ABSTRACT
Mating cues evolve rapidly and can contribute to species formation and maintenance. However, little is known about how sexual signals diverge and how this variation integrates with other barrier loci to shape the genomic landscape of reproductive isolation. Here, we elucidate the genetic basis of ultraviolet (UV) iridescence, a courtship signal that differentiates the males of Colias eurytheme butterflies from a sister species, allowing females to avoid costly heterospecific matings. Anthropogenic range expansion of the two incipient species established a large zone of secondary contact across the eastern United States with strong signatures of genomic admixtures spanning all autosomes. In contrast, Z chromosomes are highly differentiated between the two species, supporting a disproportionate role of sex chromosomes in speciation known as the large-X (or large-Z) effect. Within this chromosome-wide reproductive barrier, linkage mapping indicates that cis-regulatory variation of bric a brac (bab) underlies the male UV-iridescence polymorphism between the two species. Bab is expressed in all non-UV scales, and butterflies of either species or sex acquire widespread ectopic iridescence following its CRISPR knockout, demonstrating that Bab functions as a suppressor of UV-scale differentiation that potentiates mating cue divergence. These results highlight how a genetic switch can regulate a premating signal and integrate with other reproductive barriers during intermediate phases of speciation.
Subject(s)
Butterflies/genetics , Butterflies/radiation effects , Genes, Switch , Iridescence/genetics , Sulfur/chemistry , Ultraviolet Rays , Animals , CRISPR-Cas Systems/genetics , Chromosomes/genetics , Genes, Insect , Genetic Loci , Insect Proteins/genetics , Insect Proteins/metabolism , Iridescence/radiation effects , Male , Sexual Behavior, Animal/physiology , Species Specificity , Sympatry/genetics , Wings, Animal/metabolismABSTRACT
PURPOSE: We report a previously unrecognized mechanism of secondary glaucoma due to iridescent crystalline particles released from an irradiated iris melanoma. It masqueraded as refractory hypertensive uveitis following uncomplicated phacoemulsification. MATERIALS AND METHODS: A 58-year-old gentleman had an iris melanoma that underwent successful regression following irradiation with proton beam radiotherapy. Three years later an uncomplicated phacoemulsification with intraocular lens implant was performed and subsequently the patient presented with apparently "refractory hypertensive uveitis." Closer examination identified unique iridescent crystalline particles originating from a disintegrating tumor and dispersing within the anterior chamber and drainage angle. The patient developed a unilateral secondary open-angle glaucoma attributable to these particles. Ultrasound biomicroscopy of the anterior segment confirmed absence of tumor recurrence or intrascleral spread and systemic investigations ruled out distant metastases. RESULTS: The intraocular pressure was refractory to maximal medical treatment, but was eventually controlled with trans-scleral diode laser cyclo-photocoagulation. CONCLUSIONS: This is the first report of a secondary glaucoma attributable to trabecular blockage with iridescent crystalline particulate material released from a disintegrating, previously irradiated, iris melanoma. Proton beam radiotherapy and possibly phacoemulsification may have played a role in triggering the release of these previously undescribed particles from the atrophied tumor surface. This unique mechanism of secondary glaucoma needs to be kept in mind in such rare cases. Trans-scleral cyclodiode laser may be used as a good initial option in such cases to minimize potential risk of tumor seeding with incisional glaucoma surgery.
