Reasons Behind the Formation of Leks

Xiu，Ziyi

Psychology 489: Animal Behavior

05/09/2011

The term "lek" is created by Edward Selous, the first field student of Darwinian sexual selection. "Lek" was first used to define the polygynous arena mating system of the European game birds - the ruff and the black grouse [4]. Nowadays, "lek" is generally referred to as a cluster of male territories, together with their occupants, frequently visited by females for courtship. During the breeding seasons in leks, diverse animals such as birds, frogs and insects often set up the most intensive mating competitions, which is a quite fascinating theme within the fields of animal behavior as well as evolutionary biology [9].

The lekkng behavior sheds light on the studies on the sexual selection mechanism. As what is suggested by Darwin, sexual selection plays an essential role on lek-breeding species, because they often show gender-differed morphological and behavioral components that indicate sexual selection [4]. Since females have a less reproductive potential because of limited gametes produced and the considerably parental care requirement for raising children alone after reproduction, a stronger sexual selection against males is generated.

The reasons for finding leks will be explored comprehensively by dividing into 2 categories based on genders. As for males, there are hypotheses of "female choice", "hot spot", and "hotshot", as well as a minor "kin selection" theory suggesting added benefits. After that, female profits are also analyzed with 3 primary models, with one direct benefits model and 2 indirect ones ("Fisherian process" and "good gene" hypotheses), and the sensory drive model separated from direct and indirect benefits.

The formation of leks on the males' side

Scientists doubt about the reason why would so many males get aggregated in leks, especially the reason for those unflavored subordinate males choosing to join leks rather than doing other worthwhile stuffs. The most convincing reason for males joining leks is increasing their chances of encountering females, and thus their mating successes as a whole. All the three prominent models will be discussed, including the "hotshot," "hot spot," and "female preference" models, with an extra model specially concerned about indirect benefits gained from "kin selection" by cooperating with relatives.

Female choice model

First comes the female choice model. The female choice hypothesis suggests that high mobility of the lek-breeding females may favor aggregated display of males, since the display provides a good chance for females to find good mates with the least cost, as well as a reduced risk of predation [7]. Therefore, the aggregated crowd of males can get a better chance of attracting females' attention. According to the study of blue-crowned manakin Lepidothrix coronata, females would travel further to reach larger leks rather than staying in their own less crowded birth sites [6]. What's more, the study of a bower-building cichlid fish also shows that the female encounter rate of males has a significant positive relationship with the size of leks. However, the specific reason behind the size could not be perfectly tested [16].

The other potential benefit female can gain by visiting larger leks would be the reduction of predators because the cluster of males could deter predators away from the nest sites [7]. However, according to the study of a kind of Uganda kob, predation risk is not likely to be a main factor for the formation of leks. The research analyzed both the predation risks within and between leks. There is only a little difference of predation between leks and individual territories. Moreover, even though there is a significant lower risk for males in the center of a lek than the risk for surrounded males, it does not prove that leks are formed to reduce perdition. This result could also be interpreted by the higher benefits gained for mating success by peripheral males that overweight the cost of more predators encountered in leks [2]. On the other hand, the female kobs may gain some benefits by mating on leks because of the less time needed to detect predators, and thus reduce their predation risks by mating on leks, especially when females are managed to locate in the center [2].

Hotspot model

The second model is the "hotspot" model. This hypothesis suggests that males are forming leks based on female density [16]. Even though there is no evidence found in the cichlid fish study [16] discussed previously, with the potential reason suggesting that males may lack sufficient information of female concentrations, a study of ochre-bellied flycatcher shows the opposite result. The flycatcher study shows that lek locations are higher related to the identified female routes followed by females constantly overtime [14]. Another study of 4 neotropical bird species confirms that leks may also be formed based on resources. As for these species, because of similar diets, leks are found to be clustered based on the environmental features that suggest resources. To conclude, the research discussed above makes this model quite plausible [15].

Hotshot model

The last model would be the "hotshot" model, which indicates that inferior males are forming leks to surround the attractive males, in order to increase their own attractiveness. This model is also studied in the cichlid fish research [16], with a weak support by citing that in larger leks, attacks between males are more for central males than the subordinates, and also larger bowers controlled by central males, indicating a higher cost of holding better territories. However, it does not show clear causation between the preferred males and the lek size. While in the great snipe study cited in [7], the snipe males are found to display repeatedly, with a positive correlation between the times of display and mating success. After competing with each other, the attractive males take the central place. With the removal of subordinate males, their previous places are quickly taken over, whereas the removal of favored males caused reallocation of the lek. Therefore, the leks are very likely to be based on the central males, and thus the "hotshot" hypothesis is also supported with evidence.

Kin selection model

Another hypothesis related to the "hotshot" model