Abstract
Damselfishes (Pomacentridae) are one of the most behaviourally diverse,
colourful and species rich reef fish families. One remarkable
characteristic of damselfishes is that they communicate in ultraviolet
(UV) light. Not only are they sensitive to UV they are also prone to
have UV-reflective colours and patterns enabling social signalling.
Using more than 50 species, we aimed to uncover the evolutionary history
of UV colour and UV vision in damselfishes. We find that all
damselfishes had UV-transmitting lenses, expressed the UV-sensitive
SWS1 opsin gene, and most displayed UV-reflective patterns and
colours. We find evidence for several tuning events across the
radiation, and while SWS1 gene duplications are generally very
rare amongst teleosts, our phylogenetic reconstructions uncovered two
independent duplication events, one close to the base of the most
species-rich clade in the subfamily Pomacentrinae, and one in an
individual Chromis species. Using amino acid comparisons, we found that
known spectral tuning sites were altered several times in parallel
across the damselfish radiation (through sequence change and duplication
followed by sequence change), causing repeated shifts in peak spectral
absorbance of around 10 nm. Pomacentrine damselfishes expressed either
one or both copies of SWS1, likely to further finetune UV-signal
detection and differentiation. This highly advanced and modified UV
vision among damselfishes, in particular the duplication of SWS1
among Pomacentrinae, might be seen as a key evolutionary innovation that
facilitated the evolution of the exuberant variety of UV reflectance
traits and possibly the diversification of this coral reef fish lineage.