Hybridization and phylogeography of the Mozambique tilapia Oreochromis mossambicus in southern Africa evidenced by mitochondrial and microsatellite DNA genotyping

Abstract

Many Oreochromis species utilized in aquaculture were extensively introduced outside their native range in Africa. Given their recent evolutionary radiation, these species hybridize easily, posing a threat to the integrity of local adaptation. The objective of this work was to study the genetic diversity of the Mozambique tilapia (Oreochromis mossambicus) in its native range, southern Africa, and provide a method for identifying hybrids with genetic markers. We genotyped the mitochondrial DNA (mtDNA) control region (385 bp) of wild and farmed O. mossambicus, wild and farmed O. niloticus and morphologic wild hybrids. These data were complemented with published sequences of parapatric and sympatric Oreochromis taxa. Phylogeographic analysis showed the presence of two O. mossambicus lineages, the southernmost representing a recent Holocene radiation. Hybridization of O. mossambicus was indicated by the presence of O. niloticus and O. mortimeri-andersonii mtDNA specimens in the Limpopo basin and of O. karongae mtDNA in specimens from Malawi. We also genotyped seven suspected hybrid individuals from the Limpopo River, and 137 wild and farmed Mozambique and Nile tilapia samples with five microsatellite markers. Factorial Component Analysis, Bayesian clustering and assignment analyses consistently delineated an O. mossambicus and an O. niloticus group, with the putative hybrids positioned in between. Different levels of hybridization were detected by the Bayesian assignment. The complex nature of hybridization and introgression between cichlid species raises major concerns for the long-term integrity of Mozambique tilapia.

A case of complete loss of gill parasites in the invasive cichlid Oreochromis mossambicus

“…First, the history of the New Caledonian O. mossambicus populations could have included some factors such as an early and effective chemical treatment against parasites along with the naturalization of the species in the island. Gill parasites of cichlids are also very sensitive to salinity variation (Hadiroseyani et al 2009), and O. mossambicus has the peculiarity to be an euryhaline species with dispersal events through coastal saline waters strongly suspected in the native range (D'Amato et al 2007). Thus, one or several dispersal events through saltwater at an early stage of the invasion in New Caledonia could have caused the absence of parasites observed in contemporary populations.…”

Broad Niche Overlap between Invasive Nile Tilapia Oreochromis niloticus and Indigenous Congenerics in Southern Africa: Should We be Concerned?

“…Feral populations of O. niloticus are already established in the Runde-Save, Buzi, and Limpopo river systems where adverse ecological impacts such as reduced abundance of indigenous species have already been documented [11]. In addition, similar to the Kafue River, the Oreochromis cichlid population in the Limpopo River may already be comprised of a hybrid swarm that consists of fish with an admixture of O. niloticus, O. andersonii, and O. mossambicus [48,49]. The presence of the O. andersonii mitochondrial haplotypes in the Limpopo River system indicates another invasion event, also linked to aquaculture.…”

Genetic structure and gene flow in an endangered native tilapia fish (Oreochromis esculentus) compared to invasive Nile tilapia (Oreochromis niloticus) in Yala swamp, East Africa

“…Further, O. niloticus is a more flexible and efficient algae feeder than O. esculentus, which likely contributes to its competitive success (Batjakas et al 1997). Invasive O. niloticus also often hybridize with the native tilapia species in the natural environment, further displacing endemic species (Agnèse et al 1998;Canonico et al 2005;D'Amato et al 2007). …”