TY - JOUR T1 - A case for sympatric speciation by cannibalism in South-American annual killifish (<em>Austrolebias</em>) JF - bioRxiv DO - 10.1101/121806 SP - 121806 AU - Tom JM Van Dooren AU - Henri A Thomassen AU - Femmie Smit AU - Andrew J Helmstetter AU - Vincent Savolainen Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/03/29/121806.abstract N2 - Adult body sizes in Austrolebias annual killifish vary a lot between species. The current hypothesis is that large sizes and specialized piscivory have evolved in successive vicariance speciation events with gradual evolution. We revisit this hypothesis using size measures combined with range data and new phylogenetic trees based on mitochondrial and nuclear molecular markers. Our analysis repeats biogeographic and Ornstein-Uehlenbeck trait evolution modeling across the posterior distributions of phylogenetic trees. We identify three events where large evolved from small. Our mtDNA phylogenetic trees reject the null hypothesis that all speciations were allopatric, but we note that some sympatric speciations might mark introgression events. Vicariance is unlikely to have played an important role: this type of speciation event can be simplified out of the biogeographic models. We propose a new scenario for the emergence of large piscivorous Austrolebias species: giant-dwarf speciation. In this eco-evolutionary scenario a large morph evolves in a population due to disruptive selection driven by character displacement and cannibalism. It can lead to the emergence of a sympatric large and small species pair. The clade containing A. elongatus seems a plausible case of giant-dwarf speciation. The species in it experience stabilizing selection with an optimum shifted towards larger bodies and longer jaws. The branch leading to this clade has the fastest evolving jaw lengths across the phylogeny. Our analysis suggests a potential alternative giant-dwarf scenario where large body size evolved in sympatry first, followed by a fast increase in body and jaw length for one daughter species in a subsequent event. A. wolterstorffi is selected towards a larger body and longer jaw, but evolves with slower rates than the elongatus clade. Discordance between mitochondrial and nuclear gene trees suggests introgression and the timing of trait divergence cannot be determined well at this point. For the clade with the remaining large species, we can reject the giant-dwarf hypothesis. The absence of substantial and rapid jaw length evolution suggests that they evolved due to other selective processes. ER -