Pseudogenisation of the Short-wavelength Sensitive 1 (SWS1) Opsin Gene in Two New Zealand Endemic Passerine Species: The Yellowhead (Mohoua ochrocephala) and Brown Creeper (M. novaeseelandiae)

Perception of ultraviolet (UV) light, mediated by the avian short-wavelength sensitive-1 (SWS1) opsin, is important for birds in a range of functional contexts, including foraging, mate choice, and offspring recognition. The maximum absorption wavelength of avian SWS1 opsins can shift in and out of UV wavelengths because of residue changes at functionally critical positions in the SWS1 second transmembrane domain. Indeed sequencing of a short SWS1 gene 'spectral tuning' coding region allows assignment of avian vision as either ultraviolet sensitive (UVS) or violet sensitive (VS). Here, we report frameshift mutations in the SWS1 'spectral tuning' regions of two endemic New Zealand passerine species: the Yellowhead or Mohua (Mohoua ochrocephala) and the Brown Creeper or Pipipi (M. novaeseelandiae). The findings indicate a total absence of functional SWS1 opsins in these two species in contrast to their congeneric, the Whitehead or Popokotea (M. albicilla) which is predicted to have UVS vision. Associated alternations in light perception might have critical implications for color-associated behaviors in these two Mohoua species, including discrimination of their own eggs from those of the genus' specialist brood parasite, the Pacific Long-tailed Cuckoo or Koekoea (Urodynamis taitensis). In combination with recent evidence for frameshift based loss of opsin functioning in penguins, we suggest that loss of opsin function in avian lineages may be more widespread than previously assumed and may be of adaptive significance.