Figure 4
The "out of Tanganyika" scenario of haplochromine evolution in Africa. (a) Several haplochromine lineages independently left Lake Tanganyika and colonized large parts of Africa via past and present river connections. Some of these lineages seeded cichlid radiations in distant lakes. The phylogeographic scenario is in agreement with palaeo-geological reconstructions of the evolution of the East African Rift region. LT is the oldest of the rift lakes. Its central basin began to form between 9 and 12 MYA, the northern (8-7 MYA) and the southern basin (2–4 MYA) began to fill at later periods [76]; deepwater conditions exist since about 5–6 MYA [78]. LM (2–4 MYA) and LV (750,000 years) are considerably younger. (b) Proposed lake level of Lake Tanganyika during the last four million years [76, 77, 79] indicating major low- and high-stands. (c) Chronogram of the haplochromine evolution in Africa as reconstructed with r8s [72, 73] based on the maximum likelihood topology. The size of each clade represents its species number. The modern haplochromines are a recent and rapidly speciating lineage. Our molecular clock calibration suggested about 2 MYA (1.15 – 3.89 MYA) for the most recent common ancestor in the Congolese/Southern African lineage and ca. 2.4 MYA (1.22 – 4.02 MYA) for their split from the common ancestor with the Pseudocrenilabrus-, Astatoreochromis-, and modern haplochromine lineage. This lies in the range of the proposed high lake-level stand of LT between the minima at 3.5 MYA and 1.1 MYA (650–700 m below present level) [76, 77] making an overflow through the Lukuga valley possible, thus opening the connection between LT and the Congo drainage. The asterisks mark nodes with a significant burst of lineage diversification (p c < 0.01) [21]. Aa... Astatoreochromis alluaudi, CSA... Congolese/South African lineage, Hb... Haplochromis bloyeti, LMF... Lake Malawi species flock, LVS... Lake Victoria Region Superflock, MO... Malagarasi Orthochromis assemblage, Pm... Pseudocrenilabrus multicolor, Pp...Pseudocrenilabrus philander, Ps... Pseudocrenilabrus- lineage, Tr... Tropheini.