Transcript Chapter 11 sexual selection (slides 19-35)

• Signal honesty
– “Good genes”
models versus
runaway models
• Conditional
handicap
• Revealing
handicap or
“index”
From Zahavi 1975 J. Theor. Biol. 53:205-214
• Predation
costs
• Physiological
costs
From Ryan et al. 1982. Am. Nat. 119:136-139
http://gallery.pictopia.com/natgeo/photo/1112965/
• Leks
• Theory: Heritability of
fitness relevant traits
should rapidly decline
• Solutions
http://www.arthurgrosset.com/sabirds/photos/
manman8933.jpg
Video by Mark E. Berres 2002
– Accumulation of
deleterious mutations
– Selection pressure
varies over time & space
– Females seek
compatible genes
• A form of changing
selection pressure
–
–
Coevolving “parasites” are
a moving target
Mixed results
• Immunocompetence
handicaps
From Milinski & Bakker 1990 Nature 344:330-333
• Female sensory or
cognitive bias
– Origin
• Practical
• Incidental
• Males ‘exploit’ bias
• In tungara frogs
– Chuck is derived,
relative to basilar
papilla tuning
From Ryan et al. 1990 Nature 343:66-67
• Genetic
– Heterozygosity
masks deleterious
recessives
– MHC
– Evidence
• Inbreeding
avoidance
• Female preference
for genetically
dissimilar males
http://lancaster.unl.edu/pest/images/Cockroaches/gm_roaches.jpg
From Lihoreau et al . 2007 Behav. Ecol. 20:46-53
• Competition in
female genital
tract between
sperm of two or
more males
• As scramble
competition
• As interference
competition
– May exist
• Sperm removal
• Toxic ejaculates
– Protect own sperm
– Harm other males’
sperm
– Alter female
behavior
• Higher fecundity
• Lower promiscuity
– Harm to female is
a byproduct
• Female choice that
occurs within a
female’s body
• Sperm selection
• Copulatory
performance
– Intromission rate and
paternity in Linyphia
litigiosa
• Implantation & abortion
From Watson & Lighton 1994 Anim. Behav. 48:615-626
• Forced monogamy on
fruit flies
– Monogamous
• Less toxic ejaculates
• Lower male courtship
rate
• Less female resistance
to toxic ejaculates
• Lower body / testes
size, sperm count
– Polygamous
• Females laid more eggs
• “The worst blunder in sexual preference”
• Now thought that species recognition
relies on subset of mate choice traits
• Two mechanisms
– Allopatric divergence
– Reinforcement
• Negative selection on marginal types if hybrid
matings produce less viable offspring
–
Reproductive character displacement
• Pre-reproductive isolation
– Sexually selected characters can diversify
rapidly given small initial changes
•
•
•
Drift
Founder effects
Local conditions
– Many closely related species differ primarily in
sexually selected traits
• Natural selection could drive divergence
– Isolated populations adapt to environment …
– … and these adaptations affect their sexual signals
From Podos 2001 Nature 409:185-188