Mating system and inbreeding depression in whitebark pine (Pinus albicaulis Engelm.)

Abstract

Mating system and inbreeding depression in quantitative traits of whitebark pine (Pinus albicaulis Engelm.) was determined using isozymes and a seedling common garden experiment. Simultaneous isozyme analysis of embryo and haploid megagametophyes from progeny arrays of families in three distinct geographic regions (Oregon, Montana, and southern British Columbia) was used to estimate parental and progeny inbreeding coefficients, as well as regional and family mean multilocus outcrossing rates (t m ). Quantitative trait family means of seedlings from the same families growing in two temperature treatments in a common garden experiment were regressed on the estimated inbreeding coefficient to determine the presence and magnitude of inbreeding depression. Regional estimates of t m ranged from 0.73 to 0.93, with a mean over all regions of 0.86. Family mean t m values indicated predominant outcrossing; however, some individuals experienced substantial inbreeding. The Oregon region had a significant excess of heterozygotes in the parental generation relative to Hardy-Weinberg equilibrium, while both the Oregon and southern BC regions had a heterozygote deficiency in progeny, suggesting selection against inbred individuals. Biomass in the ambient temperature treatment for the southern BC region was the only trait significantly related to inbreeding coefficient. The mean inbreeding coefficient for this region was 0.25, and based on this relationship, mean predicted biomass would be reduced by 19.6% in this region if inbred individuals are not removed by selection. The estimated outcrossing rate of whitebark pine is slightly lower than most wind-pollinated conifers, and while most individuals are highly outcrossing, some experience substantial inbreeding.

Reduced fitness at early life stages in peripheral versus core populations of Swiss stone pine (Pinus cembra) is not reflected by levels of inbreeding in seed families

“…In accordance with the results from other studies on stone pines (Krutovskii et al 1995;Politov and Krutovskii 2004;Politov et al 2006Politov et al , 2008Bower and Aitken 2007), we found significantly positive estimates of selfing rates in part of the progeny arrays, but no signs of inbreeding in adult samples. A decrease in heterozygote deficiency with increasing age is considered as an indicator for selection against inbreds during successive life stages in trees (Morgante et al 1993;Krutovskii et al 1995;Mitton et al 1997).…”

Bayesian approach reveals confounding effects of population size and seasonality on outcrossing rates in a fragmented subalpine conifer

“…Using the equilibrium equation (Ritland 1990), we can estimate the relative fitness of selfed individuals to be as low as w = 2tF/((1-t)(1-F))= 0.283. Hence, it seems reasonable to expect that inbred individuals will be outcompeted by non-inbred ones during the seedling development, as often observed in pine species (Savolainen and Hedrick 1995;Koelewijn et al 1999;Bower and Aitken 2007). On the other hand, the evolutionary theory predicts that recurrent selfing accompanied by intensive selection against inbred individuals can lead to genetic purging (Crnokrak and Barrett 2002).…”

Estimation of outcrossing rates at hierarchical levels of fruits, individuals, populations and species in Magnolia stellata

“…Plants with such systems vary widely in terms of pollination system, flowering phenology, life form and susceptibility to inbreeding depression. Furthermore, variation in outcrossing rates, caused by these factors, has been widely observed at a range of hierarchical levels, including regions (Bower and Aitken, 2007;Mable and Adam, 2007), populations (Routley et al, 1999;Bower and Aitken, 2007;Karasawa et al, 2007;Michalski and Durka, 2007;Yates et al, 2007;Ishida, 2008), individuals (El-Kassaby et al, 1993;Lee, 2000;Bower and Aitken, 2007;Nassar et al, 2007;de-Lucas et al, 2008), parts within individual plants (El-Kassaby et al, 1993;Patterson et al, 2004) and fruits (Cruzan et al, 1994). The effects of pollination systems can be illustrated by the differences between wind-pollinated and insectpollinated species.…”