Evolution of colour vision in relation to colouration in weaverbirds (Family Ploceidae) and poison dart frogs (Family Dendrobatidae)
Of an organism’s physical traits, colouration is arguably one of the most important for biotic interactions and general fitness. Colouration can provide or deny critical information in mate choice and rival assessment, individual and species recognition, predator avoidance, prey acquisition, and other major behavioural decisions. The ability to capitalize on colour signals and cues therefore grants a large fitness advantage, making vision and especially colour vision a key sensory modality for many taxa. It might therefore be expected that colouration, especially of conspecifics, could be a driver of the evolution of colour vision. This thesis explores the impact of colouration on the evolution of colour vision in two separate study systems: weaverbirds (Family Ploceidae) and poison dart frogs (Family Dendrobatidae). In both systems, colouration is used to assess sexual rivals and/or potential mates, making assessing colouration or distinguishing between colours a crucial ability. Both systems also feature multiple colour morphs within and across species, allowing for intra- and interspecies comparisons of colour vision in regard to colouration. Male weaverbirds seasonally express bright red or yellow nuptial colouration, while females maintain drab colouration year-round. Gene expression of key visual and vision-related genes, including opsin genes, was compared between sexes and seasons in the southern red bishop (Euplectes orix) and cape bishop (Euplectes capensis) using qRT-PCR. Sequences for the same four opsin and two vision-related genes were compared across a dataset of 70 ploceid species of various colours. Neither analysis found strong evidence for a relationship between colouration and colour vision. Opsin gene expression and gene sequence were also compared within and between three dendrobatid species with similar red-green polymorphisms. The opsin gene sequences were very highly conserved, with no colour vision-impacting nucleotide substitutions. The opsin expression analysis revealed some colour-based differences in the strawberry poison dart frog, but the expected influence of these differences on colour vision is subtle. However, in the multispecies comparison, gene expression varied more by species than by colour, indicating other evolutionary drivers are in play. Overall, this thesis finds little evidence that colouration is a driving factor in the evolution of colour vision in weaverbirds or poison dart frogs. Minor differences occur in relation to colour, but their effect on colour vision is limited. These findings suggest that evolution of colour vision is primarily influenced by other aspects of the environment, or that if colouration does influence colour vision, it does so as part of a more complex combination of selection pressures.
Colour Vision, Evolution, Poison Dart Frogs, RNAseq, Spectral Sensitivity, Weaverbirds
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