Transcript Evolution

Communication
BIOL 3100
How did this unique trait and behaviour evolve? What is its adaptive significance?
What do other hyenas do?
Spotted Hyena
Brown Hyena
Striped Hyena
Aardwolf
All species of Hyena engage in
chemical communication – generally
using anal scent glands to mark their
home habitat.
Males and females also inspect the
anogenital regions of conspecifics
At some point, must have added the
inspection of erect penises – but
where did the female “penis” come
from?
Because the female clitoris and male penis develop from the same embryonic
tissue, one proposal is that the psuedopenis could be a developmental effect
of high levels of male sex hormones in female hyenas.
When females of most mammals are exposed to high levels of testosterone,
the clitoris enlarges, looking like a penis
However, turns out that females have lower levels of circulating androgens
than males (though pregnant females do have higher androgen levels than
lactating females)
What happens if we administer anti-androgenic chemicals?
Turns out that the females retain their enlarged pseudopenis (though slightly
altered)
Thus, the proximate, developmental causes are unclear. Perhaps the
relationship between androgens and pseudopenis development has become
decoupled with a less costly mechanism in place.
Ultimate explanations: Adaptive value
Costs: Increased androgens can reduce fertility; birth through the clitoris can
be costly (in one study 10% of females died giving birth, in another field study,
no effects were found)
Benefits: Social Interactions?
Females are socially dominant over
males
Female social status strongly influences
reproductive success
Hans Kruuk (1972) suggested a
function to reduce tension in highly
aggressive females
Or….mimic subordinate males
An Adaptationist Hypothes
1) Female dominance evolved before the pseudopenis
2) Sexually motivated males presented an erect penis to females
3) Presentation of the erect penis would signal male identity and subordinate
status, encouraging females to accept male’s presenance rather than reject
4) Females with a pseudopenis would have been able to tap into this system
that was already established for signaling subordination
5) Benefit to signaling subordination would be remaining with the clan, rather
than being tossed out
Tapping into established signals and co-opting them for another purpose is com
In many bowerbirds, the harsh
“skrraa” call is used in
aggressive interactions
However, in one clade, that
signal has been co-opted and is
used in courting females.
In other words, the signal
already existed, but has been
put to another purpose –
females can use the signal to
make adaptive choices about
mates
Signals can be exploited
Sensory exploitation occurs when an animal
produces a novel signal that taps into the
preexisting perceptual mechanisms in a
signal receiver.
Males exploit the predatory behavior of females waiting to ambush small
copepods
1) With females in the attack position, males approach and vibrate forelegs in
front of her
2) Female grabs the male (like a copepod), but releases him unharmed
3) Male turns around and deposits spermatophores near the female that she
picks up if receptive
Perhaps males are mimicing the stimuli produced by copepod prey; the reaction
identified her as a potential mate and showed the male where to position his
spermatophores
1) Hungry, unfed females should be most responsive to males (they are)
2) Male behaviour effectively activated a preexisting detection mechanism in
females
3) However, hungry females may just want to acquire a nutrient rich
spermatophore
Female guppies prefer orange-spotted males. Why?
The body of this giant wood spider
is extremely colourful. When the
spider is present, more prey are
captured (same goes for the spider
being painted black).
What relevance does this research
have for those interested in the
sensory exploitation hypothesis for
the evolution for courtship signals
in animals?
If sensory exploitation is a major driver of
effective signals, then we should be able to
elicit responses from animals by providing
novel experimental signals they’ve never
seen before.
Species may respond to signals that
existed in the past.
If so, descendants may retain that
sensory preference, even though they
no longer exhibit those signals.
Ancestr
al state
Least auklets normally do not
have crests, but females show a
strong preference for males with
crests.
Clearly, female birds dig head crests…
So, how might this trait have evolved in the first place? Why was it favoured by selectio
Sometimes it can be costly to evolve defenses against exploitative signals
Male garter snakes “court” females by slithering on top of them and moving
their bodies against them in a way that makes it difficult to breathe.
This behaviour activates a cloacal gaping response
Natural selection works with what it’s got.
Parthenogenic whiptail
lizards (right) continue to
engage in similar
courtship and precopulatory behaviour as
their sexual counterparts.
Females that engage in
this behaviour are much
more likely to produce a
clutch of eggs than those
that don’t receive sexual
stimulation.
Illegitimate Signalers and
Receivers
Male tungara frogs often give whining calls
without chucks, despite the fact that females
prefer males who add chuck elements to their
calls.
Why not add the chucks?
The fringe-lipped back is an
illegitimate receive that
responds the tungara frog
chuck calls – the more
chucks, the more likely an
attack.
Frogs only give chucks when
predation risk is lower (like in
large groups).
Receivers can lose fitness by responding to signals generated by
illegitimate signalers (deceivers)
Femme fatale predatory Photinus moths
respond to the signals given by Photirus
moths.
In addition, after approaching the male
Photirus moths (whose signals they
illegitimately received) Photinus females
answer the males’ mating signals by
mimicking females of their own species.
Some Photinus females can mimic 3 species
of Photirus moths
Once close enough, they’ve got a meal.
How do we explain these
maladaptive responses?
1) Novel environment theory:
Maladaptive response is
caused by a proximate
mechanism that was once
adaptive, but no longer is.
Modern conditions are
different than those that
shaped the condition in the
past. Not enough time to “fix
the problem”.
2) Exploitation theory:
Maladaptive response is
caused by a mechanism that
results in fitness losses that
reduce, but do not eliminate
the net fitness gain
associated with reacting to a
given signal.