This entry was written by Luke Rudloff as part of a project done in BIAN 2133 ‘Human Reproductive Strategies’ at The Australian National University in 2019 Semester 2.
Introduction
Lekking is a mating system in which males of a species aggregate in close geographical proximity in groups known as leks, with females visiting in order to compare males and select a mate to reproduce with. Lekking is most commonly seen in birds (e.g. species of grouse, manakins, turkeys) but is also evident to have evolved across other taxa in the animal kingdom (e.g. some species of frogs, bats, ungulates). Lek mating is unique in that the males involved do not offer resources to the females, nor do they provide parental care. Rather, it appears that the sole benefit provided by males is the quality of their genes. Due to this, female choice is based on observation of sexual traits in males, and such males must put themselves on display for the chance of reproducing.
An understanding of the evolution of lekking in non-human species may help to explain instances of lekking behaviour in humans. There is still much scientific uncertainty regarding the mechanisms of the evolution of lekking, with numerous hypotheses developed to attempt to explain the evolution of leks. Such hypotheses include the ‘hotshot hypothesis’, the ‘hotspot hypothesis’ and the ‘kin selection’ hypothesis. While these hypotheses do not represent the totality of current scientific thinking on the topic, I have selected them to illustrate a variety of theoretical approaches in describing the factors behind lek formation.
In this essay, I will outline three prominent hypotheses for the evolution of lekking as a mating strategy and discuss whether they are supported by scientific literature.
Main Text
Hotspot Hypothesis
The hotspot hypothesis proposes that leks are formed in areas where females are most likely to be encountered due to their movement patterns, or environmental constraints (in a variation of this model) such as food availability (Beehler & Foster, 1988; Ryder, Black & Loiselle, 2006). Under this model, individual males settle in hotspot, separated by the diameter of a female homing range, after which subsequently arriving males are forced to aggregate around the initial males in order to remain within the female hotspot (Beehler & Foster, 1988).
Hotshot Hypothesis
The hotshot model was developed in response to female-centric models, shifting the emphasis from female choice to interactions between males (Beehler & Foster, 1988). This hypothesis was developed by Beehler and Foster (1988) who suggested that lek formation may be influenced by the presence of dominant males (or ‘hotshots’), which are those males who experience a higher rate of mating success. As lekking is a non-resource-based mating strategy, female choice appears to based upon phenotypic expression of sexual traits (e.g. ungulate horns and peacock trains), with dominant males being those most frequently selected for mating.
Kin Selection Hypothesis
The observed bias in mating success towards a small number of dominant males poses the question of why subordinate males choose to aggregate in leks. The kin selection hypothesis considers the role of relatedness between males in a lek as a possible reason for this aggregation. Proposed is the idea that subordinate males aggregate around a dominant male to whom they are related, helping the dominant male increase his mating success and subsequently receive indirect fitness benefits which outweigh the cost of helping (Krakauer, 2005).
Discussion
Lekking appears to have evolved independently across various taxa, and as such we see wide variation in lek formation, and the factors contributing to this when comparing different species. Due to this, it seems likely the case that a single hypothesis will not be sufficient to explain the evolution of lekking in all species where this behaviour is observed.
Through calculating theoretical costs and benefits associated, in conjunction with prior observations, with kin selection in wild turkeys, Krakauer (2005) was able to conclude that cooperation between kin in leks was sufficient to explain such lek formation in this species (Meleagris gallopavo). He concluded that the indirect benefits to fitness that subordinate male gained by helping dominant males, despite not reproducing themselves, far outweighed the cost of helping (Krakauer, 2005). While this hypothesis may be suitable in explaining lekking behaviour in wild turkeys, studies on species of manakins (Loiselle et al, 2006) and Neotropical hummingbirds (González & Ornelas, 2019) found that relatedness between males was too low to suggest kin selection as a plausible explanation for lek formation in these species. Loiselle and colleagues (2007) found that relatedness between lekking manakin males (among the 4 species studied) was no higher than relatedness between a random assortment of individuals. While González & Ornelas (2019) found relatedness between individuals in a hummingbird species (Wedge-tailed Sabrewing (Campylopterus curvipennis)) was greater than between leks, such relatedness insufficient in supporting kin selection as the mechanism for lek formation. Thus, while kin selection seems to be supported as a force driving lek formation in some species (see: Krakauer, 2005), it appears to have no explanatory power among others (González & Ornelas, 2019; Loiselle et al., 2006).
Models such as the hotspot and hotshot hypotheses take contrasting approaches to an explanation of lek evolution, with the hotspot model focusing on female distribution as a key factor, while the hotshot model centers on male-male interactions (Beehler & Foster, 1988). Despite the hotshot hypothesis being developed by Beehler & Foster (1988) as an alternative to female-centric models such as the hotspot, these models are not mutually exclusive. Beehler and Foster (1988) argued that the existence of traditional lekking sites (i.e. lekking sites that remain in the same location year after year) poses a problem for the hotspot model due to variation in female distribution. While this may be the case in some scenarios, a study of three manakin species found that lek sites had on average a higher biomass of fruit (the diet of the studied species) when compared with control sites (Ryder, Blake & Loiselle, 2006). This supports the idea of an environmental hotspot as female distribution is constrained by fruit availability. While the hotspot model attempts to explain lekking in reference to female distribution, with male clustering in areas where female encounters are most likely, the hotshot model proposes that clustering is caused by the presence of dominant males, to whom subordinate males aggregate to increase their chances of mating success(Beehler & Foster, 1988). This model has been supported in grouse, as well as being partially supported by studies on the little bustard, where aggregation around hotshot occurred, however lek size did not decrease with their removal, but rather a male from a neighbouring territory came and took the place of the previous hotshot (Jiguet & Bretagnolle, 2006).
Lastly, these hypotheses may help to explain instances of lekking in humans, such as during the Gerewol, where young males dress in elaborate garments and make up and put on a group-display to attempt to attract a female mate.
Conclusion
While not all-encompassing, the hotshot, hotspot and kin selection models appear to provide valuable explanations of some aspects of the evolution of leks in various lekking species. Due to the nature of its evolution, a single unifying theory for lek evolution may be unattainable, however, each of these hypotheses appears to explain aspects of lekking in various species. Because of this, it appears that explanation of lekking evolution in a given species may require consideration of the components of numerous models, including those which I didn’t discuss.
References Cited
Beehler, B., & Foster, M. (1988). Hotshots, Hotspots, and Female Preference in the Organization of Lek Mating Systems. The American Naturalist, 131(2), 203-219.
González, C., & Ornelas, J. (2019). Male relatedness, lekking behavior patterns, and the potential for kin selection in a Neotropical hummingbird. The Auk.
Jiguet, F., & Bretagnolle, V. (2006). Manipulating Lek Size and Composition Using Decoys: An Experimental Investigation of Lek Evolution Models. The American Naturalist, 168(6), 758-768.
Krakauer, A. (2005). Kin selection and cooperative courtship in wild turkeys. Nature, 434(7029), 69-72.
Loiselle, B., Ryder, T., Duraes, R., Tori, W., Blake, J., & Parker, P. (2006). Kin selection does not explain male aggregation at leks of 4 manakin species. Behavioral Ecology, 18(2), 287-291.
Ryder, T., Blake, J., & Loiselle, B. (2006). A TEST OF THE ENVIRONMENTAL HOTSPOT HYPOTHESIS FOR LEK PLACEMENT IN THREE SPECIES OF MANAKINS (PIPRIDAE) IN ECUADOR. The Auk, 123(1), 247.