The geographical variation in colouration-based behaviours of the Arabian killifish (Aphaniops dispar)

Animal colouration promotes essential biological functions, including sociosexual communication, thermoregulation, prey-predator interaction and protection from harmful radiation, which may be under conflicting pressures. One common technique to cope with colouration-based competing demands is colour change. However, colour change is susceptible to opposing selection pressures and varies intricately throughout taxonomic levels, and many areas remain unresolved, including how it evolves and interacts with other behaviours. In this thesis, I studied the geographical variation of colour change and its interaction with habitat preference in freshwater and marine populations of the Arabian killifish (Aphaniops dispar). In Chapter 2, I explored the taxonomic status of the species by examining morphometric, colour pattern and phylogenetic differences among populations. In Chapter 3, I examined the geographical variation of the achromatic and chromatic colour change and assessed their importance in conferring crypsis. In Chapter 4, I investigated the interaction between achromatic colour change, habitat preference and camouflage, and how these aspects varied between populations. The findings from Chapter 2 revealed distinct phylogenetic groups that were difficult to identify using morphometric and colour pattern analyses. The results from Chapter 3 indicated that all populations showed a greater ability to change colour achromatically, specifically becoming dark, which enhanced their camouflage. However, the chromatic colour change was more complex and varied within and between populations, but the marine populations generally showed greater chromatic responses than their freshwater counterparts. The outcomes of Chapter 4 showed that when given the choice between multiple achromatic substrates, the freshwater and marine populations did not change colour and displayed a similar habitat preference for darker substrates, despite being uncamouflaged against them. These findings highlight the importance of studying variation in colour change at the population level to understand its evolution at higher levels.