Genetic exchanges between closely related groups of organisms with different adaptations have well-documented beneficial and detrimental consequences. In plants, pollen-mediated exchanges affect the sorting of alleles across physical landscapes, and influence rates of hybridisation. How these dynamics affect the emergence and spread of novel ecological strategies remains only partially understood. Here, we use phylogenomics and population genomics to retrace the origin and spread of two geographically overlapping ecotypes of the African grass Alloteropsis angusta. Besides an ecotype inhabiting wetlands, we report the existence of a previously undescribed ecotype inhabiting miombo woodlands and grasslands. The two ecotypes are consistently associated with different nuclear groups, which represent an advanced stage of divergence with secondary low-level gene flow. However, the seed-transported chloroplast genomes are consistently shared by distinct ecotypes inhabiting the same region. These patterns suggest that the nuclear genome of one ecotype can reach the seeds of the other via occasional pollen movements with sorting of nuclear groups in subsequent generations. The contrasting ecotypes of A. angusta can thus use each other as a gateway to new locations across a large part of Africa, showing that hybridisation can facilitate the geographical dispersal of distinct ecotypes of the same grass species.

Raw USAXS data from discal region of Heliconius butterflies (H. erato and H. melpomene). The data comes from wings of individuals of two intercross families, one from each species and was used to estimate scale structure variation and a QTL analysis.

Raw USAXS data from discal region of Heliconius butterflies (H. erato and H. melpomene). The data comes from wings of individuals of two intercross families, one from each species and was used to estimate scale structure variation and a QTL analysis.

Hybrid zones, where distinct populations meet and interbreed, give insight into how differences between populations are maintained despite gene flow. Studying clines in genetic loci and adaptive traits across hybrid zones is a powerful method for understanding how selection drives differentiation within a single species, but can also be used to compare parallel divergence in different species responding to a common selective pressure. Here, we study parallel divergence of wing colouration in the butterflies Heliconius erato and H. melpomene, which are distantly related Müllerian mimics that show parallel geographic variation in both discrete variation in pigmentation, and quantitative variation in structural colour. Using geographic cline analysis, we show that clines in these traits are positioned in the roughly the same geographic region for both species, which is consistent with direct selection for mimicry. However, the width of the clines varies markedly between species. This difference is explained in part by variation in the strength of selection acting on colour traits within each species, but may also be influenced by differences in the dispersal rate and total strength of selection against hybrids between the species. Genotyping-by-sequencing also revealed weaker population structure in H. melpomene, suggesting the hybrid zones may have evolved differently in each species; which may also contribute to the patterns of phenotypic divergence in this system Overall, we conclude that multiple factors are needed to explain patterns of clinal variation within and between these species, although mimicry has probably played a central role.

These data comprise collection records of Heliconius butterfly samples collected in the Chocó-Darien ecoregion between the Andes and the Pacific in Ecuador and Colombia, and the Pacific coast of the Darien region of Panama. Samples were collected over five sampling trips between 2014 and 2016. Data were collected for a study of clinal variation across this region in Heliconius erato and Heliconius melpomene, so focus on these two species. However, in most cases all observed Heliconius species were collected. The dataset includes photographs of the wings of most of the specimens, which were used for an analysis of colour and pattern variation. Many of these individuals also have genomic information available for them on the European Nucleotide Archive (ENA) - the data includes ENA accession numbers.Data were collected as part of a NERC fellowship project (NE/K008498/1).