EVOLUTION TAG TEAM, Part 2: Sex & the Synconium

The second in an ongoing series of biology’s greatest duos. (Check out Parts One and Three)

(Via: Mastering Horticulture)

Common Name (Plants): Fig Trees

  • A.K.A.: Genus Ficus

Common Name (Wasps): Fig Wasps

  • A.K.A.: Family Agaonidae

Vital Stats:

  • Approximately 800 species of figs
  • Most are trees, but some are shrubs and vines
  • Approximately 640 species (20 genera) of fig wasps
  • All are obligate pollinators of figs

Found: Throughout the Tropics

It Does What?!

Snacked on any Fig Newtons lately? Tasty, right? Like the ad says, “A cookie is just a cookie, but a Newton is fruit and cake.”  …And wasps.

They must have run out of space on the package for that last part.

Before you toss out your favourite teatime treat, I should point out that without those wasps, the figs themselves wouldn’t exist. [Personally, I love Fig Newtons and will eat them regardless of any insects present.] This plant-insect pairing actually represents one of the most stable symbioses out there, with evidence suggesting it has existed for over 65 million years.

Now with 10% more Wings
(Via: Wikipedia)

While it’s not entirely clear how this arrangement evolved in the first place, fig trees produce a unique structure called a synconium, in which the flowers are actually inside the part we think of as the fruit. This synconium, which can contain up to 7000 flowers, depending on the fig species, has a tiny hole at the tip called an ostiole. In order for the flowers to be pollinated and the fruit to grow, a female wasp must squeeze through that hole, often losing her wings and antennae in the process, and distribute pollen that she carries in a sac on her abdomen. As she does so, she also uses her ovipositor to reach down into some of the female flowers and lay her eggs in their ovaries, where a gall is formed and the larvae can develop. Then she dies and ends up in a cookie. The End.

But hold on, let’s remove humans from the equation for a moment. She dies, but her eggs hatch into little moth larvae which use the growing fig for nutrition. Once they’re old enough, the young wasps mate with one another inside the fig (another nice mental image for snacktime), and the females gather pollen from the male flowers and store it inside their abdominal pollen baskets (yes, that’s actually what they’re called). The wingless male wasps have a simple, three step life: 1) mate with females, 2) chew a hole through the fig so they can leave, 3) die. That’s pretty much it for them. They may escape the nursery with the females, but they’ll die shortly thereafter, regardless. In fact, even the females have a pretty rough deal; from the time they’re old enough to mate, they have about forty-eight hours to get their eggs fertilized, gather pollen, find a new synconium, distribute the pollen, and lay their eggs. Two days, and their life is over. No pursuit of happiness for the fig wasp, I’m afraid.

“What does it all mean?”
(Via: BugGuide.net)

As with any long-standing mutualism, there are, of course, parasites ready and waiting to take advantage of it. These parasites are wasps which are able to enter the synconium and lay their eggs, but which do not pollinate the fig. Although their eggs will crowd out those of the fig wasps, decreasing the number of fig wasp larvae born, they are kept in check by the fact that any unpollinated synconium will be aborted by the tree and drop to the ground, taking the parasite eggs with it. The nonpollinating wasps are therefore kept from being a serious threat to the tree’s pollinators.

So there you have it, another of evolution’s great matches. The wasps get an edible nursery, the trees get pollinated, and we get tasty fruits with suspicious crunchy bits that probably aren’t dead wasp bodies, so just try not to think about it too much…

Seeds, or wasp eggs? You be the judge!
(Via: This Site)

[Fun Fact: The symbiosis between fig species and their corresponding wasp partners is so specific (often 1:1), that the shape of the ostiole actually matches the shape of the head of the wasp species which will pollinate it.]

[For those who would like to read about figs and fig wasps in much greater detail (such as how this works when the male and female flowers are in different figs), check out this excellent site for all you could ever want to know.]

Says Who?

  • Compton et al. (2010) Biology Letters 6: 838-842
  • Cook et al. (2004) Journal of Evolutionary Biology 17: 238-246
  • Kjellberg et al. (2001)Proceedings of the Royal Society of London, Biology 268: 1113-1121
  • Proffit et al. (2009) Entomologia Experimentalis et Applicata 131: 46-57
  • Zhang et al. (2009) Naturwissenschaften 96: 543-549
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Advertising in the Wild… Not So Very Different (Ophrys sp.)

(Via: lastdragon.org)

Common Name: Bee Orchids

A.K.A.: Genus Ophrys

Vital Stats:

  • 30-40 recognised species in the genus
  • Grows to a height of 15-50 cm (6-20”)
  • The name Ophrys comes from a word meaning “eyebrow” in Greek, for the fuzzy edges of the petals
  • First mentioned in ancient Roman literature by Pliny the Elder (23-79 A.D.)

Found: Throughout most of Europe and the British Isles

It Does What?!

We tend to think of animals (including humans) as using plants to serve our ends exclusively- we eat them, clothe ourselves with them, build homes with them, and so on. But for all the obvious ways in which the animal kingdom takes advantage of the plants, there are numerous, more subtle, ways that they use us to do their bidding. One of those ways is as pollinators; plants enlist animals to help them reproduce. And while that enlistment often takes a rather mundane form – a bit of pollen brushed onto a bird’s head as it sips nectar, say – sometimes a group of plants will get a bit more creative about it. Such is the case with the bee orchids.

These highly specialised flowers depend on very specific relationships with their pollinators; often only a single species of bee (or wasp, in some cases) will pollinate a given species of orchid. Without those pollinators, the orchids can’t produce seed and would die out. So how do you control a free-roving creature that has other places to be? Why, sex, obviously. (Isn’t that the basis of most advertising?) The bee orchid has evolved a flower that not only looks, but smells like a virgin female of the bee species which pollinates it.

May not be appropriate for younger readers.
(Via: This Site)

At a distance, the bee detects the pheromones of a receptive female. Once he moves in closer, there she is, sitting on a flower, minding her own business. So he flies in and attempts to do his man-bee thing, only to find that he’s just tried to mate with a plant. Mortified (I imagine), he takes off, but with a small packet of pollen stuck to his head. He’s memorised the scent of this flower now and won’t return to it, but amazingly, the orchids vary their scent just slightly from one flower to the next, even on the same plant, so that the duped bee can never learn to distinguish an orchid from a female. What’s more, because the scent is more different between plants than between flowers on the same plant, he is more likely to proceed to a different plant, decreasing the chances that an orchid will self-fertilise.

Hilariously, researchers have shown that, due to their higher levels of scent variation compared to true female bees (variety being the spice of life, right guys?), male bees actually prefer the artificial pheromones of the orchids over real, live females. In experiments where males were given a choice between mating with an orchid and mating with a bee, they usually chose the flower, even if they had already experienced the real thing.

So there you have it. Plants: master manipulators of us poor, stupid animals.

Who could resist?
(Via: Wikia)

Says Who?

  • Ayasse et al. (2000) Evolution 54(6): 1995-2006
  • Ayasse et al. (2003) Proceedings of the Royal Society, London B. 270: 517-522
  • Streinzer et al. (2009) Journal of Experimental Biology 212: 1365-1370
  • Vereecken & Schiestl (2008) Proceedings of the National Academy of Science 105(21): 7484-7488
  • Vereecken et al. (2010) Botanical Review 76: 220-240