Population history and gene dispersal inferred from spatial genetic structure of a Central African timber tree, Distemonanthus benthamianus (Caesalpinioideae)

Abstract

African rainforests have undergone major distribution range shifts during the Quaternary, but few studies have investigated their impact on the genetic diversity of plant species and we lack knowledge on the extent of gene flow to predict how plant species can cope with such environmental changes. Analysis of the spatial genetic structure (SGS) of a species is an effective method to determine major directions of the demographic history of its populations and to estimate the extent of gene dispersal. This study characterises the SGS of an African tropical timber tree species, Distemonanthus benthamianus, at various spatial scales in Cameroon and Gabon. Displaying a large continuous distribution in the Lower Guinea domain, this is a model species to detect signs of past population fragmentation and recolonization, and to estimate the extent of gene dispersal. Ten microsatellite loci were used to genotype 295 adult trees sampled from eight populations. Three clearly differentiated gene pools were resolved at this regional scale and could be linked to the biogeographical history of the region, rather than to physical barriers to gene flow. A comparison with the distribution of gene pools observed for two other tree species living in the same region invalidates the basic assumption that all species share the same Quaternary refuges and recolonization pathways. In four populations, significant and similar patterns of SGS were detected. Indirect estimates of gene dispersal distances (sigma) obtained for three populations ranged from 400 to 1200 m, whereas neighbourhood size estimates ranged from 50 to 110.

The ancient tropical rainforest tree Symphonia globulifera L. f. (Clusiaceae) was not restricted to postulated Pleistocene refugia in Atlantic Equatorial Africa

“…In the GP located in South Cameroon and Gabon, wide-ranging LGM persistence of the species enabled rapid post-glacial recovery of population sizes, especially through pollen flow, and only an older bottleneck remained traceable. In this region, S. globulifera did not display SSR substructure, contrarily to other forest tree species (Born et al, 2011;Debout et al, 2011;Daïnou et al, 2010). Furthermore, our study suggested ecotypic differentiation between coastal or swamp forest and terra firme S. globulifera.…”

“…In Aucoumea klaineana, genetic diversity is structured in four differentiated gene pools (GPs; identified using nuclear microsatellites), the location of which coincides with refugia postulated from species distribution data in Gabon (Born et al, 2011). However, genetic patterns in three pioneer (Distemonanthus benthamianus, Erythrophleum suaveolens and Milicia excelsa) and one non-pioneer (Greenwayodendron suaveolens) species were not in agreement with postulated refuges but showed a common north-south divide in Lower Guinea, which was suggested to reflect the seasonal inversion near the equator (Daïnou et al, 2010;Dauby et al, 2010;Debout et al, 2011;Duminil et al, 2010). These emerging trends allow formulation of hypotheses on biogeographic scenarios and evolutionary processes operating within species that can be evaluated with multilocus genetic data (preferably using loci with contrasting inheritance) using statistical phylogeographic approaches (Knowles, 2009).…”

Speciation slowing down in widespread and long-living tree taxa: insights from the tropical timber tree genus Milicia (Moraceae)

“…The North-South divide nearby the Equator between these two clusters has been documented for other forest tree species (Duminil et al, 2010;Debout et al, 2011) and a significant floristic shift has recently been demonstrated at that latitude (Gonmadje, 2012). Cluster K5 centered on the Democratic Republic of the Congo may represent populations spreading from inland forest refuges surrounding the Congo River.…”

Application of PCR Technologies to Humans, Animals, Plants and Pathogens from Central Africa

“…First results show that some refugia were shared among several tree species with one main refugium in the North and one in the South of the thermal equator (e.g. Milicia excelsa in [53], Erythrophleum suaveolens in [55], Irvingia gabonensis in [56], Distemonanthus benthamianus in [60].…”

“…Several phylogeographic studies using either cpDNA polymorphism [52,53,54,55,56,57] and/or nuclear markers such as RAPD [58] and microsatellite markers [53,59,60] have recently been published, considering Central African trees as model species, to give insight into the historical biogeography of the region. For most of the studied species, the genetic diversity is very spatially structured throughout the species distribution giving strong phylogeographic signals.…”