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Duration:03:19
Uploaded:2020-05-26
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The rat's tail plant, or Babiana ringens earns its name for the distinct stem that grows above its flowers. But what's the purpose of this odd looking appendage?

Hosted by: Michael Aranda

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Sources:

https://bsapubs.onlinelibrary.wiley.com/doi/10.3732/ajb.1100295
https://academic.oup.com/aob/article/109/3/667/129786
https://www.eurekalert.org/pub_releases/2012-06/ajob-hso060712.php
https://www.nature.com/articles/435041a?draft=collection
https://onlinelibrary.wiley.com/doi/abs/10.1111/plb.12474
(Intro)

Babiana ringens is a small, South African flowering plant.  It's often called "The Rat's Tail" plant because, well, it has a weird stick-like bit that sort of looks like a rat's tail growing out of it, but it's not trying to mimic the local rodents.  Scientists think that tail is actually a perch for birds.  

Botanically speaking, that appendage-like structure is actually a naked inflorescence axis, which is a fancy term for a flower stem that doesn't have any flowers on it.  The plant produces other inflorescences that do flower, of course, they're just all much shorter, putting the flowers near the ground below that so-called rat's tail.  This is probably to keep them out of the mouths of antelopes.  They seem to prefer stems and flowers that are higher up.  

One 2012 study in The American Journal of Botany even found that plants that only had flowers near the ground fared better and produced more seeds, but the placement is somewhat inconvenient for birds who like to drink the plant's nectar.  To reach such low flowers, they'd normally have to try and hover amid the brush or land on the ground, which leaves them vulnerable to all kinds of predators. 

That's where the tail comes in.  It's a nice, convenient perch where the birds can land to reach into the flowers from above.  The perches are mostly for one specific bird, the malachite sunbird, which is the plant's primary pollinator.  Each perch is angled in such a way that the birds have to hang upside down to drink the plant's nectar.  That puts their chests in prime position to brush against the pollen-bearing parts of the flower.  Later, this pollen coating gets dusted onto other rat tail flowers when the bird drinks their nectar, and that helps the plants reproduce.

The plants can self-fertilize so they don't strictly speaking need the birds, but plants fertilized by pollen from another plant tend to produce more offspring, so the perches allow the birds to help the plants thrive over much larger areas, and the sunbirds seem to be benefit from the perch, too.

Biologists have a few hypotheses but one is that it's a good place to rest and feed as they can do that without their beautiful long feathers getting dirty or damaged, and the bigger the perch, the better.  The males think that, anyway, which is probably because they need to look their best to attract their less colorful mates.  Female sunbirds don't seem to care much whether there's a perch or not, but the sad thing is, the special perch might be disappearing in some parts of the plants' range.  

It seems like, for some plants, the perch isn't as beneficial as it used to be, thanks to changes in their environment, a phenomenon called relaxed selection.  The average perch length is shorter in some areas, for instance, and botanists have even spotted perches with flowers.  Both probably occur because the perches aren't being visited as often.  Shorter stems are found in places with a greater variety of flowering plants, likely because malachite sunbirds prefer the other flowers, and if the birds aren't really pollinating the rat's tails, the longer perches don't confer the same reproductive edge.  Flowered perches may similarly indicate choosier birds, or they may be a sign that the birds are going away. 

Studies suggest that malachite sunbirds are less abundant in areas that have been altered by human activity, so it may be that the plants are losing their ecological partners because we're messing up their homelands.  Either way, these rat-like tails are an awesome example of how interactions between organisms can quite literally shape species.

We hope you enjoyed learning about these weird and wonderful plants.  If you did, you'll probably love our episode on how deceitful plants can be.  Also, you might consider clicking that subscribe button and ringing that notification bell.  That way, you don't miss any of our daily episodes.  And as always, thanks for watching SciShow.

(Endscreen/Credits)