Inbreeding and conservation genetics in whitebark pine

Abstract

Whitebark pine (Pinus albicaulisEngelm.) is threatened across its native rangeby an exotic fungal pathogen introduced withinthe last century. Mortality has beenextensive, and projected potential range shiftsbased on impending climate change have revealedfurther pressures to survival and adaptationfor this long-lived, high-elevation conifer. Quantifying genetic variation and the matingsystem of whitebark pine in its northern rangeprovides a basis for effective conservationmeasures. Isozyme analysis of vegetative budtissue revealed high expected heterozygosity(0.262), moderate population differentiation(FST = 0.061) and highly significantcorrelations between observed heterozygosityand geographic variables (R2 = 0.36,latitude; R2 = 0.30 longitude), supportingthe hypothesis that this species recolonizedits current northern range following glacialretreat from several refugia in the Washingtonand Oregon Cascades and in the northernRockies. Mating system analysis based onsimultaneous isozyme analyses of embryo andhaploid megagametophyte tissues foundrelatively high levels of consanguineous matingand selfing for a conifer (tm =0.73) within populations. Avian seeddistribution by the Clark's nutcracker (Nucifragia columbiana Wilson) appears to bethe overriding factor influencing geneticpatterns: being a mutualistic seed disperser,caches comprised of related seeds develop intoclumped stands with strong family substructure. While it is a critical wildlife habitatcomponent, lack of commercial utilization hasmade in situ adaptation the primaryconservation focus. Encouraging regenerationsuccess and nutcracker caching by maintainingnatural fire regimes will provide anecosystem-based conservation solution; however,in the Rocky Mountains between 52° N and47° N, disease-resistant individualsshould be located and propagated in order toensure long-term survival of the species inhigh pathogen hazard areas.