Vision in two sympatric species of pullosquilla (stomatopoda, lysiosquilloidea) living in different depth ranges

Abstract

We examined the visual systems of two species of the lysiosquilloid stomatopod crustacean genus Pullosquilla living sympatrically in waters around the island of Moorea, French Polynesia. P. litoralis lives in bright, shallow environments to a maximum depth of less than 2 m, while P. thomassini occupies depths to at least 37m. By occupying different environments in the same geographic regions, the closely related species pair affords a rare opportunity to examine the effect of photic environment on visual evolutionary adaptation. We quantified retinal anatomy, determined the spectral diversity of visual pigments, and measured the absorption spectra of intrarhabdomal filters in retinas of both species to compare their complements of spectral receptors. The two species were similar in most respects, but the visual pigment in the main retina of P. thomassini had λmax at 467 nm, compared to 509 nm in the corresponding retinal region of P. litoralis. The absorption of visual pigments in Row 3 of the midband, the region of the retina most sensitive to long wavelengths, could not be determined in P. thomassini, but the intrarhabdomal filter of this row was transparent in a shorter‐wavelength region than the Row 3 filter of P. litoralis, implying that long‐wavelength sensitivity in this deeper‐living species is blue‐shifted compared to the shallow‐living species. Overall, the visual system of P. thomassini appears better adapted to life in a dim, spectrally limited world.