Chapter 13 Flashcards
Sexual selection
two special kinds of natural selection:
1) Members of one sex create a
reproductive differential among
themselves by competing for
opportunities to mate
Compete for territory
2) Members of one sex create a
reproductive differential in the other sex
by preferring some individuals as mates
Most common type among birds
Understand how differences in reproductive investment typically lead to the evolution of female mate choice
- In birds, it is usually the female that chooses the male (although not always)
Drives the evolution of male secondary sexual characteristics - large expensive gametes, more investment, the best mate (whereas males look for cheaper and more eugh)
Understand how male Long-tailed Widowbirds are an example of sexual selection
- Males of this polygynous (male mates with multiple females)* species are black with red and buff on their shoulders and have tails about sixteen inches long
- The tails are prominently exhibited as the male flies slowly in aerial display over his territory
- females prefer the long tails, male ability to attract females directly correlates with this
What are Leks?
- Members of one sex create a reproductive differential among themselves by competing for opportunities to mate
- It’s typically the females doing the choosing
- Female comparisons of male displays are a key ingredient of leks
A lek: an aggregation of male display territories that include no other
resources for reproduction other than opportunities to mate
3 primary models for evolution of leks
- hot spot
- hot shot
- female preference
“hot spot” model
males gather at sites where they are most likely to encounter roaming females
“hotshot” model
- males gather around experienced, attractive, or dominant males to increase their chances of being noticed within large aggregation
female preference model
females prefer to visit large clusters of males
over small clusters or solitary males
Succesful males
-Sage Grouse: Socially dominant birds that hold central positions on the lek and are more active and visually or vocally attractive or both than are unsuccessful males
- Blue Manakin: cooperate group displays required to excite and attract females (line dancing)
- Birds of paradise have bright colors to show off!!
Effects of sexual selection in Birds of Paradise
- Most paradisaeids are polygynous with female-only parental care; A few species are socially monogamous
- Males perform elaborate and highly stereotyped courtship displays
- The type of display varies substantially among species, and display behaviors
have evolved to show off specialized plumes and iridescent plumage patches and
brightly colored skin in bizarre and exaggerated fashion
lek or dispersed lek breeding in Birds of Paradise
- Males gather at specific sites that females may visit to compare the display
quality of multiple males at one time
Examples of birds of paradise
- Wilson’s bird of paradise: all primary colors, and even green on the neck to shine at female, curly tail with color in certain angles
- Western Parotia: dancing with feathers out in circle, shaking of the head/antennas
- Greater bird of paradise: fluffy long yellow tail to attract
Sexual Selection in Bower birds
- Males build solitary display courts on which they construct and decorate
elaborate stick or grass structures, called bowers, which provide platforms for
both courtship and copulatio
Two types of bowers built by bowerbirds
Maypole bowers: consist of sticks built around a central sapling, or maypole, with a circular runway around it
Avenue bowers: have two parallel walls with a narrow passage in
between for the visiting female to observe the male. 5 spp
Modestly colored species tend to have more elaborate bowers than do
brightly colored species
bowers signal at larger brain than other species and nonbower birds
Examples of bowerbirds
- Satin Bowerbird: build twig circle surrounded in blue coloration to attract mate
- Great Bowerbird: builds ring in nature coloration to attract mate
