The role of evolution in mating behavior of lekking species  (Page 10/11)

Marion Petrie and researchers at the University of Newcastle, UK attempted to determine the relatedness of peacocks on leks to conclude whether relatedness plays a role in the persistence of group display behaviors in the species. They studied 4 peacock leks at Whipsnade Park, UK, totaling 21 organisms (Petrie 1999). They used multilocus fingerprinting as a method of determining relatedness among the peacocks, as closely related individuals share a greater number of bands. Petrie and team compared the degree of relatedness in peacocks within the same lek to peacocks between leks and found the organisms on the same lek to be more closely related, to about the degree of half-siblings (Petrie 1999).

Because the males do not assist in the rearing of young, birds have no opportunity to learn the identity of their father, which makes Petrie’s results surprising. One possible explanation could be that the peacocks simply don’t disperse far from their nests, but the results of Petrie’s study refuted this by showing that the birds need not even be born in the park for them to show preference in displaying with kin. In fact, “when the birds established their permanent adult display sites several years after their release there was a clear tendency for known brothers or half-brothers to display close together” (Petrie 1999).

Another possible explanation for this behavior is that the related birds have a genetically based preference for a particular type of display site. In other words, they don’t actually choose the site based on the fact that relatives are there but indirectly lek with relatives because they all prefer the same type of location. However, this, too, can be refuted because the male peacocks showed no preference in lekking on the sites at which their fathers lekked. If the genetic basis of preference is true, it can be expected that they would share the preference with their father as well. Because this is not seen in the data, the explanation can be rejected (Petrie 1999). The researchers then concluded that kin selection is a viable explanation of the results, with the benefits of inclusive fitness due to relatedness outweighing the costs of forming a lek and displaying communally.

Opposition

Manakins

Two separate studies on manakins, one headed by Bette Loiselle at the University of Missouri-St. Louis and the other by David McDonald, oppose the findings of Petrie. The Loiselle study covered 4 manakin species ( Pipra filicauda, Pipra pipra, Lepidothrix coronata, and Chiroxiphia pareola ) in Ecuador. In these species, the males lek at essentially the same location annually. The leks were monitored for activity and genetic samples were taken to study relatedness (Loiselle 2006). The results of the study found that “in no case were males within leks more related than expected by chance” (Graph 3). The data showed that the male manakins appeared to join leks randomly and without correlation to relatedness (Loiselle 2006). The McDonald study, also covering manakins, found that the “mean relatedness among network males was less than zero.” Because of this and the fact that neither direct nor indirect relationships preferred kin, the manakin networks showed no evidence of the kin selection hypothesis (McDonald 2007).