Transparency

• Provides camouflage

• Involves the whole organism

• Has evolved multiple times

The outcome of a predator/prey interaction depends on:

Sighting distance = the maximum distance at which a prey animal is detected by an animal relying on visual cues

Transparency allows:a) Prey with short sighting distance reduce their

encounters with visually orienting prey

c) Raptors to get within striking distance before being detected

b) Ambush predators with short sighting distance to increase chances of entangling prey before being detected and avoided

UV (~320nm)

Predator solutions to catching transparent prey…

1. UV visionfound in mantis shrimp,

cladocerans, copepods, decapods, horseshoe crabs, and even a polychaete worm!

2. Polarization visionlight is polarized when it enters water

Unpolarized light Polarized light

http://oceanexplorer.noaa.gov/explorations/04deepscope/logs/aug12/aug12.html

The Great Barrier Reef taken through a polarizing filter held in front of the camera horizontally, vertically, and at 45º.

The fourth image is coded with color to show that much of the water is horizontally polarized (coded here as red). By Justin Marshall and Tom Cronin

http://oceanexplorer.noaa.gov/explorations/04deepscope/background/polarization/polarization.html

Polarized vision – view of a copepod through…

unpolarized light polarized light

Polarization vision helps detect transparent preyShashar, Hanlon, Petz, Nature 1998,

Whale shark• filter plankton using gill rakers

Blue whale – feeding• ‘gulp’ feeders – sieve plankton through sheets of baleen• ~ 3,600 kg drill/day for about 120 days

Pharynx (branchial basket)

Ascidian (tunicate)

(Ph. Urochordata)

atrium

Branchial baskets For feeding & locomotion

Shared tunic

Direction oflocomotion

Water jet

(Ph. Urochordata – Cl. Thaliacea)

Larvacean

(Ph. Urochordata – Cl. Larvacea)

Tadpole larva

tailtail

pharynx

water current

water current

pharynx

Larvacean in its mucous house

Mucous house:

• secreted by the trunk epidermis

Water:

• food is concentrated and passed to the pharynx

• Filtered water exits, jetting the house forward.

Oikopleura – Mucous house

Outer filter

Food concentrating filter

Copepods ‘shape’ their fluid motion either to advertise or conceal themselves in the plankton. HOW does this work?

Imaged with Schlieran photography

2. When it ‘hovers’ it creates a laminar feeding current using fine setae on the second antennae. this disturbance appears as lines of

equal speed of fluid: these are called isotachs.

1. As the copepod moves through water it creates a fluid disturbance.

“Organizing the fluid medium”:

3. The sensors on the antennae detect changes in speed of the isotachs in three directions and so the copepod can detect water-borne signals in 3 dimensions:

x, y, z and a fourth dimension, time.

Euplokamis: ctenophore

tentillum

tentillum