Early Inbreeding Depression Selects for High Outcrossing Rates inAquilegia formosaandAquilegia pubescens

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.