Time and Origin of Cichlid Colonization of the Lower Congo Rapids

Julia Schwarzer,Ulrich K Schliewen,Seraphin N Ifuta,Bernhard Misof,Nicolas Salamin

doi:10.1371/journal.pone.0022380

Julia Schwarzer, Ulrich K Schliewen + Show 3 more

Open Access

https://doi.org/10.1371/journal.pone.0022380

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Abstract

Most freshwater diversity is arguably located in networks of rivers and streams, but, in contrast to lacustrine systems riverine radiations, are largely understudied. The extensive rapids of the lower Congo River is one of the few river stretches inhabited by a locally endemic cichlid species flock as well as several species pairs, for which we provide evidence that they have radiated in situ. We use more that 2,000 AFLP markers as well as multilocus sequence datasets to reconstruct their origin, phylogenetic history, as well as the timing of colonization and speciation of two Lower Congo cichlid genera, Steatocranus and Nanochromis. Based on a representative taxon sampling and well resolved phylogenetic hypotheses we demonstrate that a high level of riverine diversity originated in the lower Congo within about 5 mya, which is concordant with age estimates for the hydrological origin of the modern lower Congo River. A spatial genetic structure is present in all widely distributed lineages corresponding to a trisection of the lower Congo River into major biogeographic areas, each with locally endemic species assemblages. With the present study, we provide a phylogenetic framework for a complex system that may serve as a link between African riverine cichlid diversity and the megadiverse cichlid radiations of the East African lakes. Beyond this we give for the first time a biologically estimated age for the origin of the lower Congo River rapids, one of the most extreme freshwater habitats on earth.

Highlights

The rapids of the Lower Congo River rank among the most spectacular habitats for animal life on earth
Before reaching the Atlantic Ocean, all water collected in a drainage basin encompassing one eighth of the African continent is flushed through an intermittently narrow and deep rocky channel, creating the world’s most extensive rapids [5]
Its origin is most likely related to a river capture event, i.e. a small coastal river hypothetically tapped the interior Congo basin, and subsequently created a novel outlet for the whole Congo drainage [5]

Summary

Introduction

The rapids of the Lower Congo River rank among the most spectacular habitats for animal life on earth. Its origin is most likely related to a river capture event, i.e. a small coastal river hypothetically tapped the interior Congo basin (sometimes referred to as ‘‘Palaeo-lake Congo’’), and subsequently created a novel outlet for the whole Congo drainage [5]. Before this event, in the Pliocene, the Atlantic Rise had dammed the course of the Congo River hereby creating a large endorheic basin (‘‘lake’’) in the western Congo basin, that nowadays is thought to survive in part as Malebo Pool [5]. The distribution of all five genera except for the nearly pan-African catch-all genus ‘‘Haplochromis’’ is restricted to the Congo basin [9]

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