Spectral transmission of the principal-eye corneas of jumping spiders: implications for ultraviolet vision

Abstract

SUMMARYUltraviolet (UV) vision plays an important role in interspecific and intraspecific communication in many animals. However, UV vision and its adaptive significance have been investigated in only approximately 1% of more than 5000 species of jumping spiders (Araneae: Salticidae), renowned for their unique, complex eyes that support exceptional spatial acuity and visually based behaviour. To appreciate the adaptive significance of UV vision, it is important to establish whether salticids can perceive UV and whether the perception of UV varies with ecological factors such as light environment. In this study, we measured the UVtransmission properties of the principal-eye corneas of 128 salticid species. We found that the corneas of all measured species were able to transmit UV light, making the perception of UV possible. Three classes of corneal spectral transmission curves were identified; the majority of species had a Class II curve with a less-steep slope and a gradual onset of the transmission cut-off; all the remaining species had a Class I curve with a very steep slope and a sharp cut-off except for one species that had a Class III curve with an intermediate step, which appeared as a shoulder on the descending part of the transmission curve. The T 50 cut-off transmission values (the wavelength at which 50% of the maximum transmission is reached) in salticid corneas vary with species and light habitat. The corneas of species inhabiting open bush had a higher relative transmission at short wavelengths in the UV than forest species. This is the first investigation of corneal transmission in spiders and suggests that UV perception is widespread in salticids.

The spectral transmission of non-salticid spider corneas

“…the crab spider E. tricuspidata; Table 1), spiders inhabiting forest shade and burrows where there is a lower level of illumination or a shift in the ambient light spectrum to longer wavelengths tended to have corneas with a higher T 50 cutoff value than those living in open areas, where there are high levels of sunlight. This is consistent with the salticids that have already been examined (Hu et al, 2012).…”

“…Our recent study has also shown that the spectral transmission of salticid corneas varies with light habitat (Hu et al, 2012): the corneas of salticids inhabiting open bush have a higher relative transmission at short wavelengths in the UV spectrum than do species living in the forest. Non-salticid spiders also live in a wide range of habitats that differ greatly in photic conditions.…”

“…Some salticids are known to have photoreceptors sensitive to UV (Harland et al, 2012) and UV-transmitting corneas are widespread in salticids (Hu et al, 2012). By measuring the corneal transmission of the eyes of 38 non-salticid spider species belonging to 13 families, we found that the corneas of the majority of the species transmitted UV wavelengths below 400 nm, with a range from 306 to 381 nm.…”

“…Any consideration of UV vision in animals must therefore take into account the spectral transmission properties of their ocular media (e.g. Siebeck and Marshall, 2000;Siebeck and Marshall, 2001;Siebeck and Marshall, 2007;Hu et al, 2012). Previous studies of ocular media transmission have almost exclusively been conducted on vertebrates, particularly on fishes, and have documented considerable variations in lens and corneal transmission properties (e.g.…”

“…A recent study measuring the UV transmission properties of the principal-eye corneas of 128 salticid species revealed that the corneas of all species examined transmit UV light above 290 nm (Hu et al, 2012). With about 40,000 species of non-salticid spiders (Platnick, 2014), measuring the spectral corneal transmission may be a quick way to assess the possibility of UV vision in a large number of species (Siebeck and Marshall, 2000;Siebeck and Marshall, 2001;Siebeck and Marshall, 2007).…”