Ecological and molecular insights into the function of colourful signals in aquatic environments

Discovering the processes that drive the emergence of new species and connecting it to biodiversity in its past, present, and future form has been one of the central questions of natural scientists for over a century. Two ways in which we can start to unravel the mechanisms that have created such diversity is to investigate: 1) the selective pressures that can initiate/drive and 2) the molecular capacities allowing evolutionary changes to happen. A convenient approach to study how environmental cues and molecular processes are linked to appearance is by investigating the emergence of similar phenotypes, whether they evolve in response to likewise selective pressures and/or in response to molecular or developmental constraints. Here, mimics because they imitate unrelated species (the model), are a classical example in which to study phenotypic convergence.
CHAPTER1 (Published in Current Biology, 2015); Using a combination of behavioural, cell histological, neurophysiological and molecular approaches, the first chapter of my PhD thesis aimed to uncover the triggers for colour change in a small coral reef fish mimic, the dottyback, Pseudochromis fuscus. Yellow morphs are mainly found on live coral in association with yellow damselfish species such as the ambon- (Pomacentrus amboinensis) and the lemon damselfish (P. moluccensis), while brown morphs occur mainly on coral rubble in association with brown damselfishes such as the whitetail damselfish (P. chrysurus). Potential environmental cues that could be associated with colour change therefore included: i) aggressive mimicry, dottyback morphs associate with similarly coloured damselfishes to increase foraging success by preventing detection by juvenile fish prey; ii) social mimicry, differently coloured morphs hide among similarly coloured damselfish to reduce detection and predation risk from their own predators; and iii) crypsis, different coloured morphs match the colour of their background habitat to prevent detection from predators or potential prey.
CHAPTER 2 (Published in The Journal of Experimental Biology, 2016); The second chapter aimed at investigating the triggers for ontogenetic colour changes and how these interrelate to the development of the visual system in dottybacks. Although adult dottybacks were found to be aggressive mimics that change colour to impersonate the colouration of the prevalent damselfish community, little was known about the early life stages of this fish. Using a developmental time series in combination with wild caught dottyback specimens I show multiple colour changes during dottyback ontogeny and link them to crucial life history transitions of dottybacks. Moreover, changes in the visual system were found to precede ontogenetic colour changes, and theoretical fish visual models were subsequently used to investigate the potential benefits of this pattern.
CHAPTER 3 (Published in PNAS, 2015); Work for chapter 3 was done in collaboration with Dr. Zuzana Musilová at the University of Basel and was based on the discovery of multiple novel visual genes (opsins) in the dottyback (Chapter 2), which arose through gene duplications. One of these novel gene duplicates was found in the violet-blue opsin sub-family (SWS2); however, initial reconstruction of the SWS2 phylogeny suggested a much older, non- dottyback specific origin of the duplication event. Therefore, in chapter three we performed a thorough investigation of SWS2 by exploring the evolutionary history of this family in close to 100 fish species representing most fish lineages across the modern fish phylogeny.