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.
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Sperm competition and sexual selection
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
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
26. The Environment Institute
Where ideas grow
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