The East African cichlid radiations are characterised by repeated and rapid diversification into many distinct species with different ecological specialisations and by a history of hybridization events between non-sister 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 specialised on: feeding by sifting sand. Some of the F2 hybrids phenotypically resembled fish of species that are specialised on sand sifting. We combined experimental behavioural and morphometric approaches to test whether the F2 hybrids are transgressive in both morphology and behaviour related to sand sifting. We then performed a quantitative trait loci (QTL) analysis using RADseq markers to investigate the genetic architecture of morphological and behavioural 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 behaviour in some of the F2 hybrids. Moreover, we find QTLs for morphology and for sand sifting behaviour, 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.

GenotypeTable_CALxTAE.vcf contains 10’166 quality filtered SNPs / genotypes for 126 individuals (114 F2s (“CALTAEF2”), 7 CAL (“ASTCAL”) & 5 TAE (“PROTAE”) parental species individuals). These are then subset to loci fixed between the parental species (see Methods) for linkage map construction.

LinkageMap_CALxTAE.txt gives the position of 931 loci on the linkage map.

GenoPheno_CALxTAE.csv contains phenotypes and genotypes for 109 F2 individuals in the format for QTL mapping in R/qtl. Phenotypes: 5 size corrected linear distances (EpD, EyL, LJL, ML, HW), calculated mouth angle (MA), measured standard length (SL), shape principal component analysis (PCA) scores (PCs 1-10), strike counts for males (M) and females (F), log10(max efficiency) for males, and sex.

SampleOverview_CALxTAE.csv lists all individuals that were used in this study and in which part of the study they were used. Individuals 1-73 and 221-223 are previously preserved individuals that had died of natural causes in the aquarium between 2010-2016.

all_fish_219.TPS and sandsifters_21.TPS contain the coordinates obtained by placing landmarks on photographs in TPSdig 2.10. all_fish_219.TPS contains all F2 hybrid and parental species individuals, sandsifters_21.TPS the 21 sand sifting species.