Abstract
The East African cichlid radiations are characterized by repeated and rapid diversification into many distinct species with different ecological specializations and by a history of hybridization events between nonsister species. Such hybridization might provide important fuel for adaptive radiation. Interspecific hybrids can have extreme trait values or novel trait combinations and such transgressive phenotypes may allow some hybrids to explore ecological niches neither of the parental species could tap into. Here, we investigate the potential of second‐generation (F2) hybrids between two generalist cichlid species from Lake Malawi to exploit a resource neither parental species is specialized on: feeding by sifting sand. Some of the F2 hybrids phenotypically resembled fish of species that are specialized on sand sifting. We combined experimental behavioral and morphometric approaches to test whether the F2 hybrids are transgressive in both morphology and behavior related to sand sifting. We then performed a quantitative trait loci (QTL) analysis using RADseq markers to investigate the genetic architecture of morphological and behavioral traits. We show that transgression is present in several morphological traits, that novel trait combinations occur, and we observe transgressive trait values in sand sifting behavior in some of the F2 hybrids. Moreover, we find QTLs for morphology and for sand sifting behavior, suggesting the existence of some loci with moderate to large effects. We demonstrate that hybridization has the potential to rapidly generate novel and ecologically relevant phenotypes that may be suited to a niche neither of the parental species occupies. Interspecific hybridization may thereby contribute to the rapid generation of ecological diversity in cichlid radiations.
Highlights
Adaptive radiation describes the phenomenon of rapid diversification of a single lineage into an array of many species with ecologically varied adaptations (Losos, 2010; Schluter, 20002000)
Note: Nearest, nearest marker to a quantitative trait loci (QTL) at an interpolated marker where genotypes were inferred with calc.genoprob; Pun-LG, linkage group number corresponding to the anchored Pundamilia nyererei reference genome (Feulner et al, 2018); Ore-LG, linkage group number corresponding to the Oreochromis niloticus reference genome (Simakov et al, 2014); 95% CI Bayesian 95% confidence interval; cM, position in centi Morgan; Percent variance (PVE), percent variance explained, calculated as 1–10−(2*/n)*LOD following (Broman et al, 2003)
We experimentally investigated transgressive segregation in morphology and behavior that may result in the potential to exploit a novel ecological niche in a second-generation (F2) hybrid cross between two trophic generalist species of Lake Malawi cichlids, in which some of the hybrids phenotypically resembled sand sifting species in the adaptive radiation of Lake Malawi cichlids (Fryer & Iles, 1972; Konings, 2010)
Summary
Adaptive radiation describes the phenomenon of rapid diversification of a single lineage into an array of many species with ecologically varied adaptations (Losos, 2010; Schluter, 20002000). Segregation variance typically results from recombination between parental species when quantitative trait loci (QTL) with antagonistic effects are present within each parental lineage and different between them, which have additive effects when recombined in the hybrid offspring (Abbott et al, 2013; Rieseberg et al, 1999; Rieseberg, Widmer, Arntz, & Burke, 2003; Seehausen, 2004) These requirements for transgressive segregation seem to be common in both plants and animals (Rieseberg et al, 2003). The two parental species belong to two out of seven main lineages within the radiation (Malinsky et al, 2018), Astatotilapia calliptera and Protomelas taeniolatus Previous studies of this cross have shown high levels of transgression in morphology in both first- (F1) and second (F2)-generation hybrids (Selz, Lucek, et al, 2014; Stelkens et al, 2009), as well high levels of transgression in colorspace in the F1 hybrids. We demonstrate that in addition to transgression in morphology and the appearance of novel trait combinations, some of our F2 hybrids show high transgressive values in behaviors related to sand sifting, and may have the potential to occupy a novel feeding niche
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