Sneaker "jack" males outcompete dominant "hooknose" males under sperm competition in Chinook salmon (Oncorhynchus tshawytscha)


Young, B.; Conti, D.V.; Dean, M.D.

Ecology and Evolution 3(15): 4987-4997

2014


In a variety of taxa, males deploy alternative reproductive tactics to secure fertilizations. In many species, small "sneaker" males attempt to steal fertilizations while avoiding encounters with larger, more aggressive, dominant males. Sneaker males usually face a number of disadvantages, including reduced access to females and the higher likelihood that upon ejaculation, their sperm face competition from other males. Nevertheless, sneaker males represent an evolutionarily stable strategy under a wide range of conditions. Game theory suggests that sneaker males compensate for these disadvantages by investing disproportionately in spermatogenesis, by producing more sperm per unit body mass (the "fair raffle") and/or by producing higher quality sperm (the "loaded raffle"). Here, we test these models by competing sperm from sneaker "jack" males against sperm from dominant "hooknose" males in Chinook salmon. Using two complementary approaches, we reject the fair raffle in favor of the loaded raffle and estimate that jack males were ∼1.35 times as likely as hooknose males to fertilize eggs under controlled competitive conditions. Interestingly, the direction and magnitude of this skew in paternity shifted according to individual female egg donors, suggesting cryptic female choice could moderate the outcomes of sperm competition in this externally fertilizing species.

Ecology
and
Evolution
0
en
Access
Sneaker
"jack"
males
outcompete
dominant
"hooknose"
males
under
sperm
competition
in
Chinook
salmon
(Oncorhynchus
tshawytscha)
Brent
Young',
David
V.
Conti
2
&
Matthew
D.
Dean'
'Molecular
and
Computational
Biology,
University
of
Southern
California,
Ray
R.
Irani
Building
room
304A,
1050
Childs
Way,
Los
Angeles,
California
90089
2
Department
of
Preventive
Medicine,
Keck
School
of
Medicine,
University
of
Southern
California,
2001
N.
Soto
Street
202S,
Los
Angeles,
California
90089
Keywords
Hooknose,
jack,
salmon,
sexual
selection,
sneaker
male,
sperm
competition.
Correspondence
Matthew
D.
Dean,
Molecular
and
Computational
Biology,
University
of
Southern
California,
Ray
R.
Irani
Building
room
304A,
1050
Childs
Way,
Los
Angeles,
CA
90089.
Tel.:
+1
213
740
5513;
Fax:
213
740
8631;
E-mail:
matthew.dean@usc.edu
Funding
Information
Funding
was
provided
by
USC
startup
funds
(MDD).
Received:
16
August
2013;
Revised:
29
September
2013;
Accepted:
2
October
2013
Ecology
and
Evolution
2013;
3(15):
4987-
4997
doi:
10.1002/ece3.869
Abstract
In
a
variety
of
taxa,
males
deploy
alternative
reproductive
tactics
to
secure
fertilizations.
In
many
species,
small
"sneaker"
males
attempt
to
steal
fertiliza-
tions
while
avoiding
encounters
with
larger,
more
aggressive,
dominant
males.
Sneaker
males
usually
face
a
number
of
disadvantages,
including
reduced
access
to
females
and
the
higher
likelihood
that
upon
ejaculation,
their
sperm
face
competition
from
other
males.
Nevertheless,
sneaker
males
represent
an
evolu-
tionarily
stable
strategy
under
a
wide
range
of
conditions.
Game
theory
suggests
that
sneaker
males
compensate
for
these
disadvantages
by
investing
dispropor-
tionately
in
spermatogenesis,
by
producing
more
sperm
per
unit
body
mass
(the
"fair
raffle")
and/or
by
producing
higher
quality
sperm
(the
"loaded
raf-
fle").
Here,
we
test
these
models
by
competing
sperm
from
sneaker
"jack"
males
against
sperm
from
dominant
"hooknose"
males
in
Chinook
salmon.
Using
two
complementary
approaches,
we
reject
the
fair
raffle
in
favor
of
the
loaded
raffle
and
estimate
that
jack
males
were
—1.35
times
as
likely
as
hook-
nose
males
to
fertilize
eggs
under
controlled
competitive
conditions.
Interest-
ingly,
the
direction
and
magnitude
of
this
skew
in
paternity
shifted
according
to
individual
female
egg
donors,
suggesting
cryptic
female
choice
could
moder-
ate
the
outcomes
of
sperm
competition
in
this
externally
fertilizing
species.
Introduction
Evolutionary
processes
have
produced
a
stunning
variety
of
characteristics
that
appear
adaptive
for
male
reproduc-
tive
success,
including
morphological
weaponry,
genitalic,
and
sperm
features,
and
alternative
mating
strategies
(Andersson
1994).
While
dominant
males
fight
to
secure
territory
and
access
to
females,
many
species
include
"sneaker"
males
that
forego
the
physiological
costs
associ-
ated
with
dominance
and
instead
attempt
to
reproduce
surreptitiously.
Sneaker
males
usually
encounter
numer-
ous
obstacles
to
fertilization,
including
reduced
access
to
females,
and
the
virtual
guarantee
that
their
sperm
will
be
competing
with
sperm
from
other
males.
Nevertheless,
sneaking
represents
an
evolutionarily
stable
strategy
under
many
conditions.
How
sneaker
males
compensate
for
their
apparent
reproductive
disadvantages
is
a
subject
of
much
interest.
Using
game
theory,
Parker
(1990b)
formalized
the
"sneak-guard"
model
to
identify
conditions
where
sneaker
males
represent
an
evolutionarily
stable
strategy
(Maynard
Smith
1982;
Gross
1985,
1991,
1996;
Parker
1990a,b;
Tanaka
et
al.
2009).
Finite
resources
create
a
fundamental
trade-off
between
development
of
precopulatory
(i.e.,
weaponry)
versus
postcopulatory
(i.e.,
sperm
competitive
ability)
traits
(Parker
1990a;
Pitcher
et
al.
2009;
Tazzyman
et
al.
2009;
Fitzpatrick
et
al.
2012).
In
general,
dominant
males
invest
in
weaponry
that
can
be
used
to
monopolize
access
to
females,
while
sneaker
males
invest
in
ejaculates
to
win
fertilizations
through
sperm
competition.
Under
the
sneak-guard
model,
sneaker
males
invest
in
ejaculates
via
two
nonexclusive
mechanisms,
the
"fair
©
2013
The
Authors.
Ecology
and
Evolution
published
by
John
Wiley
&
Sons
Ltd.
4987
This
is
an
open
access
article
under
the
terms
of
the
Creative
Commons
Attribution
License,
which
permits
use,
distribution
and
reproduction
in
any
medium,
provided
the
original
work
is
properly
cited.
Sneaker
Males
Have
Competitive
Sperm
B.
Young
et
al.
raffle"
versus
the
"loaded
raffle".
A
fair
raffle
implies
that
sperm
competition
outcomes
are
determined
by
the
rela-
tive
quantity
of
competing
sperm,
and
selection
favors
sneaker
males
that
produce
more
sperm
per
unit
body
mass
than
dominants.
Consistent
with
this
prediction,
sneaker
males
in
many
different
species
have
larger
testes
relative
to
their
body
mass
compared
with
dominant
males
(Stockley
and
Purvis
1993;
Gage
et
al.
1995;
Stockley
et
al.
1997;
Taborsky
1998;
Simmons
et
al.
1999;
Rasotto
and
Mazzoldi
2002;
Neff
et
al.
2003;
Schulte-
Hostedde
et
al.
2005;
Rudolfsen
et
al.
2006;
Montgomerie
and
Fitzpatrick
2009;
Simmons
and
Fitzpatrick
2012).
Under
a
loaded
raffle,
selection
favors
sneaker
males
that
produce
higher
quality
sperm
compared
with
dominant
males
(Parker
1990a).
Sperm
quality
can
include
enhanced
velocity
and/or
ATP
stores
(Taborsky
1998;
Uglem
et
al.
2001;
VladiC
and
Jarvi
2001;
Burness
et
al.
2004;
Fitzpatrick
et
al.
2007;
Locatello
et
al.
2007;
Pitcher
et
al.
2009;
VladiC
et
al.
2010;
Beausoleil
et
al.
2012;
Tourmente
et
al.
2013),
increased
longevity
(Smith
and
Ryan
2010),
and/or
morphological
features
(Stockley
et
al.
1997;
Simmons
et
al.
1999;
Balshine
et
al.
2001;
Burness
et
al.
2004;
Snook
2005;
Smith
and
Ryan
2010;
Gomez
Montoto
et
al.
2011;
Tourmente
et
al.
2011).
Dif-
ferences
in
sperm
quality
can
also
arise
from
a
male's
behavioral
adaptations,
such
as
better-timed
sperm
release
close
to
eggs.
Most
direct
studies
of
sperm
competition
among
domi-
nant
and
sneaker
males
have
been
unable
to
distinguish
the
fair
and
loaded
raffle
models.
Fu
et
al.
(2001)
esti-
mated
that
sneaker
bluegill
males
fertilized
78%
of
embryos
when
in
competition
with
a
dominant
male,
but
it
is
not
clear
whether
this
was
due
to
differences
in
spawning
behavior,
ejaculate
volume,
density,
and/or
sperm
quality.
Stoltz
and
Neff
(2006)
estimated
that
snea-
ker
male
sperm
was
nearly
twice
as
competitive
as
domi-
nant
male
sperm,
but
sneaker
male
sperm
were
released
closer
to
the
female's
eggs
to
mimic
natural
conditions.
VladiC
et
al.
(2010)
competed
sperm
from
sneaker
and
dominant
males
in
Atlantic
salmon,
finding
that
sneaker
males
fertilized
3.6x
as
many
offspring
as
dominant
males
after
sperm
numbers
were
controlled.
Other
sperm
competition
experiments
controlled
sperm
count
and
dis-
tance
to
female
gametes,
but
competing
males
were
cho-
sen
randomly
instead
of
explicitly
testing
a
dominant
versus
sneaker
male
(Evans
et
al.
2003;
Gage
et
al.
2004;
Hoysak
et
al.
2004;
Liljedal
et
al.
2008;
Boschetto
et
al.
2011).
Here,
we
perform
controlled
in
vitro
sperm
competi-
tion
experiments
between
dominant
"hooknose"
and
sneaker
"jack"
males
in
Chinook
salmon
(Oncorhynchus
tshawytscha).
Using
a
combination
of
maximum
likeli-
hood,
logistic
regression,
and
independent
subsampling,
we
reject
the
fair
raffle
in
favor
of
the
loaded
raffle
model,
demonstrating
that
sneaker
jack
males
make
competitively
superior
sperm
to
dominant
males.
Although
jack
males
outcompeted
hooknoses
overall,
the
magnitude
and
even
the
direction
of
their
competitive
superiority
shifted
with
individual
female
egg
donor,
suggesting
females
influence
the
outcomes
of
sperm
competition.
Materials
and
Methods
Study
system
Chinook
salmon
offer
an
ideal
study
species
for
asking
whether
a
sneak-guard
system
follows
the
fair
or
loaded
raffle.
Young
fry
leave
their
natal
stream
during
the
smolt
and
spend
the
next
few
years
in
the
open
ocean
(Healey
1991).
As
in
many
salmonids,
large
dominant
"hooknose"
males
return
to
their
natal
streams
after
3-7
years,
and
possess
elaborate
secondary
sexual
charac-
teristics
such
as
a
kype
(the
"hooked
nose"),
a
defensive
hump,
and
elongated
teeth,
which
they
use
to
fight
for
dominance
and
establish
access
to
nesting
females
(Gross
1985;
Healey
1991;
Quinn
and
Foote
1994;
Allen
et
al.
2007). Sneaker
males,
referred
to
as
"jacks",
are
roughly
half
the
size
of
hooknose
males
and
do
not
develop
any
of
these
secondary
sexual
characteristics
(Berejikian
et
al.
2010;
Williamson
et
al.
2010).
Instead,
jacks
take
on
cryptic
coloration
and
occupy
the
peripheral
edges
of
rivers,
where
they
wait
for
hooknose
males
to
begin
spawning
with
females,
then
dart
in
and
around
the
spawning
pair
to
release
their
sperm
while
avoiding
aggressive
interactions
with
dominant
males
(Heath
et
al.
1994;
Fleming
and
Reynolds
2004).
Because
dominant
males
vigorously
defend
nesting
females,
they
are
expected
to
outcompete
jack
males
for
access
to
ova
(Rutter
1903;
Ginzburg
1972;
Gile
and
Fer-
guson
1995;
Perchec
et
al.
1998;
Hoysak
and
Liley
2001;
Kime
et
al.
2001;
Cosson
2010;
Serum
et
al.
2011).
Con-
sistent
with
this
expectation,
sneaker
males
only
sire
about
20%
of
offspring
under
natural
spawning
condi-
tions
when
competing
against
dominant
males
(Hutch-
ings
and
Myers
1988;
Jordan
and
Youngson
1992;
Berejikian
et
al.
2010).
However,
in
spite
of
their
repro-
ductive
disadvantages,
jacks
represent
—10%
of
the
males
in
the
population,
across
multiple
salmonid
species
(Myers
et
al.
1998;
Appleby
et
al.
2003;
Carlson
et
al.
2004;
Fleming
and
Reynolds
2004).
In
combination
with
the
high
heritability
of
jacking
(Heath
et
al.
2002;
Bereji-
kian
et
al.
2011),
these
results
suggest
that
sneaking
is
an
evolutionarily
stable
strategy
in
this
system
and
that
jacks
compensate
for
their
disadvantaged
mating
posi-
tions
via
other
mechanisms
such
as
sperm
competitive
ability.
4988
0
2013
The
Authors.
Ecology
and
Evolution
published
by
John
Wiley
&
Sons
Ltd.
B.
Young
et
al.
Sneaker
Males
Have
Competitive
Sperm
Fish
selection
and
gamete
collection
Our
experimental
design
represents
a
trade-off
between
testing
numerous
fully
independent
parents
versus
multi-
ple
observations
from
the
same
gamete
combinations.
We
increased
the
number
of
observations
per
sperm-egg
com-
bination
in
order
to
test
for
sperm-by-egg
interactions.
We
account
for
the
non-independence
of
this
approach
using
a
variety
of
statistical
methods
and
subsampling
as
described
below.
A
total
of
five
females,
five
jack
males,
and
five
domi-
nant
hooknose
males
(Appendix
S1)
were
collected
at
the
Big
Creek
Hatchery
weir
(Oregon
Department
of
Fish
and
Wildlife)
in
northwestern
Oregon
during
early
Octo-
ber
of
the
2008
spawning
season.
Jack
males
were
distin-
guished
from
hooknose
males
based
on
their
smaller
size,
lack
of
defensive
hump,
lack
of
kype,
smaller
teeth,
and
cryptic
coloration
resembling
a
female.
Only
sexually
mature
fish
in
good
physical
condition
without
injuries,
fungus,
and
fin
wear
were
selected.
Prior
to
gamete
collection,
fish
were
wiped
dry
with
paper
towels
to
preclude
contamination
with
water
and
mucus.
Sperm
were
collected
in
a
beaker
by
gently
bending
the
male
and
immediately
placed
at
4°C.
Sperm
are
quies-
cent
at
this
stage
and
do
not
become
active
until
exposure
to
water
(Kime
et
al.
2001;
Cosson
2010).
Females
were
euthanized
and
egg
masses
dissected.
Eggs
from
each
female
were
divided
into
five
approximately
equal
batches
for
sub-
sequent
exposure
to
sperm.
Sperm
count
for
each
male
was
measured
with
three
independent
spermatocrit
reads;
the
ejaculate
was
centrifuged
and
the
percent
of
packed
sperm
taken
as
a
measurement
of
sperm
count
per
ejaculate
(Bou-
ck
and
Jacobson
1976;
Appendix
S2).
Jack
and
hooknose
sperm
are
indistinguishable
in
their
sperm
head
length
or
width,
or
flagellum
length
(Flannery
et
al.
2013),
so
sper-
matocrit
measurements
are
appropriate
for
comparing
sperm
counts
between
males.
No
formal
attempt
was
made
to
equalize
sperm
counts
across
treatments,
but
no
signifi-
cant
difference
was
observed
between
jack
and
hooknose
spermatocrit
(F
1
,
20
=
0.98,
P
=
0.33;
Appendix
S2).
There-
fore,
paternity
skew
between
male
morphs
cannot
be
Table
1.
Paternity
under
sperm
competition
ascribed
to
differences
in
sperm
count.
In
an
attempt
to
minimize
experimental
noise
associated
with
similar
exper-
iments
(Gharrett
and
Shirley
1985;
Withler
1988),
each
jack:hooknose
sperm
mixture
was
mixed
once,
then
applied
to
five
different
aliquots
of
female
eggs
(five
total
sperm
mixtures
rather
than
25
total
sperm
mixtures,
Table
1).
Experimental
crosses/mating
scheme
To
include
male—female
interaction
terms,
a
variant
of
the
North
Carolina
II
breeding
design
(Comstock
and
Robinson
1948)
was
employed,
with
each
of
five
rows
representing
eggs
from
one
female,
and
each
of
five
columns
representing
a
unique
mixture
of
sperm
from
one
hooknose
and
one
jack
male
(5
mL
sperm
from
one
hooknose
male,
5
mL
from
one
jack
male,
10
males
total;
Table
1).
Sperm
combinations
were
mixed
by
gently
swirling
a
beaker
for
5
min.
Approximately
500
eggs
from
each
female
were
placed
on
one
side
of
a
new
beaker
and
1
mL
of
the
sperm
mixture
on
the
opposite
side.
Gametes
were
mixed
with
the
turbulent
addition
of
1000
mL
of
natural
temperature
Big
Creek
river
water
and
swirled
for
10
sec.
The
egg—sperm
mixtures
were
allowed
to
stand
for
5
min
before
transfer
to
Heath
tray
incubators
at
the
Big
Creek
Hatchery
facilities.
Fertilized
eggs
were
reared
according
to
standard
hatchery
practices,
with
each
indi-
vidual
replicate
in
a
separate
tray.
Mortalities
were
removed
and
collected
each
week
until
the
eyed
stage
(approximately
40
days
postfertilization),
at
which
time,
all
eggs
were
euthanized
and
preserved
for
subsequent
genetic
analysis.
Mortality
was
so
low
(<5%)
that
even
if
one
male
type
sired
all
the
dead
eggs
in
a
tray,
our
con-
clusions
below
would
not
change.
Genetic
analysis/parentage
assignment
DNA
was
extracted
from
muscle
tissue
taken
from
the
15
possible
parents
and
from
the
heads
of
individual
embryos
using
an
Epicentre
MPC
extraction
kit,
following
the
manufacturer's
instructions.
Three
microsatellite
loci
OTS213
(Greig
et
al.
2003),
OTS107
(Nelson
and
Bea-
Hooknose
1:Jack
1
Hooknose
2:Jack
2
Hooknose
3:Jack
3
Hooknose
4:Jack
4
Hooknose
5:Jack
5
Row
sum
Female
1
31:55
(0.36:0.64)
31:49
(0.39:0.61)
39:49
(0.44:0.56)
25:44
(0.36:0.64)
17:29
(0.37:0.63)
143:226
(0.39:0.61)
Female
2
26:35
(0.43:0.57)
18:28
(0.39:0.61)
19:27
(0.41:0.59)
32:45
(0.42:0.58)
10:36
(0.22:0.78)
105:171
(0.38:0.62)
Female
3
47:44
(0.52:0.48)
37:47
(0.44:0.56)
14:28
(0.33:0.67)
27:41
(0.40:0.60)
39:29
(0.57:0.43)
164:189
(0.46:0.54)
Female
4
42:35
(0.55:0.45)
38:8
(0.83:0.17)
32:14
(0.70:0.30)
7:39
(0.15:0.85)
23:45
(0.34:0.66)
142:141
(0.50:0.50)
Female
5
28:17
(0.62:0.38)
22:47
(0.32:0.68)
31:14
(0.69:0.31)
10:59
(0.14:0.86)
39:50
(0.44:0.56)
130:187
(0.41:0.59)
Column
174:186
(0.48:0.52)
146:179
(0.45:0.55)
135:132
(0.51:0.49)
101:228
(0.31:0.69)
128:189
(0.40:0.60)
684:914
(0.43:0.57)
sum
Number
of
embryos
sired
by
hooknose:jack
(proportions
in
parentheses).
©
2013
The
Authors.
Ecology
and
Evolution
published
by
John
Wiley
&
Sons
Ltd.
4989
Sneaker
Males
Have
Competitive
Sperm
B.
Young
et
al.
cham
1999),
and
RT212
(Spies
et
al.
2005)
allowed
unambiguous
paternity
assignment
in
any
given
cross
(Appendix
S1).
One
primer
in
each
pair
was
dyed
with
HEX
or
FAM
for
downstream
scoring.
PCR
amplifica-
tions
consisted
of
2
min
of
denaturation
at
94°C,
fol-
lowed
by
35
cycles
of
30
sec
denaturation
(94°C),
30
sec
annealing
(each
locus-specific
temperature),
40
sec
elon-
gation
(72°C),
and
a
final
5
min
extension
at
72°C.
Genotyping
was
performed
by
the
University
of
Arizona
Genetics
Core
on
an
ABI
Prism
3730
DNA
Analyzer
(Applied
Biosystems,
Grand
Island,
NY).
A
total
of
1598
embryos
were
genotyped,
with
an
average
63.9
embryos
genotyped
from
each
of
the
25
combinations
of
sperm
and
eggs
(range
=
42-91,
standard
deviation
=
17.1,
Table
1).
Statistical
analyses
We
employed
two
distinct
methods
to
test
for
competi-
tive
differences
between
jack
male
sperm
and
hooknose
male
sperm.
The
first
was
a
maximum-likelihood
method
that
considers
each
brood
as
an
independent
observation,
and
the
second
was
a
logistic
regression
that
considers
each
embryo
as
an
independent
observation.
For
the
max-
imum-likelihood
approach,
we
also
subsampled
totally
independent
datasets
from
the
full
dataset.
There
are
120
different
ways
to
sample
the
5
x
5
experimental
design
where
no
rows
or
columns
are
shared.
Maximum
likelihood
Neff
and
Wahl
(2004)
developed
a
maximum-likelihood
method
to
test
whether
sperm
competition
outcomes
follow
fair
or
loaded
raffles.
For
each
of
25
broods
(Table
1),
paternity
outcomes
follow:
Si
N
1
N1
+
N2
=
rS2
where
N
i
and
N2
are
the
numbers
of
offspring
sired
by
male
1
and
male
2
in
a
brood,
respectively;
S
i
and
S2
are
the
numbers
of
sperm
transferred
by
male
1
and
male
2
(taken
as
the
average
of
the
three
spermatocrit
values
taken
per
male,
Appendix
S2),
respectively;
r
is
the
competitive
ability
of
the
second
male's
relative
to
the
first
male's
sperm;
t
is
a
measure
of
the
economy
of
scale
to
sperm
number.
Essentially,
t
measures
whether
the
returns
on
transferring
additional
sperm
follow
a
linear
trend.
If
t
=
0,
then
the
above
equation
reduces
to
1/(1
+
r),
indicating
that
sperm
competition
outcomes
are
independent
of
rela-
tive
sperm
number
and
determined
only
by
r.
An
individ-
ual
that
makes
higher
quality
sperm
gains
less
per
additional
sperm
transferred
if
0
<
t
<
1,
but
gains
dispro-
portionately
more
if
t
>
1.
The
method
optimizes
r
and
t
across
the
entire
set
of
broods
and
estimates
95%
confi-
dence
intervals
through
permutation
(Neff
and
Wahl
2004).
These
confidence
intervals
were
used
to
test
the
fair
raffle
model,
where
r
=
1
(no
differences
in
sperm
competi-
tive
ability)
and
t
=
1
(sperm
competition
outcomes
related
only
to
S
i
relative
to
S2
and
r),
as
well
as
the
sperm-
independent
model,
where
t
=
0.
Because
spermatocrit
numbers
did
not
significantly
differ
between
jack
and
hooknose
males
(Appendix
S2),
our
study
was
probably
underpowered
to
uncover
differences
due
sperm
quantity.
However,
our
primary
goal
was
to
test
the
null
hypothesis
r
=
1,
the
prediction
under
a
fair
raffle.
We
applied
the
maximum-likelihood
method
to
the
entire
dataset,
as
well
as
each
of
the
120
independent
subsamples.
Logistic
regression
A
second
method
used
logistic
regression
to
model
the
log
odds
of
the
probability
that
a
jack
male
sired
an
embryo:
logit(Pr[Y
i
=
11F,
M)
5
5
=
p
+
Fi)
+
E
/3mh(mih
Mh
)
j=2
h=2
5 5
E
E
Ant
i
h(4
x
(mih
moi
j=2
h=2
Y,
is
a
variable
indicating
if
offspring
i
was
sired
by
a
jack
(Y,
=
1)
or
hooknose
male
(Y,
=
0),
and
Fii
and
Mu,
are
indicator
variables
denoting
the
contributing
female
j
or
male
sperm
mixture
h,
respectively.
It
should
be
empha-
sized
that
M
refers
to
a
single
sperm
mixture
from
two
males.
These
variables
were
mean-centered
to
allow
the
expit(a)
to
equal
the
overall
probability
of
a
jack
in
the
sample.
Each
13
represented
the
log
odds
ratio
and
a
Wald
test
used
to
determine
whether
a
factor
significantly
affected
this
ratio.
We
tested
the
fit
of
the
data
to
different
models
to
under-
stand
the
effects
of
male
and
female
variables
on
the
proba-
bility
an
offspring
was
sired
by
a
jack
male.
Model
1
was
a
null
model
that
simply
calculated
the
overall
mean
Y„
with-
out
any
variables.
Model
2,
Model
3,
and
Model
4
added
M
i
h,
F
t
i,
or
both,
respectively,
to
test
whether
the
identity
of
the
female
egg
donor
and/or
male
sperm
mixture
influ-
enced
Model
5
added
an
interaction
between
the
sexes.
Models
were
compared
using
a
likelihood
ratio
test
(LRT).
All
tests
were
performed
with
customized
Python
(www.
python.org
)
and
R
(www.r-project.com
)
scripts.
Skewed
paternity,
sex
ratio,
and
growth
rates
Strong
paternity
skew
could
be
correlated
with
sex
ratio
if
sex-linked
meiotic
drive
reduced
the
ability
of
one
male
4990
0
2013
The
Authors.
Ecology
and
Evolution
published
by
John
Wiley
&
Sons
Ltd.
B.
Young
et
al.
Sneaker
Males
Have
Competitive
Sperm
to
compete.
We
tested
for
sex
skew
by
amplifying
X-
and
Y-specific
regions
(Devlin
et
al.
1994)
from
a
subset
of
embryos
from
two
gamete
combinations
that
revealed
highly
skewed
paternity
(Hooknose
2:Jack
2+
Female
4
and
Hooknose
4:Jack
4+
Female
4,
Table
1).
Strong
paternity
skew
could
also
be
correlated
with
dif-
ferences
in
embryonic
developmental
rate
if
cryptic
female
choice
yielded
offspring
genotypes
that
grew
fast.
In
sal-
monids,
there
are
paternal
and
maternal
contributions
to
egg
size
and
egg
metabolic
rate
(Pakkasmaa
et
al.
2001,
2006).
Although
not
a
primary
objective,
we
tested
for
differential
growth
rate,
we
weighed
embryo
+
yolk
from
a
subset
of
embryos
from
four
gamete
combinations
with
skewed
paternity
(Hooknose
2:Jack
2+
Female
4,
Hook-
nose
2:Jack
2+
Female
5,
Hooknose
4:Jack
4+
Female
3,
and
Hooknose
4:Jack
4+
Female
5).
All
tests
were
per-
formed
with
customized
Python
(www.python.org
)
and
R
(www.r-project.com
)
scripts.
Results
Jack
males
outcompeted
hooknose
males
Because
we
genotyped
loci
known
to
discriminate
com-
peting
males
(Appendix
S1),
all
1598
embryos
that
were
genotyped
were
scored
unambiguously
for
paternity.
Maximum
likelihood
The
methods
of
Neff
and
Wahl
(2004)
rejected
the
fair
raf-
fle
model
(r
=
1
and
t
=
1).
Specifically,
jack
sperm
were
estimated
to
be
r
=
1.34x
as
competitive
as
hooknose
sperm,
significantly
different
than
r
=
1
(P
<
0.0001)
and
very
consistent
with
the
1.36x
estimated
from
logistic
regression
analyses
presented
below.
t
was
estimated
to
be
<10
-12
,
which
was
not
significantly
different
from
either
t
=
0
or
t
=
1
(P
=
0.99,
P
=
0.50,
respectively).
From
the
5
x
5
Table
1,
there
are
120
possible
ways
to
sample
five
cells
with
no
rows
or
columns
in
common. Of
these,
82
rejected
the
null
hypothesis
r
=
1
(P
<
0.05),
in
favor
of
the
alternative
that
jack
males
were
superior
under
controlled
sperm
competition.
The
average
±
standard
deviation
r
in
these
cases
was
1.52
±
0.25.
In
contrast,
only
one
independent
subsample
favored
the
alternative
that
hooknose
males
were
competitively
superior.
Logistic
regression
Overall,
an
embryo
had
a
probability
of
0.576
of
being
sired
by
a
jack
male,
significantly
different
from
the
null
expectation
of
0.50
(P
=
3.97
x
10
-8
,
Table
2).
In
other
words,
jack
sperm
were
0.576/(1
0.576)
=
1.36x
as
competitive
as
hooknose
sperm,
a
number
that
is
very
similar
to
the
maximum-likelihood
estimates
presented
above.
Female
4
deviated
significantly
from
background,
with
a
preference
for
hooknose
sperm
(P
=
0.007,
Table
2).
Two
sperm
mixtures
were
significantly
more
jack-skewed
than
background.
Jack
4
sired
0.711
of
the
embryos
when
in
competition
with
Hooknose
4,
and
Jack
5
sired
0.601
of
the
offspring
when
in
competition
with
Hooknose
5;
both
were
significantly
higher
than
back-
ground
(P
=
2.05
x
10
-7
,
P
=
0.014,
respectively,
Table
2).
A
model
including
sperm
aliquot
as
a
fixed
effect
explained
the
data
significantly
better
than
a
model
ignor-
ing
it
(Model
2
vs.
Model
1,
f
=
32.70,
df
=
4,
P
=
10
-6
,
Table
3),
as
did
a
model
including
female
donor
(Model
3
vs.
Model
1,
2(
2
=
13.63,
df
=
4,
P
=
0.01),
showing
that
the
general
superiority
of
jack
male
sperm
was
not
uniform
across
sperm
aliquot
or
egg
donor.
A
model
including
both
male
and
female
fit
the
data
significantly
better
than
models
with
only
male
(Model
4
vs.
Model
2,
x
2
=
13.29,
df
=
4,
P
=
0.01)
or
only
female
(Model
4
vs.
Model
3,
f
=
32.37,
df
=
4,
P
=
10
-6
,
Table
3).
Taken
together,
these
results
suggest
that
both
sperm
mixture
and
egg
donor
influence
the
outcomes
of
sperm
competition.
Females
may
influence
the
outcomes
of
sperm
competition
In
the
logistic
regression
framework,
a
model
including
an
interaction
term
between
sperm
mixture
and
egg
donor
fit
the
data
significantly
better
than
a
model
with
only
additive
male
and
female
effects
(Model
5
vs.
Model
4,
f
=
93.82,
df
=
16,
P
=
10
-13
,
Table
3).
This
effect
is
best
illustrated
by
the
Hooknose
2:Jack
2
sperm
mixture.
Jack
2
sired
0.798/(1
0.798)
=
3.95x
more
offspring
than
Hooknose
2
when
combined
with
Female
5
(P
=
0.008,
Table
2)
but
0.221/(1
0.221)
=
0.28x
as
many
offspring
as
Hooknose
2
when
combined
with
Female
4
(P
=
0.023,
Table
2).
Thus,
the
outcomes
of
sperm
competition
between
two
particular
males
depended
upon
female
genotype.
An
alternative
explanation
to
explain
the
sperm-by-egg
interaction
term
is
that
random
effects
were
very
high.
However,
we
emphasize
that
the
same
exact
sperm
aliquot
was
delivered
across
the
eggs
from
five
females.
Therefore,
random
effects
are
unlikely
to
explain
the
sperm-by-egg
interaction
term.
Paternity
skew
was
not
correlated
with
sex
ratio
or
growth
rates
There
was
no
evidence
that
paternity
skew
was
related
to
meiotic
drive
of
the
sex
chromosomes.
For
the
Hooknose
©
2013
The
Authors.
Ecology
and
Evolution
published
by
John
Wiley
&
Sons
Ltd.
4991
Sneaker
Males
Have
Competitive
Sperm
Table
2.
Coefficients
estimated
from
full
model
(Model
5)
B.
Young
et
al.
Coefficients
(Model
parameter)
Estimate
SE
P
(sired
by
Jack)
z-value
Pr
(*I)
Significance
(P)
Intercept
0.306 0.056 0.576
5.492
3.97E-08
<0.001
Female
2
(F2)
0.057
0.171
0.514
0.333
0.739
Female
3
(F
3
)
-0.306
0.157
0.424
-1.953
0.051
Female
4
(F
4
)
-0.492
0.184
0.379
-2.674
0.007
<0.01
Female
5
(F
5
)
-0.159
0.172
0.460
-0.924
0.355
Hooknose
2:Jack
2
(M2)
0.072
0.166 0.518
0.432
0.666
Hooknose
3:Jack
3
(M
3
)
-0.075
0.173
0.481
-0.437
0.662
Hooknose
4:Jack
4
(M4)
0.900
0.173
0.711
5.195
2.05E-07
<0.001
Hooknose
5:Jack
5
(M
5
)
0.409
0.167
0.601
2.456
0.014
<0.05
Female
2
*
Hooknose
2:Jack
2
(F
2
*
M2)
0.260
0.511
0.565
0.509
0.611
Female
3
*
Hooknose
2:Jack
2
(F
3
*
M
2
)
0.421
0.442
0.604
0.952
0.341
Female
4
*
Hooknose
2:Jack
2
(F
4
*
M2)
-1.260
0.554
0.221
-2.275
0.023
<0.05
Female
5
*
Hooknose
2:Jack
2
(F
5
*
M
2
)
1.374
0.514
0.798
2.671
0.008
<0.01
Female
2
*
Hooknose
3:Jack
3
(F
2
*
M3)
0.399
0.503
0.599
0.793
0.428
Female
3
*
Hooknose
3:Jack
3
(F
3
*
M
3
)
1.104
0.498
0.751
2.219
0.026
<0.05
Female
4
*
Hooknose
3:Jack
3
(F
4
*
M3)
-0.299
0.502
0.426
-0.597
0.551
Female
5
*
Hooknose
3:Jack
3
(F
5
*
M
3
)
0.049
0.543
0.512
0.091
0.928
Female
2
*
Hooknose
4:Jack
4
(F
2
*
M4)
0.052
0.483 0.513
0.107
0.915
Female
3
*
Hooknose
4:Jack
4
(F
3
*
M
4
)
0.492
0.468
0.621
1.052
0.293
Female
4
*
Hooknose
4:Jack
4
(F
4
*
M4)
1.908
0.578
0.871
3.301
0.001
<0.001
Female
5
*
Hooknose
4:Jack
4
(F
5
*
M
4
)
2.282
0.570
0.907
4.005
0.000
<0.001
Female
2
*
Hooknose
5:Jack
5
(F
2
*
Ms)
1.023
0.582
0.736
1.758
0.079
Female
3
*
Hooknose
5:Jack
5
(F
3
*
M
5
)
-0.191
0.498
0.452
-0.384
0.701
Female
4
*
Hooknose
5:Jack
5
(F
4
*
Ms)
0.893
0.512
0.709
1.745
0.081
Female
5
*
Hooknose
5:Jack
5
(F
5
*
M
5
)
0.787
0.533
0.687
1.476
0.140
Significance
indicates
factors
that
differed
from
an
overall
null
model.
Table
3.
Comparison
of
logistic
regression
models
using
likelihood
ratio
test
Model
number
Variables
added
Model
architecture
Residual
deviance
df
Model
comparisons
cum
1
Null
Y
-
1
2182.1
1597
2
Male
Y
-
Male
2149.4
1593
2
vs.
1:
x
2
=
32.70,
df
=
4,
P
=
10
-6
3
Female
Y
-
Female
2168.4
1593
3
vs.
1:
x
2
=
13.63,
df
=
4,
P
=
0.01
4
Both
Y
-
Male
+
Female
2136.1
1589
4
vs.
2:
x
2
=
13.29,
df
=
4,
P
=
0.01
4
vs.
3:
x
2
=
32.37,
df
=
4,
P
=
10
-6
5
Interaction
Y
-
Male
+
Female
2042.3
1573
5
vs.
4:
x
2
=
93.82,
df
=
16,
P
=
10
-13
+
interaction
Significant
LRT
signifies
a
better
fit
to
the
data
in
the
more
complex
model.
LRT,
likelihood
ratio
test.
2:Jack
2+
Female
4
combination,
11
males
and
nine
females
were
sired
by
the
hooknose
male
while
two
males
and
one
female
were
sired
by
the
jack
male.
For
the
Hooknose
4:Jack
4+
Female
4
combination,
three
males
and
two
females
were
sired
by
the
hooknose
male
while
eight
males
and
nine
females
were
sired
by
the
jack
male.
Pooling
these
data
revealed
19
male
and
18
female
off-
spring
sired
by
the
winning
male,
compared with
five
males
and
three
females
sired
by
the
losing
male
(Fisher's
Exact
Test,
P
=
0.71).
There
was
no
evidence
that
growth
rate
of
embryos
cor-
related
with
winning
sires.
Pooling
across
the
four
gamete
combinations
surveyed
in
this
manner,
69
embryos
sired
by
the
winning
male
(median
embryo:total
egg
weight
=
0.188
g)
were
not
significantly
different
from
the
23
embryos
sired
by
losing
males
(median
embryo:total
egg
weight
=
0.187
g,
Mann-Whitney
P
=
0.66).
Discussion
Sneak-guard
mating
systems
are
prevalent
among
animal
species,
but
the
mechanisms
by
which
sneaker
males
maintain
reproductive
fitness
remain
incompletely
charac-
terized
(Gross
1996;
Taborsky
1998).
Here,
we
reject
the
4992
0
2013
The
Authors.
Ecology
and
Evolution
published
by
John
Wiley
&
Sons
Ltd.
B.
Young
et
al.
Sneaker
Males
Have
Competitive
Sperm
fair
raffle
model,
showing
that
sperm
from
sneaker
jack
males
were
competitively
superior
to
sperm
from
domi-
nant
hooknose
males
in
controlled
in
vitro
fertilization
experiments.
Thus,
sperm
competition
outcomes
in
Chi-
nook
salmon
are
best
explained
as
a
loaded
raffle
(Parker
1990a),
helping
to
explain
the
stability
of
sneaker
males
in
this
system.
Several
hypotheses
could
explain
the
general
superiority
of
jack
sperm
over
hooknose
sperm.
First,
jack
sperm
swim
faster
than
hooknose
sperm
(Flannery
et
al.
2013),
and
sperm
velocity
is
a
primary
determinant
of
fertiliza-
tion
success
in
sperm
competition
in
numerous
fish
species
(Burness
et
al.
2004;
Gage
et
al.
2004;
Liljedal
et
al.
2008;
Rudolfsen
et
al.
2008;
Boschetto
et
al.
2011;
Evans
et
al.
2013)
and
other
external
fertilizers
(Levitan
1993, 1996,
2000;
Kupriyanova
and
Havenhand
2002;
Marshall
et
al.
2002).
The
speed
with
which
sperm
can
locate
an
egg
is
important.
In
Sockeye
salmon,
over
80%
of
eggs
are
fertilized
within
5
sec
of
gamete
activation
(Hoysak
and
Liley
2001)
and
sperm
generally
live
<1
min
upon
activation
(Kime
et
al.
2001;
Cosson
2010).
Second,
the
exact
combination
of
sperm
and
egg
pro-
teins
can
influence
fertilization
in
external
fertilizers
(Vac-
quier
1998;
Swanson
and
Vacquier
2002;
Bernasconi
et
al.
2004).
In
salmon,
sperm
bind
to
"sperm
guidance"
glyco-
proteins
as
they
traverse
through
the
mucus
layer
and
into
the
micropyle,
which
is
the
site
of
fertilization
(Yan-
agimachi
et
al.
1992;
Iwamatsu
et
al.
1997;
Mengerink
and
Vacquier
2001),
and
it
is
possible
that
jack
and
hook-
nose
sperm
respond
differently
to
egg
proteins.
Different
combinations
of
male
and
female
proteins
translate
into
differential
fertilization
rates
in
many
externally
species
(Gaffney
et
al.
1993;
Palumbi
1999;
Boudry
et
al.
2002;
Evans
and
Marshall
2005;
Geyer
and
Palumbi
2005;
Mar-
shall
and
Evans
2005;
Levitan
and
Ferrell
2006;
Levitan
and
Stapper
2010;
Levitan
2012).
Third,
if
inbreeding
avoidance
mechanisms
exist
in
Chinook
salmon,
they
are
likely
to
favor
jack
male
sperm.
Spawning
hooknose
males
and
females
could
have
been
born
in
the
same
river
and
same
year,
and
could
be
close
relatives.
Because
jack
males
return
to
spawn
at
least
1
year
earlier
than
females
of
their
same
cohort,
they
should
be
less
genetically
related
to
currently
spawning
females
than
dominant
hooknose
males.
In
guppies,
a
male's
sperm
displayed
higher
velocity
in
the
presence
of
ovarian
fluid
from
an
unrelated
female,
suggesting
a
mechanism
by
which
females
may
bias
paternity
toward
unrelated
males
(Gasparini
and
Pilastro
2011;
Gasparini
et
al.
2012).
Salmonid
sperm
motility
is
influenced
by
female
ovarian
fluid
(Rosengrave
et
al.
2008;
Flannery
2011;
Yeates
et
al.
in
press).
Generally,
however,
domi-
nant
male
sperm
swim
faster
in
female
ovarian
fluid
com-
pared
with
jack
males
(the
opposite
trend
is
observed
in
river
water;
Flannery
2011).
Mechanisms
of
inbreeding
avoidance,
if
they
exist,
may
be
more
complicated
than
simple
predictions
based
on
interactions
between
sperm
and
ovarian
fluid,
however.
For
example,
genetic
variation
at
the
major
histocompatibility
locus
has
been
shown
to
affect
gamete
interactions
(Skarstein
et
al.
2005;
Yeates
et
al.
2009).
Our
finding
that
jack
males
make
competitively
supe-
rior
sperm
calls
into
question
a
common
viewpoint
that
jack
males
are
less
fit
than
dominant
males
and
are
"mak-
ing
the
best
of
a
bad
situation".
Reichard
et
al.
(2007)
reviewed
theoretical
and
empirical
examples
where
females
might
actually
benefit
from
allowing
sneaker
males
to
fertilize
their
eggs,
including
increased
genetic
diversity
in
their
offspring.
Interestingly,
female
bluegill
spawn
more
eggs
when
sneaker
males
are
present,
and
sneaker
males
in
that
system
also
fertilize
a
disproportion-
ate
share
of
eggs
(Fu
et
al.
2001).
This
could
be
an
exam-
ple
whereby
female
choice
favors
fertilization
by
sneaker
males.
In
fact,
precocious
sexual
maturity
might
be
a
general
indication
that
sneaker
males
are
more
genetically
robust
to
environmental
stresses,
a
very
different
view-
point
than
one
that
assumes
they
are
poor
quality
indi-
viduals.
Interestingly,
over-feeding
in
hatcheries
often
leads
to
increased
rates
of
jacking,
consistent
with
this
interpretation.
We
set
out
to
elucidate
the
apparent
stability
of
jack
males
in
the
mating
ecology
of
Chinook
salmon.
Using
controlled
in
vitro
sperm
competition
experiments,
we
demonstrated
that
sneaker
jack
males
outcompete
domi-
nant
hooknose
males
via
a
loaded
raffle.
Therefore,
jacks
appear
to
invest
disproportionately
in
sperm
quality.
Two
distinct
methods
estimated
that
jack
sperm
were
—1.3x
as
competitive
as
hooknose
sperm.
In
addition,
female
egg
donors
affected
sperm
competition
outcomes,
though
the
underlying
mechanisms
remain
unknown.
Future
investi-
gations
into the
molecular
basis
of
the
loaded
raffle
will
lead
to
greater
insight
into the
stability
of
this
sneaker
male
morphotype
in
Chinook
salmon.
Acknowledgments
We
thank
Ken
Johnson
(Oregon
Department
of
Fish
and
Wildlife)
and
the
staff
at
the
Big
Creek
Hatchery
for
their
assistance
in
obtaining
adult
Chinook
salmon
and
subse-
quent
husbandry.
Selene
and
Sam
Tyndale
assisted
with
field
work.
Jose
Jaime,
Jeanney
Kang,
Karen
Lu,
Charlie
Sanchez,
Neal
Shah,
and
Veronica
Winget
assisted
with
DNA
extractions
and
genotyping.
Alex
Riegel
(U.
Arizona
Genetics
Core)
assisted
with
genotyping.
Fengzhu
Sun,
Andrew
Smith,
and
Ian
Ehrenreich
discussed
statistical
modeling
strategies.
Michael
Kessler,
Jim
Dines,
and
members
of
the
Nuzhdin
Lab
(especially
Julia
Saltz)
gave
©
2013
The
Authors.
Ecology
and
Evolution
published
by
John
Wiley
&
Sons
Ltd.
4993
Sneaker
Males
Have
Competitive
Sperm
B.
Young
et
al.
helpful
comments
on
the
manuscript.
This
study
was
funded
by
startup
funds
provided
by
the
University
of
Southern
California.
Conflict
of
Interest
None
declared.
References
Allen,
C.,
H.
Jr
Rich,
and
T.
Quinn.
2007.
Condition-dependent
reproductive
tactics
by
large
and
small
anadromous
male
sockeye
salmon
Oncorhynchus
nerka.
J.
Fish
Biol.
70:1302-1307.
Andersson,
M.
1994.
Sexual
selection.
Princeton
Univ.
Press,
Princeton,
NJ.
Appleby,
A.
E.,
J.
M.
Tipping,
and
P.
R.
Seidel.
2003.
The
effect
of
using
two-year-old
male
coho
salmon
in
hatchery
broodstock
on
adult
returns.
N.
Am.
J.
Aquac.
65:60-62.
Balshine,
S.,
B.
J.
Leach,
F.
Neat,
N.
Y.
Werner,
and
R.
Montgomerie.
2001.
Sperm
size
of
African
cichlids
in
relation
to
sperm
competition.
Behay.
Ecol.
12:726-731.
Beausoleil,
J.-M.
J.,
S.
M.
Doucet,
D.
D.
Heath,
and
T.
E.
Pitcher.
2012.
Spawning
coloration,
female
choice
and
sperm
competition
in
the
redside
dace,
Clinostomus
elongatus.
Anim.
Behay.
83:969-977.
Berejikian,
B.
A.,
D.
M.
Van
Doornik,
R.
C.
Endicott,
T.
L
Hoffnagle,
E.
P.
Tezak,
M.
E.
Moore,
et
al.
2010.
Mating
success
of
alternative
male
phenotypes
and
evidence
for
frequency-dependent
selection
in
Chinook
salmon,
Oncorhynchus
tshawytscha.
Can.
J.
Fish.
Aquat.
Sci.
67:1933-1941.
Berejikian,
B.
A.,
D.
M.
Van
Doornik,
and
J. J.
Atkins.
2011.
Alternative
male
reproductive
phenotypes
affect
offspring
growth
rates
in
Chinook
salmon.
Trans.
Am.
Fish.
Soc.
140:1206-1212.
Bernasconi,
G.,
T.
L.
Ashman,
T.
R.
Birkhead,
J.
D.
Bishop,
U.
Grossniklaus,
E.
Kubli,
et
al.
2004.
Evolutionary
ecology
of
the
prezygotic
stage.
Science
303:971-975.
Boschetto,
C.,
C.
Gasparini,
and
A.
Pilastro.
2011.
Sperm
number
and
velocity
affect
sperm
competition
success
in
the
guppy
(Poecilia
reticulata).
Behay.
Ecol.
Sociobiol.
65:813-
821.
Bouck,
G.
R.,
and
J.
Jacobson.
1976.
Estimation
of
salmonid
sperm
concentration
by
microhematocrit
technique.
Trans.
Am.
Fish.
Soc.
105:534-535.
Boudry,
P.,
B.
Collet,
F.
Corneae,
V.
Hervouet,
and
F.
Bonhomme.
2002.
High
variance
in
reproductive
success
of
the
Pacific
oyster
(Crassostrea
gigas,
Thunberg)
revealed
by
microsatellite-based
parentage
analysis
of
multifactorial
crosses.
Aquaculture
204:283-296.
Burness,
G.,
S.
J.
Casselman,
A.
I.
Schulte-Hostedde,
C.
D.
Moyes,
and
R.
Montgomerie.
2004.
Sperm
swimming
speed
and
energetics
vary
with
sperm
competition
risk
in
bluegill
(Lepomis
macrochirus).
Behay.
Ecol.
Sociobiol.
56:65-70.
Carlson,
S.
M.,
H.
B.
Jr
Rich,
and
T.
P.
Quinn.
2004.
Reproductive
life-span
and
sources
of
mortality
for
alternative
male
life-history
strategies
in
sockeye
salmon,
Oncorhynchus
nerka.
Can.
J.
Zool.
82:1878-1885.
Comstock,
R.
E.,
and
H.
F.
Robinson.
1948.
The
components
of
genetic
variance
in
populations
of
biparental
progenies
and
their
use
in
estimating
the
average
degree
of
dominance.
Biometrics
4:254-266.
Cosson,
J.
2010.
Frenetic
activation
of
fish
spermatozoa
flagella
entails
short-term
motility,
portending
their
precocious
decadence.
J.
Fish
Biol.
76:240-279.
Devlin,
R.
H.,
B.
K.
McNeil,
I.
I.
Solar,
and
E.
M.
Donaldson.
1994.
A
rapid
PCR-based
test
for
Y-chromosomal
DNA
allows
simple
production
of
all-female
strains
of
Chinook
salmon.
Aquaculture
128:211-220.
Evans,
J.
P.,
and
D.
J.
Marshall.
2005.
Male-by-female
interactions
influence
fertilization
success
and
mediate
the
benefits
of
polyandry
in
the
sea
urchin
Heliocidaris
erythrogramma.
Evolution
59:106-112.
Evans,
J.
P.,
P.
Rosengrave,
C.
Gasparini,
and
N.
J.
Gemmell,
2013.
Delineating
the
roles
of
males
and
females
in
sperm
competition.
Proc.
R.
Soc.
B
280:20132047.
Evans,
J.
P.,
L.
Zane,
S.
Francescato,
and
A.
Pilastro.
2003.
Directional
postcopulatory
sexual
selection
revealed
by
artificial
insemination.
Nature
421:360-363.
Fitzpatrick,
J.
L.,
J.
K.
Desjardins,
N.
Milligan,
R.
Montgomerie,
and
S.
Balshine.
2007.
Reproductive-tactic-specific
variation
in
sperm
swimming
speeds
in
a
shell-brooding
cichlid.
Biol.
Reprod.
77:280-284.
Fitzpatrick,
J.
L.,
M.
Almbro,
A.
Gonzalez-Voyer,
N.
Kolm,
and
L.
W.
Simmons.
2012.
Male
contest
competition
and
the
coevolution
of
weaponry
and
testes
in
pinnipeds.
Evolution
66:3595-3604.
Flannery,
E.
W.
2011.
Sperm
competition
and
the
alternative
reproductive
tactics
of
Chinook
salmon.
Pp.
106.
Biology.
Univ.
of
Windsor,
Canada.
Flannery,
E.
W.,
I.
A.
Butts,
M.
Slowinska,
A.
Ciereszko,
and
T.
E.
Pitcher.
2013.
Reproductive
investment
patterns,
sperm
characteristics,
and
seminal
plasma
physiology
in
alternative
reproductive
tactics
of
Chinook
salmon
(Oncorhynchus
tshawytscha).
Biol.
J.
Linn.
Soc.
108:99-108.
Fleming,
I.
and
J.
Reynolds.
2004.
Salmonid
breeding
systems.
Pp.
264-294
in
A.
P.
Hendry
and
S.
C.
Stearns,
eds.
Evolution
illuminated:
salmon
and
their
relatives.
Oxford
Univ.
Press,
Oxford,
U.K.
Fu,
P.,
B.
D.
Neff,
and
M.
R.
Gross.
2001.
Tactic-specific
success
in
sperm
competition.
Proc.
R.
Soc.
Lond.
B
Biol.
Sci.
268:1105-1112.
Gaffney,
P.
M.,
C.
M.
Bernat,
and
S.
K.
Jr
Allen.
1993.
Gametic
incompatibility
in
wild
and
cultured
populations
of
the
eastern
oyster,
Crassostrea
virginica
(Gmelin).
Aquaculture
115:273-284.
Gage,
M.
J.
G.,
P.
Stockley,
and
G.
A.
Parker.
1995.
Effects
of
alternative
male
mating
strategies
on
characteristics
of
sperm
4994
0
2013
The
Authors.
Ecology
and
Evolution
published
by
John
Wiley
&
Sons
Ltd.
B.
Young
et
al.
Sneaker
Males
Have
Competitive
Sperm
production
in
the
atlantic
salmon
(Salmo
salar):
theoretical
and
empirical
investigations.
Philos.
Trans.
R.
Soc.
B
Biol.
Sci.
350:391-399.
Gage,
M.,
C.
Macfarlane,
S.
Yeates,
R.
Ward,
J.
Searle,
and
G.
Parker.
2004.
Spermatozoal
traits
and
sperm
competition
in
Atlantic
salmon:
relative
sperm
velocity
is
the
primary
determinant
of
fertilization
success.
Curr.
Biol.
14:44
17.
Gasparini,
C.,
and
A.
Pilastro.
2011.
Cryptic
female
preference
for
genetically
unrelated
males
is
mediated
by
ovarian
fluid
in
the
guppy.
Proc.
R.
Soc.
Lond.
B
Biol.
Sci.
278:2495-2501.
Gasparini,
C.,
G.
Andreatta,
and
A.
Pilastro.
2012.
Ovarian
fluid
of
receptive
females
enhances
sperm
velocity.
Naturwissenschaften
99:417-420.
Geyer,
L.
B.,
and
S.
R.
Palumbi.
2005.
Conspecific
sperm
precedence
in
two
species
of
tropical
sea
urchins.
Evolution
59:97-105.
Gharrett,
A.,
and
S.
Shirley.
1985.
A
genetic
examination
of
spawning
methodology
in
a
salmon
hatchery.
Aquaculture
47:245-256.
Gile,
S.
R.,
and
M.
M.
Ferguson.
1995.
Factors
affecting
male
potency
in
pooled
gamete
crosses
of
rainbow
trout,
Oncorhynchus
mykiss.
Environ.
Biol.
Fishes
42:267-275.
Ginzburg,
A.
S.
1972.
Fertilization
in
fishes
and
the
problem
of
polyspermy.
Pp.
366
in
Z.
Blake,
B.
Golek,
eds.
Israel
Program
for
Scientific
Translations,
Jerusalem,
Israel.
Gomez
Montoto,
L.,
C.
Magana,
M.
Tourmente,
J.
Martin-Coello,
C.
Crespo,
J.
J.
Luque-Larena,
et
al.
2011.
Sperm
competition,
sperm
numbers
and
sperm
quality
in
muroid
rodents.
PLoS
ONE
6:e18173.
Greig,
C.,
D.
P.
Jacobson,
and
M.
A.
Banks.
2003.
New
tetranucleotide
microsatellites
for
fine-scale
discrimination
among
endangered
chinook
salmon
(Oncorhynchus
tshawytscha).
Mol.
Ecol.
Notes
3:376-379.
Gross,
M.
R.
1985.
Disruptive
selection
for
alternative
life
histories
in
salmon.
Nature
313:47-48.
Gross,
M.
R.
1991.
Evolution
of
alternative
reproductive
strategies:
frequency-dependent
sexual
selection
in
male
bluegill
sunfish.
Philos.
Trans.
R.
Soc.
B
Biol.
Sci.
332:59-66.
Gross,
M.
R.
1996.
Alternative
reproductive
strategies
and
tactics:
diversity
within
sexes.
Trends
Ecol.
Evol.
11:92-98.
Healey,
M.
C.
1991.
Life
history
of
chinook
salmon
(Oncorhynchus
tshawytscha).
pp.
311-393
in
C.
Groot
and
L.
Margolis,
eds.
Pacific
salmon
life
histories.
University
of
Washington
Press,
Seattle,
Washington.
Heath,
D.
D.,
R.
H.
Devlin,
J.
W.
Heath,
and
G.
K.
Iwama.
1994.
Genetic,
environmental
and
interaction
effects
on
the
incidence
of
jacking
in
Oncorhynchus
tshawytscha
(Chinook
salmon).
Heredity
72:146-154.
Heath,
D.,
L.
Rankin,
C.
Bryden,
J.
Heath,
and
J.
Shrimpton.
2002.
Heritability
and
Y-chromosome
influence
in
the
jack
male
life
history
of
chinook
salmon
(Oncorhynchus
tshawytscha).
Heredity
89:311-317.
Hoysak,
D.,
and
N.
Liley.
2001.
Fertilization
dynamics
in
sockeye
salmon
and
a
comparison
of
sperm
from
alternative
male
phenotypes.
J.
Fish
Biol.
58:1286-1300.
Hoysak,
D.
J.,
N.
R.
Liley,
and
E.
B.
Taylor.
2004.
Raffles,
roles,
and
the
outcome
of
sperm
competition
in
sockeye
salmon.
Can.
J.
Zool.
82:1017-1026.
Hutchings,
J.
and
R.
Myers.
1988.
Mating
success
of
alternative
maturation
phenotypes
in
male
Atlantic
salmon,
Salmo
salar.
Oecologia
75:169-174.
Iwamatsu,
T.,
N.
Yoshizaki,
and
Y.
Shibata.
1997.
Changes
in
the
chorion
and
sperm
entry
into
the
micropyle
during
fertilization
in
the
teleostean
fish,
Oryzias
latipes.
Dev.
Growth
Differ.
39:33-41.
Jordan,
W.,
and
A.
Youngson.
1992.
The
use
of
genetic
marking
to
assess
the
reproductive
success
of
mature
male
Atlantic
salmon
parr
(Salmo
salar,
L.)
under
natural
spawning
conditions.
J.
Fish
Biol.
41:613-618.
Kime,
D.,
K.
Van
Look,
B.
McAllister,
G.
Huyskens,
E.
Rurangwa,
and
F.
011evier.
2001.
Computer-assisted
sperm
analysis
(CASA)
as
a
tool
for
monitoring
sperm
quality
in
fish.
Comp.
Biochem.
Physiol.
C:
Toxicol.
Pharmacol.
130:425-433.
Kupriyanova,
E.,
and
J.
N.
Havenhand.
2002.
Variation
in
sperm
swimming
behaviour
and
its
effect
on
fertilization
success
in
the
serpulid
polychaete
Galeolaria
caespitosa.
Invertebr.
Reprod.
Dev.
41:21-26.
Levitan,
D.
R.
1993.
The
importance
of
sperm
limitation
to
the
evolution
of
egg
size
in
marine
invertebrates.
Am.
Nat.
141:517-536.
Levitan,
D.
R.
1996.
Effects
of
gamete
traits
on
fertilization
in
the
sea
and
the
evolution
of
sexual
dimorphism.
Nature
382:153-155.
Levitan,
D.
R.
2000.
Sperm
velocity
and
longevity
trade
off
each
other
and
influence
fertilization
in
the
sea
urchin
Lytechinus
variegatus.
Proc.
R.
Soc.
Lond.
B
Biol.
Sci.
267:531-534.
Levitan,
D.
R.
2012.
Contemporary
evolution
of
sea
urchin
gamete-recognition
proteins:
experimental
evidence
of
density-dependent
gamete
performance
predicts
shifts
in
allele
frequencies
over
time.
Evolution
66:1722-1736.
Levitan,
D.
R.,
and
D.
L.
Ferrell.
2006.
Selection
on
gamete
recognition
proteins
depends
on
sex,
density,
and
genotype
frequency.
Science
312:267-269.
Levitan,
D.
R.,
and
A.
P.
Stapper.
2010.
Simultaneous
positive
and
negative
frequency-dependent
selection
on
sperm
bindin,
a
gamete
recognition
protein
in
the
sea
urchin
Strongylocentrotus
purpuratus.
Evolution
64:785-797.
Liljedal,
S.,
G.
Rudolfsen,
and
I.
Folstad.
2008.
Factors
predicting
male
fertilization
success
in
an
external
fertilizer.
Behay.
Ecol.
Sociobiol.
62:1805-1811.
Locatello,
L.,
A.
Pilastro,
R.
Deana,
A.
Zarpellon,
and
M.
B.
Rasotto.
2007.
Variation
pattern
of
sperm
quality
traits
in
two
gobies
with
alternative
mating
tactics.
Funct.
Ecol.
21:975-981.
©
2013
The
Authors.
Ecology
and
Evolution
published
by
John
Wiley
&
Sons
Ltd.
4995
Sneaker
Males
Have
Competitive
Sperm
B.
Young
et
al.
Marshall,
D.
J.,
and
J.
P.
Evans.
2005.
The
benefits
of
polyandry
in
the
free-spawning
polychaete
Galeolaria
caespitosa.
J.
Evol.
Biol.
18:735-741.
Marshall,
D.
J.,
C.
A.
Styan,
and
M.
J.
Keough.
2002.
Sperm
environment
affects
offspring
quality
in
broadcast
spawning
marine
invertebrates.
Ecol.
Lett.
5:173-176.
Maynard
Smith,
J.
1982.
Evolution
and
the
theory
of
games.
Cambridge
Univ.
Press,
Cambridge,
U.K.
Mengerink,
K.
J.
and
V.
D.
Vacquier.
2001.
Glycobiology
of
sperm-egg
interactions
in
deuterostomes.
Glycobiology
11:37R-43R.
Montgomerie,
R.
and
J.
Fitzpatrick.
2009.
Testis
size,
sperm
size,
and
sperm
competition.
Pp.
1-53
in
B.
G.
M.
Jamieson,
ed.
Reproductive
biology
and
phylogeny
of
fishes.
Science
Publishers
Inc.,
Enfield,
NH.
Myers,
J.
M.,
R.
G.
Kope,
G.
J.
Bryant,
D.
Teel,
L.
J.
Lierheimer,
T.
C.
Wainwright,
et
al.
1998.
Status
review
of
Chinook
salmon
from
Washington,
Idaho,
Oregon,
and
California.
US
Dept.
Comm.,
NOAA
Tech.
Memo.
NMFS-NWFSC-35,
443
pp.
Neff,
B.
D.
and
L.
M.
Wahl.
2004.
Mechanisms
of
sperm
competition:
testing
the
fair
raffle.
Evolution
58:1846-1851.
Neff,
B.
D.,
P.
Fu,
and
M.
R.
Gross.
2003.
Sperm
investment
and
alternative
mating
tactics
in
bluegill
sunfish
(Lepomis
macrochirus).
Behay.
Ecol.
14:634-641.
Nelson,
R.
J.
and
T.
D.
Beacham.
1999.
Isolation
and
cross
species
amplification
of
microsatellite
loci
useful
for
study
of
Pacific
salmon.
Anim.
Genet.
30:228-229.
Pakkasmaa,
S.,
N.
Peuhkuri,
A.
Laurila,
H.
Hirvonen,
and
E.
Ranta.
2001.
Female
and
male
contribution
to
egg
size
in
salmonids.
Evol.
Ecol.
15:143-153.
Pakkasmaa,
S.,
0.-P.
Penttinen,
and
J.
Piironen.
2006.
Metabolic
rate
of
Arctic
charr
eggs
depends
on
their
parentage.
J.
Comp.
Physiol.
B.
176:387-391.
Palumbi,
S.
R.
1999.
All
males
are
not
created
equal:
fertility
differences
depend
on
gamete
recognition
polymorphisms
in
sea
urchins.
Proc.
Nail
Acad.
Sci.
USA
96:12632-12637.
Parker,
G.
1990a.
Sperm
competition
games:
raffles
and
roles.
Proc.
R.
Soc.
Lond.
B
Biol.
Sci.
242:120-126.
Parker,
G.
1990b.
Sperm
competition
games:
sneaks
and
extra-pair
copulations.
Proc.
R.
Soc.
Lond.
B
Biol.
Sci.
242:127-133.
Perchec,
G.,
M.
Cosson,
J.
Cosson,
C.
Jeulin,
and
R.
Billard.
1998.
Morphological
and
kinetic
changes
of
carp
(Cyprinus
carpio)
spermatozoa
after
initiation
of
motility
in
distilled
water.
Cell
Motil.
Cytoskelet.
35:113-120.
Pitcher,
T.
E.,
S.
M.
Doucet,
J.
M.
J.
Beausoleil,
and
D.
Hanley.
2009.
Secondary
sexual
characters
and
sperm
traits
in
coho
salmon
Oncorhynchus
kisutch.
J.
Fish
Biol.
74:1450-
1461.
Quinn,
T.
P.,
and
C.
J.
Foote.
1994.
The
effects
of
body
size
and
sexual
dimorphism
on
the
reproductive
behaviour
of
sockeye
salmon,
Oncorhynchus
nerka.
Anim.
Behay.
48:751-
761.
Rasotto,
M.
B.,
and
C.
Mazzoldi.
2002.
Male
traits
associated
with
alternative
reproductive
tactics
in
Gobius
niger.
J.
Fish
Biol.
61:173-184.
Reichard,
M.,
S.
C.
Le
Comber,
and
C.
Smith.
2007.
Sneaking
from
a
female
perspective.
Anim.
Behay.
74:679-688.
Rosengrave,
P.,
N.
J.
Gemmell,
V.
Metcalf,
K.
McBride,
and
R.
Montgomerie.
2008.
A
mechanism
for
cryptic
female
choice
in
chinook
salmon.
Behay.
Ecol.
19:1179-1185.
Rudolfsen,
G.,
L.
Figenschou,
I.
Folstad,
H.
Tveiten,
and
M.
Figenschou.
2006.
Rapid
adjustments
of
sperm
characteristics
in
relation
to
social
status.
Proc.
R.
Soc.
Lond.
B
Biol.
Sci.
273:325-332.
Rudolfsen,
G.,
L.
Figenschou,
I.
Folstad,
and
0.
Kleven.
2008.
Sperm
velocity
influence
paternity
in
the
Atlantic
cod
(Gad
us
morhua
L.).
Aquac.
Res.
39:212-216.
Rutter,
C.
1903.
Natural
history
of
the
quinnat
salmon.
A
report
of
investigations
in
the
Sacramento
River,
1896-1901.
Bull.
U.S.
Fish
Comm.
for
1902
22:65-141.
Schulte-Hostedde,
A.
I.,
J.
S.
Millar,
and
G.
J.
Hickling.
2005.
Condition
dependence
of
testis
size
in
small
mammals.
Evol.
Ecol.
Res.
7:143-149.
Simmons,
L.
W.,
and
J.
L.
Fitzpatrick.
2012.
Sperm
wars
and
the
evolution
of
male
fertility.
Reproduction
144:519-534.
Simmons,
L.,
J.
Tomkins,
and
J.
Hunt.
1999.
Sperm
competition
games
played
by
dimorphic
male
beetles.
Proc.
R.
Soc.
Lond.
B
Biol.
Sci.
266:145-150.
Skarstein,
F.,
I.
Folstad,
S.
Liljedal,
and
M.
Grahn.
2005.
MHC
and
fertilization
success
in
the
Arctic
charr
(Salvelinus
alpinus).
Behay.
Ecol.
Sociobiol.
57:374-380.
Smith,
C.
C.,
and
M.
J.
Ryan.
2010.
Evolution
of
sperm
quality
but not
quantity
in
the
internally
fertilized
fish
Xiphophorus
nigrensis.
J.
Evol.
Biol.
23:1759-1771.
Snook,
R.
2005.
Sperm
in
competition:
not
playing
by
the
numbers.
Trends
Ecol.
Evol.
20:46-53.
Sarum,
V.,
L.
Figenschou,
G.
Rudolfsen,
and
I.
Folstad.
2011.
Spawning
behaviour
of
Arctic
charr
(Salvelinus
alpinus):
risk
of
sperm
competition
and
timing
of
milt
release
for
sneaker
and
dominant
males.
Behaviour
148:1157-1172.
Spies,
I.
B.,
D.
J.
Brasier,
P.
T.
L.
O'Reilly,
T.
R.
Seamons,
and
P.
Bentzen.
2005.
Development
and
characterization
of
novel
tetra-,
tri-,
and
dinucleotide
microsatellite
markers
in
rainbow
trout
(Oncorhynchus
mykiss).
Mol.
Ecol.
Notes
5:278-281.
Stockley,
P.,
and
A.
Purvis.
1993.
Sperm
competition
in
mammals:
a
comparative
study
of
male
roles
and
relative
investment
in
sperm
production.
Funct.
Ecol.
7:560-570.
Stockley,
P.,
M.
J.
G.
Gage,
G.
A.
Parker,
and
A.
P.
Moller.
1997.
Sperm
competition
in
fishes:
the
evolution
of
testis
size
and
ejaculate
characteristics.
Am.
Nat.
149:933-954.
Stoltz,
J.
A.,
and
B.
D.
Neff.
2006.
Sperm
competition
in
a
fish
with
external
fertilization:
the
contribution
of
sperm
number,
speed
and
length.
J.
Evol.
Biol.
19:1873-1881.
4996
0
2013
The
Authors.
Ecology
and
Evolution
published
by
John
Wiley
&
Sons
Ltd.
B.
Young
et
al.
Sneaker
Males
Have
Competitive
Sperm
Swanson,
W.
J.,
and
V.
D.
Vacquier.
2002.
The
rapid
evolution
of
reproductive
proteins.
Nat.
Rev.
Genet.
3:137-144.
Taborsky,
M.
1998.
Sperm
competition
in
fish:bourgeois'
males
and
parasitic
spawning.
Trends
Ecol.
Evol.
13:222-227.
Tanaka,
Y.,
T.
Hayashi,
D.
G.
III
Miller,
K.
Tainaka,
and
J.
Yoshimura.
2009.
Breeding
games
and
dimorphism
in
male
salmon.
Anim.
Behay.
77:1409-1413.
Tazzyman,
S.
J.,
T.
Pizzari,
R.
M.
Seymour,
and
A.
Pomiankowski.
2009.
The
evolution
of
continuous
variation
in
ejaculate
expenditure
strategy.
Am.
Nat.
174:E71—E82.
Tourmente,
M.,
M.
Gomendio,
and
E.
Roldan.
2011.
Sperm
competition
and
the
evolution
of
sperm
design
in
mammals.
BMC
Evol.
Biol.
11:12.
Tourmente,
M.,
M.
Rowe,
M.
M.
Gonzalez-Barroso,
E.
Rial,
M.
Gomendio,
and
E.
R.
S.
Roldan.
2013.
Postcopulatory
sexual
selection
increases
ATP
content
in
rodent
spermatozoa.
Evolution.
67:1838-1846.
Uglem,
I.,
T.
F.
Galloway,
G.
Rosenqvist,
and
I.
Folstad.
2001.
Male
dimorphism,
sperm
traits
and
immunology
in
the
corkwing
wrasse
(Symphodus
melops
L.).
Behay.
Ecol.
Sociobiol.
50:511-518.
Vacquier,
V.
D.
1998.
Evolution
of
gamete
recognition
proteins.
Science
281:1995-1998.
VladiC,
T.
V.,
and
T.
Jarvi.
2001.
Sperm
quality
in
the
alternative
reproductive
tactics
of
Atlantic
salmon:
the
importance
of
the
loaded
raffle
mechanism.
Proc.
R.
Soc.
Lond.
B
Biol.
Sci.
268:2375-2381.
VladiC,
T.
V.,
L.
A.
Forsberg,
and
T.
Jarvi.
2010.
Sperm
competition
between
alternative
reproductive
tactics
of
the
Atlantic
salmon
in
vitro.
Aquaculture
302:265-269.
Williamson,
K.
S.,
A.
R.
Murdoch,
T.
N.
Pearsons,
E.
J.
Ward,
and
M.
J.
Ford.
2010.
Factors
influencing
the
relative
fitness
of
hatchery
and
wild
spring
Chinook
salmon
(Oncorhynchus
tshawytscha)
in
the
Wenatchee
River,
Washington,
USA.
Can.
J.
Fish.
Aquat.
Sci.
67:1840-1851.
Withler,
R.
1988.
Genetic
consequences
of
fertilizing
chinook
salmon
(Oncorhynchus
tshawytscha)
eggs
with
pooled
milt.
Aquaculture
68:15-25.
Yanagimachi,
R.,
G.
N.
Cherr,
M.
C.
Pillai,
and
J.
D.
Baldwin.
1992.
Factors
controlling
sperm
entry
into
the
micropyles
of
salmonid
and
herring
eggs.
Dev.
Growth
Differ.
34:447-461.
Yeates,
S.
E.,
S.
Einum,
I.
A.
Fleming,
H.-J.
Megens,
R.
J.
M.
Stet,
K.
Hindar,
et
al.
2009.
Atlantic
salmon
eggs
favour
sperm
in
competition
that
have
similar
major
histocompatibility
alleles.
Proc.
R.
Soc.
Lond.
B
Biol.
Sci.
276:559-566.
Yeates,
S.
E.,
S.
E.
Diamond,
S.
Einum,
B.
C.
Emerson,
W.
V.
Holt,
and
M.
J.
G.
Gage.
in
press.
Cryptic
choice
of
conspecific
sperm
controlled
by
the
impact
of
ovarian
fluid
on
sperm
swimming
behaviour.
Evolution.
Supporting
Information
Additional
Supporting
Information
may
be
found
in
the
online
version
of
this
article:
Appendix
Sl.
Parental
genotypes
and
phenotypes.
Appendix
S2.
Spermatocrit
data
from
all
participating
males.
©
2013
The
Authors.
Ecology
and
Evolution
published
by
John
Wiley
&
Sons
Ltd.
4997