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Call Duration as an Indicator o Genetic Quality
in Male Gray Tree Frogs
Allison M. Welch,* Raymond D Semlitsch, H Carl Gerhardt
The good genes hypothesis predicts that mating preferences
enable females to select
mates of superior genetic quality. The genetic consequences of
the preference shown
by female gray tree frogs for long-duration calls were evaluated
by comparing the
performance of maternal half-siblings sired by males with
different call durations. Off
spring of male gray tree frogs that produced long calls showed
better performance during
larval and juvenile stages than i offspring of males that
produced short calls. These
data suggest that call duration can function as a reliable
indicator of heritable genetic
quality.
e good genes mode l of sexual selec
tion predicts that some attributes of male
courtship displays advertise genetic quality.
Preferences for such attributes should allow
females to mate with high-quality males
and thereby benefit indirectly through en-
hanced quality of offspring (1). Although
the good genes hypothesis has been tested
several times (2), few stud ies have prOVided
direct genetic evidence supporting this hy
pothesis (3). Only
one
such study involved
a species in which females cannot benefit
directly from their choice of mates (4) .
Because selection for direct benefits such as
courtship feeding or parental care should
overwhelm any selection for indirect (ge
netic) benefits (5), the role of good genes
selection in the evolution and maintenance
of female preferences is best tested in spe
cies in which females do not benefit directly
fr
om mate choice.
Female gray tree frogs Hy/a versicolcrr
strongly prefer male advertisement calls of
long duration in laboratory experiments (6,
7). In the field, females freely initiate mat
ings with calling males and do not always
choose the first male encountered (7). Be
cause males do not defend oviposition sites,
offer nuptial gifts, or contribute parental care
(8 , 9), and no difference has been found in
fertilization success as a function of call du
ration (10), there are no apparent direct
benefits of a female's mate choice. We there
fore predicted that females selecting mates
with long calls should benefit in.directly
Division of Biological Sciences, University of Missouri ,
Columbia, MO 65211 , USA.
To whom correspondence should be addressed. E-mail:
[email protected]
through increased fitness of offspring. This
prediction can be tested
by evaluating the
relation between paternal call duration and
the genetic quality of offspring.
Male gray tree frog advertisement calls
consist of rapidly repeated pulses In dense
choruses and in re sponse to playbacks, males
tend to increase call duration by increasing
the number of pulses per call (11, 12 . None-
theless, some males conSistently produce
longer calls
than
others in the same acoustic
environment (7, 12- 14), Although long
calls are usually produced at slow rates,
thereby keeping aerobic metabolic costs rel
ati ve Iy constant (11 , 14), males that produce
long calls spend less time calling per night
(11) and attend fewer choruses per season
(8) than males that produce short calls. Long
calls thus appear to impose higher nonaero
bic costs than short calls. Call duration may,
therefore, be
an
honest indicator
of
male
genetic quality.
We tested whether call duration indicates
heritable genetic quality by using maternal
half-siblingships (half-sibships) to compare
the performance of different males' off
spring while experimentally controlling for
all maternal effects. Maternal half-sibships
were generated by artificially crossing each
female with two males that had been giv
ing calls of distinctly different durations in
the same social environment Table 1).
Thus, within each maternal half-sibship,
one sibship was sired by a male with calls of
longer duration than the male siring the
other sibship . Because call duration varies
with chorus density, males' calls must be
assessed in the same social context in order
to be validly compared. Uws, in 1995 we
selected
nine
sets
of
two males
that
had
SC IENCE VOL. 280 19 JUNE 1998 www.science mag.org
mailto:[email protected]:///reader/full/www.sciencemag.orghttp:///reader/full/www.sciencemag.orghttp:///reader/full/www.sciencemag.orghttp:///reader/full/www.sciencemag.orghttp:///reader/full/www.sciencemag.orgmailto:[email protected]:///reader/full/www.sciencemag.org
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Proe, R Soc, London Ser, B264,297(1997)
29,
4, M,Petrie, Nature 371,598
5, M, and N, H Natf. Aead,
Sci. 94 1282
6, G. M. KlumpandH.
7.
Dyson,S D. Tanner, Be/JEJV bothunivariateand mll i t"""i";
'A
26, R R,Sokaland F J,
8. Hinshaw, nimBehav. 44,
27, H, Fl, Collins,
SCience 182,1305
9,
1979,286 (1979).
J,Travis, 44,502
10,
IDUICJII>iICl!OO data,
28, E,Ritke.J,G,Babb, M,K, RJ!ke, Herpelof, 24
11.
Taigen, Behav Ecol Soc/obiof,
135(1990), 12December 1997:accepted 22 April 1998
12,
13
14.
15,
16,
17
18.
19,
20,
21
22
wascalculatedas
each family surviving
onslrr1el"mmr,hirogrmvthwas asthe dit,
wet massachieved30
metamorphosisandwet massat
23, K, A Bervenand D, E, Gill,An" Zoo!.23,
C,
Smrth,
68,344
(1987),
24, Mixed-model analyses
(ANOVAs) were foreach
able,at food each
the main effectsof call identrty,
identity(1996only),and blockingfactors,as
as forinteractions, In order to account forcor-
relations between larval period and mplArnm'nhirc
mass,eachwas usedasacovariateinthe
of theother.
25,
1930 SCIENCE VO 280 19 JUNE [998
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~ ~ ~ ~ l .
;.b ' ~ ' - r : ,(o:y:, ' ; ' ;
Do females select mates based on traits
indicative of good genes ?
EXPERIMENT
Female gray tree frogs prefer
to
mate with
males that give long mating calls, Allison Welch and c o l l e g
u e ~
at the University of Missouri , tested whether the genetic
makel
of long-calling (LC) males is superior to that of short-calling
SC
males, The researchers fertilized half the eggs of each
female
with sperm from an LC male and fertilized the remaining eggs
with sperm from an SC male, The resulting half-sibling
offsprin
were raised in a common environment and tracked
for
two
yea
Recording of SC
Recording of LC
male's ca ll
male's call
. 1
~ ~
-
. 1
1
1
1
Fema le gray
tree frog
SC male gray .
LC malegri
tree frog tree
frog
l
SC sperm x Eggs x LC sperm
Offspring of
Offspring of
SC father LC father
~
itness of these ha lf-Sibling offspring compared
RESULTS
Fitness Measure
995 1996
Larval growth
NSD LC better
Larval survival
LC better NSD
Time to metamorphosis
LC better LC better
shorter)
shor
ter
NSD = no Significant difference; LC
better
= offspring of LC males
superior to offspring of SC males,
ON LUSION Because offspring fathered by an LC male had
higher fitness than their half-Siblings fathered by an SC male,
the
team concluded that the duration
of
a mal
e's
mating
call
is
in-
dicative of the male's overall genetic quality, This result
supports
the hypothesiSthat female mate choice can be based on a
trait
that indicates whether the male has good genes."
SOUR E
AM, Welch et aI., Call duration as an indicator
of gener
quality in male gray tree frogs, Science 280:1928-1930
(1998).
Inquiry Action
Read and analyze the original paper in
Inquiry in Action. Interpreting Scientific apers ,
-',f :t,iliM Why did the researchers split each female
frog's
eggs into two batches for fertilization by different males
7
Why
didn't they mate each female with a single male frog?
