Two new species of Australoheros Říčan and Kullander are described. Australoheros ykeregua sp. nov. is described from the tributaries of the río Uruguay in Misiones province, Argentina. Australoheros angiru sp. nov. is described from the tributaries of the upper rio Uruguai and middle rio Iguaçu in Brazil. The two new species are not closely related, A. ykeregua is the sister species of A. forquilha Říčan and Kullander, while A. angiru is the sister species of A. minuano Říčan and Kullander. The diversity of the genus Australoheros is reviewed using morphological and molecular phylogenetic analyses. These analyses suggest that the described species diversity of the genus in the coastal drainages of SE Brazil is overestimated and that many described species are best undestood as representing cases of intraspecific variation. The distribution patterns of Australoheros species in the Uruguay and Iguazú river drainages point to historical connections between today isolated river drainages (the lower río Iguazú with the arroyo Uruguaí, and the middle rio Iguaçu with the upper rio Uruguai). Molecular clocks are used to date these and other biogeographic patterns.
Key words: Australoheros, new species, Cichlidae, phylogeny, South America, biogeography, Brazilian shield
Etymology. The Guaraní word ykeregua means neighbor (vecino in Spanish). The etymology is based on the fact that A. ykeregua and A. forquilha have been preliminarily treated as conspecific (Říčan & Kullander 2008). New data have however demonstrated that they are two sister group species living in the same river drainage (río Uruguay), though not sympatrically.
Distribution. Australoheros ykeregua is so far known only from Argentinean territory in the tributaries of the río Uruguay below the Salto Moconá, province of Misiones.
Etymology. The Guaraní word angirû means friend, partner (amigo or compañero in Spanish). The etymology is based on the fact that A. angiru and A. kaaygua have been confused as one species (Říčan & Kullander 2008). New data have however demonstrate that they are two non-sister group species living in the same river drainage (río Iguazú), though not sympatrically.
Distribution. Australoheros angiru has a disjunct distribution in the rio Iguaçu and in the upper rio Uruguai. One locality is so far known from the middle río Uruguay in Misiones province, Argentina (Fig. 10).
Two new species of Australoheros (Teleostei: Cichlidae), with notes on diversity of the genus and biogeography of the Río de la Plata basin