Inbreeding and reintroduction: Progeny success in rare Silene populations of varied density

Abstract

Genetic factors influence the populationviability of rare species, yet the fitnessconsequences of inbred and outbred progeny areseldom tested empirically in reintroductionstrategies designed for species recovery orhabitat restoration. Rare and endangeredplants of Silene (Caryophyllaceae) occuron four continents, including North America. In Oregon, inbred and outbred progeny weremonitored for three years after experimentalreintroduction of a narrow endemic, S.douglasii var. oraria, into formerlygrazed habitat within its presumed historicalrange. Survival and reproduction were comparedfor progeny that were derived from the seeds ofself- versus cross-pollinated flowersproduced in situ at Cascade Head, aUNESCO Biosphere Reserve where the largest ofthree extant populations occurs. Progeny ofcross-pollinated flowers had significantlygreater field survival in all years than didoffspring of selfed or open-pollinated flowers(P < 0.01). Outbred progeny alsosignificantly exceeded other treatment cohortsin canopy area, and produced more reproductivestems and flowers than other progeny types ofthe same maternity. For plots varying in plantdensity, mortality was greatest in thehigh-density competitive regime but thesurvivors reached significantly larger sizesand reproductive capacities than in low densityplots (P < 0.05). In all, successfulconservation plans involving reintroduction mayrequire genetically diverse progeny to offsetinbreeding depression as well as suitableplanting densities and source populations.