1 7 2 Sensory Systems Polarized Vision Magnetoreception Thermoreception BIO 361T Fall 2014 1 When Saharan desert ants forage for food they leave the nest and wander until they locate a food item They then carry the food item in a straight path back to their nest Come up with two hypotheses as to how an ant could take a meandering outbound path and return on a direct path Count number of steps for distance integrated with sun compass for direction Wittlinger et al 2006 However goal of this question is not to come up with the right answer it is to consider sensory input and desired output and create plausible mechanisms that connect the two Actual mechanism will be covered in discussion 2 Design an experiment to test each of your hypotheses including proper controls to eliminate potentially confounding variables factors that may affect navigation orientation but are not the focus of your study and methods for measuring outcomes Altered step length by gluing pig bristles or clipping legs same number of steps will go either more or less distance train ants to travel particular path in the lab without any visual or olfactory cues after outbound journey alter leg length measure length of inbound journey Again goal is not to explain how step counter or sun compass work It is to consider experimental design and confounding factors Simply stating control the environment is insufficient This is a non trivial issue What do you need to control How will you do it You are not done designing your experiment until you could give me a list of supplies you ll need to conduct it 3 Why do you think there has been selection for this efficient navigation behavior In the Sahara there is a narrow window between when it is cool enough for predators to be abundant and when it is hot enough to kill the ants Further why do you think selection in desert ants is stronger than other ants 2 4 In addition to detecting polarized light and magnetic fields come up with five other mechanisms types of information by which an animal could infer distance traveled direction traveled or both Explain each of your answers including whether any limitations like mode of locomotion habitat weather etc Optic flow honeybees Counting steps desert ants Energy expended tested in desert ants by varying load carried Leaving chemical trails Visual landmarks mostly for flying animals Olfactory landmarks Trails left by conspecifics limited to group living animals Taught by experienced individuals Follow other organisms that have directional patterns such as food plant growth or migratory prey 5 Insects have hygroreceptors that detect environmental humidity and surface wetness which provide important cues for reproduction and survival Humans on the other hand have no receptors for detecting wetness or humidity that we know of Given what you know about sensory systems how do we detect humidity How do we detect wetness A combination of thermoreception specifically cool thermoreception and tactile mechanoreception Think of evaporation which carries heat away with it leaving your skin relatively cooler In combination with differential wind movement of skin and hair on skin we perceive this as drier Also consider moving your hand across a wet table How do you know it s wet Evidence of wetness reception being a combination of cool thermoreception and tactile reception As something gets colder we can detect its wetness better Hairy skin has more thermoreceptors than glabrous non hairy skin Would you expect to be able to detect wetness more on the top of your forearm or with the tip of your finger Filingeri et al 2014
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