Getting Started

2. Getting Started • Initial interests: • Sensory system adaptation to a particular environment • Field research  field intensive • Not brittle stars • why the lightfoots? • Initial observations indicated that the organism had a sophisticated sensory system • Quick response • Alert behavior • Environment • Presents unique and identifiable adaptive challenges to the organism

3. Sally Lightfoot (GrapsusGrapsus) • Background • Beige to grey grapsoid crab • Coloration changes with age and gender • Up to 4 inches in carapace width • Found in water as well as in the tidal rocks • Environmental Pressures • Predation: birds • Food Source: algae and small invertebrates • Shifting water level and high winds

4. Getting Crabs • Sally Lightfoot’s were collected on the western side of North Point • Were found on all three geological tide zones • Camouflaged well on the rock  crab vision needed • Exceptional level of alertness and evasive strategy • Always spotted us first • Moved so as to face the threat at all times • Knew exactly where to run... even when cornered • Going into cracks and jumping in the water .

5. Formulating a Research question • Observations of crab environment and behavior led to the formulation of a research question: • Which sensory system is primarily responsible for the exceptional alertness of a sally lightfoot? • Hypothesis:the primary sensory system involved should be the visual system. • Based on environmental pressures: • Predation • Wind/waves • Movement • By comparing responses to different sensory stimuli, a primary sensory system canbe identified • Vision • Audition

6. Discussion • Summery of Results • Visual stimuli – light condition: high response frequency to the stimuli indicating a clear sensation of the visual stimuli being presented • Significant difference from the control condition • Individual variability in response type – based on size/gender? • Visual stimuli – Moonlight Condition: low frequency of response, not significantly different from control condition. • Occasional response indicates a reduced visual acuity in dim light conditions • Were found in the darkest part of the container • Auditory Stimulus: no response elicited, no significant difference • crabs seem not to respond to an auditory stimulus • Visual stimuli - Ablated Eye Condition: no response • Serves as a good control • Tactile Stimuli: high response frequency

7. Discussion cont. • Implications: • High frequerncy of response to visual stimuli (light condition) indicates that this sensory system is used by the organism to sense its enviornment. • Crabs saw us and hid themselves long before we saw them, this sense is also useful in evading their main predator the osprey. • High visual acuity may suggest a high population of cones in crab eye • Reduced response under dim conditions suggests that this species is diurnal and has the ability to sense contrast. • High population of cones in the eye would lead to reduced vision in dim light • ability to sense contrast useful when finding shelter in holes • Reduced activity of predators at night reduces need for visual processing

8. Discussion cont. • Implications: • Crabs with Ablated eyes did not respond to the visual stimuli • Indicates that the visual system is responsible for the responses observed in the field and in the lab • Auditory stimulation failed to elicit response • Audition is not an effective sense in a loud environment • Tactile stimulation elicited a strong response indicating the importance of this sense • practical importance of this sense is marginal compared to vision

9. Further research • The refined visual system of the Sally lightfoot warrants more investigation: • Mapping of visual field: observed a difference in response depending on angle of approach • Response Variability: differences in response to visual stimuli were observed to depend on size and gender