Genomic rearrangements in trypanosomatids: an alternative to the "one gene" evolutionary hypotheses?

Most molecular. trees of trypanosomatids are based on point mutations withi n DNA sequences. In contrast there ara very few evolutionary studies consid ering DNA (re) arrangement as genetic characters. Waiting for the completio n of the various parasite genome projects, first information may already be obtained from chromosome size-polymorphism, using the appropriate algorith ms for data processing. Three illustrative models are presented here. First , the case of Leishmania (Viannia) braziliensis/L. (V.) peruviana is descri bed. Thanks to a fast evolution rate (due essentially to amplification/dele tion of tandemly repeated genes), molecular karyotyping seems particularly appropriate for studying recent evolutionary divergence, including eco-geog raphical diversification. Secondly, karyotype evolution is consider-ed at t he level of whole genus Leishmania. Despite the fast chromosome evolution r ate, there is qualitative congruence with MLEE- and RAPD-based evolutionary hypotheses. Significant differences may be observed between major lineages , likely corresponding to major and less frequent rearrangements (fusion/fi ssion, translocation). Thirdly, comparison is made with Trypanosoma cruzi. Again congruence is observed with other hypotheses and major lineages are d elineated by significant chromosome rearrangements. The level of karyotype polymorphism within that "species" is similar to the one observed in "genus " Leishmania. The relativity of the species concept among these two groups of parasites is discussed.