Saturday, July 16, 2016

[Ichthyology • 2016] Phylogeny and Phylogeography of Altolamprologus: Ancient Introgression and Recent Divergence in A Rock-Dwelling Lake Tanganyika Cichlid Genus

Fig. 1 A Typical representatives of Altolamprologus calvus, A. compressiceps and A. sp. “shell”. Photographs courtesy of Wolfgang Gessl ( B Map of Lake Tanganyika with sampling localities. Numbers in parentheses refer to sample sizes; different colours indicate different species (red, A. calvus; blue, A. compressiceps; green, A. sp. “shell”). The three deepwater basins are indicated by grey shading

Stenotopic specialization to a fragmented habitat promotes the evolution of genetic structure. It is not yet clear whether small-scale population structure generally translates into large-scale intraspecific divergence. In the present survey of mitochondrial genetic structure in the Lake Tanganyika endemic Altolamprologus (Teleostei, Cichlidae), a rock-dwelling cichlid genus comprising A. compressiceps and A. calvus, habitat-induced population fragmentation contrasts with weak phylogeographic structure and recent divergence among genetic clades. Low rates of dispersal, perhaps along gastropod shell beds that connect patches of rocky habitat, and periodic secondary contact during lake level fluctuations are apparently sufficient to maintain genetic connectivity within each of the two Altolamprologus species. The picture of genetic cohesion was interrupted by a single highly divergent haplotype clade in A. compressiceps restricted to the northern part of the lake. Comparisons between mitochondrial and nuclear phylogenetic reconstructions suggested that the divergent mitochondrial clade originated from ancient interspecific introgression. Finally, ‘isolation-with-migration’ models indicated that divergence between the two Altolamprologus species was recent (67–142 KYA) and proceeded with little if any gene flow. As in other rock-dwelling cichlids, recent population expansions were inferred in both Altolamprologus species, which may be connected with drastic lake level fluctuations.

Keywords: Cichlidae, Mitochondrial replacement, Phylogeography, Lake level fluctuations, Lamprologini, Hybridization

In numerous studies of lacustrine cichlids, the species’ ecological specialization predicts population genetic differentiation on small geographic scales. The present study shows that population fragmentation and small-scale differentiation do not necessarily translate into distinct lake-wide structure. The discrepancy between population genetic and phylogeographic structures may arise from the different time scales relevant for the evolution of either. In particular, population differentiation—i.e. significant differences in allele and haplotype frequencies between populations—can evolve despite low gene flow within relatively short periods of time. Over longer periods of time, however, even low levels of gene flow can mediate genetic connectivity across substantial geographic distances.

Stephan Koblmüller, Bruno Nevado, Lawrence Makasa, Maarten Van Steenberge, Maarten P. M. Vanhove, Erik Verheyen, Christian Sturmbauer and Kristina M. Sefc. 2016. Phylogeny and Phylogeography of Altolamprologus: Ancient Introgression and Recent Divergence in A Rock-Dwelling Lake Tanganyika Cichlid Genus. Hydrobiologia [ADVANCES IN CICHLID RESEARCH II]. DOI: 10.1007/s10750-016-2896-2