Week Twelve Flashcards
What is the sperm record held by?
Drosophila bifurca.
59mm sperm are over 20x male body length
What is the tradeoff for having large sperm?
D. bifurca takes 17d to mature after eclosion.
D. melanogaster (1.8mm) exhaust stores after several successive matings.
-Become temporarily sterile if presented with 5-10 virgin females in succession
-Males may be smaller and slower growing because of testes and sperm maturation/ investment.
What are the benefits to having giant sperm?
- Nutrition: The sperm tail nourishes the zygote (or itself)
- Chemical warfare: sperm tails bind accessory gland secretions which act in aid of male fertilization success
- Defence: long tails aid in anchoring sperm and excluding other male’s sperm
- Big sperm are more attractive to the male repro tract: evolution of longer sperm self-perpetuating via Fisherian runaway sexual selection.
- Big sperm reflect viability or fitness overall: indicators of good genetic quality in male.
Who wins, short or long sperm? (second male precedence)
Long sperm showed enhanced performance in long reproductive tracts
When would males cooperate?
It would seem that sperm is the ultimate case of scramble competition.
- intra-ejaculate competition
BUT if there is strong competition between males, then that can favour intra-ejaculate cooperation (=help my brother)
- Sperm band together when suicide increases fitness
- –Inter-ejaculate competition must be intense!!!
Is the quality of sperm based on the sperm’s genotype, or other factors?
Control of sperm structure is by the male, NOT the sperm’s genotype.
-Sperm cannot evolve to ‘cheat’ based upon the genotype they carry…..possibly…..
What is the largest penis structure in the world?
The sky pillar in Changchun china.
- Longwan Chaman amusement park.
Why is there a suggested lock and key model for male and female genitalia?
It has been suggested as a means of preventing harmful hybridization events.
Can closely related species mate with one another?
Mechanisms to avoid it?
They overlap in range, so they have a variety of pre-mating mechanisms to discourage hybridization.
- Genitalia are an obvious means of doing so, where there is a close fit between female and male.
- Genitalia are the only reliable means of distinguishing species in some groups!
What would the lock and key mechanism predict with monogamous matings?
These matings should have the most exclusive fit between mates.
- Helps prevent interspecific mating (between other species) and hybrid inferiority.
What did they find with genitals and polygamous species?
Polygamous species were found to have higher levels of genitalic diversity.
- If female wants lots of sperm, an arms race is started; mate competition.
In the lock and key model, which is more diverse?
The keys are almost always more diverse than “locks”
What is the penis an adaptation in the first place?
With internal fertilization comes the pressure to place sperm closer to the oviduct.
- The penis is an adaptation to move sperm closer to the unfertilized egg.
- -Increase fertilization efficiency
- -Reduce ejaculate size, investment in testis tissue
- -Allow fertilization within protected environment for zygote.
Why are 97% of birds capable of internal fertilization without a penis?
Sex happens with only a brief engagement of male and female cloacas
- It is an adaption to flight
- Internal testes
- Usually only one ovary
Do Buffalo weaver finches have penises? Why?
The male organ is actually a fake penis.
-Male only uses the ‘pseudopenis’ to engage the female and stimulate her prior to ejaculating; it is not a pipe.
What does William Eberhard think of the evolution of the penis?
He suggests that the penis evolved to tickle a female’s fancy and is used as a stimulant, and release egg through pleasure.
-Promiscuous female could use stimulatory ability as a means by which to judge a male’s quality and condition.
We have proportionately the largest penis among our immediate relatives, why might this be?
Upright walking stance allows large penis?
- Trigger orgasm for upsuck hypothesis?
- Promote pair bonding?
- Sperm displacement?
What is the upsuck hypothesis?
Cervix dips down and facilitates fertilization.
-Synchronized with ejaculation is super helpful.
What are the highlights of sperm competition in marriage?
Semen-displacing copulatory behaviors are explored in married couples.
- The time wives spend with other men and husbands’ sexual behavior are related.
- Men’s sexual behaviors are related to differences in sexual interest between spouses.
Why does Lloyd think science can be led astray?
What is her (and stephen gould’s) conclusion?
Our tendency to assume that a phenomenon in biology must have an adaptive basis has led to publication bias.
- -Weak and inadequate tests and comparative evidence
- -Less discriminating review processes
Lloyd concludes that Stephen Gould’s “byproduct hypothesis” is most compelling.
- -Women have orgasms because they have clitorises.
- -Women have clits because men have penises.
What do Palicev and Wagner argue about induced ovulation?
They believe it is essential in mammals.
- With orgasm comes a surge of hormone release
- Neuroendocrine discharge of prolactin and oxytocin
- Some other placental mammals require this hormone release to stimulate ovulation.
Why are humans unique in the primates and unusual in mammals?
They do not have a baculum!!!!
- Might relate to our upright stance
- In this sense, hydraulics are more critical to penile function than others.
- Declines with age
How is erectile dysfunction reduced?
Mechanism?
Sildenafil - developed as hypertension and angina treatment, ‘Viagra’ proved potent for ED.
-Increases nitric oxide in corpus cavernosum; NO binds to cGMP receptors; increased cGMP causes vasodilation of arteries to penis
Lets’ revisit this: What do sfps do in drosophila melanogaster?
They have diverse antimicrobial functions -Stimulate egg production -Increase oviposition rate -Decrease sexual receptivity -Decrease female attractiveness -Helps transport and store sperm Release rival sperm from storage -incapacitate rival's sperm? -Form mating plug -Reduce female longevity
