Invertebrate Mating Systems and Mating Strategies2

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Invertebrate Mating Systems and Mating
Strategies(2)
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Sexual Selection

• Selection for traits that are solely concerned
  with increasing mating success
• Example Glow-worms and Fireflies
• Bioluminescence in Glow-worms is under natural
  selection, as its function is to attract prey
• Bioluminescence in Fireflies is under sexual
  selection, as its function in males is to attract
  females

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Sexual Selection

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

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Mating Systems
The typical pattern of mate finding,
reproduction, and parenting of offspring for a
given species.
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You cant mate if you dont meet

• Some invertebrates reproduce without mating
• Marine Free spawners
• e.g. Polychaete heteronereids, corals
• Soil Invertebrates Many males deposit
  spermatophores in the soil and leave for females
  to find
• e.g. Collembola, Pseudoscorpions

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Mating SystemsClassifying Mating SystemsWhat
factors are important?

• Number of Mates
• Monogamy/Polygyny/Polyandry/Promiscuity
• Defence
• Resources
• Mates
• Spatial Temporal Parameters

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Classification of Mating Systems(based on Emlen
Oring, 1977)
Female Behaviour
Male Behaviour
Mating System

• Females dispersed
• Females wander (a) Males form no bond Scramble
  Comp.
• (b) Males form pair-bond Monogamy
• (2) Females (a) Males form no bond Scramble
  Comp.
• with territory (b) Male occupies female
  range Monogamy
• (c) male defends range of several females R.D.
  Polygyny
• (B) Females aggregated
• Female groups (a) Males enter female
  groups Scramble Comp.
• wander (b) Males defend female groups H.D.
  Polygyny
• (c) Males defend mating territory Lek
• (2) Female groups (a) Males enter group
  territory Scramble Comp.
• with Territory (b) Males defend female
  groups H.D. Polygyny

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Scramble Competition Promiscuity

• No Male/Female Bonds
• No Defence
• High Possibility of
• Sperm Competition
• E.g. Horseshoe Crabs
• (Limulus polyphemus)

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Social Monogamy

• Male/Female Pair Bond
• Sometimes Mate defence or Mate Guarding
• Emphasis on Social Monogamy rather than sexual
  monogamy

E.g. Clown Shrimp (Lebbeus grandimanus)
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Harem (Female) Defence Polygyny

• Few known examples in Invertebrates
• Females aggregated
• Male defence of females rather than resources

Corophium volutator
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Resource Defence Polygyny

• Male Defence of a valuable resource
• Feeding site
• Oviposition site
• Shelter
• Single male secures multiple mates

e.g. The Pseudoscorpion, Cordylochernes
scorpioides, defends the space under the Elytra
of the Harlequin Beetle Acrocinus longimanus
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Lek Mating Systems

• Mating arena
• No resource defence
• Female mate choice
• No male parental care
• Often all females mate
• with one male

Papilio zelicaon
Magicicada cassini
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Why did leks evolve?

• Leks probably evolved from resource defence
  systems
• Female densities too high to defend
• Resources too widespread to defend
• The Lek Paradox
• Why do all females mate with the same male?
• Why do the other males bother turning up?
• Why has male variation not been selected out?

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Alternative Mating Strategies

• Two or more distinct male strategies
• Often associated with different male morphologies
• Some males defend females or resources
• Other males are sneaky
• Different strategies may or may not lead to equal
  reproductive success

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Dimorphism in courtship displayJumping
spidersMaevia inclemens
Grey male Crouching display
Tufted male Exaggerated display
Female Cant talk, eating
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Female impersonation in giant cuttlefishSepia
apama
Big male defend females Small males pretend to
be females Evidence of both mating and
fertilization success for sneaky males
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Alternative mating strategies

• Sponge-dwelling isopods
• Paracerceis sculpta
• Crustacea Isopoda
• Three male morphs!
• Fighter
• Female impersonator
• Sneaker
• Equal reproductive
• success at a population
• level

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Threshold dimorphisms European earwig Forficula
auricularia
Two male morphs -macrolabic -brachylabic Relates
to body size, but not a continuous
relationship. Males that are larger than a
particular threshold develop larger forceps
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Threshold dimorphisms European earwig Forficula
auricularia
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Geographic variation in threshold
dimorphism European earwig Forficula auricularia
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Other threshold dimorphisms
Dung beetle Onthophagus taurus
Bulb mite Rhizoglyphus robini
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Next Lecture Sperm Competition Cryptic
Female Choice