Desert ants are known to use landmarks (reference points), pedometers (memorising step counts), and optic flow (rate of passing objects across its eye to estimate navigation speed) to navigate across deserts. A desert ant is trained to walk 100 m from its nest to a feeder in an artificial arena as depicted in the schematic. The arena had a single tall landmark placed at 40 m from the nest. At the feeder, certain manipulations were performed before allowing the ant to return to its nest with the food.
Manipulation 1: Stilts were attached to its legs, which doubled the step length.
Manipulation 2: The optic flow of the arena was doubled.
While the ant uses the landmark exclusively for long-distance ($\gt $55 m) navigation, it switches to optic flow and pedometer simultaneously and exclusively for short-distance navigation. Due to the manipulations, the distance from the feeder where the ant will search its nest is:
Show Hint
Break down multi-cue navigation experiments into distinct physiological phases. Identify which cue dominates in which phase, calculate the contribution of each manipulated cue, and then combine them as specified.
Step 1: Understanding the Question:
The question asks for the distance from the feeder where a trained desert ant will search for its nest, following two experimental manipulations (stilts that double step length and a doubled optic flow in the arena).
Step 2: Key Formula or Approach:
Under long-distance navigation ($\gt 55\ \text{m}$), the ant relies exclusively on landmarks.
Under short-distance navigation ($\lt 55\ \text{m}$), the ant integrates both optic flow and pedometer inputs simultaneously.
We need to calculate the actual distance traveled in each segment of the journey back to the nest.
Step 3: Detailed Explanation:
• The ant is at the feeder, located 100 m from the nest. The landmark is located 40 m from the nest (which is 60 m from the feeder).
• First, the ant begins its return journey from the feeder (at 100 m) to the nest (at 0 m).
• Since the initial distance to the landmark is $100 - 40 = 60\ \text{m}$, which is greater than 55 m, the ant uses the landmark exclusively for long-distance navigation.
• Thus, it ignores the altered step length and doubled optic flow during this phase, and successfully reaches the landmark, covering exactly 60 m.
• Now, the ant is at the landmark (40 m from the nest). The remaining distance to the nest is 40 m, which is less than 55 m.
• For this short-distance navigation phase, the ant switches to using both the pedometer and optic flow simultaneously.
• Let us analyze the effect of each cue:
itemize
• With stilts, the ant's step length is doubled. To cover the 40 m distance based on its internal step counter (which expects a normal step length), the ant would have to take the number of steps that would normally cover 40 m. Since each step is now twice as long, this pedometer cue on its own would cause the ant to walk $40 \times 2 = 80\ \text{m}$.
• The optic flow of the arena is doubled. This means the visual system registers double the normal motion per unit distance. To perceive a visual travel of 40 m, the ant only needs to physically move $40 / 2 = 20\ \text{m}$.
Since the ant integrates these two sensory inputs simultaneously (by averaging the two estimates), the distance it travels after the landmark is:
\[ \text{Distance after landmark} = \frac{80\ \text{m} + 20\ \text{m}}{2} = 50\ \text{m} \]
Thus, the total distance traveled from the feeder is:
\[ \text{Total distance} = 60\ \text{m} + 50\ \text{m} = 110\ \text{m} \]
itemize
Step 4: Final Answer:
Therefore, the distance from the feeder where the ant will search for its nest is 110 m.
