Reflector in body photophores of lanternfish Diaphus watasei - functional structure and ecological role for successful - counterillumination
Year: 2020
Type: dissertation
Abstract: AIM: Bioluminescent mesopelagic fishes have pigmented filters on ventral body photophores to match downwelling sunlight at these depths and generally migrate to shallower waters to feed at night.Lanternfishes photophores have exceptional colourless lenses and specular blue-green reflector.Reflector has an unique "honeycomb-like" pattern of hexagon iridophores composed by guanine-like platelets.The aim of this thesis was to analyse the reflector in lanternfish Diaphus watasei and explain the mechanisms to project a successful counterillumination.METHODS: Iridophores platelets were observed under light microscope for morphological analyses.Reflector shape was estimated from histological sections.Extracts of photophores purified luciferase was mixed in a spectrometer with commercial coelenterazine to determine the reaction spectra.Reflection spectra of fresh fishes photophore reflectors was measured under light microscope linked to a spectrometer.Osmoregulation modulation on defrosted photophores was investigated submerging photophores on hypertonic, isotonic and hypotonic solutions.RESULTS: Regular hexagonal shape of iridophores on body photophores was found to be statistically different (p < 0.01, n=50) from all other reflective tissues.Approximated quadratic curves (R 2 =0.95 -1.00) and eccentricity close to 1 (e= 0.98 -1.02) revealed a parabola-like shape of reflector with focus points on photocytes.Diaphus luciferin-luciferase reaction was found to emit λmax= 454 nm.Reflector spectra of fresh photophores revealed variation between 460 -470 nm.On defrosted photophores, reflection spectra is isotonic media (499 -532 nm) were found to be modified to shorter wavelengths on hypertonic media (479 -483 nm).DISCUSSION: Unique regular hexagon allows simultaneous light reflection from all iridophores on the same angle while minimizing gaps and, consequently, light losses.Parabolalike shape of reflector with focus point located on photocytes ensures all the light from photogenic cells is reflected ventrally.Angle of light emission from body photophores in D. watasei matches the vertical angle of downwelling light on mesopelagic depths.Reflector alters luciferin-luciferase reaction spectra to match downwelling sunlight (Paitio et al., 2019).Iridophores are tunable by osmoregulation suggesting reflectors to match light spectra during vertical migrations from dusk to dawn.(Paitio et al., in preparation).In summary, it was found that that Diaphus body photophores achieve successful counterillumination by matching the angle of downwelling light and adapt spectra during vertical migrations.vii viii
Author: José, Paitio
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7145784751