Lek mating systems in birds - a model for studying sexual selection.

Bradbury and Gibson (1983) described leks as ‘assemblies of adult males which females visit solely for the purpose of copulation’. Males of lek-breeding species provide only genetic material to resulting offspring, interacting with females only during mating (DuVal & Kempenaers 2008, Pruett-Jones & Pruett-Jones 1990). Lek mating systems have long been used to study sexual selection, as lekking species are known for extraordinary sexual dimorphism in ornamentation, plumage colour and size (Hess et al. 2012). Mating success among displaying males is generally highly skewed, with few males often responsible for the majority of matings (DuVal & Kempenaers 2008). There has been much discussion as to whether male-male competition or female choosiness is the primary driver of this behaviour and subsequent variance in male mating success (Pruett-Jones & Pruett-Jones 1990).

In some species of Birds of Paradise such as the Greater Bird of Paradise (Paradisaea apoda), males form leks in which they perform their communal courtship displays https://www.youtube.com/watch?v=KIYkpwyKEhY. Viewed on 3rd May 2017. 

Lance-tailed Manakins (Chiroxiphia lanceolata) form leks that consist of alpha males, each of which are assisted in their display by beta helpers that do not mate with any of the females attracted by their display (DuVal & Kempenaers 2008). Research has shown that both inter- and intrasexual selection occur within this species in distinct episodes, with male-male competition occurring to obtain alpha status and female mate choice occurring among displaying alpha males (DuVal & Kempenaers 2008). Nearly all chicks are sired by lekking alpha males, however the way females choose which alpha male or males to mate with is still yet to be determined - they may employ a compatability criterion, selecting for good genes and genetic compatibility or their choice may be random and determined purely by the placement of males and their accessibility (DuVal & Kempenaers 2008, Neff & Pitcher 2005). 

Male Lance-tailed Manakins (Chiroxiphia lanceolata) performing a courtship display. One is an alpha male the other a beta male assisting in the performance. Only the alpha male gets to mate with an impressed female. Are the beta males doing this to learn the right moves for if or when they gain alpha status??? https://www.youtube.com/watch?v=cAwevkUaB2Q. Viewed on 3rd May 2017.

I have found quite a lot of conflicting information regarding the factors influencing the formation of leks and the highly variable success rates within the males of the lekking species. This has once again highlighted how little we still know about bird behaviour. Each species of bird has apparently evolved its own unique mating system, and while it is sometimes possible to find similarities between these mating systems, drawing conclusions that attempt to describe all mating systems, or even one mating system, often results in unneeded controversy!!! There is plenty of variation within one mating system such as lekking, so the variation between mating systems is mind-boggling. Whether a mating system is more influenced by inter- or intrasexual selection is often extremely hard to determine and as we see in the Lance-tailed Manakin (Chiroxiphia lanceolata)  the two are often inextricably linked.


References

Bradbury, J.W. & Gibson, R.M. 1983. "Leks and mate choice", in P.Bateson (ed.), Mate choice, Cambridge University Press, Cambridge, pp.109-138.

DuVal, E.H. & Kempenaers, B. 2008, "Sexual selection in a lekking bird: the relative opportunity for selection by female choice and male competition", Proceedings of the Royal Society B: Biological Sciences, vol. 275, no. 1646, pp. 1995-2003. 

Hess, B.D., Dunn, P.O. & Whittingham, L.A. 2012, "Females choose multiple mates in the lekking Greater Prairie-Chicken (Tympanuchus cupido)", The Auk, vol. 129, no. 1, pp. 133-139.

Neff, B.D. & Pitcher, T.E. 2005, "Genetic quality and sexual selection: an integrated framework for good genes and compatible genes", Molecular Ecology, vol. 14, no. 1, pp. 19-38. 

Pruett-Jones, S.G. & Pruett-Jones, M.A. 1990, "Sexual selection through female choice in Lawes' Parotia, a lek-mating Bird of Paradise", Evolution, vol. 44, no. 3, pp. 486-501.