This document summarizes a presentation by Professor Leigh Simmons on sperm competition and sexual selection. It discusses Darwin's original ideas on the topic and how research has expanded since the 1970s to study behavior, morphology, and physiology related to sperm competition across many insect species. Specific studies are highlighted on sperm displacement behavior in yellow dung flies and experimental evolution of ejaculate expenditure in response to varying levels of sperm competition. The research has provided insights into the evolution of male genital morphology and ejaculate quality under monogamous versus polygamous mating systems.

1. The Environment Institute
Where ideas grow
Professor Leigh Simmons
Sperm competition and sexual selection

2. Sperm Competition and
Sexual Selection
Leigh W Simmons
Centre for Evolutionary Biology,
University of Western Australia

3. The Origin of Species, 1859
“…… [sexual selection] depends, not
on a struggle for existence in
relation to other organic beings or
to external conditions, but on a
struggle between the individuals of
one sex, generally the males, for
the possession of the other sex. The
result is not death to the
unsuccessful competitor, but few or
no offspring.” (chapter iv)

4. The Decent of Man and Selection
in Relation to Sex, Darwin 1871

5. Sperm Competition and
its Evolutionary
Consequences in the
Insects, Parker 1970
• behaviour
• morphology • physiology

6. Sperm Competition and
its Evolutionary
Consequences in the
Insects, Parker 1970
300
Number of publications
200
100
• ISI July 2009 70’s 80’s 90’s 00’s
Year

7. • Behaviour
Sperm displacement and
optimal copula duration in the
yellow dung fly, Scatophaga
stercoraria
• Image from Hosken 1999
• Parker 1970

8. • Behaviour
Sperm displacement and
optimal copula duration in the
yellow dung fly, Scatophaga
stercoraria
Large males
P2
Small males
• Image from Hosken 1999
156.5 min tl* ts*
• Evolution, 46, 366

9. • Behaviour
Sperm displacement and
optimal copula duration in the
yellow dung fly, Scatophaga
stercoraria
200
Copula duration (min)
180
t*
160
140
120
100
80
60
40
20
• Image from Hosken 1999 0
-20
5 10 15 20 25 30 35 40 45 50 55
Hind tibia length 3
• Evolution, 54, 924

10. • Physiology
Modelling the ESS ejaculate expenditure
Total
Reproductive
Expenditure expenditure on
gaining matings
n matings
W = n.v
gain v per mating
ejaculate
expenditure, x
• Parker 1998

11. • Physiology
Modelling the ESS ejaculate expenditure
0.50
A
ESS ejaculate expenditure
r =1.0
0.40
0.30
r =0.5
0.20
r =0.1
0.10
r =0.01
0.00
0.00 0.20 0.40 0.60 0.80 1.00
Probability of double mating, q
• Parker et al 1997

12. • Physiology
Evolution of ejaculate expenditure
.8
.6
.4
.2
0
-.2
-.4
-.6
-1.2 -1 -.75 -.5 -.25 0 .25 .5 .75 1 1.25
Crinia georgiana
Contrasts in sperm competition index
• J. Evol. Biol., 15, 347

13. • Physiology
Evolution of ejaculate expenditure
2.2
A
2.0
1.8
1.6
1.4
1.2 Crinia georgiana
0.3 0.5 0.7 0.9 1.1 1.3 1.5
log Maximum male density
• unpublished

14. • Physiology
Sperm competition games
between sneaks and guards
ESS Ejaculate expenditure
0.3
0.2
0.1
0.0
0.0 0.2 0.4 0.6 0.8 1.0
Probability of a sneak mating

15. • Physiology
Behavioural
biology of
onthophagine
dung beetles

16. Testis size variation across alternative
mating tactics of dung beetles
.1 5 1
.1 .8
.0 5 .6
0 .4
.2
-.0 5
0
-.1
-.2
-.1 5
-.4
-.2 -.6 -.4 -.2 0 .2 .4 .6 .8
-.4 -.3 -.2 -.1 0 .1 .2 .3 .4
• Evolution, 61, 2684

17. Experimental evolution: breeding regimes
Mating Brooding Incubation Maturation
Px3
10 10 X6 50 Ne ~ 106
Mx3
X 60 50 Ne = 100

18. • Physiology
Evolution of ejaculate expenditure
0.12
Sperm competition
0.08
0.04
0.00
-0.04
-0.08
Enforced monogamy
-0.12
4 6 8 10 12 14 16 18 20 22
Generation
• Evolution, 62, 2580

19. • Physiology
Evolution of ejaculate quality
Mating regime: Monogamous polygamous
1.5
A
• % motile
1.0 • VAP
• Longevity
0.5
0.0
-0.5
-1.0
-1.5
monogamy
Monogamous polygyny
Polygamous
Selection history
• Evolution in press

20. • Morphology
Evolution of male genital morphology among
Onthophagines
O. furcus
O. taurus
O. sticticus
O. punctatus O. hirtus
O. vacca

21. • Morphology
Evolution of male genital morphology among
Onthophagines
1
5
• Biol. J. Linn. Soc., 93, 257

22. • Morphology
Evolution of male genital morphology among
Onthophagines
• Curr. Biol., 19, 1442

23. • Morphology
Evolution of male genital morphology among
Onthophagines
1.00
0.50
0.00
-4.0 -2.0 0.0 2.0 4.0
Aedeagus shape (PC2)
• Curr. Biol., 19, 1442

24. • Morphology
Evolution of male genital morphology among
Onthophagines 0.8
0.6
0.4
0.2
0.0
-0.2
-0.4
-0.6
-0.8
1 2 3 1 2 3
Monogamy Polygamy
• Curr. Biol., 19, 1442

25. Acknowledgements
• Clarissa House
• John Hunt
• Paco García-González
• Joseph Tomkins
• Michael Werner
• Phil Byrne
• Martin Dziminski
• Dale Roberts
• Renée Firman
• Maxine Beveridge

26. The Environment Institute
Where ideas grow
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Dr Damien Fordham
Predicting ecological turmoil: modelling the dynamics of
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