Tuesday, September 19, 2017

Impatiens capensis pollination (Bonus: even bees can be clumsy)

I know I haven't blogged in quite a while. Life got very hectic for a while. In the months my last post, I have finished my M.Sc., gotten published, and moved to the University of Toronto to start my Ph.D.!

Over the weekend I got a chance to take a long walk with my patient and long-suffering husband, who indulged my snagging his new blackberry to take a ton of footage of bees visiting the tens of thousands (at least!) of Impatiens capensis (common name jewel-weed) in the ravine park near our new home. I made all sorts of exciting videos, but today I'm going to share just a few simple ones, as the others will take quite a bit of research and time to write up. I will post these throughout the fall because they're very exciting.

NOTE: I have been informed that my videos don't work on mobile. I'm working on it, but in the meantime they do run on desktop.
UPDATE: try clicking the title of the video instead (treat as link) on mobile. Opens in youtube app. If you don't have youtube app, please report back telling me what it does when you click the video link!

To start, here's a picture of the plant itself:

Impatiens capensis whole plant view

Let's take a quick look at some general reproductive biology of I. capensis. The plant is monoecious, meaning that each plant reproduces through both male and female function; however, each individual flower is unisexual (i.e., any given flower is either male or female but not both). In the photo below, I show three flowers on the same individual. If you look at the top of the "mouth" of each of the lower two flowers in the picture, you will see that each has a different structure; the middle flower has a large, bulbous, whitish structure, while the rightmost flower has a slender green structure.

Impatiens capensis male (middle) and female (right) flower
The middle flower is a male flower; the whitish deposit on it is pollen, ready to be deposited on the back of a pollinator that climbs into the flower looking for nectar (the nectar is in the nectar spur, the little narrow tube curling off the back of the flower, visible on the middle flower). The rightmost flower is a female flower, with a stigma ready to pick up pollen from the back of a visiting insect.

The flower has some rather complex floral anatomy I won't get into right now. There's a pretty good explanation of which parts are sepals and which parts are petals here for those interested. The important thing to note is the lower lip, made of two structures wrapping around the front of the flower, one on each side, that form a sort of landing area of pollinators. They also restrict the width of the flower opening (see photos below).

Impatiens capensis male flower front view. Note that the two sides of the "landing" petals on the front are not fused, just overlapping, and that their shape, because they come down from above around the opening of the cone, reduces the size of the entrance into the flower

Impatiens capensis male flower side view. Notice that the lower "landing" petals are not attached to the conical structure behind.

So I'm going to skip over all sorts of exciting stuff about this plant (why does it have unisexual flowers? Why place pollen on a visitor's back? What's up with that super-complex floral shape?) in order to move straight to some awesome video of assorted Hymenopterans (bees, wasps, ants) visiting this awesome flower!

So I noted above that the '"landing" petals form not just a place for a pollinator to land on the flower, but also a constriction around the opening of the conical part; remember that the nectar is all the way at the back of that cone, in the little nectar spur curling down under the flower. There are several strategies to get past the opening to access this nectar (and then leave again after): one is to simply be small enough to fit through the constriction made by the landing petals; that's how Apis mellifera (honeybee) is doing it (note at 10:00 that you can really see the pollen on this honey bee's back!):

Backing out of the flower can be quite tricky. I managed to get some footage of a visiting wasp finding an alternate method of exiting, which capitalises on the fact that the landing platform and the conical structure behind are not attached to each other:

The Bombus sp. (bumblebee) workers I saw visiting the plants, however, were too big to fit through the opening. But, have no fear! They worked it out anyway. Here's one worker diligently visiting lots of flowers. She's making more room for herself by using her strong back legs (2 pairs) to push the landing petals apart a bit, so that she can shove her head and thorax into the flower and get at the nectar. You'll notice that she doesn't have much difficulty leaving, either, since she's well placed with four legs outside the flower. As far as I can tell, she's just dropping right out of the flower and then flying away.

Here's a longer video of the same bee, diligently visiting a lot of flowers in a row. There's also a little bonus at the end of this video. If you've been clumsy and felt ridiculous for it recently, I have something to comfort you: even bees can be clumsy. If you watch closely at the end, you'll see her climb into a flower, and then she and the flower both fall off the plant to the ground!

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