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Postcopulatory Sexual Selection Long Miao Institute of Biophysics, CAS April 25, 2011.

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Presentation on theme: "Postcopulatory Sexual Selection Long Miao Institute of Biophysics, CAS April 25, 2011."— Presentation transcript:

1 Postcopulatory Sexual Selection Long Miao ( Institute of Biophysics, CAS April 25, 2011

2 Male-Male Competition Andersson, 1994 “Sexual Selection” 5 fundamental areas of male-male competition –Scrambles –Endurance Rivalry –Contests –Sperm competition –Mate choice (Female choice)

3 Sperm Competition Competition between the sperm of 2 or more males within the reproductive tract of the female Typically Post copulatory sperm competition –Competition between males after copulation With few ova= huge battle –promiscuity go for broke Involves –Physiological events that occur after insemination –Behaviors before & after copulation –Morphology

4 The Father of Sperm Competition Geoff Parker, 1970 Studied sexual selection in Yellow Dungfly Looked at patterns of male-male competition

5 Yellow Dungfly

6 What’s poo got to do with it… Female arrives at dung patty ready to mate After copulation lays eggs on dung Males mount & copulate with female as soon as she arrives Larger males removes male from female & copulates with her Females mate with multiple males throughout day

7 Cow Patties

8 Yellow Dungfly

9 Parker’s Observations Under such extreme male male competition Parker realized competition between males continues through action of their sperm Copulation is not enough, sperm must make it to the egg Defined sperm competition –The competition between ejaculates of different males for the fertilization of a female’s eggs


11 Parker’s Observations Sexual selection occurs in the reproductive tract –Fertilization not copulation is the driving force –Males “win” by Inseminating more sperm per ejaculate Faster swimming sperm Inseminate moderate amounts of sperm & remove sperm from the last guy Disabling rival sperm Sperm competition results in opposing selection forces in males

12 The Trade-off Selection favors BOTH –Males that fertilize females that have been inseminated by other males –Males who prevent females they have inseminated from being fertilized by another male Results in counter adaptations among competing male strategies –Ex producing larger ejaculates vs better mate guarding strategies What? –Males want to go around & fertilize as many females as possible, but this is hard to do while they are mate guarding

13 Darwin & Sperm Competition

14 2 General categories of Sperm Competition Adaptations that preventing rival sperm from copulating with the mate –Mate guarding, sequestering, frequent copulation, production of mating plug, displacing rival sperm Adaptations that increase the Ability of one male’s sperm to outcompete the sperm of another male –production of abundant sperm, fast sperm

15 Cuckoldry Female infidelity Derived from cuckoo Male loses some of his reproductive fitness to another male


17 Sperm Precedence The sperm that fertilizes the egg effected by the order of fertilization

18 Sperm Precedence First male precedence –First male fertilizes the majority of eggs Last male precedence –Last male fertilizes the majority of eggs promiscuity

19 Sperm Competition Adaptations that preventing rival males from copulating with the mate –Mate Guarding

20 Mate Guarding Male increases the amount of time he spends in close association with a fertile female Male guards female partners from mating with other males Tactic for reducing or preventing sperm competition Typically occurs when female is receptive for a short time period Costs of mate guarding –Interferes with male foraging –Vulnerable to predators

21 Sand Martin

22 Male guards female 7-8 days Begins few days before she lays first egg Male remains next to female during her fertile period Male presence reduces risk other males copulating with female

23 Red-winged Blackbird David Westneat Male guards females –Male experimentally removed from territory –Female copulations with other males increased 100X Males Compromise guarding for foraging time –When males given food paternity went up

24 Mate guarding strategies Mate grasping Prolonged copulations Frequent Copulations Mate sequestering Mating plugs

25 Yellow Dungfly Mate Grasping Male remains on female’s back as she lays eggs

26 Pre-copulatory Guarding Occurs in species where the first male has the best chance fertilizing the female’s egg

27 Freshwater Shrimp Males use specialized legs to carry females around Males attach to female 9 days before she is receptive

28 Mate Guarding- Amplexus Salamanders & Frogs

29 Mate Guarding- Prolonged Copulation Male & females remain in copulation May last hours to days Male prevents other males by staying attached

30 Yellow Dungfly Prolonged copulation…male remains with female 40min

31 Prolonged Copulation

32 Frequent Copulations Male who increases copulation events with female prevents mating with other males Animals frequently mate more often than necessary for fertilization

33 Mate Guarding- Frequent Copulation Giant water bug aka “toe biter” Male fertilizes females eggs As female lays eggs she sticks them to the males back –Lays 1-2 eggs at a time Cycle can last up to 36 hours (144 eggs) Male fertilizes over 99% of eggs

34 Giant Water Bug

35 Days….

36 Frequent Copulations Mountain Lion Ave 9 copulations per hour

37 Mate Sequestering Male limits female contact with other males by isolating her –Physical isolation –Chemical isolation

38 Mate Sequestering Physical Isolation

39 Douglas Fir Bark Beetle Male sequesters female in gallery

40 Mate Sequestering Chemical isolation Reducing Attractiveness of mates “Anti-aphrodisiac” Substances that reduce the females attractiveness Ex. Make her smell like a male Reduce her pheromonal output

41 Chemical Mate Guarding Green veined white butterfly Males inject methyl salicylate along with sperm –Chemical compound derived from host plant Smell repels other males

42 Green veined white butterfly

43 Spider- Linyphia litigiosa Male disrupts female’s chemical signals Male that finds virgin female will reduce evaporation of attractive pheromones from her web by packing it into a tight mass

44 Central American Bee Mandibular gland rubs secretions onto female makes her smell like a male Conceals female

45 Darkling Beetle Male rubs anti- aphrodisiac pheromone with genitals Makes female less attractive to other males

46 Mating Plugs Aka copulatory plugs Male produced substances or structures which are transferred to the female after copulation Seal genital opening Ex guinea pig, chimpanzee, lemur, masked palm civet,

47 Red-sided Garter Snake

48 Intense male competition Male produces gelatinous secretion in ejaculate Secretion hardens in the female oviduct


50 Ground Squirrels Intense competition for females Male emerges from hibernation first Testes grow Females emerge & within 4 days are receptive –1-2 hours

51 Mating Plugs


53 Orb Spider Argiope bruennichi

54 Male transfers sperm packet to female reproductive tract using pedipalp Pedipalp breaks off in female & created mating plug

55 Orb Spider Argiope bruennichi

56 Honey Bee Uses own body as a copulatory plug Male dies after reproduction Harvester ant

57 Fly with no common name Ceratopogonid Johannseniella nitida Tiny male crawls into female genital opening to create mating plug

58 Ring-tailed Lemur

59 Other Functions of Mating Plugs… Sperm storage reservoir Reduce leakage

60 Displace Rival Sperm displace a previous male’s sperm Mechanism for last male precedence –Last male fertilizes the majority of the offspring by removing previos males’ sperm Adaptations –Physical –Chemical

61 Black-winged Damselfly Females mate with multiple males within a few hours Sperm storage in spermotheca Male penis shaped like scrub brush During copulation male abdomen pumps up & down “scrubbing” out the sperm of other males –90-100% of sperm removed

62 What’s a Spermatheca?

63 Black-winged Damselfly

64 Fertilization success depends on: 1. Physical traits of sperm: numbers of sperm inseminated, quality, size, morphology, speed, cooperation of close-related 2. Seminal fluid and its components produced by several accessory glands in male body 3. Cryptic female choice

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