A large-scale phylogeny of Synodontis (Mochokidae, Siluriformes) reveals the influence of geological events on continental diversity during the Cenozoic.

To explain the spatial variability of fish taxa at a large scale, two alternative proposals are usually evoked. In recent years, the debate has centred on the relative roles of present and historical processes in shaping biodiversity patterns. In Africa, attempts to understand the processes that determine the large scale distribution of fishes and exploration of historical contingencies have been under-investigated given that most of the phylogenetic studies focus on the history of the Great Lakes. Here, we explore phylogeographic events in the evolutionary history of Synodontis (Mohokidae, Siluriformes) over Africa during the Cenozoic focusing on the putative role of historical processes. We discuss how known geological events together with hydrographical changes contributed to shape Synodontis biogeographical history. Synodontis was chosen on the basis of its high diversity and distribution in Africa: it consists of approximately 120 species that are widely distributed in all hydrographic basins except the Maghreb and South Africa. We propose the most comprehensive phylogeny of this catfish genus. Our results provide support for the 'hydrogeological' hypothesis, which proposes that palaeohydrological changes linked with the geological context may have been the cause of diversification of freshwater fish deep in the Tertiary. More precisely, the two main geological structures that participated to shape the hydrographical network in Africa, namely the Central African Shear zone and the East African rift system, appear as strong drivers of Synodontis diversification and evolution.

Early divergence among the Alestidae (Teleostei, Ostariophyses, Characiformes): mitochondrial evidences and congruence with morphological data.

The African family Alestidae (Ostariophysii: Characiformes) includes today 13 genera, among which seven are monospecific. The size range observed in the family greatly varies with species ranging from 21 mm up to 130 cm for more than 50 kg. Among the Alestidae, three tribes were previously identified: the Alestini, the Hydrocinini and the Petersiini, that include all the miniaturised species. Previous phylogenetic studies mainly focussed on the relationships between the genera Alestes, Brycinus, Bryconaethiops and Hydrocynus and left the phylogenetic affinities of the genera from the tribe Petersiini unexplored. We assessed the molecular phylogenetic relationships within the family using partial mitochondrial ribosomal DNA sequences of the 12S and 16S genes and evaluated the congruence with available morphological characters by separate and combined analyses. We especially focussed on the phylogenetic status of the tribe Petersiini and further investigated the early divergence among the family. Our results lead to the identification of two major lineages and to the description of three new clades. The relationships inferred allowed us to reject monophyly of the genera Brycinus, Micralestes and Rhabdalestes and to suggest that the genus Bryconaethiops should be removed from the tribe Alestini. We also have shown that miniaturization occurred more than once, contrary to the predictions of the present classification.

Phylogeography of the piranha genera Serrasalmus and Pygocentrus: implications for the diversification of the Neotropical ichthyofauna.

The phylogenetic relationships within the piranhas were assessed using mitochondrial sequences with the aim of testing several hypotheses proposed to explain the origin of Neotropical diversity (palaeogeography, hydrogeology and museum hypotheses). Sequences of the ribosomal 16S gene (510 bp) and control region (980 bp) were obtained from 15 localities throughout the main South American rivers for 21 of the 28 extant piranha species. The results indicate that the genus Serrasalmus is monophyletic and comprises three major clades. The phylogeographical analyses of these clades allowed the identification of five vicariant events, extensive dispersal and four lineage duplications suggesting the occurrence of sympatric speciation. Biogeographical patterns are consistent with the prediction made by the museum hypothesis that lineages from the Precambrian shields are older than those from the lowlands of the Amazon. The vicariant events inferred here match the distribution of the palaeoarches and several postdispersal speciation events are identified, thereby matching the predictions of the palaeogeography and hydrogeology hypotheses, respectively. Molecular clock calibration of the control region sequences indicates that the main lineages differentiated from their most recent common ancestor at 9 million years ago in the proto Amazon-Orinoco and the present rate of diversification is the highest reported to date for large carnivorous Characiformes. The present results emphasize that an interaction among geology, sea-level changes, and hydrography created opportunities for cladogenesis in the piranhas at different temporal and geographical scales.