Lek mating

A lek is an aggregation of male animals gathered to engage in competitive displays and courtship rituals, known as lekking, to entice visiting females which are surveying prospective partners with which to mate. It can also refer to a space used by displaying males to defend their own share of territory for the breeding season. A lekking species is characterised by male displays, strong female mate choice, and the conferring of indirect benefits to males and reduced costs to females. Although most prevalent among birds such as black grouse, lekking is also found in a wide range of vertebrates including some bony fish, amphibians, reptiles, mammals, and arthropods including crustaceans and insects. A classical lek consists of male territories in visual and auditory range of each other. An exploded lek, as seen in the kākāpō (the owl parrot), has more widely separated territories, but still in auditory range. Lekking is associated with an apparent paradox: strong sexual selection by females for specific male traits ought to erode genetic diversity by Fisherian runaway, but diversity is maintained and runaway does not occur. Many attempts have been made to explain it away, but the paradox remains.

Etymology The term derives from the Swedish lek ([leːk] ), a noun which typically denotes pleasurable and less rule-bound games and activities ("play", as by children), or from the Swedish verb "leka", to play. Written English use of lek dates from the late 1860s and early 1870s. Llewelyn Lloyd's The Game birds and wild fowl of Sweden and Norway (1867) introduces it (capitalised and in single quotes, as 'Lek') explicitly as a Swedish term.

Taxonomic range Lekking was originally described in the Tetraonidae (grouse, boldface in cladogram), in particular the black grouse (Swedish: "orrlek") and capercaillie (Swedish: "tjäderlek"), but it is widely distributed phylogenetically among other birds, and in many other animal groups within the vertebrates and the arthropods, as shown in the cladogram. The presence of a group name means that some species in that group lek; groups with no lekking members are not shown.

There is also evidence from scrape marks left by dinosaurs that suggest they also indulged in leks.

Lekking behaviour

Types There are two types of lekking arrangement: classical and exploded. In the classic lekking system, male territories are in visual and auditory range of their neighbours. In an exploded lek, males are further away from one another than they would be in a classical lek. Males in an exploded lek are outside visual range of one another, but they stay within earshot. Exploded lek territories are much larger than classic systems and more variable in size. A well-known example of exploded leks is the "booming" call of the kākāpō, the males of which position themselves many kilometres apart from one another to signal to potential mates.

Stability Lek territories of different taxa are stable and do not vary in terms of size and location. Males often return to the same mating sites because of female fidelity. Avian females such as the black grouse and great snipe are faithful to males and not to mating sites. Successful males congregate in the same area as the previous breeding season because it is familiar to them, while females return to reunite with their males. Females do not return to a mating site if their male partner is not present. Another possible explanation for lek stability is from male hierarchies within a lek. In some species of manakin, subordinate betas may inherit an alpha's display site, increasing the chances of female visitation. Rank may also contribute to the stability of lek size, as lower ranking males may congregate to achieve a perceived optimal size to attract females.

Female mating preferences A meta analysis of 27 species found that qualities such as lekking size, male display rate, and the rate of male aggression exhibit positive correlation with male success rates. A positive correlation was also found between attendance, magnitude of exaggerated traits, age, frequency of fights, and mating success. This female preference leads to mating skew, with some males being more successful at copulating with females. The variation in mating success is quite large in lek mating systems with 70–80% of matings being attributed to only 10–20% of the males present.

Costs and benefits

The main benefit for both sexes is mating success. For males, the costs stem from females' preferences. The traits that are selected for may be energetically costly to maintain and may cause increased predation. For example, increased vocalization rate caused a decrease in the mass of male great snipes. Other costs can derive from male combat. For example, male great snipes regularly fight to display dominance or defend their territory, with females preferring victorious males. Aggressive male black grouse are preferred over non-aggressive males and when the males fight they tear feathers from each other's tails. Lekking is associated with sexual dimorphism across a range of bird taxa. At first glance, it may seem that females receive no direct benefits from lekking, since the males are only contributing genes to the offspring in the absence of parental care or other benefits. However, lekking reduces the cost of female searching because the congregating of males makes mate selection easier. Females do not have to travel as far, since they are able to evaluate and compare multiple males within the same vicinity. Further, having the males in one place may reduce the amount of time a female is vulnerable to predators. When under predatory pressure, female marbled reed frogs consistently choose leks near their release sites; high male calling rates were observed to reduce female search time.

The lek paradox

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