TitleConspicuous visual signals do not coevolve with increased body size in marine sea slugs
Publication TypeJournal Article
Year of Publication2014
AuthorsCheney K.L., Cortesi F., How M.J., Wilson N.G., Blomberg S.P., Winters A.E., Umanzoer S., Marshall N.J.
Volume27
Pagination676-687
Date PublishedApr
Type of ArticleArticle
ISBN Number1010-061X
Accession NumberBIOSIS:PREV201400333474
Keywords01500, Evolution, 07508, Ecology: environmental biology - Animal, 07512,, 64026, Invertebrata:, adaptation, Animals, Invertebrates, Mollusks, comparative, experimental morphology, physiology and pathology -, Ecology: environmental biology - Oceanography, Evolution and, Gastropoda [61200], Marine Ecology (Ecology, Environmental Sciences), Mollusca, Mollusca, Invertebrata, Animalia, thermoregulation, chemical defence, spectral sensitivity, conspicuous, visual signal, predatory selection pressure, [slug] [nudibranch] [opisthobranch]
AbstractMany taxa use conspicuous colouration to attract mates, signal chemical defences (aposematism) or for thermoregulation. Conspicuousness is a key feature of aposematic signals, and experimental evidence suggests that predators avoid conspicuous prey more readily when they exhibit larger body size and/or pattern elements. Aposematic prey species may therefore evolve a larger body size due to predatory selection pressures, or alternatively, larger prey species may be more likely to evolve aposematic colouration. Therefore, a positive correlation between conspicuousness and body size should exist. Here, we investigated whether there was a phylogenetic correlation between the conspicuousness of animal patterns and body size using an intriguing, understudied model system to examine questions on the evolution of animal signals, namely nudibranchs (opisthobranch molluscs). We also used new ways to compare animal patterns quantitatively with their background habitat in terms of intensity variance and spatial frequency power spectra. In studies of aposematism, conspicuousness is usually quantified using the spectral contrast of animal colour patches against its background; however, other components of visual signals, such as pattern, luminance and spectral sensitivities of potential observers, are largely ignored. Contrary to our prediction, we found that the conspicuousness of body patterns in over 70 nudibranch species decreased as body size increased, indicating that crypsis was not limited to a smaller body size. Therefore, alternative selective pressures on body size and development of colour patterns, other than those inflicted by visual hunting predators, may act more strongly on the evolution of aposematism in nudibranch molluscs.