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<p>Abstract</p> <p>Background</p> <p>Sister species divergence and reproductive isolation commonly results from ecological adaptation. In mimetic <it>Heliconius </it>butterflies, shifts in colour pattern contribute to pre- and post-mating reproductive isolation and are commonly correlated with speciation. Closely related mimetic species are therefore not expected, as they should lack several important sources of reproductive isolation.</p> <p>Results</p> <p>Here we present phenotypic, behavioral and genetic evidence for the coexistence of two sympatric 'cryptic' species near Florencia in the eastern Andes of Colombia that share the same orange rayed colour pattern. These represent <it>H. melpomene malleti </it>and a novel taxon in the <it>H. cydno </it>group, here designated as novel race of <it>Heliconius timareta</it>, <it>Heliconius timareta florencia</it>. No-choice mating experiments show that these sympatric forms have strong assortative mating (≈96%) despite great similarity in colour pattern, implying enhanced divergence in pheromonal signals.</p> <p>Conclusion</p> <p>We hypothesize that these species might have resulted from recent convergence in colour pattern, perhaps facilitated by hybrid introgression of wing pattern genes.</p>