Abstract
Species diversity is unequally distributed across the globe, with the greatest concentration occurring in the tropics. Even within the tropics, there are significant differences in the numbers of taxa found in each continental region. Manilkara is a pantropical genus of trees in the Sapotaceae comprising c. 78 species. Its distribution allows for biogeographic investigation and testing of whether rates of diversification differ amongst tropical regions. The age and geographical origin of Manilkara are inferred to determine whether Gondwanan break-up, boreotropical migration or long distance dispersal have shaped its current disjunct distribution. Diversification rates through time are also analyzed to determine whether the timing and tempo of speciation on each continent coincides with geoclimatic events. Bayesian analyses of nuclear (ITS) and plastid (rpl32-trnL, rps16-trnK, and trnS-trnFM) sequences were used to reconstruct a species level phylogeny of Manilkara and related genera in the tribe Mimusopeae. Analyses of the nuclear data using a fossil-calibrated relaxed molecular clock indicate that Manilkara evolved 32–29 million years ago (Mya) in Africa. Lineages within the genus dispersed to the Neotropics 26–18 Mya and to Asia 28–15 Mya. Higher speciation rates are found in the Neotropical Manilkara clade than in either African or Asian clades. Dating of regional diversification correlates with known palaeoclimatic events. In South America, the divergence between Atlantic coastal forest and Amazonian clades coincides with the formation of drier Cerrado and Caatinga habitats between them. In Africa diversification coincides with Tertiary cycles of aridification and uplift of the east African plateaux. In Southeast Asia dispersal may have been limited by the relatively recent emergence of land in New Guinea and islands further east c. 10 Mya.
Highlights
Biodiversity is unevenly distributed across the globe and is most intensely concentrated in the tropics, in wet tropical forests, which are the most species-rich biomes on the planet
The dataset includes representatives of the tribe Mimusopeae as well as multiple representatives of the tribes Isonandreae and Sideroxyleae, which belong to the subfamily Sapotoideae, in order to accommodate calibration of fossils related to those groups
The mean age of subtribe Manilkarinae is estimated to be 32 million years ago (Mya) (HPD 36–29 Mya; node K) and the genus Manilkara is resolved as 29 Mya (HPD 32–28 Mya; node Q), both having originated during the Oligocene
Summary
Biodiversity is unevenly distributed across the globe and is most intensely concentrated in the tropics, in wet tropical forests, which are the most species-rich biomes on the planet. There are significant differences in the floristic composition and the numbers of taxa found in each of the continental regions. 50,000 for Southeast Asia (Whitmore, 1998). 27,000 species of flowering plants in tropical Africa (Lebrun, 2001; Lebrun and Stork, 2003), compared with c. This uneven species diversity raises the fundamental question of how variation in the pattern and tempo of speciation and extinction among continents might have driven observed patterns. Differences in diversity have been attributed to higher extinction rates in Africa (Richards, 1973) and faster diversification in the Neotropics (Gentry, 1982). Dated molecular phylogenies suggest speciation in response to recent climatic changes (such as aridification, e.g., Couvreur et al, 2008; Simon et al, 2009) or geological phenomena (such as mountain uplift in the Neotropics, e.g., Richardson et al, 2001; Hughes and Eastwood, 2006)
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