Here’s a joke:
A man was eating in a fancy restaurant, and
there was a gorgeous woman eating at the table next to his. After eyeing her
romantically all night, he decides to go and talk to her. Suddenly, at this
moment, she sneezes and her glass eye goes flying out of its socket toward the
man’s direction. With lightning quick reflexes, he catches the eye in mid-air.
“Oh my gosh, I am so sorry,” she says as she
pops her eye back into the socket. “Let me buy you dinner to make it up to
you.” From there, the two would enjoy a wonderful dinner together, and
afterwards the woman invites him back to her place for a drink. They went back
to the house together, and after some time conversing, she took him into her
bedroom.
The next morning, as he awoke, she had already
gotten up and brought him breakfast in bed. The man was amazed and said “You
know, you’ve been beyond unbelievable. Are you this nice to every guy you
meet?”
“No”, she replies. “You just happened to catch
my eye!” [1]
Here’s reality:
The concept of love at
first sight was once romanticized by media and popular culture. Today, it is a
fable of the past, as dating websites and other social devices normalize remote
conversations that help one decide if they like an individual before they even
meet their potential suitor vis-a-vis.
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| [2] |
Fortunately, the rest of the animal kingdom doesn’t have access to
the technology we do. Other organisms still have to rely on various social cues
relayed during interactions they will have with their potential mate. Mate
choice directly affects an organism’s reproductive fitness, and the process of
sexual selection has generated an incredible array of evolved traits and
behaviors in many cases.
The classic, and perhaps still the most ostentatious, example of
this is the peacock. In 1871, Charles Darwin noted the ornamental feather
display of peacock as a trait that potentially evolved as product of evolution.
The male peafowl, or peacock, usually has colorfully iridescent plumage and a
distinct “train” of feathers that comprise its tail. Often, each feather has
patterned structural coloration that results in a gorgeous “eye” at the
center of the feather, thus giving the phrase “love at first sight” a whole new
meaning.
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| [3] |
During breeding seasons, peacocks aggregate to collectively
display their “outfits” to interested peahens, which approach these
aggregations seeking to be fertilized. If the female likes what she sees, the
female will approach the side or back of the male. The male will then lift his
lateral wings up and down, and as the females move towards the front of the
male, the male will turn towards the female, rattle his feathers, and then turn
away. Females assess these displays and choose a mate, therefore contributing
to the males’ reproductive success. Yet, this is analogous to the dinner with
the girl in our joke. What’s the glass eye? How does the peacock get the female
to approach him?
While the number of eyespots on a males’ train and courtship
behavior have been shown to have relationships with male mating success,
Jessica Yorzinski and her colleagues wanted to examine what exactly was
catching the eye of the female peahen. To examine the relationship between what
females pay attention to during courtship, and mating success, Yorzinski et al.
tracked the gaze of peahens during the process of courtship. They did so by
training captive peahens to wear wireless eye-trackers that continuously
recorded data on the direction and movement of a peahen’s area centralis, which
Yorzinski defines as the region of a peahen’s eye most similar to a human
fovea. The statistical analysis of this data presented regions of interest in
the male’s frontal and backside display that were categorized as 1) viewed at
levels greater than expected by chance (white), 2) viewed at levels less than
expected by chance (yellow), and 3) viewed at levels not different from chance (green).
From this analysis, Yorzinski and her team concluded that from a fair distance,
the flamboyant upper train is where females spend the majority of their time
gazing. However, their results also suggest that the female peahen spends a
greater deal of time assessing the lower train when in close distance of the peacock,
mostly ignoring the head, crest, and upper train.
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| [4] |
Hey
peahen, eyes up here!
It seems, though the upper train, with the pretty colors and the
eyespots centered on the iridescent feathers and all, is clearly the most
conspicuously extravagant part of any peacock, it is one of the parts that gets
no attention when the birds are in close proximity to one another. The part of the peacock every evolutionist suggests evolved due
to pressures from sexual selection isn’t getting very much love from the peahen
during close-range attraction signaling these days. Perhaps it’s because the
peahen approached the peacock knowing most peacocks have this pretty display on
their upper train, so this aspect of them no longer makes them special. This
goes back to what the villain Syndrome says when he threatens to give the world
super powers in The Incredibles: “Everyone can be super! And when everyone’s
super… no one will be.”
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| [5] http://a.dilcdn.com/bl/wp-content/uploads/sites/2/2013/11/Incredibles_hair.jpg |
The fact of the matter is that when
a peahen has decided to approach a peacock, she has already examined the upper
train. Up close, the peahen is therefore judging other qualities of the
peacock, specifically lower eyespots, dense lower feathers, and legs. When the
female is up-close is also when the male begins the wing shaking and rattling.
These traits and behaviors both serve to attract and maintain the attention of
the peahen, and provide evidence for the evolution of these attributes due to
sexual selection.
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| [6] |
So to close this post, here’s another (this time, original) joke:
A
father hears his daughter is dating a guy she met on the internet, and demands
to meet him. The daughter obliges, and before her next date, she brings her new
boyfriend to her parents’ house to meet her father.
After
a bit of chatting between the boyfriend and the father, the father says “So you
met my daughter online huh? What kind of line did you use to pick her up”.
The boyfriend replies “LAN.”
[7]
Journal Citation:
Yorzinski, Jessica L., Gail L. Patricelli, Jason S. Babcock, John M. Pearson, and Michael L. Platt. “Through Their Eyes: Selective Attention in Peahens during Courtship.” The Journal of Experimental Biology 216, no. 16 (August 15, 2013): 3035–46. doi:10.1242/jeb.087338.
Media Credits:
[1] Paraphrased from Comedy Central Jokes: http://jokes.cc.com/funny-dirty-jokes/eouvko/love-at-first-sight
[2] Image by someecards: http://www.dailyvowelmovements.com/2013/02/ive-loved-you-from-moment-i-first.html
[3] Public domain image: http://commons.wikimedia.org/wiki/File:Peacock_terms.png
[4] Image from Yorzinski et. al.: http://jeb.biologists.org/content/216/16/3035.full
[5] © Disney/Pixar. All Rights Reserved: http://blogs.disney.com/oh-my-disney/2013/11/05/15-things-weve-learned-from-the-incredibles/
[6] Image from Yorzinki et. al.: http://jeb.biologists.org/content/216/16/3035.full
[7] Video by National Geographic: https://www.youtube.com/watch?v=TTwT1-TpFhE
Thanks for making the blog post fun to read! I really liked the use of technology to study the bird's eye movements. I really wanted to see photographs of what these camera helmets looked like on the birds. And using this complicated apparatus naturally brings up the question of whether the captive, helmet-wearing peahens were acting the same as wild peahens would. Maybe other researchers have already studied gaze direction in wild peahens with other methods? If not then that would be an interesting future study.
ReplyDeleteI loved that you incorporated humor at the beginning at the end. I couldn't help but chuckle throughout :) I also had this image of a "robo peahen" when I read about the eye trackers. The National Geographic clip was great as well--I was actually a little disappointed when it cut off at "dirty tricks" at the end.
ReplyDeleteI was surprised to learn that peahens have already judged the upper train of the male by the time peahens get closed--somehow, it made sense to me that the male would have shaken his feathers to get the peahen to come closer. An article describing more about how peahens behave at closer ranges would be awesome.
Thanks for the fun blog post! It was interesting to read about the wireless eye-trackers that the peahens wear. Like Madison and Beverly, I am curious about what these eye-trackers look like and how they might impact the peahen's behavior. It also reminds me of the paper we read a few weeks ago, in which the researches kept track of which direction birds foraging in groups were looking. I wonder if wireless eye tracking devices could be applied in contexts like that as well.
ReplyDeleteThat was a fun post! I loved the use of jokes. I'm actually curious about the role of females in this whole equation. I'm not shocked that the ornamentation of the males is due to sexual selection by the females, as per the Zahavi Handicap Hypothesis, but I noticed that the females too look rather conspicuous. They're not nearly as bright as the males, but they do have some iridescent feathers and a crest--I'm curious about how that all came about. Was that also sexually selected, or a by-product of the male selection, or simple drift, or even somehow adaptive?
ReplyDeleteGood incorporation of humor. Though given their ability to track where the pea-hens are looking, I'm curious as to what parts the other senses play. Now that we know what they look at, there is of course the overall dance, but perhaps there is an aural aspect as well. I think it's pretty cool that they judge different parts at different distances, and I'd love to hear more about how mate selection is spread across different senses, in peacocks and others.
ReplyDelete