Early Inbreeding Depression Selects for High Outcrossing Rates inAquilegia formosaandAquilegia pubescens

Abstract

Theory suggests that mating-system parameters in plants may be strongly influenced by pollinator type. We examined the outcrossing rate, biparental inbreeding, and inbreeding depression in two closely related species of Aquilegia, A. formosa and A. pubescens, that differ in their major floral visitors (hummingbird and hawkmoth, respectively). Population-level estimates of the outcrossing rate were generally high, ranging from 0.42 to 0.89 and averaging 0.79 for A. formosa and 0.69 for A. pubescens; however, the two rates did not differ significantly. The similarities in the outcrossing rates of the two species suggest that both hummingbird and hawkmoth pollination systems provide pollen movement patterns that promote a high degree of outcrossing. However, we also found that a substantial amount of outcrossing (13%-46%) was due to mating between relatives (biparental inbreeding). Using Ritland's genetic marker-based approach to estimate inbreeding depression, we found complete selection against inbred progeny (inbreeding depression =1). We estimated when inbreeding depression is expressed by comparing the inbreeding coefficient across various life-history stages. We found that inbreeding depression is generally strong between seed germination and establishment and also occurs between seedling establishment and reproductive maturity. Our findings indicate that inbreeding depression likely removes selfed and biparentally inbred progenies from populations before flowering. This intense inbreeding depression will thus cause strong selection for any trait that increases the level of outcrossing with nonrelatives.

The Use of Sequence-Based SSR Mining for the Development of a Vast Collection of Microsatellites in <i>Aquilegia formosa</i>

“…Similar results have been observed in germplasm screens of potato and water melon using EST-SSR loci [31] [32]. Perhaps the high levels of polymorphism observed in transcript-based SSRs for A. formosa adults in the H. J. Andrews experimental forest could be due to the fact that homozygotes are eliminated in the adult population as a result of the strong inbreeding depression that exists in the species [33]. The 30 polymorphic SSRs were more than sufficient to separate all 16 A. formosa individuals from the H. J. Andrews experimental forest in a principal coordinate analysis (PCoA) (Figure 2).…”

The Distribution of Genetic Diversity Within and Among Populations of the Rocky Mountain Columbine: The Impact of Gene Flow, Pollinators, and Mating System

“…These patterns suggest poor survival of inbred progeny, which could be explained by the high inbreeding depression typically observed in this plant species (Montalvo 1994;Brunet and Sweet 2006b). Seeds resulting from self-fertilization may contribute little to the next generation, as has been found in other columbine species (Herlihy and Eckert 2002;Yang and Hodges 2010). If this were the case, selfed seeds would have little impact on the population genetic structure of A. coerulea plants.…”

The Genetics of Self-Compatibility and Associated Floral Characters inTolpis(Asteraceae) in the Canary Islands

“…Higher selfing may also decrease hybridization with closely related sympatric species (Antonovics 1968;Levin 1978Levin , 2000; Fishman and Wyatt 1999;Wendt et al 2002;Grossenbacher and Whittall 2011). Potential downsides of selfing include inbreeding depression and reduced genetic variation, since selfing increases homozygosity and lowers the effective population size (Goodwillie et al 2005;Yang and Hodges 2010).…”