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
What kinds of indicators may males use to choose a female?
- Some male birds appear to adjust their investment in parental care in relation to
the quality of their mate - Example Eurasian blue tit:
Carotenoid-based female coloration was positively linked to key indicators of bird
lifetime reproductive success: clutch size, fledgling success and recruitment
Genetic benefits of mate choice
- “good genes” hypothesis: Exaggerated male plumage and courtship displays truthfully signal genetic or physiological superiority
Example: Female Bobolinks prefer males in good condition with longer flight displays; average number of females that (unaltered)
males attracted increased with their relative
condition
Genetic benefit: Zebra Finch
- Males with redder beaks are considered more attractive to females
- Direct correlation between carotenoids in a zebra finch’s diet and its sexual attractiveness and ability to have a strong immune system
Material benefits of Mate choice
- Material Benefits (direct benefits hypothesis)
- Sexual ornaments communicate a potential mate’s ability to provide resources or
protections that enhance the female’s survivorship or her fecundity
Example of Material benefits
- courtship feedings, shows they can provide
- increase in feeding increases maternal health and offspring health
- Ex: northern cardinal
Material benefit in a raptor
American Kestrel
- Males with the brightest orange cere (bill skin, arrow) are most likely to be the best providers late into the nestling period, when offspring survival is critical but food can be harder to find
Arbitrary choice and runaway selection hypotheses
- Sexual ornamentation evolves through arbitrary choice and runaway selection for
aesthetically pleasing ornaments - Sexy males, it is presumed, will have sexy sons that are more popular than others,
driving both the evolution of genes for the ornament and genes for the preference
Monogamy
Genetic monogamy: a mating
system in which a female mates with
only one male.
ex: Common Loons
Social monogamy: in birds, a mating system in
which one female forms a lasting pair bond with one male, although she may also copulate with
other males.
Example: Dovekies
Polygamy
- Any mating system that includes multiple mates of the opposite sex
Polygyny
- one male, multiple females
Polyandry
- one female, multiple males
Polygynandry
- female mates with several males, each of which also mate with several females
Promiscuity
- no prolonged pair bonds formed, mating system
Serial monogamy
- monogamous within a breeding season
Understand the 2 types of “cheating” (extra-pair copulations) in monogamous species:
Cuckoldry: older males will sneak a copulation with another female that hopefully will result in an egg
Egg dumping: females will sneak her egg into another female’s nest
How do extra-pair copulation attempts relate to a female’s fertile period?
- The rate of territorial intrusions by other males, EPC attempts, and successful EPCs drops off during the female
fertile period, as expected - When males were experimentally fooled into thinking that their mate was past her fertile period (via the addition
of a model egg in a newly lined nest), they left her unguarded, allowing other males to engage in more territorial
intrusions and gain more EPC
