Small‐scale spatial genetic structure in the Central African rainforest tree species Aucoumea klaineana: a stepwise approach to infer the impact of limited gene dispersal, population history and habitat fragmentation

Abstract

Under the isolation-by-distance model, the strength of spatial genetic structure (SGS) depends on seed and pollen dispersal and genetic drift, which in turn depends on local demographic structure. SGS can also be influenced by historical events such as admixture of differentiated gene pools. We analysed the fine-scale SGS in six populations of a pioneer tree species endemic to Central Africa, Aucoumea klaineana. To infer the impacts of limited gene dispersal, population history and habitat fragmentation on isolation by distance, we followed a stepwise approach consisting of a Bayesian clustering method to detect differentiated gene pools followed by the analysis of kinship-distance curves. Interestingly, despite considerable variation in density, the five populations situated under continuous forest cover displayed very similar extent of SGS. This is likely due to an increase in dispersal distance with decreased tree density. Admixture between two gene pools was detected in one of these five populations creating a distinctive pattern of SGS. In the last population sampled in open habitat, the genetic diversity was in the same range as in the other populations despite a recent habitat fragmentation. This result may due to the increase of gene dispersal compensating the effect of the disturbance as suggested by the reduced extent of SGS estimated in this population. Thus, in A. klaineana, the balance between drift and dispersal may facilitate the maintenance of genetic diversity. Finally, from the strength of the SGS and population density, an indirect estimate of gene dispersal distances was obtained for one site: the quadratic mean parent-offspring distance, sigma(g), ranged between 210 m and 570 m.

Increased inbreeding and strong kinship structure in Taxus baccata estimated from both AFLP and SSR data

“…This could explain a linear rather than a log-linear relationship between kinship and distance observed for AFLP markers in Wierzchlas (Figure 4) (Born et al, 2008). Nonetheless, the lack of concordance between AFLPs and SSRs points to some ambiguity in the pattern, which cannot be resolved using the available data.…”

Fine-scale spatial genetic dynamics over the life cycle of the tropical tree Prunus africana

“…D e is normally unknown but different values of N e /N, whereby N e is the effective population size and N the census one, can be used to approximate this quantity (Vekemans and Hardy, 2004;Born et al, 2008). As the ratio N e /N typically ranges between 0.1 and 0.5 (Frankham 1995;Born et al, 2008), we used the observed adult density, 0.00022 individuals m -2 as an upper limit estimate, as well as 0.00022/10 as a lower limit estimate of the effective population density D e . The distance range for the regression was set between s and 20 s, assuming a mutation rate m of 10 À3 for nuclear microsatellites (see Heuertz et al, 2003).…”

Biogeography and evolution of seeder and resprouter forms of Erica coccinea (Ericaceae) in the fire-prone Cape fynbos

“…Similar patterns of introgressive gene flow after secondary contact of previously separated lineages have been found in other plant species (e.g. in temperate or tropical trees, Latta and Mitton 1999;Born et al 2008). Although the flowering phenologies of seeder and resprouter E. coccinea populations hardly overlap (see ''Introduction''), there may still be-or could have been in the recent past-some opportunities for hybridization and gene flow across regeneration forms.…”