Zool 250
Best Annotated Bibliography 2009
Submitted by Nicole Severin


Kozmick, Z., J. Ruzickova, K. Jonasova, Y. Matsumoto, P. Vopalensky, I. Kozmikova, H. Strnad, S. Kawamura, J. Piatigorsky, V. Paces, and C. Vlcek. 2008. Assembly of the cnidarian camera-type eye from vertebrate-like components. Proceedings of the National Academy of Sciences of the United States of America 105: 8989 - 8993.

Box jellyfish (Tripedalia cystophora) are noted for their highly sophisticated visual equipment, atypical of other invertebrates. In addition to the two pit-shaped and two slit-shaped pigment eye cups present in each rhopalium, T. cystophora also have two camera eyes made up of a cornea, retina, and lens. Their molecular components have been found to closely resemble those of vertebrates, spurring the question: Does this similarity between cubozoan eyes and vertebrate eyes imply convergent evolution or common ancestry?

In this study, genetic and spectroscopic analyses were used to evaluate the eye components of T. cystophora. The retina was found to be comprised of ciliary photoreceptors that utilize c-opsins and a phosphodiesterase (PDE) cascade, which are characteristic of vertebrate eyes. Melanin was discovered to be the exclusive dark pigment, as in vertebrate eyes, although the photoreceptor and pigment functions operate in a single cell in T. cystophora. In addition, both cubozoans and vertebrates share a surprising number of genes, as well a crystalline lens; however, vertebrates use different transcription factors and taxon-specific proteins in the recruitment of the crystalline lens.

Using the principle of parsimony, Kozmik et al. conclude that, despite the incredible similarity between molecular eye make-up, the visual systems in cubozoans and vertebrates are likely the results of independent recruitment and parallel evolution. Regardless, this provides some interesting implications as to the development of the eye in evolutionary history, and leads to the suggestion that the primitive cup-like eyes on the cubozoan's rhopalium were the precursor to camera eyes.

(251 words)


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(posted Dec. 22 2010)