Nuclear markers reveal unexpected genetic variation and a Congolese-Nilotic origin of the Lake Victoria cichlid species flock

Abstract

Phylogenetic analyses based on mitochondrial (mt) DNA have indicated that the cichlid species flock of the Lake Victoria region is derived from a single ancestral species found in East African rivers, closely related to the ancestor of the Lake Malawi cichlid species flock. The Lake Victoria flock contains ten times less mtDNA variation than the Lake Malawi radiation, consistent with current estimates of the ages of the lakes. We present results of a phylogenetic investigation using nuclear (amplified fragment length polymorphism) markers and a wider coverage of riverine haplochromines. We demonstrate that the Lake Victoria-Edward flock is derived from the morphologically and ecologically diverse cichlid genus Thoracochromis from the Congo and Nile, rather than from the phenotypically conservative East African Astatotilapia. This implies that the ability to express much of the morphological diversity found in the species flock may by far pre-date the origin of the flock. Our data indicate that the nuclear diversity of the Lake Victoria-Edward species flock is similar to that of the Lake Malawi flock, indicating that the genetic diversity is considerably older than the 15 000 years that have passed since the lake began to refill. Most of this variation is manifested in trans-species polymorphisms, indicating very recent cladogenesis from a genetically very diverse founder stock. Our data do not confirm strict monophyly of either of the species flocks, but raise the possibility that these flocks have arisen from hybrid swarms.

Repeated trans-watershed hybridization among haplochromine cichlids (Cichlidae) was triggered by Neogene landscape evolution

“…This is unfortunate because it has been assumed that Lake Tanganyika, on the edge of vast Congo basin, is the origin of haplochromine diversification [9]. Furthermore, several studies have identified selected Congolian haplochromines as sister taxon to 'modern haplochromine' sublineages [10], or as sistergroup to members of the southern African serranochromine species flock, which is assumed to have originated in the Kalahari Palaeolakes, previously referred to as the Makgadikgadi flock [1,8,9,11].…”

“…Multilocus nuclear datasets are available only for a subset of haplochromine taxa focusing on particular subgroups from the Lake Victoria region [10], Lake Malawi [6,7] or Lake Tanganyika [5]. In these analyses, riverine haplochromines inhabiting different regions of the Congo basin and Angola are represented by very few Congo basin taxa [10], whereas those in the Upper Kwanza basin (Angola) have yet to be represented at all. This is unfortunate because it has been assumed that Lake Tanganyika, on the edge of vast Congo basin, is the origin of haplochromine diversification [9].…”

“…Other studies have provided phylogenetic evidence for massive introgression and hybridization among ancient lineages in evolving species flocks [12][13][14][15], but phylogenetic tests for a potential contribution of hybridization to the evolution of haplochromine lineages remain scarce ( [7], but see [10,16]). Here, our extensive taxon sampling focuses on riverine haplochromines.…”

“…In general, available comprehensive analyses of haplochromines including several important riverine lineages have relied exclusively on mitochondrial DNA (mtDNA) [8,9]. Multilocus nuclear datasets are available only for a subset of haplochromine taxa focusing on particular subgroups from the Lake Victoria region [10], Lake Malawi [6,7] or Lake Tanganyika [5]. In these analyses, riverine haplochromines inhabiting different regions of the Congo basin and Angola are represented by very few Congo basin taxa [10], whereas those in the Upper Kwanza basin (Angola) have yet to be represented at all.…”

Sperm competition and offspring viability at hybridization in Australian tree frogs, Litoria peronii and L. tyleri

“…An example of this is (at least sometimes) the case of the fire-bellied toads (Vines et al, 2003, but see Nurnberger et al, 2005. Another set of examples come from hybridization resulting in new, successful species of Lake Malawi cichlids as a result of genetic mosaicism (Salzburger et al, 2002;Seehausen et al, 2003;Seehausen, 2004). Finally, one of the most detailed studies showed that hybridization effects on offspring viability can be sex-specific, consistent with Haldane's rule.…”