1 / 27

Ecology of Sexual Behavior

Ecology of Sexual Behavior. From Dr. Tatiana’s Sex Advice to All Creation Adapted by Dr. JodyLee Estrada Duek. The History of Sexual Assumptions. A. J. Bateman published a paper in 1948 in the journal Heredity Claimed he had proved males evolved for lovemaking

blevinsjohn
Download Presentation

Ecology of Sexual Behavior

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Ecology of Sexual Behavior From Dr. Tatiana’s Sex Advice to All Creation Adapted by Dr. JodyLee Estrada Duek

  2. The History of Sexual Assumptions • A. J. Bateman published a paper in 1948 in the journal Heredity • Claimed he had proved • males evolved for lovemaking • females evolved for making babies • Work based on Drosophila melanogaster • NOTE: there are over 2000 species of Drosophila

  3. Bateman’s Study • Kept equal numbers male & female in small bottles for 3-4 days • Males still keen to mate as often as possible • Females rejected advances after 1 or 2 events • RESULT: • For males – more partners = more offspring • For females – it made no difference

  4. Bateman’s Explanation #1 • Males produce tiny, cheap sperm • Females produce a few large, expensive eggs • Females in many species store sperm for days, months, even years; 1 mating can last a lifetime • One male could fertilize eggs of many females

  5. Bateman’s Explanation #2 • Limits to reproduction are: • For females, how fast can make eggs and/or rear the young • For males, how many females they can find and mate with

  6. THEREFORE… • Males naturally philanderers • Females naturally chaste childraisers, indifferent or hostile to mating more than absolutely necessary (the “I have a headache” theory)

  7. Bateman’s Principle • Men are cads, women are saints… or • Males optimize genetically with multiple mates • For females mating more than absolutely needed is a waste of time

  8. Since 1948… • Patriarchal types agreed • Feminists complained about unfairness • Scientists expounded, espoused it, added extra reasons for female chastity • Fear of venereal disease • Risk of being caught by a predator • Humans fought about it

  9. Examples cited • Species where females mate only once • Alfalfa leaf-cutter bee (a solitary bee) • Species where males attempt to mate constantly when in season • Frogs and toads

  10. However …And now for something completely different…

  11. In D. melanogaster… • Females will multiple mate, but only a few times each week, and… • Females who mate once have fewer eggs than those who mate several times • So Bateman’s experiment was too short, he quit too soon… • In a related species, D. hydei, females mate several times every morning

  12. Why didn’t anyone speak up? • Argument sounded reasonable • Seemed to be supported by thousands of observations on hundreds of species • Some scientists noticed that some females mated with multiple males but it was assumed • Females had “malfunctioned” • Males had “led them astray”

  13. Enter genetic studies, stage left • In the 1980s parentage could be established • Females were hardly ever faithful to one mate • Rampant promiscuity was everywhere

  14. Female benefits • Higher rates of conception or more eggs with multiple partners • Rabbits, Gunnison’s prairie dogs • Sand lizards • More eggs fertilized (in a large clutch) if spawning promiscuously • Slippery dick (a coral reef fish)

  15. This female promiscuity leads to… • A true war between the sexes • The last male to mate probably has a better chance of siring offspring • Males compete to have their sperm be what counts

  16. Males try to • Deposit more of their sperm • Remove the sperm of rivals • Damselfly penis has horns and bristles to scour inside female before leaving his sperm • Get female to eject prior sperm • Moth Olceclostera seraphica rubs penile parts together on female’s body, vibrations convince females to eject • Dunnock: a small bird, gently pecks genitalia • Block further sperm entry • Ghost spider crab makes “jelly”, seals off prior sperm

  17. One example • An African Bird: red-billed buffalo weaver • Female is extremely promiscuous • Male has a pseudophallus; stimulates female with this for about ½ hour • He then ejaculates from genital opening • Male who stimulates female “most vigorously” presumably has his sperm utilized for her eggs

  18. A general rule… • In species where females practice serial monogamy, penises generally small compared to body size, unornamented • Male gorilla – about 500 pounds, 2 inch penis • If females are promiscuous, penises adapted • Argentine lake duck – about 4 pounds, 8 inch penis with spines – see next slides

  19. Pseudophallus • Most birds do not have an intromissive organ • Typically male touches cloaca to female, passes sperm or sperm packet • Ducks and geese have a pseudophallus • Forcible “rape” is only known in ducks and geese

  20. Argentine lake duck • 42.5 cm in length is the record • The male may use the brush-like tip of its penis to scrub the sperm of previous mates from the female's oviduct.

  21. Another mechanism • Blockage • In honeybees, male genitals break off in female, he explodes with a loud snap – he dies, she is blocked with a “chastity belt” • Dozens to thousands of males chase 1 queen • He is not likely to mate again, this is his only chance • However, a Queen bee needs multiple mates • because of the sex-determining gene • if a male has her allele she’ll have sterile sons • she must outcross & be heterozygous

  22. So if you’re the second bee… • Honeybee penis has a structure on the tip to remove the genitalia of prior male • How did this evolve? • 1 queen was promiscuous, was successful • Her genes multiplied in the population • 1 male exploded, prevented rivals from mating • His genes multiplied • 1 queen could remove plug herself, or 1 male could remove rival plug…

  23. A genetic race… • Males evolve mechanisms to control access to the female • Rat penis is nearly prehensile, does a “toilet plunger” maneuver to suction out a plug • Females evolve mechanisms to evade male control • Fox squirrel reaches around and removes a male plug and eats it

  24. So… • Just seducing all the females doesn’t work if they don’t use your sperm • Better off trying to maximize eggs fertilized • Splendid fairy wren male – 8 billion sperm • Sperm competition • Experiments with yellow dung flies shows that if there is sperm competition average male testes size increases in 10 generations • Seahorses (female deposits eggs in his pouch, he fertilizes, carries) have extremely low sperm count

  25. And… • Sperm die in huge numbers as they move through female’s body • May be digested, ejected, rounded up • Possibly a few saved and stored, rest discarded A Human Example Vagina usually acidic – only 10% of sperm survive Cervical mucus – perhaps 10% pass White blood cells attack In Fallopian tubes have gone from 180 million to a few hundred sperm

  26. Other ideas • Sperm size and shape • D. bifurca produces sperm 20X longer than it is (3 mm, 60 mm) • Tandem sperm – opossum, water beetles, millipedes • Hooked sperm – koalas, rodents, crickets • Wheel sperm – crayfish • Corkscrew sperm – land snails • 100 tail sperm, crawling sperm • Sperm packets

  27. For more ideas… read the book

More Related