EEB382 mclennan lec 1.pdf

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University of Toronto St. George
Ecology & Evolutionary Biology
Deborah Mc Lennan

EEB382 Lec 1- D. Mclennan October 26, 2012 PHOTON acts like a WAVE: transfer of energy AND transfer of mass (i.e a person standing in a stadium transmitting 'the wave' stays in one place, but transfers energy) - in water, complicated vision light: long wavelengths (red/orange) absorbed: takes away from environment - anything organic takes out short ones (blues/purples) - algae absorbs most of the wavelengths (reflects green) - SCATTERING: - small molecules scatter blue light, thus we see sky as blue (blue is a short wavelength) (just like water with water molecules-scatters short wavelengths) - light scattered from many different things and hits the fish's eye - creates THE VEILING EFFECT and makes everything look cloudly-you lose images because of big droplets of water in fog (scattering wavelengths of light) - fish: spend entire life swimming through fog - different wavelengths that dominate in different aquatic backgrounds - 100m down: nothing left but blue (all long waves absorbed at top) - thus deeper you go, the bluer the light becomes. ABSORPTION OF PHOTONS: - organic matter- blue - water- orange and red - plants- everything except green - below about 30m, not very much light left PEAT BOGS (black water?): - a lot of decay - tannic acid or tannin (distinct red-brown water from tea for example) - absorbs a lot of short wavelengths of light - light doesnʼt penetrate more than 3 or 4 metres - background shifted to red-brown, long wavelengths i.e. Rio Negro (?): in Brazil where two rivers come together and flow for 15 km together, separated: 2 completely different visual environments (black water on one river) Aquatic Ecosystems are visually complicated- depends on whatʼs present in water, time of day. FISH EYE PHYSIOLOGY: - middle of iris= pupil (where light enters) - we can contract/expand pupil - lampreys- can expand/contract pupil a bit (round pupil) - ray-finned fish- canʼt expand/contract at all (thus can only move away or towards the light to adjust to light in their environment) (Actinopterygii), thus behavioural modifications - sharks- complicated pupil: different pupil shapes- round, horizontal, etc. i.e. fin rays-flap of tissue over eye (not studied) - i.e. deep sea sharks: donʼt have ability to change pupils-fixed (not light to adjust to) - i.e. spiny dogfish: travels up and down, even if 200m down, pupils can adjust, but pupil doesnʼt expand very quickly: takes 30 minutes vs. us (Takes few minutes), but pupil contracts very quickly - back to eye physiology: - i.e. eye= bag of water and needs covering: CORNEA, holds eye together - f(x) of eye: focus light rays at back of eye to form an image EEB382 Lec 1- D. Mclennan October 26, 2012 - Terrestrial animals: cornea focuses, light waves bend behind cornea because filled with water (i.e. rainbow- refraction of water droplets in air) - Aquatic animals: light transfer from fluid to fluid - ray finned fishes= spherical LENSES(ours is elliptical), theyʼve no cornea to help them and thus need to really focus light, thus spherical (high refractive index). - gets really thin or really fat- lens changing shape very quickly (as you get older, lens crystallizes, becomes harder to focus) - i.e. sharks: donʼt have round lens, theyʼve a ligament that holds lens in eyeball (move lens in eye forward/backward). - sharks/teleosts donʼt focus very well - i.e. study: different focus fish vs. humans v.s lizards (fish not able to focus due to being in water having no cornea to focus light) - TAPETUM LUCIDUM: guanine crystals- ray finned fishes/sharks have this at back of eye (weʼve lost it however), thus layer of reflective crystals in eye, eye missed by retina, hits layer of crystal and reflects back to retina again. Same in cats. (i.e. eye shine, shine bright light at tarpetum lucidum and shines back at us) - (i.e. red eye: flash is so intense and close, goes straight to eye, and rebounds at back of eye, and absorbs all wave lengths and reflects red back (dense blood supply at back of eye) - PHOTO RECEPTORS IN RETINA: tissue at back-photoreceptor cells - rods: long and thin--photopigment at very top (stacked pancakes) - photon counters, they respond to NUMBER of photons- respond equally to different wavelengths - BETTER at low light (deep water: fish have more rods)--look at light vs dark
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