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Introgressive hybridization in a trophically polymorphic cichlid.

ABSTRACT: Trophically polymorphic species could represent lineages that are rapidly diverging along an ecological axis or could phenotypically mark the collapse of species through introgressive hybridization. We investigated patterns of introgression between the trophically polymorphic cichlid fish Herichthys minckleyi and its relative H. cyanoguttatus using a combination of population genetics and species tree analyses. We first examined the distribution of mitochondrial haplotypes within the alternative H. minckleyi pharyngeal jaw morphotypes that are endemic to the small desert valley of Cuatro Ciénegas. We recovered two clusters of mitochondrial haplotypes. The first contained a number of slightly differentiated cytochrome b (cytb) haplotypes that showed some phylogeographic signal and were present in both jaw morphotypes. The other haplotype was monomorphic, highly differentiated from the other cluster, present in equal frequencies in the morphotypes, and identical to H. cyanoguttatus haplotypes found outside Cuatro Ciénegas. Then, we investigated whether H. minckleyi individuals with the H. cyanoguttatus cytb were more evolutionarily similar to H. cyanoguttatus or other H. minckleyi using a species tree analysis of 84 nuclear loci. Both H. minckleyi pharyngeal morphotypes, regardless of their cytb haplotype, were quite distinct from H. cyanoguttatus. However, hybridization could be blurring subdivision within H. minckleyi as the alternative jaw morphotypes were not genetically distinct from one another. Accounting for introgression from H. cyanoguttatus will be essential to understand the evolution of the trophically polymorphic cichlid H. minckleyi.

SUBMITTER: Hulsey CD

PROVIDER: S-EPMC3856752 | biostudies-literature | 2013 Nov

REPOSITORIES: biostudies-literature

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Project description:BackgroundBaboons of the genus Papio are distributed over wide ranges of Africa and even colonized parts of the Arabian Peninsula. Traditionally, five phenotypically distinct species are recognized, but recent molecular studies were not able to resolve their phylogenetic relationships. Moreover, these studies revealed para- and polyphyletic (hereafter paraphyletic) mitochondrial clades for baboons from eastern Africa, and it was hypothesized that introgressive hybridization might have contributed substantially to their evolutionary history. To further elucidate the phylogenetic relationships among baboons, we extended earlier studies by analysing the complete mitochondrial cytochrome b gene and the 'Brown region' from 67 specimens collected at 53 sites, which represent all species and which cover most of the baboons' range.ResultsBased on phylogenetic tree reconstructions seven well supported major haplogroups were detected, which reflect geographic populations and discordance between mitochondrial phylogeny and baboon morphology. Our divergence age estimates indicate an initial separation into southern and northern baboon clades 2.09 (1.54-2.71) million years ago (mya). We found deep divergences between haplogroups within several species (~2 mya, northern and southern yellow baboons, western and eastern olive baboons and northern and southern chacma baboons), but also recent divergence ages among species (< 0.7 mya, yellow, olive and hamadryas baboons in eastern Africa).ConclusionOur study confirms earlier findings for eastern Africa, but shows that baboon species from other parts of the continent are also mitochondrially paraphyletic. The phylogenetic patterns suggest a complex evolutionary history with multiple phases of isolation and reconnection of populations. Most likely all these biogeographic events were triggered by multiple cycles of expansion and retreat of savannah biomes during Pleistocene glacial and inter-glacial periods. During contact phases of populations reticulate events (i.e. introgressive hybridization) were highly likely, similar to ongoing hybridization, which is observed between East African baboon populations. Defining the extent of the introgressive hybridization will require further molecular studies that incorporate additional sampling sites and nuclear loci.

Project description:Schistosomiasis is a disease of great medical and veterinary importance in tropical and subtropical regions, caused by parasitic flatworms of the genus Schistosoma (subclass Digenea). Following major water development schemes in the 1980s, schistosomiasis has become an important parasitic disease of children living in the Senegal River Basin (SRB). During molecular parasitological surveys, nuclear and mitochondrial markers revealed unexpected natural interactions between a bovine and human Schistosoma species: S. bovis and S. haematobium, respectively. Hybrid schistosomes recovered from the urine and faeces of children and the intermediate snail hosts of both parental species, Bulinus truncatus and B. globosus, presented a nuclear ITS rRNA sequence identical to S. haematobium, while the partial mitochondrial cox1 sequence was identified as S. bovis. Molecular data suggest that the hybrids are not 1st generation and are a result of parental and/or hybrid backcrosses, indicating a stable hybrid zone. Larval stages with the reverse genetic profile were also found and are suggested to be F1 progeny. The data provide indisputable evidence for the occurrence of bidirectional introgressive hybridization between a bovine and a human Schistosoma species. Hybrid species have been found infecting B. truncatus, a snail species that is now very abundant throughout the SRB. The recent increase in urinary schistosomiasis in the villages along the SRB could therefore be a direct effect of the increased transmission through B. truncatus. Hybridization between schistosomes under laboratory conditions has been shown to result in heterosis (higher fecundity, faster maturation time, wider intermediate host spectrum), having important implications on disease prevalence, pathology and treatment. If this new hybrid exhibits the same hybrid vigour, it could develop into an emerging pathogen, necessitating further control strategies in zones where both parental species overlap.

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Introgressive hybridization in a trophically polymorphic cichlid.

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