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Welcome to the DragonflyIssuesInEvolution13 Wiki

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 Selection

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.)

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

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

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

Natural_Selection_Tale_of_the_Peacock-0 — Natural Selection Tale of the Peacock-0

Sexual_Selection_&_Evolution — Sexual Selection & Evolution

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

Lek

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_Lek — 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 Ornamentation

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).