Animal Behavior/Lek Polygyny
Lek polygyny is a mating system common in polygynous species of insects and birds in which the male provides no parental care to its offspring. The lek mating system is uniquely driven by the females’ pursuit of their mate, rather than the males'. Males of lekking species do not hunt for receptive females. Males form aggregates in neutral locations devoid any resources valuable to females. The group of males performs intricate vocal, visual or chemical displays to lure receptive females to their lekking site. In most lekking species, these group displays typically increase the ratio of visiting females per males. At the lekking site, visiting females are able to compare the males’ physiques and courtship displays, picking the most attractive male as their mate (Alcock, 2001). Thus, the few, most attractive males will do the majority of the mating (about 99%), while the subordinate males do no mating at all (Sherman, 1999).
Alternative Hypothesis: Kin Selection Hypothesis
The Lek Polygyny mating system promotes a heavily skewed mating success rate among lekking males. Although most of the individuals in a lek never receive a mating opportunity, lek polygamy continues to flourish among various species of birds and insects (Sherman, 1999). This suggests that the fitness of subordinate males must somehow be indirectly benefited by communal displays. A number of hypotheses have been proposed to explain the reasons behind lekking behavior. Widely recognized hypotheses include the Hotspot Hypothesis, the Hotshot Hypothesis, and the Female Preference Hypothesis (Alcock, 2001). Petrie et al. (1999) proposed an alternative hypothesis predicting that lekking behavior is driven by kin selection.
In the kin selection hypothesis, Petrie et al. (1999) suggests that if all the males in a lek were genetically related, then the males (even the subordinate males) would receive fitness benefits. Petrie et al. (1999) demonstrated the kin selection hypothesis by determining the genetic structure of different lekking groups of the Whipsnade Park peacock population. Peacocks, a typical lekking species, form aggregates at neutral display sites. Peacocks use their calls to attract receptive peahens. Upon the arrival of a peahen, the peacocks cease calling and perform intricate plumage displays. As common in lekking species, the peacocks with the most appealing courtship displays have a high mating success while the subordinate peacocks have no mates. The lekking sites of peacocks are carefully chosen and after a male’s fourth year of lekking, he will establish his permanent lekking site. Peacocks will return to this same lekking site every mating season (Petrie et al., 1999).
Using multilocus fingerprinting, Petrie et al. (1999) compared the genetic similarity of within and between the lekking groups of Whipsnade Park’s peacocks. The results supported the proposed kin selection hypothesis. As predicted, the degree of band-sharing within the leks was substantially higher than the band-sharing between the leks. The band sharing within the leks was indicative of that of half-siblings. After this discovery, Petrie et al. (1999) proposed subsequent hypotheses of why these lekking groups consisted of related individuals. Petrie et al. (1999) suggested that related peacocks tended to display together because their dispersal was concentrated around their natal sites. This hypothesis was rejected when peacocks of mixed relatedness were reared away from their natal sites but, upon reintroduction into the Whipsnade Park population, joined leks with closely related peacocks. It was then suggested that peacocks’ tendency to congregate with relatives was due to a shared genetic preference for habitat-selection. This was rejected due to the homogenous environmental features of the park. Petrie et al. (1999) concluded that unique structure of the peacock leks was driven by kin selection based on self-referent phenotypic matching (“Armpit Effect”). Petrie et al. (1994) predicted that peacocks match heritable similarities of their own phenotype with those of other males. Because the authors believed that peacocks do not participate in the rearing of their offspring, they posit that a peafowl’s recognition of their father must be genetically innate. The tendency to form leks with relatives, therefore, occurs in the absence of social cues to their identity. By cooperatively forming leks with genetically related individuals, subordinate peacocks forfeit their chances of mating, but increase the chance that their genes will be passed on via successful relatives. The indirect benefits of fitness seen in peacock lekking displays outweigh the costs of communal displays (Petrie et al., 1999).
There are four distinct genera of Peafowl: Pavo, Afropavo, Rheiinartia and Argusianus. Though it is frequently reported that male peafowl do not participate in nest defense or rearing paternal care of young has been observed in all four genera. Only the common Indian Peafowl Pavo cristatus is frequently kept in captivity. Its behaviors in zoo settings may not reflect its evolutionary history to the degree that wild populations of the species might.
According to the hotspot hypothesis, males form leks because females frequently visit certain "hotspots".
The hotshot hypothesis predicts that males form leks because subordinate males congregate around highly attractive males to increase their chance of being noticed by receptive females.
Female Preference Hypothesis
The female preference hypothesis predicts that males form leks because female like to visit large clusters of males consisting of a variety of potential mates from which she can quickly and safely compare the quality of her mating choices.
Alcock, J. Animal Behavior. 7th ed. Sunderland: Sinauer Associates, 2002.
Petrie M, Krupa A, Burke T: Peacocks lek with relatives even in the absence of social and environmental cues. Nature 401: 155-157 (1999).
Sherman PW: Bird of a feather flock together. Nature 401:119-120 (1999).
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