Evolutionary processes in an environmental challenging site: the soda-lake Natron (Tanzania).

Lakes Natron and Magadi are neighbouring small soda localised in the Eastern Rift Valley, between Kenya and Tanzania, and are the remnants of the Paleolake Orolonga after a split that occurred around 9,000 years BP. These basins represent a really harsh environment, characterized by a complex geo-morphological structure, which may increase, by habitat fragmentation and isolation, the effects of evolutionary forces (like genetic drift and selection) on the native species and populations. These lakes harbour a small species flock of quite recent origin, the Alcolapia flock, endemic of this region and not found in any other place around the world. This flock is characterized by four different morphotypes: A. alcalicus, A. latilabris, A. ndalalani, endemic of Lake Natron, and A. grahami, found only in the Lake Magadi. With the aim to understand the evolutionary processes that are shaping genetic diversity of this species, we have analysed by means of molecular genetics tools (mtDNA and nuclear DNA markers), 310 specimens of Alcolapia collected from eight populations placed around the Lake Natron and from one population located in the north-east part of Lake Magadi. Phylogenetic analyses based on D-loop sequences of a subset of 69 Alcolapia have shown a monophyletic structure of the flock, as suggested by the more frequent haplotype (2lat) shared by all the morphotypes and corresponding to the Orolonga haplotype identified in previous studies (Seegers et al, 1999; Wilson et al., 2000 and 2004). Besides, the main starburst radiation occurred in Lake Natron Alcolapia, which evolved in relatively recent times.