Sunday, October 11, 2015

Shake them Sexy Tail Feathers

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.

Darwin, Charles. Origin of Species (1859)

1 comment:

dee said...

Love this post! Please keep writing.

Michigan State University | College of Natural Science