Anna Fabrizio

3/9/10

University of Washington

School of Aquatic and Fisheries Sciences

Chemotaxis and foraging behavior in Octopus rubescens

Octopus physiology

• octopuses are known to have well developed vision, often used for hunting

• many octopuses live in habitats where vision is compromised

• many octopuses prey on organisms that don’t move

• octopus suckers are used for sensing “taste”

• most sensitive at the tips of arms

Octopus foraging behaviors

• 2 primary foraging behaviors:• Poke/grope• Web-over

• Both are primarily tactile in nature, but dependent on visual range

(Forsythe and Hanlon, 1995)

Web-over

Web-over

Web-over

Web-over

Octopus chemotaxis

• little research done on distance chemotaxis in octopuses

• Chase and Wells (1986)

• Blind octopuses responded to and were able to sense the general direction of chemicals in the water

• Lee (1992)

• Octopuses in Y-maze responded to specific chemical direction

• research has been done on tactile/taste discrimination by octopuses (Wells 1962)

Objective

• to expand on previous chemotaxis studies by analyzing octopus reaction to live prey

• Octopus rubescens has not been used for chemotaxis studies in the past

Behavioral experiments

Experimental tank set-up

T-wall

boxes

barrier wall

Behavioral experiments

Results

• 19 trials performed: 8 blind, 11 visual

• 1 blind trial resulted in a choice (crab)

• 6 visual trials resulted in a choice

• all chose the crab

• Behavior observations

• more response to crabs during visual trials

• color change, active motion

What does this mean?

• Can we confidently determine that octopuses CAN use distance chemotaxis from previous studies done with chemicals alone?

• Natural foraging behaviors show little evidence for the use of distance chemotaxis

• But what about circumstances that compromise vision?

Stressed out crabs

• During trials, crabs also exhibited different kinds of behavior

• when crabs could see the octopus, they held very still but were obviously in distress

• Do octopuses respond more frequently to stressed crabs than non-stressed crabs?

• Is there a physiological difference between stressed/non-stressed crabs?

Prey analysis – Hemigrapsus oregonensis

• Purpose: analyze shore crab RNA/protein to see if they express something that octopuses would respond to

• Techniques:

• SDS/PAGE

• PCR

• Specifically looking at stressed vs non-stressed

• stressed, immersed crabs excrete excessive ammonia, waste, carbon dioxide

Procedure

Protein analysis

• protein fixation and extraction from gill tissues

• SDS-PAGE gel

C2 C3 C4 C5 C6 S1 S2 S3 S4 S5 S6

ResultsGenetic analysis

• RNA fixation and extraction from gill tissues

• reverse transcription -> cDNA

• 4 primers, 3 genes – Carcinus maenas:

• CHH and CHH precursor 6: hormone expressed under stress

• Metallothionein: cysteine-rich protein that helps reduce oxidative stress

• Na+/K+ - ATPase: enzyme that helps regulate ammonia excretion

Genetic analysis

• further study into the significance of stress on prey and the ability of octopuses to find them

• more extensive research on distance chemotaxis with live prey

Future possibilities

Acknowledgments

Steven Roberts, Sam White, Mackenzie Gavery

Tim Carpenter, Kathryn Kegel

- Roberts lab

- Seattle Aquarium