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Welcome to the DragonflyIssuesInEvolution13 WikiEdit

Together all participants in Project Dragonfly Issues in Evolution Advanced Seminar in Fall 2013 will contribute words, definitions and explanations to a collaborative wiki. We will use this to advance our understanding of biological evolution and, if we are successful, yours.

Sexual SelectionEdit

A process in Natural Selection whereby individual organisms gain a genetic (breeding) advantage by attracting mates. This can occur when males of a species attract more females through successful display behavior (vocalization, demonstrations, or appearance) or through dominance of other males. 

On a simpler level, sexual selection occurs whenever an individual chooses a mate according to visual characteristics or even proximity.   “Natural selection is about living long enough to reproduce; sexual selection is about convincing others to mate with you.”-Geoffrey Miller (http://adarwinstudygroup.org/sexuality/)Bdolphin11 (talk)

Sexual Selection is one of the "Five Fingers of Evolution." You can remember it as the ring finger -- the one that a person wears their wedding ring on to tell everyone they have a mate! (See illustration, right.) 
Sexual selection

Screencap from the Paul Anderson TED-ed video: The Five Fingers of Evolution

It has been recognized as a powerful agent of evolutionary change, with "far reaching consequences." Sexual selection ca
Weaver and Nest

Photo by David Leadbetter in Oman

n influence speciation.

Intrasexual selection as discussed by Freeman & Herron (2007) involves sex to sex combat (for example males fighting males) or fighting over resources (for example a territory) to secure a mate. The opposite sex is not choosing a mate, they mate with the winners. Morphological traits or the use of tactical cleverness are involved with the success of the combat.

Intersexual selection as described by Freeman & Herron (2007) is when an individual chooses a mate based on interactions between two sexes. One example I can think of is the peacock.

Sexual Selection in Birds.

Birds are such beautiful examples of sexual selection...First there are the colours which are so evident especially with the Birds of Paradise in Papua New Guinea. Nowhere in the world can so many birds be found with such exquisite adornaments. There are feathers of course but there are wires and epaulettes too. But we can also see in less spectacular cases all around the global The Ruppell Weaver birds lose their bright yellow during the year and therefore are better camouflaged. A fantstic example of adaptation and sexual selection
Owl Camouflage

Scops Owl in Oman. photo by David Leadbetter

. Secondly, the Ruppell Weavers also have the added pressure of nest building. This is usually done by striping long fronds from palm trees and threading them to make a nest. But often the male Weaver makes more then one, usually four and the female chooses the best one. This is nothing compared to the Bowerbirds. Returning to Papua New Guinea, the Bowerbirds adorn the nests with collections of colorful leaves, berries and nuts which are neatly stacked and exhibited to attract a female. Thirdly, there are the dances that male birds perform. This is famous with the Great Crested Grebes courtship dance, but equally found around the world with the Birds of Paradise in the Old World, the Mannakins of the New World and the Grouse of Northern Europe. But perhaps the most obvious are the songs of birds - sometimes for territory, often distinguishable from the bird's call, but also used to attracting a mate. Charles Darwin wrote in The Descent of Man (1871), "The diversity of sounds...and the diversity of the means for producing such sounds, are highly remarkable. We thus gain a high idea of their importance for sexual purposes." The shape and strength of the beak are important but for the Mannakins of Ecuador there is an extra feature - club like wings that knock together to produce sounds.

  Koppel, D. (2012) The Virtuoso. National Geographic. May 2012. pp62-69

Andersson, M. B. (1994). Sexual selection. Princeton University Press.

Freeman, S. & Herron, J. (2007). Evolutionary Analysis 4th Ed. Sexual Selection, pp 401-441.

Sexual selection can make animals go to the extremes to obtain a mate to breed with.  A great mammalian example of this is the Elephant Seal.  Male elephant seals will defend their territory and fight other seals to protect it. Sometimes, this territorial protection puts them into conflict humans.   Check out the video to see how sexual selection drives male elephants seals to be highly protective of their territory. 
Elephant Seal Attacks Divers-003:12

Elephant Seal Attacks Divers-0

World's Deadliest - Elephant Seal vs02:49

World's Deadliest - Elephant Seal vs. Elephant Seal-1

A

Natural Selection Tale of the Peacock-004:01

Natural Selection Tale of the Peacock-0

Sexual Selection & Evolution08:20

Sexual Selection & Evolution

YouTube segment of the video "Why Sex" from PBS's Nova Evolution series covering sexual selection and evolution

LekEdit

lek

1 [lek] Show IPA noun, verb, lekked, lek·king. Animal Behavior . noun

1. A place where males of certain bird or mammal species assemble during breeding season to engage in competitive and territorial displays in order to attract females.
Grackles lekking

Wikipedia photo of male Great-tailed Grackles on a lek. Photograph by Michael J. Plagens, 2007.

"Lekking" is the gathering of males at a lek site. Behavior associated with lekking often consists of ritualized signals to other males in attempts to display dominance or to females to display fitness for breeding.

Although within leks there may only be on one male who gets to mate, the other males in the lek may also benefit. In a study of wild turkeys, it was found that the many of turkeys in the leks were related-- in fact, a mixture of full and half siblings. A benefit of the lek is that the dominant male was able to produce (on average) 6.1 offspring, as compared to wild turkeys who did not lek who produced (on average) 0.9 offspring. Because of this drastic increase in the number of offspring that can be produced, and because the males in the lek often share genes, this can be an example of kin selection. Although every male does not mate, by helping a relative get a mate, and thus produce more offspring than if he was not part of a lek, more of their shared genes can be passed on to future generations. This increases the unsuccessful male's inclusive fitness. (Ricklefs, 2008).

Ricklefs, R. (2008). The Economy of Nature (6th ed.). New York, NY: W.H. Freeman and Company. 

Black Grouse Lek02:21

Black Grouse Lek

This YouTube video provides a glimpse into a springtime Black Grouse lek in Norway.

Long-tailed widowbird

Male long-tailed widowbird

Sexual OrnamentationEdit

Sexual ornamentation is a characteristic that attracts a mate or stimulates reproduction. This ornamentation is not limited to morphological features, such as wattles, antlers, color, etc. but may also include song and display, such as male grouses on lekking grounds (Badyaev, 2004) and bugling and urine odor among rutting elk or wapiti. Sexual ornamentation also applies to plants that attract pollinators through the development of flowers (Badyaev, 2004). 

Badyaev, A.V. (2004) Developmental perspective on the evolution of sexual ornaments. Evolutionary Ecology Research, 975-991.

Badyaev (2004) discusses the paradox of sexual ornamentation and the costs. A more exaggerated sexual ornament may be accomplished by an increased and more efficient allocation of resources, so that a smaller increase in physical and psychological condition is amplified into a progressively larger sexual ornament. Alternatively, this ornament might be enabled by a decrease in the integration between sexual ornaments and the rest of an organism. It seems that long-growing ornaments better reflect an individual’s condition than ornaments that are shorter growing and less integrated.

Badyaev, A.V. (2004) Developmental perspective on the evolution of sexual ornaments. Evolutionary Ecology Research, 975-991.

Example: The Long-Tailed Widowbird

The male long-tailed widowbird has extremely long tail feathers in order to attract mates. The long feathers do not seem to have any other purpose, and likely slow the animal down and make it easier for predators to find. The animals with the longest tail feathers are still the most successful at obtaining mates. The likely explanation of this phenomenon is that the ability to grow and maintain such long feathers proves that the animal is fit and healthy (Freeman & Herron, 2007).

Freeman, S. & Herron, J. (2007). Evolutionary Analysis 4th Ed. Sexual Selection, pp 401-441.

Astounding Mating Dance Birds of Paradise -- High Quality02:03

Astounding Mating Dance Birds of Paradise -- High Quality

Bird of Paradise for BBC's DVD (posted by Alex Ivanov on Youtube)

Moonwalking Bird HD03:29

Moonwalking Bird HD

Moonwalking manakin! Be sure to watch until the end; especially Michael Jackson fans.

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