ABSTRACT

1
 
Table 2 Test 2 Finding the avoiders. Durations
in seconds were recorded for each arm of the
y-maze designated "short" duration, "long"
duration, and neutral. A denotes an avoider.
ABSTRACT Although mate choice is presumed to
affect individual fitness, the effect of mate
choice on offspring numbers is seldom
investigated. To test whether female flour
beetles, Tribolium confusum, actively choose
males, and whether those choices affect their
fecundity, we allowed virgin females to select
mates, and then bred them with virgin males that
females preferred or did not prefer. As a control
we also mated virgin females to virgin males at
random. Using ANOVA, we compared the 40 day
productivities of all females by mating class
(Ncrosses30, Nprogeny3,500). Our results showed
that while females actively chose males, the
number of offspring produced by females bred
either with preferred, non-preferred, or random
males, did not differ significantly between
groups (F2,290.86, p0.44). Thus, contrary to
current good genes predictions, free female
mate choice in T. confusum showed no effect on
female fecundity.
Table 1 Test 1 Finding the random walkers.
Durations in seconds were recorded for each arm
of the y-maze designated "short" duration, "long"
duration, and neutral. R denotes a random
walker.
INTRODUCTION The good genes model of sexual
selection predicts that females will choose mates
based on phenotypic traits which reflect male
genetic quality. According to this model,
females indirectly benefit by producing
high-quality offspring thus female choice and
offspring viability are presumed to be positively
correlated (Zahavi 1975, Andersson 1982, Hamilton
Zuk 1982). Although studies presenting evidence
of increased offspring viability as a result of
female choice are now common (Petrie 1994,
Drickamer et al. 2000, 2003, Gowaty et al. 2003),
parental and offspring fitnesses are confounded
in estimates of offspring viability. Predictions
about the adaptive outcomes of mate choice are
therefore difficult or impossible (Wolf Wade
2001). As a measure of parental fitness,
fecundity is unconfounded by offspring fitness.
Thus, in assessing the direct effects of mate
choice on parental fitness, fecundity has a
significant advantage over offspring viability
(Shuster Wade 2003). Although the good
genes model does not predict how female mate
choice will affect female fecundity, if female
choice improves offspring performance, choosy
females are expected to be more fecund. Studies
show that the number of progeny produced, a
component of breeder fitness, does not differ
significantly among mating pairs that preferred
each other versus mating pairs that do not prefer
each other (Petrie 1994 Drickamer et al. 2000,
2003, Gowaty et al. 2003). Thus, the aims of our
study were to determine 1) whether or not T.
confusum females show mate preferences, and if
so, 2) how female mate choice affects fecundity.
As our measure of fecundity, we measured beetle
productivity, which we defined as the number of
progeny produced per given number of females in a
given interval (Sokoloff 1977). Consistent with
the good genes hypothesis, we predicted that a
female who mated with a male she preferred would
produce significantly more offspring than a
female who mated with a male she did not prefer.
Table 3 Test 3 Finding the preferences.
Durations in seconds were recorded for each arm
of the y-maze designated "short" duration, "long"
duration, and neutral. NC denotes a
non-chooser.
Figure 1 Number of offspring produced by a
mating pair in each treatment group. Red bars
denote the means.

CONCLUSIONS Our results indicate that T.
confusum females actively choose between males
and show clear mating preferences when allowed to
do so. However, our productivity results also
show that free female mate choice may not affect
female fecundity. Although females chose mates,
the average numbers of progeny produced by
females mated with Preferred, NonPreferred and
Random males were not significantly different
from one another. Although our sample size was
somewhat small (N30 crosses, 3,500 total
progeny), our finding of conspicuous mate choice
without conspicuous fecundity returns suggests
that adaptive explanations are not always
necessary when evidence of mate choice is
observed.
METHODS Selection of Experimental Animals
(See Pictures) 1. Beetle pupae were
sexed. 2. Pupae were placed in individual
flour-filled vials and were allowed to develop
into adults. Choice Tests 3. Mate choice tests
were performed by allowing individual virgin
females to associate with individual males
isolated behind a fine mesh net in the arms of a
y-maze. Each trial lasted 30 minutes (1800
seconds). The amount of time the female spent
with each male was recorded to determine which
male she preferred and which male she did not
prefer. In detail, durations in seconds were
recorded for each arm designated "short"
duration, "long" duration, and neutral. Our
first criterion for a choice by females was met
if a female spent significantly greater than 2/3
of the trial time (67) in the male side of the
maze (i.e., in either of the arms of the y).
Thus, trials with nonsignificant values for a
G-test with df1 were eliminated as no choice,
as were significant trials with gt600 seconds in
the neutral zone (avoiders). To prevent an
experiment-wise type I error, we adjusted our
level of significance to a.05/20 trials.0025
thus Gsignificant10.83, df1. Our second
criterion for a choice by females eliminated as
no choice trials those in which females spent a
significant amount of time on the male side of
the maze, but did not spend significantly more
than ½ of the trial time in one arm of the maze.
Because our first criterion eliminated 5/20
trials (see Results), we adjusted our level of
significance to a.05/15 trials.003 thus
Gsignificant9.0, df1. Productivity
Analysis 4. Female and male beetle pairs were
mated in a flour yeast-filled vial. There were
three treatment groups as classified by the
following type of paired mating 1) a female
mated with a male she preferred, ?- P? (N7) 2)
a female mated with a male she did not prefer, ?-
NP? (N8) 3) a female mated with a random male,
?- R? (N15) 5. The total number of offspring
produced after 40 days were counted for each
mating pair.
REFERENCES 1. Andersson, M. 1982. Sexual
selection, natural selection and quality
advertisement. Biol. J. Linn. Soc. 17375-393. 2.
Drickamer, L., Gowaty, P. Holmes, C. Free
female mate choice in house mice affects
reproductive success and offspring viability and
performance. Animal Behaviour 59371-378. 3.
Drickamer, L., Gowaty, D. Wagner, D. 2003. Free
mutual mate preferences in house mice affect
reproductive success and offspring performance.
Animal Behaviour 65105-114. 4. Gowaty, P.,
Drickamer, L. Schmid-Holmes, S. 2003. Male
house mice produce fewer offspring with lower
viability and poorer performance when mated with
females they do not prefer. Animal Behaviour
6595-103. 5. Hamilton, W. Zuk, M. 1982.
Heritable true fitness and bright birds a role
for parasites? Science 218384-387. 6. Petrie, M.
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with more elaborate trains. Nature
371598-599. 7. Shuster, S. Wade, M. 2003.
Mating systems and strategies. Princeton
University Press, Princeton. 8. Sokoloff, A.
1977. The biology of Tribolium, vol. III. Oxford
University Press, London. 9. Wolf, J. Wade, M.
2001. On the assignment of fitness to parents and
offspring Whose fitness is it and when does it
matter? J. Evol. Biol. 53205-214. 10. Zahavi, A.
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RESULTS Results from choice tests (N20) We
asked three questions 1. Did females walk
randomly? One female (R) spent equal amounts of
time in the y arms and in the neutral arm of
the maze (Table 1). 2. Did females actively avoid
males? Fifteen females showed a choice, but five
females (A) showed no choice (as they did not
meet our criterion) (Table 2). 3. Did females
show no preference for either male? Of the
fifteen females that showed a choice, one female
(NC) spent equal amounts of time with both males
(Table 3). Results from breeding pairs
(N30) Females that showed no choice were
grouped under Treatment Group 3 female mated
with a random male, ?- R? . Forty day
productivities were analyzed using one way
ANOVA. The average number of progeny produced
did not differ significantly among all three
mating types Group 1(?-P?)115.415.55 Group
2(?-NP?) 101.914.54 Group 3(?- R?)
125.3.10.62 (F2,290.86, p0.44) (Figure 1).
ACKNOWLEDGEMENTS This study was done through
the Research Experiences for Undergraduates
program funded by the National Science
Foundation. Travel to the Animal Behavior
Society conference was made possible by the
Turner Award funded by the National Science
Foundation. Special thanks to Eric Anderson for
photography.