Impacts of forest fragmentation on the mating system and genetic diversity of white spruce (Picea glauca) at the landscape level

Abstract

We studied the mating system of white spruce (Picea glauca) in a landscape fragmented by agriculture in northern Ontario, Canada. We sampled 23 stands that ranged in size from 1 to 4500 trees isolated by 250-3000 m from the nearest other stand. Six polymorphic allozyme loci from four enzyme systems were used to genotype approximately 10 000 embryos from 104 families. We detected no allele frequency heterogeneity in the pollen pool among stands or families (F FT ¼ À0.025). Overall, estimates of outcrossing were high (t m ¼ 94% and mean t s ¼ 91%) but significantly different from unity. Bi-parental inbreeding (t m -t s ¼ 3.2%) was low but significantly different from zero. Allozyme-based outcrossing estimates did not differ significantly among three stand-size classes (SSCs): small (o10 trees), medium (10-100 trees) and large (Z100 trees). The number of effective pollen donors was high in all SSCs, but was significantly lower in small stands (N ep ¼ 62.5) than in medium-sized and large stands (both N ep ¼ 143). The primary selfing rate was significantly higher in medium stands than in large stands. We found no significant difference in genetic diversity measures in the filial (seed) population among SSCs. Overall, these results indicate that white spruce stands in this fragmented landscape are resistant to genetic diversity losses, primarily through high pollen-mediated gene-flow and early selection against inbred embryos. We discuss the importance of using seed data, in conjunction with genetic data, to evaluate the impacts of fragmentation on natural populations.

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

“…Although we are rather skeptical about a definitely causal linkage between these two characteristics, this might be reasonable to expect that higher fecundity leads to lower outcrossing rate (Shea 1987). Nonetheless, similarly as in O'Connel et al (2006), we failed to show that a tree size, used as a proxy for fecundity, is associated with outcrossing rates. Therefore, further studies are needed to confirm the role of both male fecundity and masting behavior in shaping mating system parameters of P. cembra.…”

Mating system and pollen gene flow in Mediterranean maritime pine

“…At the stand and population level, mating patterns are affected by natural factors such as population density and size, mode of pollination, flowering synchrony and phenological patterns (El-Kassaby and Jaquish, 1996;Robledo-Arnuncio et al, 2004a;Gérard et al, 2006;O'Connell et al, 2006), as well as management and silvicultural practices (Murawski et al, 1994;El-Kassaby et al, 2003). At the individual level, plant size and shape (in particular crown shape in trees), gender expression, male and female reproductive effort and within-stand social position can also affect mating patterns (Burczyk et al, 1996(Burczyk et al, , 2002Dow and Ashley, 1998;O'Connell et al, 2004;García et al, 2005;Verdú et al, 2006).…”

Restricted pollen flow of Dieffenbachia seguine populations in fragmented and continuous tropical forest

“…For conservation purposes, we need to determine whether habitat fragmentation affects connectivity among populations (Burczyk et al, 2004;O'Connell et al, 2006;Sork and Smouse, 2006), that is, whether population fragments have different pollination dynamics than do continuous populations (Smouse and Sork, 2004). Measurement of the extent of contemporary pollen flow enhances our understanding of the impact of landscape and ecological context on the factors that influence pollen dispersal on local populations and the scale over which they operate (Sork et al, 1999;Dyer and Sork, 2001;Burczyk et al, 2004).…”