al 2004; Edmands 2007; Frankham et al 2011)
Our aim was to determine (a) to what extent inbreeding and outbreeding depression and heterosis affect offspring performance, (b) how the genetic diversity of parent populations compares to their offspring, and (c) whether or not we need to worry about mixing populations during genetic rescue
Summary
Human activities have fragmented the habitats of many species. Habitat fragmentation increases spatial isolation and reduces gene flow, exposing populations to the effects of demographic, environmental and genetic stochasticity (Oostermeijer et al 2003). The opposite can occur: a reduction in offspring performance known as outbreeding depression (Tallmon et al 2004) This can result from mixing gene pools of ecologically and genetically distant populations, which may lead to a breakdown of epistatic (co-adapted) gene complexes associated with local adaptation (Lynch 1991; Dudash and Fenster 2000; Luijten et al 2002; Tallmon et al 2004; Edmands 2007; Frankham et al 2011). Experimental data on outbreeding depression are still relatively scarce compared to data on inbreeding depression
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
