Hoefler and Colleagues (2009) Concluded That Male Spider Leg Raise

Hoefler and colleagues (2009) concluded that male spider leg raise displays are an indicator of quality to females. What assumption underlies this conclusion?

A) Leg raise displays vary with age.
B) Female fitness is unrelated to female mate choice.
C) Female choice is density-dependent.
D) Leg raise displays are physiologically costly.
E) Females detect leg raise displays as a vibratory signal.