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Sometimes the males and females of a species can look really different from each other. This is pretty common in animals (think peacocks), but there are some plant species out there with extreme sexual dimorphism! And now scientists think they have a pretty good idea how and why this happens,

Hosted by: Rose Bear Don't Walk

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Sources:

Thumbnail Image Credit:
https://commons.wikimedia.org/wiki/File:Leucadendron_rubrum_m_Nicola_van_Berkel_4.jpg

https://commons.wikimedia.org/wiki/Category:Leucadendron_rubrum#/media/File:Leucadendron_rubrum_f_Nicola_van_Berkel_1.jpg

Sexual dimorphism in flowering plants (2012)
https://academic.oup.com/jxb/article/64/1/67/631641

Canopy seed storage is associated with sexual dimorphism in the woody dioecious genus Leucadendron (2010)
https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2745.2009.01623.x

Causes of secondary sexual differences in plants — Evidence from extreme leaf dimorphism in Leucadendron (Proteaceae) (2010)
https://www.sciencedirect.com/science/article/pii/S0254629910001481?via%3Dihub

Fynbos info: https://www.worldwildlife.org/ecoregions/at1202

Pollination https://www.ncbi.nlm.nih.gov/books/NBK9991/

Dimorphism sources
https://academic.oup.com/jxb/article/66/20/6083/552631
http://www.plantcell.org/content/plantcell/1/8/737.full.pdf
This episode is sponsored by Surfshark.

You can get Surfshark VPN at https://surfshark.deals/SciShow, and enter the promo code “SciShow” for 83% off and 3 extra months for free. If you went for a hike around the coastal Cape region of South Africa, you might run into a flowering plant with a beautiful multi-colored cone on top.

It’s called the Spinning Top Conebush. A few meters away, you might find another plant with bushier branches, yellow flowers, and much smaller leaves. And you’d be forgiven for having no idea they’re the same plant.

But we think there’s a good reason this plant has evolved two totally different forms. And it’s all about giving its offspring their best chance. In the vast majority of flowering plants, male and female reproductive organs occur in the same individual plant, and often the same flower.

They’re called monoecious plants. Meanwhile, maybe 10 percent of flowering plants species are dioecious, there are distinct male and female individuals. Asparagus is a good example.

Sometimes the male and female plants look really different from each other in a phenomenon called sexual dimorphism. It’s more familiar in animals -- think peacocks. But dioecious plants are relatively rare, and even in most of those species, male and female individuals look alike.

That’s what makes the spinning top conebush so unique. The leaves on the female plants can be up to ten times bigger than those of male plants. Females also have fewer, shorter branches.

Then there’s the most obvious difference: the females have cones. For years, scientists have studied those differences to figure out why this plant is so dimorphic. One thought was that the males might be smaller in order to consume less water and save it for the cone-bearing females.

But research in 2009 found that both sexes consume water at the same rate. Another hypothesis is that females are taller and stockier to catch more pollen in the wind, but also narrower so they don’t get carried away by a stiff breeze. But the strongest evidence supports the idea that this is the plant version of parental care.

Because apparently, parental care isn’t limited to animals! See, this plant takes advantage of its fire-prone ecosystem. Female conebush plants store seeds in their cones for a long time and wait until fire comes along to help them disperse the seed a strategy called serotiny.

Taking care of seeds for an undefined amount of time takes a lot of energy, so the female plants had to evolve to be more energy-efficient. Since the female plants carry so much of the reproductive burden, they’re under greater pressure to adapt. On the other hand, as long as male plants can spread pollen, they’re good.

A 2010 study looked at different plants in the same genus as the spinning top conebush. Of those, the species that had the older cones, and therefore more serotiny, also had more dimorphism, with shorter and fewer branches. The researchers concluded that in species that took more care of their seeds, the females also evolved to save energy by being less branchy than the males.

So not only is parental care a thing that plants can do, it seems to influence their evolution in a big way! If you ever get the chance to take that hike in South Africa, you’re going to need protection as you travel. Surfshark VPN can help you with things like accessing your bank account without getting locked out, and reaching your favorite sites no matter what country you’re in.

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