Platys and swordtails are related tropical freshwater fish. In studies, researchers have shown that female platys prefer males with swordtails, even though males of their own species do not have them. This was discovered by attaching artificial swordtails to platys males.What does this suggest about the origin of the swordtail feature?

Question

A.  Female preference for swords may have predated the origin of the feature itself.
B.  Evolution of swords later led to evolution of female preference for swords.
C.  The same gene that causes sword development also causes development of neural circuits for female preference.
D.  Adjacent genes on the same chromosome cause sword development and development of neural circuits for female preference.


Clarify question:
What is the key concept addressed by the question?

What type of thinking is required?

Gather Content:
What do you already know about the evolutionary origins of a characteristic involved in sexual selection? What other information is related to the question? 

Choose Answer:
Given what you now know, what information is most likely to produce the correct answer?

Reflection on Process:
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

A.  Female preference for swords may have predated the origin of the feature itself.

Clarify question:
What is the key concept addressed by the question?
What is the origin of a feature in swordtail fish that is involved in sexual selection in a related species. 

What type of thinking is required?
This is an analyze question. You are given 4 different explanations for the observation of female preference for long tails in species of fish where the males do not normally have long tail fins. 

Gather Content:
What do you already know about the evolutionary origins of a characteristic involved in sexual selection? What other information is related to the question? 
Male swordtails have long tail fins that they use to attract females. Closely related fish species (platys) also preferentially mate with males with long tail fins, but the long tail fins aren’t found in the platys males. This was discovered by attaching artificial swordtails to platys males. The question is asking you to pick be best explanation for the observation in female platys. If the genes for the production of swordtails and the neural mechanism for preference were the same genes, then in all species where females show a preference for swordtails, the male would have swordtails.

Choose Answer:
Given what you now know, what information is most likely to produce the correct answer?
The genes for preference may have evolved first in an ancestral species, followed by the development of swordtails in only one of the species that evolved.

Reflection on Process:
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
Did you choose the correct answer? The key here is to recognize that the preference for a particular male trait precedes the development of that trait.