Based on the scatter plot, what conclusion would you draw about whether exposure to cane toads is having a selective effect on black snakes?

• A. Exposure selects for snakes that are more affected by the toxin.
• B. There is no selective effect.
• C. Exposure appears to select for snakes that are less affected by the toxin.
• D. The toxin enhances swimming speed across all snakes.

Answer: (C)

Exposure to a toxin can act as a selective pressure, meaning individuals with traits that reduce harm from the toxin are more likely to survive and reproduce. If the scatter plot shows that some snakes experience little or no negative effect from exposure while others are strongly affected, that pattern indicates differential survival or performance based on tolerance. Over time, this selects for snakes that are less affected by the toxin because they leave more offspring. So the conclusion is that exposure appears to select for snakes that are less affected by the toxin.

The alternate idea that there is no selective effect would require no clear pattern in the data. The idea that the toxin universally enhances swimming speed across all snakes would require a uniform increase for everyone, not just a subset. And suggesting the toxin selects for snakes that are more affected would imply the more harmed snakes have higher fitness, which contradicts how a toxin typically acts as a stressor favoring tolerance.