Hybridization can generate novel phenotypes distinct from those of parental lineages, a phenomenon known as transgressive trait variation. Transgressive phenotypes might negatively or positively affect hybrid fitness, and increase available variation. Closely related species of Heliconius butterflies regularly produce hybrids in nature and hybridization is thought to play a role in the diversification of novel wing colour patterns despite strong stabilizing selection due to interspecific mimicry. Here, we studied wing phenotypes in first and second generation hybrids produced by controlled crosses between either two co-mimetic species of Heliconius or between two non-mimetic species. We quantified wing size, shape and colour pattern variation and asked whether hybrids displayed transgressive wing phenotypes. Discrete traits underlain by major-effect loci, such as the presence or absence of colour patches, generate novel phenotypes. For quantitative traits, such as wing shape or subtle colour pattern characters, hybrids only exceed the parental range in specific dimensions of the morphological space. Overall, our study addresses some of the challenges in defining and measuring phenotypic transgression for multivariate traits and our data suggest that the extent to which transgressive trait variation in hybrids contributes to phenotypic diversity depends on the complexity and the genetic architecture of the traits.

The data deposited here are the raw quantification of wing shape and pattern of Heliconius butterflies resulting from controlled inter-specific crosses and individuals from the parental species. They were obtained by analysing wing pictures through an analysis of pattern with a method called CPM (Le Poul et al, 2014) and geometric morphometry.

In the pattern tab, each column is a principal component of an analysis of pattern taking into account the colour of each pixel.

In the shape tab, each column is the coordinate of the landmarks (20 for the forewing, FW, 18 for the hindwing, HW)

In all tabs, 4 columns include the id of the specimen, its sex, origin and species status (Panama: CP = H. cydno chioneus, MP = H. melpomene rosina, MPxCP = F1 hybrid between H. cydno chioneus and H. melpomene rosina, CPx(MPxCP)= backcross towards H. cydno chioneus, MPx(MPxCP)= backcross towards H. melpomene rosina  --- Peru: T= H. timareta thelxinoe, M, H. melpomene amaryllis, F1= F1 hybrid between H. timareta thelxinoe and .H melpomene amaryllis, BT= backcross towards H. timareta thelxinoe, BM= backcross towards H. melpomene amaryllis)

Original pictures and scripts used to analyse the datasets can be provided by the 1st author (CM) upon request.