Canadian Forest Service Publications
Reproductive barriers and hybridity in two spruces, Picea rubens and Picea mariana, sympatric in eastern North America. 2005. Major, J.E.; Mosseler, A.; Johnsen, K.H.; Rajora, O.P.; Barsi, D.C.; Kim, K.H.; Park, J.-M.; Campbell, M. Canadian Journal of Botany 83: 163-175.
Issued by: Atlantic Forestry Centre
Catalog ID: 25260
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Hybridization between red spruce (Picea rubens Sarg.) and black spruce (Picea mariana (Mill.) B.S.P.), late- and early successional species, respectively, has resulted in identification and management problems. We investigated the nature and magnitude of reproductive and life-cycle success barriers in controlled intra- and inter-specific crosses of red and black spruce. We quantified a number of reproductive, germination, phenological, and performance traits, and examined traits by parental pedigree and hybrid index. Species' pollen had no effect on number of aborted or nonpollinated ovules. Controlled intraspecific crosses had, on average, 6.6 times more filled seeds than interspecific crosses. Cone and seed morphometric traits were species specific, with seed traits showing negative hybridization effects on both species. Germination, cotyledon number, and seedling height had significant species-specific traits, with hybrids showing an additive or slightly negative heterosis. Severe, negative heterosis appears to be of limited importance as an isolating barrier between red and black spruce. Reproductive phenology was remarkable similar among species and hybrid progenies when grown in common garden experiments. Crossability barriers are clearly paramount in maintaining the separation of the speices. Ecological separation based on ecophysiological differences (e.g., shade tolerance) also represents an important prezygotic barrier for minimizing the negative effects of hybridization (e.g., postzygotic inviability) on reproductive fitness.