Last weeks excuse for some hearty biscuit eating and sometimes on-topic science chat was a recent paper on prey choice in fish by Miller and Pawlik published in the latest edition of Animal Behaviour.
Using prey choice experiments the authors found that bluehead wrasse (Thalassoma bifasciatum) were able to learn to avoid unpalatable prey based on visual cues. They also showed that by continually testing prey for palatability the fish were able to constantly assess the reliability of learned cues and consequently rapidly adapt to changes in prey appearance and edibility.
Specifically the bluehead’s were able to learn and remember unpalatable or palatable prey using some colours (red, blue and orange) but not others (yellow, purple, white and green), irrespective of prey position within the tank. They were also shown to have a pre-experimental bias against all the aforementioned colours of prey and avoided yellow, purple and green coloured prey whether they were palatable or not. In a reversal experiment the fish then overcame a pre-experimental bias against red prey when it was no longer unpalatable.
The authors suggest that the bluehead’s inability to learn prey palatability from certain colours was most likely due to limitations in visual system sensitivity. They also postulate that the bluehead’s ability to adapt quickly to changes in the appearance of defended prey, particularly in comparison to terrestrial predators, is due to the huge variation in the palatability of brightly coloured prey, i.e. absence of consistent truly aposematic colouration and complex mimicry schemes among marine invertebrates.
While we all agreed that it was a neat experiment, the first of its kind for fish! We were divided on whether we would extrapolate from the results of such an artificial experiment to the same extent that the authors did – an age old debate in biology but one still always worth discussing (see Ecotron refs below). The point was made that firstly only one fish species was tested and though this generalist fish is ubiquitous throughout the Caribbean, the individuals were then taken from only one population. Other more specialist predators for example may react to prey colouration and palatability in different ways.
We also discussed what experiments we would carry out following on from this study. One suggestion was to look at whether the early environment of fish would affect their behavioural development. That is, whether fish maturing in a really super diverse and colourful environment with high prey diversity would develop more flexible prey choice strategies than fish maturing in a low diversity and/or low colour variability environment and also whether this would affect any pre-experimental biases towards colour.
Also as this study was on coral reef fish the discussion strayed to differences in tropical and temperate fish colouration. This then lead to an interesting conversation about the high number of colourful animals in the tropics in comparison to temperate climates and possible causes. Links to biodiversity, light wavelengths and intensity of light, niche number and higher number of toxic animals were all suggested. Unfortunately at this point we ran out of biscuits so the issue will remain unsolved ……………… …………until next week.
Miller, A., & Pawlik, J. (2013). Do coral reef fish learn to avoid unpalatable prey using visual cues? Animal Behaviour, 85 (2), 339-347 DOI: 10.1016/j.anbehav.2012.11.002
Daehler, C., & Strong, D. (1996). Can You Bottle Nature? The Roles of Microcosms in Ecological Research Ecology, 77 (3) DOI: 10.2307/2265487
Fraser, L., & Keddy, P. (1997). The role of experimental microcosms in ecological research Trends in Ecology & Evolution, 12 (12), 478-481 DOI: 10.1016/S0169-5347(97)01220-2
Lawton, J. (1995). Ecological Experiments with Model Systems Science, 269 (5222), 328-331 DOI: 10.1126/science.269.5222.328