The story of the fig and its wasp

Inside the rounded fruit of a fig tree is a maze of flowers. That is, a fig is not actually a fruit; it is an inflorescence—a cluster of many flowers and seeds contained inside a bulbous stem. Because of this unusual arrangement, the seeds—technically the ovaries of the fig—require a specialized pollinator that is adapted to navigate within these confined quarters. Here begins the story of the relationship between figs and fig wasps. The queen of the fig wasp is almost the perfect size for the job—except, despite her tiny body, she often times will lose her wings and antennae as she enters through a tight opening in the fig. “The only link the fig cavity has to the outside world is through a tiny bract-lined opening at the apex of the fig, called the ostiole, and it is by means of this passage that the pollinating fig wasp gains access to the florets,” as described in Figweb, a site by Iziko Museums of Cape Town. Once inside, the queen travels within the chamber, depositing her eggs and simultaneously shedding the pollen she carried with her from another fig. This last task, while not the queen’s primary goal, is an important one: She is fertilizing the fig’s ovaries. After the queen has laid her eggs, she dies and is digested by the fig, providing nourishment. Once the queen’s eggs hatch, male and female wasps assume very different roles. They first mate with each other (yes, brothers and sisters), and then the females collect pollen—in some species, actively gathering it in a specialized pouch and in others, accumulating it inadvertently—while the wingless males begin carving a path to the fig’s exterior. This activity is not for their own escape but rather to create an opening for the females to exit. The females will pollinate another fig as queens. The males will spend their entire lifecycle within a single fruit. While this tree-wasp relationship may not be common knowledge to all fig-eaters, it is well-known to biologists as one of the most solid examples of coevolution. “One of the best activities to do with an introductory biology class is to pass around Fig Newtons, let them take a bite and then tell them the story of the fig wasp life cycle,” said tropical plant ecologist Greg Goldsmith as we recently hiked through a cloud forest in Monteverde, Costa Rica. “It’s a fascinating story.” After learning the story of the fig and its wasp, the most common question is, “Do we eat wasps when we eat figs?” The short answer is that it depends—that is, some figs are parthenocarpic, meaning they are...

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Fungus makes zombie ants administer ‘death bite’ at noon

Researcher David Hughes has expanded research on a parasitic fungus and its carpenter ant host. As explained in an excerpt from a previous EcoTone post: Scientists have found that the parasitic fungus Ophiocordyceps unilateralis has possibly been invading carpenter ants (Camponotus) for 48 million years. The parasite not only infects the ant, but it manipulates the ant’s behavior, driving it to bite the underside of the leaf at the veins. Once the ant hits an optimal location, the fungus grows rapidly, killing the ant and preparing it to release a new spore. During this process, the ants leave distinct marks, also known as “death bites,” on the leaves as they bite the veins in search of a prime spot for fungal growth. It is this unique pattern that led researcher David Hughes to a 48 million year old leaf with similar markings. According to a Nature News article, Hughes contacted Conrad Labandeira, a palaeoecologist at the Smithsonian’s National Museum of Natural History, who, as it turns out, had noticed a leaf with similar markings. As Hughes said in the article, “It is not normal ant behavior to bite into the leaf vein because it has no real nutritional value to the ant and can in fact be toxic in some plant species.” This finding, as he explained in a Biology Letters study published [last year], indicated that the carpenter ants were infected with the parasitic fungus when the ant made the leaf marks. As reported in Discover Magazine’s blog 80beats, “If Hughes’ dating is correct, then the fungi have had plenty of time to fine-tune their zombifying practice into the ruthlessly efficient mind control we see today.” These findings were recently backed up in a study published by Hughes, now a researcher at Pennsylvania State University, and colleagues in the journal BMC Ecology this week. They found that the ants bit on the leaf veins around noon—a time that appeared to be specific for the fungus. As Hughes said in a Live Science article, “Synchronized arrival of zombie ants at the graveyards is a remarkable phenomenon. It adds a layer of complexity on what is already an impressive feat. However, although ants bite at noon they don’t in fact die until sunset. Likely this strategy ensures (the fungus) has a long cool night ahead of it during which time it can literally burst out of the ant’s head to begin the growth of the spore-releasing stalk.” The ants—in the case of the most recent study, Camponotus leonardi—live in the canopy of trees but come to the forest floor occasionally. It is here that they contract the fungus. It is...

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Spreading SEEDS, growing diversity

SEEDS is an education program of Ecological Society of America (ESA), and Iman is one of several SEEDS students who will be attending and presenting research at ESA’s upcoming Annual Meeting in Pittsburgh.

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