Lecture 8.pdf

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Ecology & Evolutionary Biology
Michael Denny

Lecture 8 Courtship and Mating Systems CourtshipDuring courtship one sex usually the male sends signals to the female to induce her to mateCourtship functions to attract a mate stimulate and synchronize receptivity and it can convey information about the potential mate o This information can include the sex of the individual the state of readiness size and experience of the potential mate and the quality of the mate or quality of their territoryIn birds courtship displays can take a variety of forms including song plumage badges displays dance gifts of food and in the most unusual case built structures the bowers of BowerbirdsIn most species courtship displays are short and not very distinctive often no more than some song calls and some body or wing postures o But there are also the audacious and spectacular displays of birds such as the Indian Peafowl Peacock or the Birds of ParadisePerhaps the most audacious plumage ornamentation and courtship is seen in male Birds of ParadiseIn the Ragianna BoP Paradisaea raggiana males gather at communal display trees call and display their long orange plumes to visiting females o Tribespeople in New Guinea have prized the long plumes of Ragianna for centuriesCarolas Parotia Parotia carolae also tends a courtship arena but it performs an elaborate balletlike dance routine to visiting femalesSexual SelectionIn many bird species males are more brightly plumaged in the breeding season than females and they initiate coursthip and give elaborate courtship displaysDarwin was quite perplexed by the extreme sexual dimorphism in birds In one famous quote he opined The sight of a feather in a peacocks tail whenever I gaze at it makes me sick It made him sick with worry as his new theory of evolution had to explain the audacious plumage displays and courtships of birds and other animalsHis dilemma was to explain traits such as the long tails of male Indian peafowl in terms of survival and reproduction How could the peacock tail be adaptive in terms of survivalAnisogamyAt the root of these marked differences in sex roles is anisogamy the huge difference in gamete size between eggs and spermMales invest much less energy and time in their sperm than females do in their eggsOnce mated a female is busy with offspring whereas males are available to mate again o As a consequence there will usually be a surplus of males relative to potential female mates in the population at any time malebiased operational sex ratioMales may have to compete for access to the females and females can be choosyBateman 1948 first demonstrated variation in male mating success and related it to sexual selection His socalled Batemans principles are males have a higher variance in the number of offspring than femalesmales have higher variance in number of mates than females female drosophila typically mate just once males have a positive correlation between number of mates and number of offspring in females this relationship asymptotes quicklySexual selection sometimes coined female selection on males occur on traits if they vary in males and affect their reproductive success by influencing male competition for access to females OR the attractiveness of males to females female choiceDarwin developed the concept of sexual selection and realized that in some instances the benefits of having audacious plumage which ensured that you obtained matings outweighed the possible costs in higher predation risk and reduced longterm survivalIn malemale competition for mates intrasexual selection males may fight each other for access or compete with each other for resources that females need to accessIn birds territoriality is an example of intrasexual competitionConsequences o Female reproductive success is limited by resources energy to mature eggs rear young o Male reproductive success is limited by access to females number of matingsFemale Choice
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