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Bees aren’t the only pollinators out there. Some of the other, more surprising pollinators aren't just unconventional, they give us unique examples of how the relationship between pollinators and plants evolved in the first place.

Hosted by: Olivia Gordon

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Sources:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2701755/pdf/mcp122.pdf

Shrew:
https://www.springer.com/about+springer/media/springer+select?SGWID=0-11001-6-1032821-0
https://royalsocietypublishing.org/doi/full/10.1098/rspb.2010.2175
http://www.thegoodscentscompany.com/data/rw1005661.html
https://www.researchgate.net/publication/236984018_Nectar_feeding_by_the_Cape_rock_elephant-shrew_Elephantulus_edwardii_Macroscelidea_-_A_primarily_insectivorous_mammal_pollinates_the_parasite_Hyobanche_atropurpurea_Orobanchaceae [PDF]

Lizard:
https://www.fs.fed.us/wildflowers/pollinators/documents/unusualpollinator.pdf
https://www.cell.com/trends/ecology-evolution/fulltext/S0169-5347(03)00004-1
https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/fee.2137
https://www.publish.csiro.au/bt/BT08179

Cockroach:
https://www.nationalgeographic.com/news/2017/05/cockroaches-pollination-insects-chile-animals/
https://www.sciencedirect.com/science/article/pii/S0085562616301844
https://www.researchgate.net/publication/238110557_Cockroach_Pollination_and_Breeding_System_of_Uvaria_elmeri_Annonaceae_in_a_Lowland_Mixed-Dipterocarp_Forest_in_Sarawak [PDF]
https://www.researchgate.net/publication/5288189_Cockroaches_as_Pollinators_of_Clusia_aff_sellowiana_Clusiaceae_on_Inselbergs_in_French_Guiana [PDF]

Crustaceans:
https://www.nature.com/articles/ncomms12980#discussion
https://www.int-res.com/articles/feature/m469p001.pdf [PDF]

Chocolate midge:
https://askentomologists.com/2015/01/07/the-budding-relationship-of-a-midge-and-the-chocolate-flower/
https://www.sciencenewsforstudents.org/article/blooms-chocolate-tree-are-crazy-hard-pollinate
https://www.sciencefriday.com/articles/meet-the-flies-that-pollinate-cocoa-trees/
http://agris.fao.org/agris-search/search.do?recordID=MY8605427
https://www.worldcocoafoundation.org/wp-content/uploads/files_mf/groenveld2010.pdf [PDF]

Images:
Petra Wester Institute of Sensory Ecology, Heinrich-Heine-University, Universitätsstr. 1, 40225 Düsseldorf, Germany:

http://www.pollinationecology.org/index.php?journal=jpe&page=article&op=view&path%5B%5D=349
https://www.flickr.com/photos/lungfish2000/4642573995/
http://www.pollinationecology.org/index.php?journal=jpe&page=article&op=view&path%5B%5D=349
https://en.wikipedia.org/wiki/File:Rhynchocyon_petersi_from_side.jpg
https://en.wikipedia.org/wiki/File:Trachylepis_atlantica_eating.jpg
https://en.wikipedia.org/wiki/File:Fernando_de_Noronha_-_dois_Irm%C3%A3os_-_praia_do_sancho.jpg
https://en.wikipedia.org/wiki/File:Mabuia_Noronha_Skink.jpg
https://commons.wikimedia.org/wiki/File:Clusia_lanceolata.jpg
https://commons.wikimedia.org/wiki/File:Hemithyrsocera_palliata_8780.jpg
https://en.wikipedia.org/wiki/File:Thalassia_testudinum_(turtle_grass)_(South_Pigeon_Creek_estuary,_San_Salvador_Island,_Bahamas)_3_(15859724719).jpg
https://commons.wikimedia.org/wiki/File:Theobroma_cacao4.jpg
[♪ INTRO].

Ah, spring. Plants are sprouting, flowers are blooming, and you know what that means: bees and pollination!

But bees aren’t the only pollinators out there. In fact, we’re often so caught up in our love of our stripey friends that we overlook some of the other, more surprising pollinators. And it’s not just that they’re unconventional, either:.

Each gives us a unique example of how the relationship between pollinators and plants evolved in the first place. So, here are five pollinators that aren’t bees. Pollinators are important for plants because they move pollen from the male flowers to female ones.

Basically, they’re taking the plant equivalent of sperm and moving it to the part of the plant that contains the ovaries. After that, a plant can make seeds or fruit that grow to become new plants. In some cases, this process can happen by wind or rain.

But animal pollination helps make sure pollen gets spread from plant to plant and not accidentally to the same plant, which would lead to inbreeding. And when animals are involved, that’s when things get interesting. First, take elephant shrews.

They use their long snouts to burrow in soil or leaf litter in search of insects, berries, or plant shoots. Then, they flick their tongues to send that food into their mouths, similar to how anteaters do it. But their distinctive look is also perfect for getting the nectar deep inside flowers.

Which they do, thanks to their sweet cravings. When elephant shrews go for the nectar, pollen gets buried in their snout fur, which they then transfer to other flowers during their next meal. And… boom!

Pollination. Scientists have confirmed that elephant shrews pollinate a bunch of flowers including the Pagoda lily and Northern vampire cup. And not only have the shrews evolved snouts that are great at getting inside flowers, the flowers have evolved ways to make sure the shrews get a good dusting of pollen.

The pagoda lily flower, for example, is long and curved, so the elephant shrew has to wiggle its snout inside to get at the nectar. Meanwhile, other flowers have evolved ways to get mammals like the shrews interested in them in the first place. Like, the northern vampire cup has two chemicals called 3-hexanone and 1-hexen-3-one in its nectar that work together to lure animals in. 3-hexanone gives foods a sweet, rummy smell and taste, so it might signal to mammals that the nectar is full of sugary energy.

And while it isn’t clear what 1-hexen-3-one does, scientists think it might help repel animals that aren’t pollinators, or enhance the nectar’s taste somehow. In any case, elephant shrews get a sugary snack, and the plant gets pollinated. And that’s the kind of win-win relationship pollination is all about.

Sometimes, it’s not the sugar, but the water in nectar that pollinators are after. That’s the case for the Noronha skink. This spotted lizard is native to a group of Brazilian islands, and it’s what you might call an opportunistic eater.

It can be found foraging on the ground in search of food, ranging from eggs, to bits of bird and fish carcass, to human leftovers like cookie crumbs. But when it gets bored of these meals, it will venture up trees in search of something juicer and sweeter. On its home islands of Fernando de Noronha, that something is the nectar from mulungu tree flowers.

And while it’s sidled up to these blooms, the lizard can’t help but get bits of pollen stuck in its scales. Then, as the skink wanders from flower to flower, it drags the pollen with them. Part of the reason lizards are so enticed by the nectar is that the mulungu tree flowers during the dry period, when there’s not much water on the island.

In fact, the nectar is pretty diluted compared to other species of Brazilian trees, making it a great thirst-quencher for the lizards, and other animals, including some birds! Now, you might be thinking it’s kind of strange to have lizards pollinating flowers. And for a while, scientists did, too.

But now, they believe lizards might play a more important role in pollination on islands than previously thought. That’s because, on islands, lizard populations can grow to much higher numbers than on the mainland, thanks to a lower risk of being picked off by predators. That lower predation risk also means lizards can spend more time looking for exotic foods to include in their diet, like nectar, pollen, and fruit.

Now, scientists want to know more about the relationship between lizards and flowers, especially things like if they evolved together, or if the flowers have some special way to attract these animals. Cockroaches probably conjure up images of pest control vans, not pollination. But there are at least two species of them that act as pollinators in the tropics of South Malaysia and French Guiana in South America.

One is called A. platystylata, and it’s a fan of tropical Clusia trees because of a liquid it gets from the base of the petals. The liquid isn’t especially appetizing, it’s not sweet like nectar, but it might have some resin in it that the roaches can use for making their nests. And when they’re rummaging in Clusia flowers, maybe for those building materials, these cockroaches pick up pollen on their rough bodies and transport it between flowers.

Kind of like with the northern vampire cup in our first example,. Clusia flowers even produce a scent that’s appealing to these roaches to lure them in, which shows that the plants could have evolved to attract these insects specifically. Meanwhile, the other roach pollinator, called H. palliata, does seem to get some food reward from the flowers it pollinates.

It munches on pollen from a species of woody climber plant in Costa Rican rainforests, which gives the insect the protein it needs to grow and reproduce. So far, these are the only two confirmed roach pollinators, but in mid-2017, scientists in Chile uncovered evidence of a possible third one, called M. brevipennis, feeding on nectar and pollen from evening primrose and puya trees. This insect may have become an accidental pollinator while looking for a damp place to lay its eggs, but at this point, scientists aren’t 100% sure.

After all, you have to watch these insects really closely to make sure that they are in fact spreading pollen to other flowers. But it’s something researchers are planning to do soon. Usually when we think about animal pollination, we think about it on land.

But there’s recent evidence that it happens underwater, too. Which came as a surprise to a lot of people, including scientists! The vast majority of underwater plant fertilization and seed-spreading happens through ocean currents, just like wind might carry seeds on the surface.

And lots of plants have adaptations for this. For instance, male and female plants are separated, and female plants have parts that look like tentacles to catch pollen from the males as it flows by. But in 2012, researchers found around 65 species of crustaceans, including microscopic plankton and tiny shrimp, visiting seagrass meadows in Puerto Morelos reef lagoon in Mexico.

The crustaceans were feeding on seagrass pollen and a jelly-like substance called mucilage. The scientists suggested the crustaceans may be pollinators, because a few individuals had pollen stuck to their bodies, but they had no evidence. Then in 2016, they brought the animals and the plants into the lab.

When they did, they saw that the pollen grains from male flowers were getting caught up in the sticky mucilage and clinging to the crustaceans’ antennas, mouthparts, and bodies. They also found pollen on female flowers and concluded that it must have come from the crustaceans since there was no water flow in the tanks. And it wasn’t just that the pollen was being moved around:.

The pollinated, female plants also started to sprout thanks to their crustacean friends! So, the system works! The scientists called this new method zoobenthophily, meaning “pollination by animals on the seafloor.” And they think it can boost the likelihood that a plant will make plant babies.

Also, this method means that plants can reproduce even when there aren’t strong water currents around. Plus, crustaceans can carry pollen further than currents can because, well, they swim. That helps mix up the seagrass’ genes too, instead of the same plants always breeding with their neighbors.

But, it is also worth noting that all this crab-pollination was going on in the lab. No one has seen this underwater in the wild. That’s mostly because scientists didn’t consider it a possibility before, though!

So it’s time to really start looking. Finally, without this next group of pollinators, one of our favourite sugary treats might not exist. I’m talking about chocolate.

Biting midges from the family Ceratopogonidae are the only known pollinators of cacao trees. These grayish flies, which are only about the size of poppy seeds, are so important for cacao, they’re also called chocolate midges. See, even though cacao trees have both male and female flowers, they can’t self-fertilize because of a defense called self-incompatibility.

Basically, to prevent inbreeding, pollen from male flowers won’t form an embryo with ovaries from a female flower of the same tree. Also, other pollinators have a tough time getting at the pollen-making parts of the flower, called anthers, which are hidden under a flower hood. Bigger insects like bees, for instance, wouldn’t stand a chance at squeezing into the tight space.

That leaves pollination entirely up to the tiny midges. But hey, at least the trees help out:. Research suggests the timing of cacao tree flowering syncs up with when the midges are around during the rainy season.

After a couple of big downpours, the midges look for a shaded, damp place to lay their eggs, including in rotting cacao husks. And eventually, they find their way to the plant’s flowers. At this point, scientists still aren’t sure exactly what attracts the midges to the flowers, since they don’t make any nectar, and there’s no evidence that their smell is attractive, either.

But! If the midges aren’t attracted to the flowers themselves, just the general area around the trees, that might help explain why pollination rates are so terrible. Only about one in every 20 flowers and as few as one in 25 become fruit or the pods that are used to make chocolate.

In the wild, that’s not such a terrible thing:. One in 20 might be enough for a population of trees to survive. But when you’re trying to satisfy the worlds’ candy cravings… it’s not ideal.

Humans try and make up for this by hand pollinating the flowers, but making cacao pods takes a lot of energy on the tree’s part, so even then, the trees will limit how many pods actually make it to ripening. More than the other examples in this list, midges and cacao trees are a good example of how evolution between plant and pollinator happens, and how things can go wrong if there are sudden, human-made, changes to that relationship. So this year, let’s not forget the unsung heroes of the pollinating world.

They contribute to the huge diversity of plants we see on this planet. Including the tasty, chocolatey ones. Thanks for watching this episode of SciShow!

If you’re in the market for more spring- or summer-related content, you can find more of our videos at youtube.com/scishow. And if you’re interested in videos for the kids in your life, we’ve got you covered there, too. SciShow Kids has a bunch of videos about the seasons and everything that goes along with them, and you can find those videos at youtube.com/scishowkids. [♪ OUTRO].