Damsels in a hidden colour: development of ultraviolet sensitivity and
colour patterns in damselfishes (Pomacentridae)
Abstract
Damselfishes (Pomacentridae) are widespread and highly abundant on
tropical coral reefs. They exhibit diverse body colouration within and
between the ~250 species and across ontogenetic stages. In
addition to human visible colours (i.e., 400-700 nm), most adult
damselfishes reflect ultraviolet (UV, 300-400 nm) colour patches. UV
sensitivity and UV colour signals are essential for feeding and form the
basis for a secret communication channel invisible to the many UV-blind
predatory fish on the reef; however, how these traits develop across
ontogenetic stages, and their distribution across the damselfish family
is poorly characterised. Here, we used UV photography, phylogenetic
reconstructions of opsin genes, differential gene expression analysis
(DGE) of retinal samples, to investigate the development of UV vision
and colour patterns in three ontogenetic stages (pre-settlement larval,
juvenile, and adult) of eleven damselfish species. Using DGE, we found
similar gene expression between juveniles and adults, which strongly
differed from larvae. All species and all stages expressed at least one
UV-sensitive sws1 opsin gene. However, UV body colour patterns only
started to appear at the juvenile stage. Moreover, Pomacentrus species
displayed highly complex UV body patterns that were correlated with the
expression of two sws1 copies. This could mean that some damselfishes
can discriminate colours that change only in their UV component. We
demonstrate dramatic shifts in both UV sensitivity and UV colouration
across the development stages of damselfish, while highlighting the
importance of considering ontogeny when studying the coevolution of
visual systems and colour signals.