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Scientists have discovered a group of three closely related flowers that seem to break the laws of genetics. These mountain beardtongues are pollinated by either bees or butterflies, but not both, and that's the key to an incredibly weird quirk of natural selection.

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A site of thousands of citizen  science projects and events In need of help from people like you Maybe you’ve strolled past one of these plants on a hike somewhere in North America. Maybe it was their beautiful, bell-like flowers that caught your eye.

But these brightly-colored  blooms hold a scientific secret. Although their flowers might  look different close up, they’re actually all the same species… well, sort of. And that’s the rub.

They kind of mess with the whole idea of what a species is. These unassuming mountain flowers are straining scientists’ understanding of  genetics to the breaking point. [ INTRO MUSIC ] These flowers are all Beardtongues, or members of the Penstemon genus. The purple ones are the New Mexico Beardtongue and the Upright Blue Beardtongue, while the red ones are just called Beardtongues.

But more than that, they’re  all part of what’s called a species complex, referring to two or more species that are so closely related  that they almost count as one. As a quick reminder, generally we define a species  as groups of organisms that can breed with one another in nature but can’t breed with similar  organisms of another group, or species. The members of a species might look pretty similar to one another, but they don’t have to.

What differentiates these beardtongues is that each flower is specially adapted to suit the thing that pollinates it. The New Mexico and Upright Beardtongues have wide, purpley-blue flowers – perfect for attracting insects like bees who are great at seeing blue-to-ultraviolet light and want a nice little landing pad to plop down on when they gather nectar. The red Beardtongues, on the other hand, are mostly pollinated by hummingbirds, who prefer red colors and  don’t need a landing pad, since they can just hover there  to suck out the loads of nectar sitting deep in the flower’s bell.

Since the hummingbirds and bees don’t  cross over to the flowers they don’t like, red flower pollen rarely reaches  blue flowers and vice versa. That drives the species apart. But that doesn’t necessarily mean they can’t reproduce with one another.

Despite our definitions, genes may continue to be exchanged  between recently diverged species. But the way that’s happening  in beardtongues is weird. Like really weird.

To understand why, we need to talk about the law  of independent assortment. This goes all the way back to Mendel – the pea plant guy. For the most part, the different flavors of a gene – also called alleles – will be split up into reproductive cells independent from the alleles of another gene.

If gene A and gene B are on  two different chromosomes, those two chromosomes are  gonna go their separate ways. In fact, if they’re far  apart on the same chromosome, that can happen too, because chromosomes love getting together and swapping arms as reproductive cells are made. This means, say, the genes for hair color probably won’t influence the genes for some other feature, like height.

Except independent assortment also says that some genes aren’t all that independent from one another. They’re actually passed on or inherited together. Such genes are said to be linked.

Usually when this happens, the genes are physically close to each other on the same chromosome. Think about it like this: If you’re traveling in a car, you wouldn’t expect the other cars to end up in the same place you’re going. They’re all moving independently.

But if you’re on a bus, some of the other passengers will probably also get off at your the same stop. In the case of flowers, you  might have genes for shape, color or size that are all  very close to one another and passed down to baby flowers in a group. This is what actually happens  in various species of petunias.

There are genes for color, scent and size that make one  petunia species different from another and travel together in a group. And It would make sense if beardtongues were doing that. They are not.

In fact, they are bending those rules  almost to the point of snapping. When researchers in 2023 peeked under the genetic hood  of these bell-shaped beauties, they found around 21 loci, or places, on 8 chromosomes that were all traveling together  and being inherited as a group. And here’s the part where this episode becomes an unexpected plea for more people to do PhDs in plant genetics, because the language in the paper is  couched in molecular biology hedges since no one’s sat down and proved the function of  each of these genetic loci, so we can’t actually say what they do.

However, it seems like the genes in these places are key to defining the bird  and bee features of each flower. But, and here’s the rub, instead of those genes sitting close to each other on one particular chromosome, they were spread out all over  over all the whole genome. And all of the DNA in between  was not traveling together.

Think about how weird this is. Like, imagine you're on the interstate and there's a bunch of cars and there's 21 of them that are all taking the same route and ending up in the same place every time, even though they are not  planned to go to the same place. Like there’s nothing making them stick together.

So that… is asking for an explanation. The researchers think it’s because there’s strong selective pressure to keep the groups of genes that make the hummingbird-pollinated  and bee-pollinated flowers. So they’ll be passed down through  generations sticking together – or getting off at the same exit – even if that means bending  the usual inheritance rules.

Because there’s good reason  for hummingbird flowers to stay hummingbird flowers and bee flowers to stay bee flowers. Hybrid flowers, between the two, seem to be are really, really, rare. So you might get a hybrid purple baby flower.

And that flower could breed with another hybrid and to keep making these  intermediate purple flowers… but it won’t. Because the birds and the  bees are both gonna see it and go like “meh I don’t actually  care that much about that flower” and move on to a flower they actually like. then move on. That means that the hybrids are more likely to backcross with one of the parent species.

Really quickly, the offspring of the hybrids are going to end up with all blue flower traits or  all red flower traits again – because that’s what the  pollinators will pollinate. But the hybrid still happen, so genes were still swapped between the reds and the blues. Meaning our these 21 cars are selectively pressured to stay together, despite not being physically connected, but everything in between them can move.

So it looks like the reds and blues are breaking the law of independent assortment, with these 21 unconnected loci staying together. But natural selection beats out everything else, and forces those traits to stay in a group. The big question that still remains is how much of the shared  DNA between reds and blues is because the flowers recently  split into different species, and how much of it is gene  flow happening afterward.

Figuring this out could not only explain what’s going on with Beardtongues, but also help geneticists  understand the early stages of how species split off from one another. These flowers could even help uncover how species evolve new traits quickly to adapt to environmental changes, like those stemming from the climate crisis. So rather than a freak of nature, Beardtongues might just be the next pea plant, revealing brand new truths about genetics.

Hi folks, Reid here. This SciShow video is supported by SciStarter: a site with thousands of citizen science projects and events in need of help from people like you. SciStarter connects people to projects, providing you with training  and step-by-step instructions, all for free!

Using their Project Finder, you can choose an investigation  that you’re passionate about. Then, once you’ve started collecting data, you can track your progress through your SciStarter account. This April, or should I say this Citizen Science Month, SciStarter’s goal is to collectively generate over one million data points for citizen science projects.

And you can help. Whether you work at a big company like Verizon, are a member of a national organization like the Girl Scouts, or simply a curious person, SciStarter has projects to  fit your goals and interests. You can even join today to learn how.

From playing a video game that accelerates medical research, to taking pictures of nature for conservation research, to attending a citizen science event near you, there are tons of ways to get involved. Once you complete your investigation at the end of Citizen Science Month, you can find your next  adventure on! Thanks to SciStarter for supporting this SciShow video, and thank you for staying curious with us. [ OUTRO ]