Diversity gradients and phylogeographic patterns in Santiria trimera (Burseraceae), a widespread African tree typical of mature rainforests

Abstract

The divergence between Upper and Lower Guinean rainforests is explained by the discontinuity of forest between those regions throughout most of the Quaternary. The distribution of rare endemic haplotypes concurred with proposed Pleistocene rainforest refuges in west and southwest Cameroon. Overall, phylogeographic structure is consistent with the biogeographic hypotheses largely based on patterns of species diversity.

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

“…Based on geography, a Beninese GP differentiated from Lower Guinea can be expected, as has been observed for another widespread forest tree, Milicia excelsa (Daïnou et al, 2010). A biogeographic divide between Upper and Lower Guinea is reflected in both patterns of plant and animal endemism (White, 1979;Mayr and O'Hara, 1986;Linder, 2001) and, for some species, in the population genetic structure (for example, Coffea canephora (Gomez et al, 2009); Santiria trimera (Koffi et al, 2011)). This divide is presumably caused by recurrent connections and separations of both forest blocks since the end of the Pliocene, the latest opening of the Dahomey gap dating to ca 3700 BP (Maley, 1996).…”

“…GP2 is located close to the proposed Pleistocene forest refuge on the CVL (Maley, 1996;Maley and Brenac, 1998). This refuge was supported by the discovery of endemic alleles in the rainforest trees Santiria trimera (Koffi et al, 2011) and Irvingia gabonensis (Lowe et al, 2010). Therefore, one interpretation is that S. globulifera in West Cameroon shared this refuge (see previous section) and has not yet recovered from an LGM bottleneck.…”

“…For example, the two Cameroonian refuges proposed by Maley (1996) are also supported by the distribution of endemic alleles in Irvingia gabonensis (Lowe et al, 2010) and Santiria trimera (Koffi et al, 2011). 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).…”

“…The latter hypothesis is supported to some extent by the indistinctness of São Tomé and West Cameroon in the STRUCTURE analysis for K ¼ 2, suggesting a common origin of these GPs. Colonization of São Tomé along with the CVL has been proposed for Drosophila santomea (Cariou et al, 2001), whereas studies on plants more generally proposed colonization of São Tomé from Lower Guinean forests (Stévart, 2003;Koffi et al, 2011). The (dm) 2 -based UPGMA tree in S. globulifera rather supported colonization of São Tomé from the South Cameroon and Gabon region, whereas cpDNA data concurred with both colonization scenarios as H03 from São Tomé was fairly closely related to H01 from South Cameroon (locations 5 and 7, east of the CVL) and to H13 from Korup (location 2, west of the CVL).…”

Comparative Phylogeography in Rainforest Trees from Lower Guinea, Africa

“…This sampling provided increased power to detect particular shared phylogeographic patterns among the four species, though at the cost of generality. While several phylogeographic studies have examined the distribution of genetic diversity in tree species from LG [34], [38], [40]–[45], no study to our knowledge has compared diversity using the same plastid marker across taxa or attempted a multi-taxa analysis.…”