11.1 Sexual selection favors characteristics
that enhance reproductive success
• Primary sexual characteristics
– Genitalia and organs of reproduction
• Secondary sexual characteristics
– Morphological differences between the sexes that are
not directly involved in reproduction
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Bateman’s hypothesis
• Bateman’s hypothesis:
– Female reproductive
success is most
strongly limited by the
number and success of
eggs that she can
produce, whereas male
reproductive success is
limited by the number
of mates
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Figure 11-9
Figure 11-10
Figure 11-11
Figure 11-12
Figure 10.8 Differences between the sexes in sexual behavior may arise from fundamental
differences in parental investment that affect the rate at which individuals can produce offspring
Featured Research
Antlers as weapons in red deer
• Research question: Are antlers weapons used
in mate competition? (Kruuk et al. 2002)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Antlers as weapons in red deer
• Methods:
– Red deer (Cervus
elaphas)
– Collected and
weighed antlers shed
– Used blood samples
to determine
reproductive success
(paternity)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Antlers as weapons in red deer
• Results:
– Males with larger antlers
had higher reproductive
success
• Conclusion:
– Sexual selection has
influenced antlers as an
exaggerated trait in
mate choice
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Weapon size and mating success in
dung beetles
• Research question: What is the role of the
male’s horn-like projection? (Pomfret & Knell
2006)
• Hypothesis: Large horns provide an advantage
in mate competition
• Prediction: Males with the larger horn will win
most fights
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Weapon size and mating success in
dung beetles
• Methods:
– Dung beetles (Euoniticellus intermedius)
– Staged fights between males matched for body
size but not horn length
– Recorded outcome of interactions and mating
success
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Weapon size and mating success in
dung beetles
• Results:
– Males with larger horns
won more fights
• Conclusion:
– The maintenance of long
horns can be explained
by sexual selection
driven by male-male
competition
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Ornaments and mate choice in
peafowl
• Research question:
Are peacock tails an
ornament used in
mate choice? (Loyau,
Saint Jalme, & Sorci
2005)
• Males aggregate on
leks, where they
display to females
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Ornaments and mate choice in
peafowl
• Methods:
– Peacocks (Pavo cristatus)
– Measured:
• Tail length and male body size
• Number and duration of tail displays
• Number of vocalizations and copulations
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Ornaments and mate choice in
peafowl
• Results:
– Larger males with
longer tails were most
successful in defending
a display site
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Ornaments and mate choice in
peafowl
• Results:
– Males performing the
most displays and with
the greatest number of
ocelli obtained the most
copulations
• Conclusion:
– Mate competition and
mate choice are
important in evolution of
peacock tail
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
The origin of sexually selected traits:
the sensory bias hypothesis in guppies
• Research question: How does a male trait
become selected in female mate preference?
(Rodd et al. 2002)
• Hypothesis: Sensory bias hypothesis – female
mating preferences are a byproduct of
preexisting biases in a female’s sensory system
• Prediction: Males and females should be
attracted to orange-colored objects because
orange is associated with carotenoids
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
The origin of sexually selected traits:
the sensory bias hypothesis in guppies
• Methods:
– Guppies (Poecilia reticulata)
– Several populations
– Placed small color discs on
leaf in water
– Recorded all approaches
and pecks
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
The origin of sexually selected traits:
the sensory bias hypothesis in guppies
• Results:
– Males and females were
attracted to orange and
red discs
• Conclusion:
– Female mating preference
could be linked to
preexisting preference for
orange food objects
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Jones and
Hunter 1998
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
11.2 Females select males to obtain
direct material benefits
• Direct material benefits
– Material resources obtained by a female from
mating with a particular male
• Nuptial gift
– A physical resource such as a food item that a
male provides to a female to enhance his mating
success
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Female choice and nuptial gifts in
fireflies
• Research question: How does the variation in
the duration of male flashes affect female
choice and fitness? (Lewis, Cratsley, & Rooney
2004)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Female choice and nuptial gifts in
fireflies
• Methods:
– Fireflies (Photinus ignitus)
– Measured male flash
duration and
spermatophore size
– Created flashes of
different lengths and
measured female
response
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Female choice and nuptial gifts in
fireflies
• Results:
– Males with
longer flash
duration had
larger
spermatophores
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Female choice and nuptial gifts in
fireflies
• Results:
– Females responded more to
longer flashes
• Conclusion:
– Females prefer to mate with
males with the longest flash
duration and thus the largest
spermatophores, which
should increase fitness
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Female choice and territory quality in
lizards
• Research question: How
does territory quality
affect female choice and
fitness? (Calsbeek &
Sinervo 2002)
• Territory quality is based
on rockiness
(microclimates)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Female choice and territory quality in
lizards
• Methods:
– Side-blotched lizards (Uta stansburiana)
– Larger males have territories with more rocks
– Manipulated territory quality
• Added rocks to small males’ territories
• Removed rocks from large males’ territories
– Observed female mate choice
– Measured egg-laying date and egg mass of females
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Female choice and territory quality in
lizards
• Results:
– Females preferred improved
territories
– Females on improved territories
laid eggs sooner and produced
larger egg masses
• Conclusion:
– Females select males based on
territory quality and derive a
significant fitness gain by doing so
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
11.3 Female mate choice can evolve
via indirect benefits to offspring
• Indirect genetic benefits
– Genetic benefits females can obtain for their
offspring by mating with males that have high
genetic quality
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Fisherian runaway and good genes
• Runaway process
– An evolutionary process in which a male trait coevolves with a female preference for it and
becomes increasingly exaggerated
• Handicap principle
– Well-developed secondary sexual characteristics
are costly to survival but reliable signals of fitness
• Good genes
– The alleles of high-quality individuals
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Figure 11-32
Figure 16-14
Figure 16-15b
Sexual dimorphism
And behavior!
Long-tailed widowbird (male on left)
Featured Research
Mate choice for good genes in frogs
• Research question: How do females assess
male quality? (Jacquiéry et al. 2009)
• Hypothesis: Females select males for genetic
benefits based on their vocalizations
• Prediction: The most attractive males provide
the best gene alleles (fitness) to offspring
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Mate choice for good genes in frogs
• Methods:
SONG video
– European tree frogs (Hyla arborea)
– Captured and identified males from
four ponds
– Observed number of matings
– Collected egg masses and reared in lab
– Measured tadpole growth rate and
survival
– Genotyped tadpoles to determine
parentage
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Mate choice for good genes in frogs
• Results:
– Only 10 of 15 males sired
offspring
– Males that sired more
offspring produced
tadpoles with higher
growth rates
• Conclusion:
– Females select males for
genetic benefits
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Good genes and immune system
function in birds
• Research question: How does parasite load affect
mate choice? (Zuk et al. 1990)
• Hypothesis: Hamilton-Zuk hypothesis
– Parasites and pathogens play an important role in
sexual selection when secondary sexual traits are
costly and condition-dependent
• Predictions:
1. Females should prefer to mate with males that have
the greatest expression of secondary sexual traits
2. High parasite loads will reduce that expression in
males
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Good genes and immune system
function in birds
• Methods:
– Red jungle fowl (Gallus gallus)
– Infected half the males with
intestinal nematode
– Measured size and color
intensity of comb
– Conducted mate choice trials
with infected and controls
(uninfected) males
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Good genes and immune system
function in birds
• Results:
– Parasitized males had smaller,
duller combs than controls
– Females preferred control
males
• Conclusion:
– Support for Hamilton-Zuk
hypothesis
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Mate choice fitness benefits in spiders
• Research question:
What is the
importance of
pheromones as signals
of male quality in mate
choice? (Koh et al.
2009)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Mate choice fitness benefits in spiders
• Methods:
– Spitting spider (Scytodes sp.)
– Mate choice experiment in Y
test chamber
• Phase 1: Two males at end of
arms (chemical cues only)
• Phase 2: Pheromones of males
only at end of arms (on filter
paper)
– Mating experiment
• Half of females mated with
preferred male, half with
nonpreferred male
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Mate choice fitness benefits in spiders
• Results:
– In Phase 2, almost
all females chose
the pheromone of
the male they
chose in Phase 1
– Females who
mated with
preferred males
had larger egg
sacs, more and
heavier eggs, and a
higher hatch rate
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Mate choice fitness benefits in spiders
• Conclusion:
– Male pheromones may function to convey
information about male quality
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
11.4 Sexual selection can also occur
after mating
• Mate guarding
– When a male follows his mate to prevent her
from mating with rivals – beetle video; fly video
• Extra-pair young
– Offspring of a pair-bonded female produced
outside the pair bond by a third-party male
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Mate guarding in warblers
• Research question: How effective is mate
guarding? (Chuang-Dobbs, Webster, & Holmes
2001)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Mate guarding in warblers
• Methods:
– Black-throated blue
warblers (Dendroica
caerulescens)
– Observations:
• Followed focal males and
measured distance between
them and their mates
– Experiment:
• Removed some males for
one hour during female’s
fertile period
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Mate guarding in warblers
• Results:
– Males who spent more time
mate guarding had fewer
extra-pair offspring
– Experimentally removed males
had more extra-pair offspring
• Conclusion:
– Mate guarding can be an
effective strategy for increasing
paternity assurance
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Sexual selection after mating
• Sperm competition
– Competition between sperm of different males to
fertilize eggs
• Cryptic female choice
– When female influences the fertilization success of
sperm from one male over that of others
• Inbreeding depression
– A reduction in fitness as a result of mating with
close relatives
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Sperm competition in tree swallows
• Research question: How can males increase
paternity assurance? (Crowe et al. 2009)
• Hypothesis: Paternity assurance can be
enhanced through frequent copulations
• Prediction: An increase in copulation rate
should result in an increase in paternity for a
male
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Sperm competition in tree swallows
• Methods:
– Tree swallows (Tachycineta
bicolor)
– Uniquely marked birds and
collected blood samples for
genetic analysis
– Observed focal pairs for three
hours per day for two weeks
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Sperm competition in tree swallows
• Results:
– Increases in copulation rate
resulted in decrease of extrapair offspring
• Conclusion:
– Males can reduce paternity
loss from sperm competition
by increasing their copulation
frequency
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Inbreeding avoidance via cryptic female
choice in spiders
• Research question: Do
females avoid inbreeding
depression by cryptic
female choice? (Welke &
Schneider 2009)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Inbreeding avoidance via cryptic female
choice in spiders
• Methods:
– Orb spiders (Argiope lobata)
– Experiment 1– Mating trials in which a female
mated sequentially with:
• 1) Two sibling males (SS)
• 2) Two nonsibling males (NN)
• 3) Sibling and nonsibling male (SN or NS)
– Experiment 2 – Mating trials
• One male of pair was made sterile
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Inbreeding avoidance via cryptic female
choice in spiders
• Results:
– For second male:
• Females stored more sperm from
nonsibling than from sibling
• More eggs fertilized
• Conclusion:
– Females display cryptic female
choice in regard to matings with
siblings, which should reduce
inbreeding depression
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
11.5 Mate choice by females favors
alternative reproductive tactics in
males
• Alternative mating tactics
– Multiple behavioral mating phenotypes in a population
• Satellite male
– Alternative, parasitic mating tactic in which a male remains
near a bourgeois male to intercept females that are
attracted to the bourgeois male
• Sneaker male
– Alternative, parasitic mating tactic in which a male
attempts to avoid detection so that he can quickly enter a
bourgeois territory to fertilize eggs being deposited in a
nest
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Evolution of alternative reproductive
tactics
• Conditional strategy
– Use of a particular strategy based on an
individual’s condition
• Evolutionary stable strategy (ESS)
– A strategy that, if adopted by individuals in a
population, cannot be trumped by another
strategy because it yields the highest fitness
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Conditional satellite males in tree
frogs
• Research question: Does male tree frog mating
behavior represent a conditional reproductive
strategy? (Humfeld 2008)
• Hypothesis: Males will adopt reproductive
strategies based on their condition
• Predictions:
1.
Males differ in attractiveness to females;
unattractive males will be satellites
2. Satellite males should have the same call
preferences as females (lower-frequency calls)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Conditional satellite males in tree
frogs
• Methods:
– Green tree frogs (Hyla cinerea)
– Recorded calls of bourgeois
and satellite males
– Created synthesized calls
(lowest frequencies 700 Hz and
840 Hz or 840 Hz and 1120
Hz)
– Conducted choice tests for
calls with females and satellite
males
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Conditional satellite males in tree
frogs
• Results:
– Bourgeois males were larger
and produced lower-frequency
calls than satellite males
– Females and satellite males
preferred lowest-frequency
calls
• Conclusion:
– Males adopt a conditional
strategy
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
ESS and sunfish sneaker males
• Research question: What is the reproductive
success of parental and sneaker male
pumpkinseed sunfish? (Rio-Cardenas &
Webster 2008)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
ESS and sunfish sneaker males
• Methods:
– Pumpkinseed sunfish
(Lepomis gibbosus)
– Mapped all nest locations
– Captured nesting males
(parentals), females, and
sneakers at nest and all
developing eggs
– Conducted genotype
analysis
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
ESS and sunfish sneaker males
• Results:
– Parentals larger and older than
sneakers
– Parentals sired about 85% of
offspring in their nest
– Sneakers are very rare in
population, and their
reproductive success is
proportional to their abundance
• Conclusion:
– The two strategies have equal
fitness
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Two examples of alternative mating tactics.
Bryan D. Neff, and Erik I. Svensson Phil. Trans. R. Soc. B
2013;368:20120045
©2013 by The Royal Society
Roughgarden 2004
Roughgarden 2004
11.6 Learning and mating
• Mate choice copying
– When one individual observes and copies the
mating decisions of another individual
• Sexual imprinting –
–
mate choice influenced by traits seen in
‘sensitive’ period (e.g., influenced by parents’
traits)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Mate copying in guppies
• Research question: Do females copy the mate
choice of other females? (Dugatkin 1992)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Mate copying in guppies
• Methods:
– Focal female mate choice test
– Model female then placed next to nonchosen male
so that focal female could observe
– Focal female mate choice test
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Mate copying in guppies
• Results:
– 17 out of 20 females spent more time near the
male that had been near the model female
• Conclusion:
– Females switched their mate choice preference to
copy the mate choice of the model female
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
The benefit of mate copying
• Mate choice copying should only occur when
discrimination among potential mates is
difficult
– Males are very similar
– Females are inexperienced
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Nonindependent mate choice by male
mosquitofish
• Research question: Does the risk of sperm
competition affect mate choice? (Wong &
McCarthy 2009)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Nonindependent mate choice by
male mosquitofish
• Methods:
– Focal male mate choice test
– Rival male then placed next to each
female
– Focal male mate choice test
– Experiment 1 – focal male cannot
see rival
– Experiment 2 – focal male
observes rival near chosen female
– Experiment 3 – focal male
observes rival near nonchosen
female
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Featured Research
Nonindependent mate choice by male
mosquitofish
• Results:
– Experiments 1 and 3 – males
preferred larger female
– Experiment 2 – focal male
spent less time with chosen
female during the last stage
• Conclusion:
– Male mate choice is affected
by risk of sperm competition
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
From Nordell and Valone, Animal Behavior:
Concepts, Methods, and Applications, ©
2014 by Oxford University Press
Megalagrion calliphya
Beautiful Hawaiian Damselfly
R. Rasmussen MAP Summer 2016
1 .0
0.8
0.6
0.4
0.2
0.0
Individual Type
Andromorph Gynomorph
Male
Proportion Sexual Interaction Time
Andromorph Gynomorph
Male
Proportion Sexual Interactions
Figure 6. The proportion of sexual interactions between Megalagrion
calliphya focal andromorphs, gynomorphs, and males from Upper
Mountain House Road (UMHR) (Wilcoxon Each Pair test, n=9
gynomorphs, n=8 males, n=8 andromorphs, p=0.0305 between males
and andromorphs, p>0.05 for all other comparisons). In addition, the
proportion of the total time spent sexually interacting between the
three individual types at UMHR (Wilcoxon Each Pair test, n=10
gynomorphs, n=11 males, n=10 andromorphs, p=0.0365). The quartile
method was used to calculate endpoints. Outliers are signified by the *
symbol.