Bird II: Sexual
Selection and Breeding Systems – Dr, David DesRochers
SEXUAL SELECTION
(Chapter 9: Reproductive Behavior- pgs. 303-350)
·
Why are birds
selective in their choice of a mate?
o
mating is a huge
energy investment
o
you want to mate
with an individual that has designated evolutionary fitness to increase the
chance your offspring have of making it!
·
Sexual Selection as
a Mode of Natural Selection
o
strategies: many
vs. few eggs; long-lived vs. short-lived mate choice
o
female mate choice
drives evolutionary changes
·
**Sexual
dimorphism: difference in size/appearance based on sex
o
How have colorful
and ornamental male physical characteristics evolved to aid in mate attraction
despite the possibility of these same features making males more vulnerable to
predation?
o
Good Genes
Hypothesis
§
females interpret
male plumage and courtship displays to be accompanied by genetically superior
survival skills
o
Direct Benefits
Hypothesis
§
a female’s
survivorship & ability to produce offspring can be enhanced by sexual
ornamentation of a mate
§
benefits:
high-quality territories, protection from predators, lower chance of disease,
higher rate of offspring production
o
Arbitrary Choice
and Runaway Selection
§
selection for
aesthetic ornamentation provides has no benefits to mates
§
may help with
imprinting in young birds
·
Lek Displays
o
Hot Spot Model
§
Males gather where
they are most likely to encounter females
o
Hotshot Model
§
Males gather around
other males who are more likely to succeed (due to experience, attractiveness,
or dominance) in hopes of being seen or to learn
o
Female Preference
Model
§
Females prefer to
visit larger gatherings of males (more convenient shopping!)
·
Solitary Display
Courts
o
bower
= structures built for display and copulation
·
Monogamy
(~90% of
species)
o
prolonged or
life-long pair bonding
o
tremendous
investment in parent care of young
·
Cuckoldry
and promiscuity
o
when a pair-bonded
female mates with a male other than her partner
§
likely to produce
offspring unrelated to pair-bonded mate
§
mate will care for
unrelated offspring
o
Only 14% of
socially monogamous species are genetically monogamous: WHY??
BREEDING SYSTEMS
(Chapter 10: Breeding Systems- pgs. 353-399)
·
Why mate?
o
To pass on your
genes!
§
accomplished by
raising your own young and/or relatives
§
multiple
strategies, each with trade-offs
à
complex breeding systems
·
Types of breeding
systems
o
polygyny:
one male, multiple females
§
males provide
little care
§
females clump and
share male help
à
easier to monopolize resources
o
polyandry:
one female multiple males (fairly rare)
§
females are
aggressive, keep territories, and dominate courtship
§
males provide all
parental care
§
can be a range of
monogamy to polyandry in a species
§
à
sex-role reversal? variations in testosterone during incubation/brooding
§
increase in raising
of extra-pair young
·
Brood parasitism
(cheating!)
o
reproductive success without cost of individual care (except for host)
o
inter-/intraspecific forms; some are obligate brood parasites
·
Recent severe
decrease in nesting migratory birds
o
Why?
·
Cooperative
Breeding
(common)