Invertebrate Mating Systems 3 Sperm Competition

1
Invertebrate Mating Systems (3)Sperm Competition
Cryptic Female Choice inInsects
2
Sexual Selection

• What traits can be influenced by sexual
  selection?
• Morphological structures
• Behaviours
• Signals Visual, Acoustic and Chemical

3
Sexual Selection

• Intra-sexual selection
• Male/Male Competition
• Female/Female Competition
• Inter-sexual Selection
• Female Mate Choice
• Male Mate Choice

4
Sexual selection does not end with mating!

• Why?
• Females often mate with more than one male
• Females can store sperm
• One clutch of offspring often has mixed
  paternity

5
Sexual selection does not end with mating!

• Males continue to compete for fertilization
• Sperm Competition
• Females continue to choose highest quality males
  to fertilize their eggs
• Cryptic Female Choice

6
Is sperm competition important?

• Males that are superior competitors before mating
  may not end up fathering all of the offspring of
  a particular female
• Sperm also have
• to be good competitors

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Sperm storage

• Ejaculates can compete for longer than males
• Females in many animal groups can store sperm for
  long periods of time (gt30 years in some ants)
• Special storage organs called spermathecae

Different types of spermathecae in insects
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Important terms

• Sperm CompetitionCompetition between the sperm
  from two or more males for the fertilization of a
  given set of ova (Parker, 1998)
• Sperm precedence The non-random utilization of
  sperm from a particular male, when the sperm from
  two or more males mix within a female
• Sperm displacement The displacement of one
  males sperm from the genital opening of a female
  by a different male
• P2 The proportion of offspring sired by the last
  male to mate last-male paternity

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Evidence for sperm competition

• Morphological adaptations (Genitalia)
• Chemical adaptations
• Accessory Gland Products
• Mating Plugs
• Behavioural adaptations
• Mate Guarding Copulatory Courtship
• Differences in copula duration
• Sperm morphology

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Morphological adaptationsSexual selection the
evolution of animal genitalia

• Male genitalia that can position sperm in the
  most advantageous place will be selected for
• Male genitalia that can remove or reposition the
  sperm of previous males will be selected for
• Male genitalia with a titillatory function will
  be selected for

11
Morphological adaptationsSexual selection the
evolution of animal genitalia

• Sperm removal in dragonflies and damselflies
  (Order Odonata)

12
Male genitaliain dragonfliesSperm removal and
repositioning
Orthetrum cancellatum
Crocothemis erythraea
Simmons, L.W. (2001). Sperm Competition and its
Evolutionary Consequences in the Insects.
Princeton University Press.
13
Chemical/Physiological AdaptationsAccessory
Gland Products

• AGPs are chemicals produced in the accessory
  glands of the male reproductive system to be
  deposited with sperm
• AGPs often have an effect on female physiology or
  behaviour
• E.g. Acheta domestica
• Male AGPs stimulate
• oviposition in females.

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Chemical/Physiological AdaptationsMating Plugs

• Chemicals produced by a male that solidify to
  block the genital opening of a female, preventing
  other males from copulating or depositing sperm
  e.g. Butterflies and moths

Graphium sarpedon
Atrophaneura alcinous
Euryades corethrus
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Chemical/Physiological AdaptationsMating Plugs

• Mating plugs are chemicals that are produced by a
  male that solidify to block the genital opening
  of a female, preventing other males from
  copulating or depositing sperm e.g. Lepidoptera

0.75
0.48
P2
Mating Plugs
With Without
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Behavioural AdaptationsMate Guarding

• Males often associate with female mates after
  mating has occurred and rigorously defend the
  female from other males
• In a large number of insect species, the last
  male to mate achieves a higher paternity (high
  P2), so mate-guarding would reduce sperm
  competition.
• Social monogamy may be an extension of
  mate-guarding

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Behavioural AdaptationsMate Guarding

• E.g. Gerris lacustris (water strider)
• Males grip on to females during copulation using
  special appendages
• Males continue to ride around on females after
  mating has finished, preventing other males from
  attempting to mate

18
Behavioural AdaptationsMate Guarding

• E.g. Gerris lacustris (water strider)

MG Duration (min)
FFF MFF MFM MMM
Sex Ratio Treatments
19
Optimal Copula Duration

• Usually, copulation duration is positively
  correlated with sperm transferred
• In Yellow Dung Flies (Scathophaga stercoraria),
  larger males copulate for longer, and displace
  more of the previous males sperm

20
Sperm Morphology

• Drosophila exhibit extreme variation in sperm
  length

21
Sperm Morphology

• Sperm Length negatively correlated to P2 in
  Drosophila

Average P2 of Species
Average Sperm Length of Species
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Cryptic Female Choice

• Postcopulatory inter-sexual selection emphasizing
  the importance of female control over paternity
• Dispels the myth of the passive female
• Many levels of female control
• Females can discard sperm
• Females can terminate copulation
• Females can impede plugging/plug removal
• Females can bias the use of stored sperm
• Females can remove spermatophore before sperm
  transfer is complete

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Cryptic Female Choiceand Copulatory Courtship

• E.g. Red Flour Beetles
• (Tribolium castaneum)

Fertilization success
Unmanipulated males
Rate of leg rubbing
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Cryptic Female Choiceand Copulatory Courtship

• E.g. Red Flour Beetles
• (Tribolium castaneum)

Fertilization success
Unmanipulated males
Manipulated males
Rate of leg rubbing
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References

• Alcock, J. (1989). Animal Behavior an
  evolutionary approach (4th Edition). Sinauer
  Assoc. Inc. Sunderland. Chapters 12, 13, 14.
• Choe, J. C. Crespi, B. J. (Eds). (1997) The
  evolution of mating systems in insects and
  arachnids. Cambridge New York Cambridge
  University Press.
• Chapters 2, 6, 16, 19 (and all of the others
  are interesting too!)
• Eberhard, W. G. (1996) Female control sexual
  selection by cryptic female choice. Princeton
  University Press. Princeton.
• Emlen, S. T. L. W. Oring. (1977). Ecology,
  sexual selection and the evolution of mating
  systems. Science 197 215-223.
• Edvardsson, M. G. Arnqvist (2000). Copulatory
  courtship and cryptic female choice in red flour
  beetles Tribolium castaneum. Proceedings of the
  Royal Society of London B 267 559-563.
• Gwynne, D. T. (1984). Sexual selection and
  sexual differences in mormon crickets
  (Orthoptera Tettigoniidae, Anabrus simplex).
  Evolution 38(5) 1011-1022.
• Norman, M. D., J. Finn and T. Tregenza (1999).
  Female impersonation as an alternative
  reproductive strategy in giant cuttlefish.
  Proceedings of the Royal Society of London B 266
  1347-1349
• Simmons, L.W. (2001). Sperm Competition and its
  Evolutionary Consequences in the Insects.
  Princeton University Press. Princeton.

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References

• Tomkins, J. L. G. S. Brown (2004). Population
  density drives the local evolution of a threshold
  dimorphism. Nature. 431 1099-1103.
• Shuster S. M. M. J. Wade (1991). Equal mating
  success among male reproductive strategies in a
  marine isopod. Nature. 350 608-610.
• Hanlon, R. T. et al. (2005). Transient sexual
  mimicry leads to fertilization. Nature. 433. 212.