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A lek is an aggregation of male
animal
Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
s 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.
A lek can also indicate an available plot of space able to be utilized by displaying males to defend their own share of territory for the
breeding season
Seasonal breeders are animal species that successfully mate only during certain times of the year. These times of year allow for the optimization of survival of young due to factors such as ambient temperature, food and water availability, and cha ...
. A lekking species is characterised by male displays, strong female
mate choice
Mate choice is one of the primary mechanisms under which evolution can occur. It is characterized by a "selective response by animals to particular stimuli" which can be observed as behavior.Bateson, Paul Patrick Gordon. "Mate Choice." Mate Choic ...
, and the conferring of indirect benefits to males and reduced costs to females. Although most prevalent among
birds
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
such as
black grouse
The black grouse (''Lyrurus tetrix''), also known as northern black grouse, Eurasian black grouse, blackgame or blackcock, is a large game bird in the grouse family. It is a sedentary species, spanning across the Palearctic in moorland and step ...
, lekking is also found in a wide range of
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
s including some
bony fish
Osteichthyes (), popularly referred to as the bony fish, is a diverse superclass of fish that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartilag ...
,
amphibian
Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...
s,
reptile
Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...
s, and
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s, and
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...
s including
crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...
s and
insect
Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...
s.
A classical lek consists of male territories in visual and auditory range of each other. An exploded lek, as seen in the
kakapo (the owl parrot), has more widely separated territories, but still in auditory range. Lekking is associated with an apparent
paradox
A paradox is a logically self-contradictory statement or a statement that runs contrary to one's expectation. It is a statement that, despite apparently valid reasoning from true premises, leads to a seemingly self-contradictory or a logically u ...
: strong
sexual selection
Sexual selection is a mode of natural selection in which members of one biological sex mate choice, choose mates of the other sex to mating, mate with (intersexual selection), and compete with members of the same sex for access to members of t ...
by females for specific male traits ought to erode
genetic diversity
Genetic diversity is the total number of genetic characteristics in the genetic makeup of a species, it ranges widely from the number of species to differences within species and can be attributed to the span of survival for a species. It is dis ...
by
Fisherian runaway
Fisherian runaway or runaway selection is a sexual selection mechanism proposed by the mathematical biologist Ronald Fisher in the early 20th century, to account for the evolution of ostentatious male ornamentation by persistent, directional fem ...
, 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
Swedish or ' may refer to:
Anything from or related to Sweden, a country in Northern Europe. Or, specifically:
* Swedish language, a North Germanic language spoken primarily in Sweden and Finland
** Swedish alphabet, the official alphabet used by ...
''lek
Lek or LEK may refer to:
* Lek mating, mating in a lek, a type of animal territory in which males of a species gather
* Albanian lek, the currency of Albania
* Lek (magazine), a Norwegian softcore pornographic magazine
* Lek (pharmaceutical comp ...
'', a noun which typically denotes pleasurable and less rule-bound games and activities ("play", as by children). English use of ''lek'' dates to the 1860s. 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 are a group of birds from the order Galliformes, in the family Phasianidae. Grouse are presently assigned to the tribe Tetraonini (formerly the subfamily Tetraoninae and the family Tetraonidae), a classification supported by mitochondria ...
(grouse, boldface in cladogram
A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...
), in particular the black grouse
The black grouse (''Lyrurus tetrix''), also known as northern black grouse, Eurasian black grouse, blackgame or blackcock, is a large game bird in the grouse family. It is a sedentary species, spanning across the Palearctic in moorland and step ...
(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.
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 classic 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 kakapo, 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
The great snipe (''Gallinago media'') is a small stocky wader in the genus ''Gallinago''. This bird's breeding habitat is marshes and wet meadows with short vegetation in north-eastern Europe, including north-western Russia. Great snipes are mig ...
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
The manakins are a Family (biology), family, Pipridae, of small Tyranni, suboscine passerine birds. The group contains some 54 species distributed through the American tropics. The name is from Middle Dutch ''mannekijn'' "little man" (also the so ...
, 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
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...
. 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
Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...
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
Parental care is a behavioural and evolutionary strategy adopted by some animals, involving a parental investment being made to the evolutionary fitness of offspring. Patterns of parental care are widespread and highly diverse across the animal k ...
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
Since sexual selection
Sexual selection is a mode of natural selection in which members of one biological sex mate choice, choose mates of the other sex to mating, mate with (intersexual selection), and compete with members of the same sex for access to members of t ...
by females for specific male trait values should erode genetic diversity
Genetic diversity is the total number of genetic characteristics in the genetic makeup of a species, it ranges widely from the number of species to differences within species and can be attributed to the span of survival for a species. It is dis ...
, the maintenance of genetic variation in lekking species constitutes a paradox in evolutionary biology. Many attempts have been made to explain it away, but the paradox remains. There are two conditions in which the lek paradox arises. The first is that males contribute only genes and the second is that female preference does not affect fecundity
Fecundity is defined in two ways; in human demography, it is the potential for reproduction of a recorded population as opposed to a sole organism, while in population biology, it is considered similar to fertility, the natural capability to pr ...
. Female choice should lead to directional runaway selection, resulting in a greater prevalence for the selected traits. Stronger selection should lead to impaired survival, as it decreases genetic variance and ensures that more offspring have similar traits. However, lekking species do not exhibit runaway selection. In a lekking reproductive system, what male sexual characteristics can signal to females is limited, as the males provide no resources to females or parental care to their offspring. This implies that a female gains indirect benefits from her choice in the form of "good genes" for her offspring.
Amotz Zahavi
Amotz Zahavi ( he, אמוץ זהבי) (August 14, 1928 – May 12, 2017) was an Israeli evolutionary biologist, a Professor in the Department of Zoology at Tel Aviv University, and one of the founders of the Society for the Protection of Nature in ...
argued that male sexual characteristics only convey useful information to the females if these traits confer a handicap on the male. Zahavi's handicap principle may offer a resolution to the lek paradox, for if females select for the condition of male ornaments, then their offspring have better fitness. Another potential resolution to the lek paradox is Rowe and Houle's theory that sexually selected traits depend on physical condition, which might in turn, summarize many genetic loci. This is the genic capture
Genic capture is a hypothesis explaining the maintenance of genetic variance in traits under sexual selection. A classic problem in sexual selection is the fixation of alleles that are beneficial under strong selection, thereby eliminating the ben ...
hypothesis, which describes how a significant amount of the genome is involved in shaping the traits that are sexually selected. There are two assumptions in the genic capture hypothesis: the first is that sexually selected traits are dependent upon condition, and the second is that general condition is attributable to high genetic variance. In addition, W. D. Hamilton
William Donald Hamilton (1 August 1936 – 7 March 2000) was a British evolutionary biologist, recognised as one of the most significant evolutionary theorists of the 20th century.
Hamilton became known for his theoretical work expounding a ...
and Marlene Zuk proposed that sexually selected traits might signal resistance to parasites
Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted structurally to this way of lif ...
. One resolution to the lek paradox involves female preferences and how preference alone does not cause a drastic enough directional selection to diminish the genetic variance in fitness. Another conclusion is that the preferred trait is not naturally selected for or against and the trait is maintained because it implies increased attractiveness to the male.
Evolution
Several possible mechanisms have been proposed as to why males cluster into leks, including the hotshot, hotspot, black hole, kin selection, and predation protection hypotheses, as described below.
Hotshot hypothesis
The hotshot hypothesis is the only model that attributes males as the driving force behind aggregation. The hotshot model hypothesizes that attractive males, known as hotshots, garner both female and male attention. Females go to the hotshots because they are attracted to these males. Other males form leks around these hotshots as a way to lure females away from the hotshot. A manipulative experiment using the little bustard, '' Tetrax tetrax'', was done to test the various lek evolution models. The experiment involved varying the size and sex ratio of leks using decoys. To test whether or not the presence of a hotshot determined lek formation, a hotshot little bustard decoy was placed within a lek. After the fake hotshot was added to the lek, both male and female visitation to the lek increased, tending to confirm the hypothesis.
Hotspot model
The hotspot model considers the female density to be the catalyst for the clustering of males. This model predicts that leks will form where females tend to reside as a way to increase female interaction. Female manakin
The manakins are a Family (biology), family, Pipridae, of small Tyranni, suboscine passerine birds. The group contains some 54 species distributed through the American tropics. The name is from Middle Dutch ''mannekijn'' "little man" (also the so ...
traffic has been observed to be concentrated around leks, bathing sites, and fruiting areas, with males aggregated near the most visited fruiting resources.[ The hotspot model also predicts that lek size is dependent upon the number of females inhabiting a patch of land.][ To test if the number of females affects lek formation, a group of female little bustard decoys were added to a lek. The presence of these female decoys did not have an effect on lek size, tending to refute the hypothesis.]
Blackhole model
The blackhole model proposes that females have a preference for neither size nor type of male, but rather that females tend to be mobile and mate wherever leks may be located. This model predicts that female mobility is a response to male harassment. This prediction is difficult to test, but there was a negative correlation found between male aggressiveness and female visitation in the little bustard population, suggesting that the model might be correct. Evidence supporting the black hole model is mainly found in ungulates
Ungulates ( ) are members of the diverse clade Ungulata which primarily consists of large mammals with hooves. These include odd-toed ungulates such as horses, rhinoceroses, and tapirs; and even-toed ungulates such as cattle, pigs, giraffes, cam ...
.
Kin selection
An alternative hypothesis for lekking is kin selection
Kin selection is the evolutionary strategy that favours the reproductive success of an organism's relatives, even when at a cost to the organism's own survival and reproduction. Kin altruism can look like altruistic behaviour whose evolution i ...
, which assumes that males within a lek are related to one another. As females rarely mate outside of leks, it is advantageous for males to form leks. Although not all males within a lek mate with a female, the unmated males still receive fitness benefits. Kin selection explains that related males congregate to form leks, as a way to attract females and increase inclusive fitness
In evolutionary biology, inclusive fitness is one of two metrics of evolutionary success as defined by W. D. Hamilton in 1964:
* Personal fitness is the number of offspring that an individual begets (regardless of who rescues/rears/supports them ...
.[ In some species, the males at the leks show a high degree of relatedness, but this does not apply as a rule to lek-forming species in general. In a few species such as peacocks and ]black grouse
The black grouse (''Lyrurus tetrix''), also known as northern black grouse, Eurasian black grouse, blackgame or blackcock, is a large game bird in the grouse family. It is a sedentary species, spanning across the Palearctic in moorland and step ...
, leks are composed of brothers and half-brothers. The lower-ranking males gain some fitness benefit by passing their genes on through attracting mates for their brothers, since larger leks attract more females. Peacock
Peafowl is a common name for three bird species in the genera ''Pavo (genus), Pavo'' and ''Afropavo'' within the tribe Pavonini of the family Phasianidae, the pheasants and their allies. Male peafowl are referred to as peacocks, and female pea ...
s recognize and lek with their brothers, even if they have never met before.
Predation protection
Another hypothesis is predation protection, or the idea that there is a reduction in individual predation risk in a larger group. This could work both for the males within the group and any female who visits the lek. Protection also explains the presence of mixed leks, when a male of one species joins a lek of another species for protection from a common set of predators. This occurs with manakins, as well as other birds such as grouse
Grouse are a group of birds from the order Galliformes, in the family Phasianidae. Grouse are presently assigned to the tribe Tetraonini (formerly the subfamily Tetraoninae and the family Tetraonidae), a classification supported by mitochondr ...
species.
References
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