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Lecture

ANTC23H3 Lecture Notes - Baculum, Orgasm, Pleiotropy


Department
Anthropology
Course Code
ANTC23H3
Professor
Joyce Parga

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Announcements: Final exam August 23rd, 7-10pm, MW160
Penile Morphology in Primates
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Wide diversity of shapes, even among closely
related primate species
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Can have different sizes, shapes, appendages, etc.
Can use penile morphology alone to tell
galago species apart
-
A-E on the slide are all different galago species
Hypothesis requires that male and
female genitalia should be structurally
complementary within a species
Only a few examples of 'lock and key'
evidence - some species of macaque
have complementary structures of the
penis and vaginal lumen
Mating between different primate
species can actually occur
The structural complementary
genitalia is only found in a few
species
Vocalizations, olfactory
cues, behaviours, etc. are
species-specific
Other mechanisms keep species
from interbreeding
Problems
Strong support for this hypothesis is
lacking
Lock and Key hypothesis
Variant of the lock and key hypothesis
Females' bodies "recognize" males of
their species by the stimulation they
receive during mating
Induced is contingent on
copulation
Spontaneous ovulation
occurs cyclically and is not
dependent on mating (All
primates are spontaneous
ovulators)
Induced Ovulators v. Spontaneous
Ovulators
Makes more sense for species that are
induced ovulators
Genitalic recognition hypothesis
Pleiotropy: when a change to one gene
affects unrelated phenotypic traits
Unsupportable hypothesis
Pleiotropism hypothesis
Males have evolved genitalia to bypass
female 'barriers' to reproduction or to
damage the female reproductive
tract/genitalia
Not generally applicable to primates,
however it does apply in other areas of
animal and insect reproductive
behaviour
Mechanical conflict of interest hypothesis
Cryptic female choice - mate choice
during or after copulation (not
necessarily females being conscious of
this behaviour; more of a physical
reaction like a change in Ph level,
physical contractions, etc. that
facilitates fertilization)
Male genitalia have evolved to function
as an internal courtship device
Females may then unconsciously select
the sperm of certain males over others
Dispersed and polygynandrous
systems
Speculative hypothesis at present;
extremely difficult to test in primates
Cryptic female choice
-
Hypotheses:
Terms
-
Baculum or os penis
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Bone inside the penis of some animals
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Plural bacula
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Many primate species have them
May provide structural support during copulation
Tends to be near the distal end, where structural support
might be most needed
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Adaptive function
The longest intromission
Eg. The pair-sit of stump-tailed macaques
Maintenance of intromission after ejaculation has occurred
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Species with elongated bacula tend to be those having
Possible indication of prolonged intromissions during
copulation
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In the Eocene, Adapids (similar to modern-day lemurs) had an
extremely long bacula
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Human males lack a baculum, yet prolonged copulation is possible
because of increased vascularisation providing the structural rigidity
necessary for copulation
Penile Spines
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Made of keratin
When the male intromits and thrusts, the spines point
ventrally (towards the proximal end of the penis), acting
as anchors to pull the plug out
May help to dislodge or move copulatory plugs
May stimulate the female (cryptic female choice)
May aid the male in intromition, providing sensory feedback
to the male
-
Adaptive function?
Males without spines took longer to intromit and showed an
increased duration of intra-vaginal thrusting
Could have been a result of chemical interaction from the
depilatory cream
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Experimental removal of penile spines with depilatory cream
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Prosimians tend to have spines, and larger ones than anthropoids
Penile Morphology RTL
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Penis is distally concave ("plunger-shaped")
Shaped to help displace copulatory plugs via suction/negative
pressure
-
Shape may be functionally adaptive
Penile Morphology in Pan
Long, thin, tapering at the end
No other primate species have this penile shape
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Chimps and bonobos have a filiform penis
Penis may pierce through other male's sperm plugs (Dixson
1994)
Allows for deep penetration when females have sexual
swelling
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Hypothesized that the shape is functionally adaptive
Rhesus macaques film
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Macaca mulatta
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Male dispersal as a mating strategy
Function in inbreeding avoidance
Choice for novel males
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Female mate choice
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Consortships,increased affliative behaviours
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Sneak copulation as a mating strategy
Hip-push invitations to mate
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Sexual signals
Indication of sperm competition
Polygynandrous mating system
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Large relative testes size
Clutching reaction (orgasm?)
Lip smacking
Looking back and making eye contact
with males
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Female sexual behaviour
Genital Morphology
July-17-12
1:06 PM
ANTC23 Page 1
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