1. information about the environment and their own body condition through sense organs
1. perception of a signal  is not the same as differentiation among signals
2. it is generally assumed that lack of behavioral response = lack of reception
3. each is excited by a specific stimulus
1. chemical cues ("smell" and "taste")
2. mechanical cues ("touch" and "stretch")
3. auditory cues ("hearing")
4. visual cues ("sight")
2. Chemical cues and chemosensors
1. important in feeding behavior, mating, habitat selection, host selection
2. can be very sensitive to the exact chemical structure of compounds
3. Mechanoreceptors are of three major types
1. stretch receptors detect movement and position, internal and external
2. touch receptors register pressure
3. Auditory cues are a type of mechanical stimulus
1. Sound is vibration in the substrate (ground, leaf, water) or air
4. Visual cues and light receptors
1. convergent evolution of light receptors among different groups
1. Simple eyes or ocelli, are single lenses over light-sensitive nerve cells
2. compound eyes (insects, crustacea) are composed of many individual units or ommatidia
3. the vertebrate and cephalopod eye
1. convergence revealed by differences in detail
2. color perception varies
1. Different animals perceive different sections of light energy

Study questions

1.  What sensory organ could detect each of the following signals?

1. the breeze from a fly swatter
2. sugar in the hummingbird feeder
3. vibrations in a leaf from a burrowing larva
4. the song from a competing male cricket
5. scent from a flowering plant
6. the length of the day
7. the bright yellow center of a daisy (where the pollen and nectar are located)

2. The adults of both dragonflies and  aphids  have compound eyes, but those of the dragonflies are much larger and have many more ommatidia than those of the aphids. What ecological or behavioral characteristic of the dragonflies would make such elaborate eyes so important?

3. Mark each of the following statements as "True" or "False"

1. Compound eyes are capable of forming visual images that look like several repeated, slightly different, images of the "real" world.
2. Compound eyes are called compound because they are formed of hexagonal arrays of many ommatidia.
3. Insects perceive and distinguish among a wider array of colors than we do.
4. Reptiles may  perceive light in a wide array of wave lengths, but many do not distinguish colors.

5. Using the three requirements for evolution by natural selection (phenotypic variation (1) that is due at least in part to genotypic variation (2) and that gives rise to differences in survival or reproduction (3)), determine whether the predator in the description below could evolve to capture a different prey type.  (i.e., determine if all three are present).
 

Bolas spiders are a rarity in spiders:  they are specialists on moths.  In fact, they not only eat only moths, they eat only male moths.  They do this by spinning a special web, that consists simply of a single line with a glob of glue at the end.  The glue is scented with the same chemical compound that female moths produce - when the spider swings this bolas around (so named because it resembles the string with weights used by people in Argentina to capture animals), the scent spreads through the habitat and male moths come in expecting to find a female.

The scent produced by an individual spider is usually identical to the scent produced by it's parents, and only one species of moth will respond to this.  However, if there is variation in the coding of this gene, then an individual may produce more than one scent if it inherets two different copies of the gene.  Such an individual could then capture a greater diversity of male moths, which would increase it's energy intake and hence its survival and reproduction.

6.  Again using the three requirements for evolution by natural selection determine if the predator in the description below could evolve to capture prey more effectively.

Fishers are large members of the weasel family that have recently recovered from a brush with extinction (due to human hunting).  Such sudden reductions in population size followed by population growth are called "bottlenecks" and they greatly reduce genetic variation within a population.  The fishers in Vermont are particularly adept at surviving around human habitation.  Imagine that there is a mother fisher who lives near a "back-to-earth" Vermont homestead.  These folks keep a large flock of free-range hens for meat and eggs.  The fisher discovers the flock, and not only feeds hens to her kits but teaches them to hunt hens as well.  Hen-hunting fishers are "habituated" to humans, and are more likely to be trapped and killed.

Answers