Males of Some Species Sometimes Cooperate in Acquiring a Mate

Males of some species sometimes cooperate in acquiring a mate, but then only one of the group actually does most or all of the mating. For example, in a small bird called the long-tailed manakin (Chiroxiphia linearis) , two (or sometimes three) males perform remarkable acrobatic cooperative displays to attract a female. If a female is interested by the display, only one of the males, however, will mate with her, and it is always the same male. According to work by McDonald, Trainer, and colleagues (l994, 1995, 2002) , it is unlikely that the males are related to one another. Further, performance of at least some parts of the display improve with age and practice. This suggests that a subordinate male participates in this cooperative display primarily because it eventually results in an increase in his

A) ability to reciprocate in the future.
B) direct fitness.
C) indirect fitness.
D) all of the above.