Do Heliconius butterfly species exchange mimicry alleles?

Abstract

Hybridization has the potential to transfer beneficial alleles across species boundaries, and there are a growing number of examples in which this has apparently occurred. Recent studies suggest that Heliconius butterflies have transferred wing pattern mimicry alleles between species via hybridization, but ancestral polymorphism could also produce a signature of shared ancestry around mimicry genes. To distinguish between these alternative hypotheses, we measured DNA sequence divergence around putatively introgressed mimicry loci and compared this with the rest of the genome. Our results reveal that putatively introgressed regions show strongly reduced sequence divergence between co-mimetic species, suggesting that their divergence times are younger than the rest of the genome. This is consistent with introgression and not ancestral variation. We further show that this signature of introgression occurs at sites throughout the genome, not just around mimicry genes.

Borrowed alleles and convergence in serpentine adaptation

“…3D) (25), (ii) maximum relative divergence (F ST ; Fig. 3G) (26), (iii) maximum negative residuals of a diversity/differentiation (DD) metric inspired by the Hudson-Kreitman-Aguade test (DD residual test) (Fig.…”

Introgression and repeated co-option facilitated the recurrent emergence of C4photosynthesis among close relatives

“…The divergence times between species estimated from introgressed genes are expected to be younger than those estimated from other genes (e.g., Smith & Kronforst 2013; Li et al. 2014; Marcussen et al.…”

Genome-wide introgression among distantly relatedHeliconiusbutterfly species

“…A total of 50 candidate introgression loci were significant with both the D and f d tests (Table S3 in Additional file 2). In order to help distinguish between introgression and ancestral variation, we calculated DNA sequence divergence (d xy ) for each candidate introgression interval and compared this with chromosomal mean d xy (Table S4 in Additional file 2) because introgressed regions generally show lower absolute genetic divergence [47]. A total of 91 loci showed lower H. besckei-H. m. nanna d xy compared with neighboring regions and their chromosome as a whole (Table S5 in Additional file 2).…”

“…To rule out false positive introgression loci due to incomplete lineage sorting, mean pairwise sequence divergence (d xy ) was calculated among H. m. nanna, H. besckei and H. numata as a complementary analysis to the D-statistic and modified f-statistic [47]. Four individuals of the same species were used to calculate mean d xy for each chromosome using a block size of 50 kb using the following equation [47]:…”

“…Four individuals of the same species were used to calculate mean d xy for each chromosome using a block size of 50 kb using the following equation [47]:…”