The role of Pleistocene refugia and rivers in shaping gorilla genetic diversity in central Africa

Abstract

The role of Pleistocene forest refugia and rivers in the evolutionary diversification of tropical biota has been the subject of considerable debate. A range-wide analysis of gorilla mitochondrial and nuclear variation was used to test the potential role of both refugia and rivers in shaping genetic diversity in current populations. Results reveal strong patterns of regional differentiation that are consistent with refugial hypotheses for central Africa. Four major mitochondrial haplogroups are evident with the greatest divergence between eastern (A, B) and western (C, D) gorillas. Coalescent simulations reject a model of recent east-west separation during the last glacial maximum but are consistent with a divergence time within the Pleistocene. Microsatellite data also support a similar regional pattern of population genetic structure. Signatures of demographic expansion were detected in eastern lowland (B) and Gabon/Congo (D3) mitochondrial haplogroups and are consistent with a history of postglacial expansion from formerly isolated refugia. Although most mitochondrial haplogroups are regionally defined, limited admixture is evident between neighboring haplogroups. Mantel tests reveal a significant isolation-bydistance effect among western lowland gorilla populations. However, mitochondrial genetic distances also correlate with the distance required to circumnavigate intervening rivers, indicating a possible role for rivers in partitioning gorilla genetic diversity. Comparative data are needed to evaluate the importance of both mechanisms of vicariance in other African rainforest taxa.control region ͉ mitochondrial ͉ phylogeography ͉ refugium M echanisms underlying evolutionary diversification in tropical forests have intrigued biologists for more than a century. Numerous hypotheses have been proposed (1-2), of which the Pleistocene forest refugium and riverine barrier hypotheses have provoked considerable interest and controversy (3-7). Whereas most studies have focused on the Amazon and Australian wet tropics (5,(8)(9)(10), data on central African rainforest taxa remain relatively sparse.According to Pleistocene refuge theory, forest fragmentation during glacial maxima led to the isolation and subsequent diversification of forest-associated taxa (3). During periods of climate amelioration and population expansion, zones of secondary contact may have also formed between neighboring refugial populations. Although palynological and biogeographical data have been used to infer forest refugia (11-16), their precise location and role in Pleistocene diversification is controversial. Several molecular studies suggest that refugia may have played an important role in structuring montane birds (17-19), primates (20-22), and trees (23). However, other forest species such as chimpanzees (24-26) and elephants (27,28) show relatively weak regional genetic structure, suggesting that wideranging and/or savannah-tolerant species may be poor indicators of range changes in tropical forest cover. One criticism of the Pleistocene...

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

“…Along with historical factors (mainly, colonization history), environmental heterogeneity (for example, rainfall levels (Letouzey, 1968)) and physical barriers (for example, rivers (Anthony et al, 2007)) are key factors that have already been demonstrated in Africa to influence species distribution, and thus their genetic structure, but mostly for animals species. Another potential ecological barrier is due to the annual movement of the intertropical convergence zone, a band of clouds that encircles the globe near the thermal equator and determines the seasonality of precipitations.…”

“…In D. benthamianus, a (slight) relationship exists between belonging to a genetic cluster and some 'environmental' heterogeneity (presence of 'mountains' and localization of the thermal equator), contrary to Aucoumea (Born, 2007). The riverine barrier hypothesis, which has been verified with respect to the structure of genetic diversity mainly in primates (Eriksson et al, 2004;Anthony et al, 2007), remains largely untested in plants, notably in African rainforests.…”

Palaeo-precipitation is a major determinant of palm species richness patterns across Madagascar: a tropical biodiversity hotspot

“…Remnant rainforest areas have been hypothesized as glacial refugia for many organisms, for example, in Africa [19][20][21] and the New World [22]. Empirical studies have provided indirect or less commonly direct evidence that species distributions and endemism patterns can indeed be associated with Quaternary-scale habitat stability in tropical areas [7,23,24]. Today, vegetation distribution in the tropics is primarily controlled by precipitation [25], which also plays a particularly important role as the main driver of species richness at low latitudes [3].…”

Regional Action Plan for the Conservation of Western Lowland Gorillas and Central Chimpanzees 2015–2025

“…It has been shown that ape populations separated by rivers have been genetically distinct for hundreds of thousands of years (Anthony et al 2007;Fünfstück et al 2014), while forests are usually hunted out for several kilometres on either side of national roads and are subsequently avoided by wildlife. Of these 18 priority landscapes, 14 are larger than 10,000 km² and only one is smaller than 5,000 km² in size; 17 each harbour more than 5,000 great apes; 11 had great ape densities of >1 indiv./km²; 16 >0.5 indiv./km², and five are transboundary landscapes straddling international boundaries.…”