Extensive Introgression among Ancestral mtDNA Lineages: Phylogenetic Relationships of the Utaka within the Lake Malawi Cichlid Flock.

Dieter Anseeuw,Erik Verheyen,Jos Snoeks,Bruno Nevado,Paul Busselen

doi:10.1155/2012/865603

Abstract

We present a comprehensive phylogenetic analysis of the Utaka, an informal taxonomic group of cichlid species from Lake Malawi. We analyse both nuclear and mtDNA data from five Utaka species representing two (Copadichromis and Mchenga) of the three genera within Utaka. Within three of the five analysed species we find two very divergent mtDNA lineages. These lineages are widespread and occur sympatrically in conspecific individuals in different areas throughout the lake. In a broader taxonomic context including representatives of the main groups within the Lake Malawi cichlid fauna, we find that one of these lineages clusters within the non-Mbuna mtDNA clade, while the other forms a separate clade stemming from the base of the Malawian cichlid radiation. This second mtDNA lineage was only found in Utaka individuals, mostly within Copadichromis sp. “virginalis kajose” specimens. The nuclear genes analysed, on the other hand, did not show traces of divergence within each species. We suggest that the discrepancy between the mtDNA and the nuclear DNA signatures is best explained by a past hybridisation event by which the mtDNA of another species introgressed into the ancestral Copadichromis sp. “virginalis kajose” gene pool.

Highlights

The Lake Malawi cichlid fauna comprises over 800 species [1] offering a spectacular example of adaptive radiation with virtually all niches in the lake being filled by members of this family [2, 3]
In a broader taxonomic context including representatives of the main groups within the Lake Malawi cichlid fauna, we find that one of these lineages clusters within the non-Mbuna mitochondrial DNA (mtDNA) clade, while the other forms a separate clade stemming from the base of the Malawian cichlid radiation
In a wider taxonomic context involving the other Malawian cichlid lineages, the most abundant of the two lineages in the Utaka clustered within the non-Mbuna mtDNA clade, while the other formed a separate clade containing exclusively Utaka specimens, mostly C. sp. “virginalis kajose” individuals

Summary

Introduction

The Lake Malawi cichlid fauna comprises over 800 species [1] offering a spectacular example of adaptive radiation with virtually all niches in the lake being filled by members of this family [2, 3]. The phylogenetic reconstruction of Lake Malawi cichlid fauna has recovered six main mitochondrial DNA (mtDNA) lineages [5, 6, 10, 13]. Two of these lineages correspond to the Rhamphochromis and Diplotaxodon genera. The non-Mbuna genus Copadichromis has been shown to have representatives belonging to both the non-Mbuna clade, as well as to a separate lineage. The phylogenetic position of this group remains unclear with Moran et al [5] and Turner et al [13] not recovering mtDNA monophyly within this assemblage: M. eucinostomus and C. borleyi were

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