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Extensive research has been done to date on Drosophila and Tribolium eye development; however, not much is known about the molecular basis of development of extremely reduced and modified eyes in cave insects. Ptomaphagus hirtus represents an emerging model system for studying the changes at the molecular level that occurred during the evolutionary adaptation of the eye to the cave environment. Therefore, I have started exploring the morphology and organization of the reduced P. hirtus eyelet, using immunohistochemistry, laser scanning microscopy, and ultrastructural imaging approaches. My findings demonstrate that the adult eyelet lacks ommatidial subdivision and has a thick, clear cuticular lens that covers a cuticle cup that surrounds a population of approximately 130 randomly distributed unpigmented photoreceptor cells. I have evidence that the P. hirtus eyelet assembles before the onset of pupation. Interestingly, in contrast to the developmental time frame of lens secretion during the pupal stage in the compound eye of surface insects, lens deposition in P. hirtus occurs during the first 11 weeks of early adult development. To the best of my knowledge, this is the first example among insect species of postembryonic adult lens addition to the already formed eye. In sum, I speculate that retention of photoreceptor cells in the P. hirtus eyelet represents an adaptive evolutionary trait to the cave environment, in contrast to the non-adaptive adult lens deposition. Together my findings raise interesting questions that can be further addressed by future experiments.
Kulacic, Jasmina, "Developmental Evolution Of The Visual System In The Cave-Adapted Small Carrion Beetle Ptomaphagus Hirtus" (2015). Wayne State University Theses. 437.