Meeting Abstract
At macroevolutionary timescales, do novel behaviors evolve through reuse and tinkering of pre-existing underlying components? We asked whether deep homology of a dispersed light sense in mollusc mantle may have contributed to the evolution of Light-Activated Chromatophore Expansion (LACE), a novel behavior of the colored chromatophore organs in octopus skin. Opsins are the primary way animals sense light, and we have previously hypothesized that LACE uses the same r-opsin phototransduction cascade to sense light as octopus eyes. We surveyed the literature and 45 publicly available mantle transcriptomes from major molluscan lineages for the expression of opsins and related cascade genes. R-opsin cascade genes are expressed in the mantles of 18 species from 5 molluscan classes. We combined these results with mantle expression data from the literature, bringing our total count of r-opsin expressing mantles to 21. The broad distribution of r-opsin expression in mantle across molluscs suggests that ancestral cephalopod skin likely sensed light before chromatophore organs evolved. The molecular basis for light sensing, r-opsin phototransduction, is already known as a deep homology, since r-opsins arose by the last common bilaterian ancestor. Our results are consistent with the hypothesis that the dispersed light sense in the mantle is also deeply homologous and pre-dates the origins of cephalopod chromatophores and their LACE behavior in response to light, suggesting that deep homology and co-option may be important for macroevolution of behavior.
