SKILL: EVALUATING HYPOTHESES
How Did the Deep-Sea
Angler Get Its Glow?
A fish that uses a fishing pole to catch food might seem odd.
However, anglerfish do just that. The fish have a modified spine
that extends from their head, almost like a fishing pole. At the end
is a small piece of tissue that is similar in shape to a small worm.
The tissue functions like a lure that a fisherman uses to catch fish.
The anglerfish wiggles its “lure” to attract prey. If the prey fish
moves in close enough, the anglerfish opens its mouth and
swallows the prey whole. The “fishing poles” of abyssal anglerfish,
anglerfish that live in the deep sea, have an interesting adaptation.
The “lure” actually glows in the dark—it is bioluminescent.
Observations
From laboratory research and field studies, scientists made these
observations.
There are more than 200 species of anglerfish. Many of
these live in deep water.
Shallow-water species do not have glow-in-the-dark "lures."
Only female abyssal anglerfish have a "pole." They do not
have pelvic fins and are not strong swimmers.
Other deep-sea organisms, including bacteria, jellyfish,
even some squid, are bioluminescent.
Hypotheses
Consider these hypotheses.
The ancestors of abyssal anglerfish lived in shallow
waters. Some of these fish drifted into deep waters.
A bioluminescent lure helped some survive.
Light does not reach down to the bottom of the deep
sea. Bioluminescence provides an advantage for the
anglerfish because it makes its lure noticeable.
A bioluminescent lure is more valuable to a female
abyssal anglerfish than the ability to swim.
Evaluate Each Hypothesis
On Your Own For each hypothesis, think about whether all the
observations support it. Some facts may rule out some hypotheses.
Others may support them.
As a Group Decide which hypothesis is the most reasonable.
Discuss your thinking and conclusions in a small group and see
if the group can agree.
Chapter 14: The History of Life on Earth 515