Whoooah! I screamed, as this
little ball of fluff dove in catching a buzzing, honeybee right above my head.
I am amazed by a lot of things, but he was absolutely beautiful. He is an African
Paradise Flycatcher. His body length runs about 50cm, but that does not include
his long “sexy” tail feathers that stretch an additional 100cm. He is deep sea
blue and toasty brown in color and has a small crest on his head. His stamina is
impressive. And his ability to catch flying insects in midair is breathtaking. I
ask myself, how can this little bird be so swift, yet so conspicuous? And
doesn’t his long tail feathers get in the way when he is swooping in to catch a
flying critter?
I named him, PeeWee.
Why does PeeWee
have such long tail feathers?
The answer is Sexual Selection.
Sexual selection is both
intrasexual selection which involves competition between the same sex, (i.e. the
power to conquer other males in combat) and intersexual selection which is mate
choice (i.e. the power to charm the opposite sex) (Darwin, 1859)
For example, intersexual
competition can be seen between two male elephant seals physically fighting for access to
a
brood of females on the beach. But it can also act more subtly—or at least less
violently—through male ornamentation to attract potential mates in many bird
species, such as the elaborate feathers of a peacock.
For our friend PeeWee here, the length of
his tail feathers may signal to rival
males that he is vigorous, so that he can establish a territory (intrasexual)
but the tail feathers may also signal to the female that he would make an
excellent mate (intersexual).
Meet Margaery (below)
She is identical in size and
color, but without the long feathers.
I think she likes him because she
has been hanging out here for quite some time.
Why does the Margaery
choose PeeWee over the other male Flycatchers?
In many animal species, females use
male signals to choose their mates. These signals are often times visual—like
bright colors or dances, or vocal—like elaborate songs. There are three main ways
by which females can benefit by
choosing their mates based on these signals: Direct Benefit, Good Genes and
Sexy Sons (Runaway Selection).
Females may gain direct benefits when
male signals honestly indicate something about the male that will directly benefit her. For example, male lions
with larger manes, may tell the lioness that he can protect and occupy a larger
territory than males with smaller manes. Meaning, she will be protected from
other males, as well as have a lot of space to access important resources. Direct
benefits are also very important for many bird species; especially those
species where males directly contribute parental care to their offspring.
However, in many other species of birds, males only contribute through mating by
passing on their genes to their offspring.
Females might also gain good
genes benefits if traits in males are connected to heritable (genetic) characteristics.
These heritable traits say something about a male’s quality as a mate and if
the male is chosen it means his good genes will be passed on to her offspring. This
process is seen in many lekking bird species (i.e The Greater Sage grouse)
because in these types of systems, the males do not provide any parental care
(direct benefit to the female), but only pass on their genes to her offspring.
Females may
also gain Sexy Sons benefits, by Fisherian Runaway Selection. This hypothesis
states that males can have a sexy
trait that does not provide any information about his quality as a mate or does
not provide any direct benefit to the female. However, this sexy trait is still favored, because if a
female mates with a male that has this sexy
trait, her sons will also have this sexy trait. Although this process may sound
very similar to the Good Genes hypothesis, the difference is that the trait of
choice does not tell the female how good he is as a mate (no measurement of
quality), but she only likes it because it makes him sexier than any other
male.
For example,
let’s say that, PeeWee is the only male African Paradise Flycatcher in all of
the Maasai Mara with long sexy extravagant tail feathers. And let’s say that
every single female flycatchers in the Mara loved long tail feathers. When the
time comes he will court his suiters and because he is the only male with a
lusciously long tail the females will choose him over the rest.
This means that
PeeWee’s sons will inherit the genes for his sexy tail feathers, and they will
be carriers for their mother’s choosy genes (the preference gene is the gene that “told” the females to pick PeeWee and his
sexy tail feathers I the first place.) These sexy sons will mate more often
(owing to their sexiness), making lots of sexy sons and choosy daughters. Over
time, there will be a very large population of flycatcher males with long sexy
tail feathers and flycatcher females to only want to pick these male. Hence the
term runaway selection; the trait continues to get picked time and time again
over many generations all because the females thought PeeWee was the sexiest
bird in the Mara.
Regardless of
which type of sexual selection has caused the evolution of PeeWee’s sexy tail
feathers, it seems to be working out well for him. Margaery and PeeWee seem to be
hitting it off quite nicely. And hopefully, in due time, we will get to see PeeWee’s
sexy sons winning over the ladies.
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1 comment:
Love this post! Please keep writing.
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